Network Working Group J. Van Dyke
Request for Comments: 4722 E. Burger, Ed.
Category: Informational Cantata Technology, Inc.
A. Spitzer
Pingtel Corporation
November 2006
Media Server Control Markup Language (MSCML) and Protocol
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2006).
Abstract
Media Server Control Markup Language (MSCML) is a markup language
used in conjunction with SIP to provide advanced conferencing and
interactive voice response (IVR) functions. MSCML presents an
application-level control model, as opposed to device-level control
models. One use of this protocol is for communications between a
conference focus and mixer in the IETF SIP Conferencing Framework.
Van Dyke, et al. Informational [Page 1]RFC 4722 MSCML November 2006
Table of Contents
1. Introduction ....................................................4
1.1. Conventions Used in This Document ..........................5
2. MSCML Approach ..................................................5
3. Use of SIP Request Methods ......................................6
4. MSCML Design ....................................................8
4.1. Transaction Model ..........................................8
4.2. XML Usage ..................................................9
4.2.1. MSCML Time Values ...................................9
5. Advanced Conferencing ..........................................10
5.1. Conference Model ..........................................10
5.2. Configure Conference Request <configure_conference> .......11
5.3. Configure Leg Request <configure_leg> .....................13
5.4. Terminating a Conference ..................................14
5.5. Conference Manipulation ...................................15
5.6. Video Conferencing ........................................16
5.7. Conference Events .........................................17
5.8. Conferencing with Personalized Mixes ......................18
5.8.1. MSCML Elements and Attributes for
Personalized Mixes .................................19
5.8.2. Example Usage of Personalized Mixes ................20
6. Interactive Voice Response (IVR) ...............................23
6.1. Specifying Prompt Content .................................24
6.1.1. Use of the Prompt Element ..........................24
6.2. Multimedia Processing for IVR .............................30
6.3. Playing Announcements <play> ..............................31
6.4. Prompt and Collect <playcollect> ..........................32
6.4.1. Control of Digit Buffering and Barge-In ............33
6.4.2. Mapping DTMF Keys to Special Functions .............33
6.4.3. Collection Timers ..................................35
6.4.4. Logging Caller DTMF Input ..........................36
6.4.5. Specifying DTMF Grammars ...........................36
6.4.6. Playcollect Response ...............................37
6.4.7. Playcollect Example ................................38
6.5. Prompt and Record <playrecord> ............................38
6.5.1. Prompt Phase .......................................38
6.5.2. Record Phase .......................................39
6.5.3. Playrecord Example .................................41
6.6. Stop Request <stop> .......................................42
7. Call Leg Events ................................................43
7.1. Keypress Events ...........................................43
7.1.1. Keypress Subscription Examples .....................45
7.1.2. Keypress Notification Examples .....................45
7.2. Signal Events .............................................46
7.2.1. Signal Event Examples ..............................47
8. Managing Content <managecontent> ...............................48
8.1. Managecontent Example .....................................50
Van Dyke, et al. Informational [Page 2]RFC 4722 MSCML November 2006
9. Fax Processing .................................................51
9.1. Recording a Fax <faxrecord> ...............................51
9.2. Sending a Fax <faxplay> ...................................53
10. MSCML Response Attributes and Elements ........................56
10.1. Mechanism ................................................56
10.2. Base <response> Attributes ...............................56
10.3. Response Attributes and Elements for <configure_leg> .....57
10.4. Response Attributes and Elements for <play> ..............57
10.4.1. Reporting Content Retrieval Errors ...............58
10.5. Response Attributes and Elements for <playcollect> .......59
10.6. Response Attributes and Elements for <playrecord> ........60
10.7. Response Attributes and Elements for <managecontent> .....61
10.8. Response Attributes and Elements for <faxplay>
and <faxrecord> ..........................................61
11. Formal Syntax .................................................62
11.1. Schema ...................................................62
12. IANA Considerations ...........................................73
12.1. IANA Registration of MIME Media Type application/
mediaservercontrol+xml ...................................73
13. Security Considerations .......................................74
14. References ....................................................75
14.1. Normative References .....................................75
14.2. Informative References ...................................76
Appendix A. Regex Grammar Syntax .................................78
Appendix B. Contributors .........................................79
Appendix C. Acknowledgements .....................................79
Van Dyke, et al. Informational [Page 3]RFC 4722 MSCML November 2006
1. Introduction
This document describes the Media Server Control Markup Language
(MSCML) and its usage. It describes payloads that one can send to a
media server using standard SIP INVITE and INFO methods and the
capabilities these payloads implement. RFC 4240 [2] describes media
server SIP URI formats.
Prior to MSCML, there was not a standard way to deliver SIP-based
enhanced conferencing. Basic SIP constructs, such as those described
in RFC 4240 [2], serve simple n-way conferencing well. The SIP URI
provides a natural mechanism for identifying a specific SIP
conference, while INVITE and BYE methods elegantly implement
conference join and leave semantics. However, enhanced conferencing
applications also require features such as sizing and resizing, in-
conference IVR operations (e.g., recording and playing participant
names to the full conference), and conference event reporting. MSCML
payloads within standard SIP methods realize these features.
The structure and approach of MSCML satisfy the requirements set out
in RFC 4353 [10]. In particular, MSCML serves as the interface
between the conference server or focus and a centralized conference
mixer. In this case, a media server has the role of the conference
mixer.
There are two broad classes of MSCML functionality. The first class
includes primitives for advanced conferencing, such as conference
configuration, participant leg manipulation, and conference event
reporting. The second class comprises primitives for interactive
voice response (IVR). These include collecting DTMF digits and
playing and recording multimedia content.
MSCML fills the need for IVR and conference control with requests and
responses over a SIP transport. VoiceXML [11] fills the need for IVR
with requests and responses over a HTTP transport. This enables
developers to use whatever model fits their needs best.
In general, a media server offers services to SIP UACs, such as
Application Servers, Feature Servers, and Media Gateway Controllers.
See the IPCC Reference Architecture [12] for definitions of these
terms. It is unlikely, but not prohibited, for end-user SIP UACs to
have a direct signaling relationship with a media server. The term
"client" is used in this document to refer generically to an entity
that interacts with the media server using SIP and MSCML.
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RFC 4722 MSCML November 2006
The media server fulfills the role of the Media Resource Function
(MRF) in the IP Multimedia Subsystem (IMS) [13] as described by 3GPP.
MSCML and RFC 4240 [2], upon which MSCML builds, are specifically
focused on the Media resource (Mr) interface which supports
interactions between application logic and the MRF.
This document describes a working framework and protocol with which
there is considerable implementation experience. Application
developers and service providers have created several MSCML-based
services since the availability of the initial version in 2001. This
experience is highly relevant to the ongoing work of the IETF,
particularly the SIP [26], SIPPING [27], MMUSIC [28], and XCON [29]
work groups, the IMS [30] work in 3GPP, and the CCXML work in the
Voice Browser Work Group of the W3C.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
2. MSCML Approach
It is critically important to emphasize that the goal of MSCML is to
provide an application interface that follows the SIP, HTTP, and XML
development paradigm to foster easier and more rapid application
deployment. This goal is reflected in MSCML in two ways.
First, the programming model is that of peer to peer rather than
master-slave. Importantly, this allows the media server to be used
simultaneously for multiple applications rather than be tied to a
single point of control. It also enables standard SIP mechanisms to
be used for media server location and load balancing.
Second, MSCML defines constructs and primitives that are meaningful
at the application level to ensure that programmers are not
distracted by unnecessary complexity. For example, the mixing
resource operates on constructs such as conferences and call
participants rather than directly on individual media streams.
The MSCML paradigm is important to the developer community, in that
developers and operators conceptually write applications about calls,
conferences, and call legs. For the majority of developers and
applications this approach significantly simplifies and speeds
development.
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3. Use of SIP Request Methods
As mentioned above, MSCML payloads may be carried in either SIP
INVITE or INFO requests. The initial INVITE, which creates an
enhanced conference, MAY include an MSCML payload. A subsequent
INVITE to the same Request-URI joins a participant leg to the
conference. This INVITE MAY include an MSCML payload. The initial
INVITE that establishes an IVR session MUST NOT include an MSCML
payload. The client sends all mid-call MSCML payloads for
conferencing and IVR via SIP INFO requests.
SIP INVITE requests that contain both MSCML and Session Description
Protocol (SDP) body parts are used frequently in conferencing
scenarios. Therefore, the media server MUST support message bodies
with the MIME type "multipart/mixed" in SIP INVITE requests.
The media server transports MSCML responses in the final response to
the SIP INVITE containing the matching MSCML request or in a SIP INFO
message. The only allowable final response to a SIP INFO containing
a message body is a 200 OK, per RFC 2976 [3]. Therefore, if the
client sends the MSCML request via SIP INFO, the media server
responds with the MSCML response in a separate INFO request. In
general, these responses are asynchronous in nature and require a
separate transaction due to timing considerations.
There has been considerable debate on the use of the SIP INFO method
for any purpose. Our experience is that MSCML would not have been
possible without it. At the time the first MSCML specification was
published, the first SIP Event Notification draft had just been
submitted as an individual submission. At that time, there was no
mechanism to link SUBSCRIBE/NOTIFY to an existing dialog. This
prevented its use in MSCML, since all events occurred in an INVITE-
established dialog. And while SUBSCRIBE/NOTIFY was well suited for
reporting conference events, its semantics seemed inappropriate for
modifying a participant leg or conference setting where the only
"event" was the success or failure of the request. Lastly, since SIP
INFO was an established RFC, most SIP stack implementations supported
it at that time. We had few, if any, interoperability issues as a
result.
More recent developments have provided additional reasons why
SUBSCRIBE/NOTIFY is not appropriate for use in MSCML. Use of
SUBSCRIBE presents two problems. The first is semantic. The purpose
of SUBSCRIBE is to register interest in User Agent state. However,
using SUBSCRIBE for MSCML results in the SUBSCRIBE modifying the User
Agent state. The second reason SUBSCRIBE is not appropriate is
because MSCML is inherently call based. The association of a SIP
dialog with a call leg means MSCML can be incredibly straightforward.
Van Dyke, et al. Informational [Page 6]
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For example, if one used SUBSCRIBE or other SIP method to send
commands about some context, one must identify that context somehow.
Relating commands to the SIP dialog they arrive on defines the
context for free. Moreover, it is conceptually easy for the
developer. Using NOTIFY to transport MSCML responses is also not
appropriate, as the NOTIFY would be in response to an implicit
subscription. The SIP and SIPPING lists have discussed the dangers
of implicit subscription.
In order to guarantee interoperability with this specification, as
well as with SIP User Agents that are unaware of MSCML, SIP UACs that
wish to use MSCML services MUST specify a service indicator that
supports MSCML in the initial INVITE. RFC 4240 [2] defines the
service indicator "conf", which MUST be used for MSCML conferencing
applications. The service indicator "ivr" MUST be used for MSCML
interactive voice response applications. In this specification, only
"conf" and "ivr" are described.
The media server MUST support moving the call between services
through sending the media server a BYE on the existing dialog and
establishing a new dialog with an INVITE to the desired service.
Media servers SHOULD support moving between services without
requiring modification of the previously established SDP parameters.
This is achieved by sending a re-INVITE on the existing dialog in
which the Request-URI is modified to specify the new service desired
by the client. This eliminates the need for the client to send an
INVITE to the caller or gateway to establish new SDP parameters.
The media server, as a SIP UAS, MUST respond appropriately to an
INVITE that contains an MSCML body. If MSCML is not supported, the
media server MUST generate a 415 final response and include a list of
the supported content types in the response per RFC 3261 [4]. The
media server MUST also advertise its support of MSCML in responses to
OPTIONS requests, by including "application/mediaservercontrol+xml"
as a supported content type in an Accept header. This alleviates the
major issues with using INFO for the transport of application data;
namely, the User Agent's proper interpretation of what is, by design,
an opaque message request.
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4. MSCML Design
4.1. Transaction Model
To avoid undue complexity, MSCML establishes two rules regarding its
usage. The first is that only one MSCML body may be present in a SIP
request. The second is that each MSCML body may contain only one
request or response. This greatly simplifies transaction management.
MSCML syntax does provide for the unique identification of multiple
requests in a single body part. However, this is not supported in
this specification.
Per the guidelines of RFC 3470 [14], MSCML bodies MUST be well formed
and valid.
MSCML is a direct request-response protocol. There are no
provisional responses, only final responses. A request may, however,
result in multiple notifications. For example, a request for active
talker reports will result in a notification for each speaker set.
This maps to the three major element trees for MSCML: <request>,
<response>, and <notification>.
Figure 1 shows a request body. Depending on the command, one can
send the request in an INVITE or an INFO. Figure 2 shows a response
body. The SIP INFO method transports response bodies. Figure 3
shows a notification body. The SIP INFO method transports
notifications.
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<request>
... request body ...
</request>
</MediaServerControl>
Figure 1: MSCML Request Format
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<response>
... response body ...
</response>
</MediaServerControl>
Figure 2: MSCML Response Format
Van Dyke, et al. Informational [Page 8]RFC 4722 MSCML November 2006
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<notification>
... notification body ...
</notification>
</MediaServerControl>
Figure 3: MSCML Notification Format
MSCML requests MAY include a client-defined ID attribute for the
purposes of matching requests and responses. The values used for
these IDs need only be unique within the scope of the dialog in which
the requests are issued.
4.2. XML Usage
In the philosophy of XML as a text-based description language, and
not as a programming language, MSCML makes the choice of many
attribute values for readability by a human. Thus, many attributes
that would often be "boolean" instead take "yes" or "no" values. For
example, what does 'report="false"' or 'report="1"' mean? However,
'report="yes"' is clearer: I want a report. Some programmers prefer
the precision of a boolean. To satisfy both styles, MSCML defines an
XML type, "yesnoType", that takes on the values "yes" and "no" as
well as "true", "false", "1", and "0".
Many attributes in the MSCML schema have default values. In order to
limit demands on the XML parser, MSCML applies these values at the
protocol, not XML, level. The MSCML schema documents these defaults
as XML annotations to the appropriate attribute.
4.2.1. MSCML Time Values
For clarity, time values in MSCML are based on the time designations
described in the Cascading Style Sheets level 2 (CSS2) Specification
[15]. Their format consists of a number immediately followed by an
optional time unit identifier of the following form:
ms: milliseconds (default)
s: seconds
If no time unit identifier is present, the value MUST be interpreted
as being in milliseconds. As extensions to [15] MSCML allows the
string values "immediate" and "infinite", which have special meaning
for certain timers.
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5. Advanced Conferencing
5.1. Conference Model
The advanced conferencing model is a star controller model, with both
signaling and media directed to a central location. Figure 4 depicts
a typical signaling relationship between end users' UACs, a
conference application server, and a media server.
RFC 4353 [10] describes this model. The application server is an
instantiation of the conference focus. The media server is an
instantiation of the media mixer. Note that user-level constructs,
such as event notifications, are in the purview of the application
server. This is why, for example, the media server sends active
talker reports using MSCML notifications, while the application
server would instead use the conference package [16] for individual
notifications to SIP user agents. Note that we do not recommend the
use of the conference package for media server to application server
notifications because none of the filtering and membership
information is available at the media server.
+-------+
| UAC 1 |---\ Public URI +-------------+
+-------+ \ _____________| Application |
/ / | Server | Not shown:
+-------+ / / +-------------+ RTP flows directly
| UAC 2 |---/ / | Private between UACs and
+-------+ / | URI media server
. / +--------------+
: / | |
+-------+ / | Media Server |
| UAC n |---/ | |
+-------+ +--------------+
Figure 4: Conference Model
Each UAC sends an INVITE to a Public Conference URI. Presumably,
the client publishes this URI, or it is an ad hoc URI. In any
event, the client generates a Private URI, following the rules
specified by RFC 4240 [2]. That is, the URI is of the following
form:
sip:conf=UniqueID@ms.example.net
where UniqueID is a unique conference identifier and
ms.example.net is the host name or IP address of the media server.
There is nothing to prevent the UACs from contacting the media
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server directly. However, one would expect the owner of the media
server to restrict who can use its resources.
As for basic conferencing, described by RFC 4240 [2], the first
INVITE to the media server with a UniqueID creates a conference.
However, in advanced conferencing, the first INVITE MAY include a
MSCML <configure_conference> payload rather than the SDP of a
conference participant. The <configure_conference> payload
conveys extended session parameters (e.g., number of participants)
that SDP does not readily express, but the media server must know
to allocate the appropriate resources.
When the conference is created by sending an INVITE containing a
MSCML <configure_conference> payload, the resulting SIP dialog is
termed the "Conference Control Leg." This leg has several useful
properties. The lifetime of the conference is the same as that of
its control leg. This ensures that the conference remains in
existence even if all participant legs leave or have not yet
arrived. In addition, when the client terminates the Conference
Control Leg, the media server automatically terminates all
participant legs. The Conference Control Leg is also used for
play or record operations to/from the entire conference and for
active talker notifications. Full conference media operations and
active talker report subscriptions MUST be executed on the
Conference Control Leg.
Creation of a Conference Control Leg is RECOMMENDED because full
advanced conferencing capabilities are not available without it.
Clients MUST establish the Conference Control Leg in the initial
INVITE that creates the conference; it cannot be created later.
Once the client has created the conference with or without the
Conference Control Leg, participants can be joined to the
conference. This is achieved by the client's directing an INVITE
to the Private Conference URI for each participant. Using the
example conference URI given above, this would be
sip:conf=UniqueID@ms.example.net.
5.2. Configure Conference Request <configure_conference>
The <configure_conference> request has two attributes that control
the resources the media server sets aside for the conference.
These are described in the list below.
Attributes of <configure_conference>:
o reservedtalkers - optional (see note), no default value: The
maximum number of talker legs allocated for the conference. Note:
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required when establishing the Conference Control Leg but optional
in subsequent <configure_conference> requests.
o reserveconfmedia - optional, default value "yes": Controls
allocation of resources to enable playing or recording to or from
the entire conference
When the reservedtalkers+1st INVITE arrives at the media server, the
media server SHOULD generate a 486 Busy Here response. Failure to
send a 486 response to this condition can cause the media server to
oversubscribe its resources.
NOTE: It would be symmetric to have a reservedlisteners parameter.
However, the practical limitation on the media server is the
number of talkers for a mixer to monitor. In either case, the
client regulates who gets into the conference by either proxying
the INVITEs from the user agent clients or metering to whom it
gives the conference URI.
For example, to create a conference with up to 120 active talkers and
the ability to play audio into the conference or record portions or
all of the conference full mix, the client specifies both attributes,
as shown in Figure 6.
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<request>
<configure_conference reservedtalkers="120"
reserveconfmedia="yes"/>
</request>
</MediaServerControl>
Figure 6: 120 Speaker MSCML Example
In addition to these attributes, a <configure_conference> request MAY
contain a child <subscribe> element. The <subscribe> element is used
to request notifications for conference-wide active talker events.
Detailed information regarding active talker events is contained in
Section 5.7.
The client MUST include a <configure_conference> request in the
initial INVITE which establishes the conference when creating the
Conference Control Leg. The client server MUST issue asynchronous
commands, such as <play>, separately (i.e., in INFO messages) to
avoid ambiguous responses.
Media operations on the Conference Control leg are performed
internally, no external RTP streams are involved. Accordingly, the
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media server does not expect RTP on the Conference Control Leg.
Therefore, the client MUST send either no SDP or hold SDP in the
INVITE request containing a <configure_conference> payload. The
media server MUST treat SDP with all media lines set to "inactive" or
with connection addresses set to 0.0.0.0 (for backwards
compatibility) as hold SDP.
The media server sends a response when it has finished processing the
<configure_conference> request. The format of the
<configure_conference> response is detailed in Section 10.2.
5.3. Configure Leg Request <configure_leg>
Conference legs have a number of properties the client can modify.
These are set using the <configure_leg> request. This request has
the attributes described in the list below.
Attributes of <configure_leg>:
o type - optional, default value "talker": Consider this leg's audio
for inclusion in the output mix. Alternative is "listener".
o dtmfclamp - optional, default value "yes": Remove detected DTMF
digits from the input audio.
o toneclamp - optional, default value "yes": Remove tones from the
input audio. Tones include call progress tones and the like.
o mixmode - optional, default value "full": Be a candidate for the
full mix. Alternatives are "mute", to disallow media in the mix,
"parked", to disconnect the leg's media streams from the
conference for IVR operations, "preferred", to give this stream
preferential selection in the mix (i.e., even if not loudest
talker, include media, if present, from this leg in the mix), and
"private", which enables personalized mixes.
In addition to these attributes, there are four child elements
defined for <configure_leg>. These are <inputgain>, <outputgain>,
<configure_team>, and <subscribe>.
The first two, <inputgain> and <outputgain>, modify the gain applied
to the input and output audio streams, respectively. These may
contain <auto>, to use automatic gain control (AGC) or <fixed>. The
<auto> element has the attributes "startlevel", "targetlevel", and
"silencethreshold". All the parameters are in dB. The <fixed>
element has the attribute "level", which is in dB. The default for
both <inputgain> and <outputgain> is <fixed>. The media server MAY
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silently cap <inputgain> or <outputgain> requests that exceed the
gain limits imposed by the platform.
Clients most commonly manipulate only the input gain for a conference
leg and rely on the mixer to set an optimum output gain based on the
inputs currently in the mix. However, as described above, MSCML does
allow for manipulation of the output gain as well. Some of the IVR
commands, such as <play>, enable control of the output gain for
content playback operations. The interaction of conference output
gain and IVR playback gain controls is described in Section 6.1.1.
Note that <inputgain> and <outputgain> settings apply only to
conference legs and do not apply to IVR sessions.
The <configure_team> element is used to create and manipulate groups
for personalized mixes. Details of personalized mixes are discussed
in Section 5.8.
The <subscribe> element is used to request notifications for call leg
related events, such as asynchronous DTMF digit reports. Detailed
information regarding call leg events is discussed in Section 7.
If the default parameters are acceptable for the leg the client
wishes to enter into the conference, then a normal SIP INVITE, with
no MSCML body, is sufficient. However, if the client wishes to
modify one or more of the parameters, the client can include a MSCML
body in addition to the SDP body.
The client can modify the conference leg parameters during the
conference by issuing a SIP INFO on the dialog representing the
conference leg. Of course, the client cannot modify SDP in an INFO
message.
The media server sends a response when it has finished processing the
<configure_leg> request. The format of the <configure_leg> response
is detailed in Section 10.3.
5.4. Terminating a Conference
To remove a leg from the conference, the client issues a SIP BYE
request on the selected dialog representing the conference leg.
The client can terminate all legs in a conference by issuing a SIP
BYE request on the Conference Control Leg. If one or more
participants are still in the conference when the media server
receives a SIP BYE request on the Conference Control Leg, the media
server issues SIP BYE requests on all remaining conference legs to
ensure cleanup of the legs.
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RFC 4722 MSCML November 2006
The media server returns a 200 OK to the SIP BYE request as it sends
BYE requests to the other legs. This is because we cannot issue a
provisional response to a non-INVITE request, yet the teardown of the
other legs may exceed the retransmission timer limits of the original
request. While the conference is being cleaned up, the media server
MUST reject any new INVITEs to the terminated conference with a 486
Busy Here response. This response indicates that the specified
conference cannot accept any new members, pending deletion.
5.5. Conference Manipulation
Once the conference has begun, the client can manipulate the
conference as a whole or a particular participant leg by issuing
commands on the associated SIP dialog. For example, by sending MSCML
requests on the Conference Control Leg the client can request that
the media server record the conference, play a prompt to the
conference, or request reports on active talker events. Similarly,
the client may mute a participant leg, configure a personalized mix
or request reports for call leg events, such as DTMF keypresses.
Figure 7 shows an example of an MSCML command that plays a prompt to
all conference participants.
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<request>
<play>
<prompt>
<audio url="http://prompts.example.net/en_US/welcome.au"/>
</prompt>
</play>
</request>
</MediaServerControl>
Figure 7: Full Conference Audio Command - Play
A client can modify a leg by issuing an INFO on the dialog associated
with the participant leg. For example, Figure 8 mutes a conference
leg.
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<request>
<configure_leg mixmode="mute"/>
</request>
</MediaServerControl>
Figure 8: Sample Change Leg Command
Van Dyke, et al. Informational [Page 15]RFC 4722 MSCML November 2006
In Figure 7, we saw a request to play a prompt to the entire
conference. The client can also request to play a prompt to an
individual call leg. In that case, the MSCML request is issued
within the SIP dialog of the desired conference participant.
Section 6 describes the interactive voice response (IVR) services
offered by MSCML. If an IVR command arrives on the control channel,
it takes effect on the whole conference. This is a mechanism for
playing prompts to the entire conference (e.g., announcing new
participants). If an IVR command arrives on an individual leg, it
only affects that leg. This is a mechanism for interacting with
users, such as the creation of "waiting rooms", allowing a user to
mute themselves using key presses, allowing a moderator to out-dial,
etc.
A participant leg MUST be configured with mixmode="parked" prior to
the issuance of any IVR commands with prompt content ('prompturl'
attribute or <prompt> element). Parking the leg isolates the
participant's input and output media from the conference and allows
use of those streams for playing and recording purposes. However,
the mixmode has no effect if just digit collection or recording is
desired. <playcollect> and <playrecord> requests without prompt
content MAY be sent on participant legs without setting
mixmode="parked".
5.6. Video Conferencing
MSCML-controlled advanced conferences, as well as RFC 4240 [2]
controlled basic conferences, implicitly support video conferencing
in the form of video switching. In video switching, the video stream
of the loudest talker (with some hysteresis) is sent to all
participants other than that talker. The loudest talker receives the
video stream from the immediately prior loudest talker.
Media servers MUST ensure that participants receive video media
compatible with their session. For example, a participant who has
established an H.263 video stream will not receive video from another
participant employing H.264 media. Media servers SHOULD implement
video transcoding to minimize media incompatibilities between
participants.
The media server MUST switch video streams only when it receives a
refresh video frame. A refresh frame contains all the video
information required to decode that frame (i.e., there is no
dependency on data from previous video frames).
Van Dyke, et al. Informational [Page 16]RFC 4722 MSCML November 2006
Refresh frames are large and generally sent infrequently to conserve
network bandwidth. The media server MUST implement standard
mechanisms to request that the new loudest talker's video encoder
transmits a refresh frame to ensure that video can be switched
quickly.
5.7. Conference Events
A client can subscribe for periodic active talker event reports that
indicate which participants are included in the conference mix. As
these are conference-level events, the subscription and notifications
are sent on the Conference Control Leg.
Media servers MAY impose limits on the minimum interval for active
talker reports for performance reasons. If the client request is
below the imposed minimum, the media server SHOULD set the interval
to the minimum value supported. To limit unnecessary notification
traffic, the media server SHOULD NOT send a report if the active
talker information for the conference has not changed during the
reporting interval.
A request for an active talker report is in Figure 9. The active
talker report enumerates the current call legs in the mix.
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<request>
<configure_conference>
<subscribe>
<events>
<activetalkers report="yes" interval="60s"/>
</events>
</subscribe>
</configure_conference>
</request>
</MediaServerControl>
Figure 9: Active Talker Request
Event notifications are sent in SIP INFO messages. Figure 10 shows
an example of a report.
Van Dyke, et al. Informational [Page 17]RFC 4722 MSCML November 2006
<?xml version="1.0" encoding="utf-8"?>
<MediaServerControl version="1.0">
<notification>
<conference uniqueid="ab34h76z" numtalkers="47">
<activetalkers>
<talker callid="myhost4sn123"/>
<talker callid="myhost2sn456"/>
<talker callid="myhost12sn78"/>
</activetalkers>
</conference>
</notification>
</MediaServerControl>
Figure 10: Active Talker Event Example
The value of the "callid" attribute in the <talker> element
corresponds to the value of the SIP Call-ID header of the associated
dialog. This enables the client to associate the active talker with
a specific participant leg.
5.8. Conferencing with Personalized Mixes
MSCML enables clients to create personalized mixes through the
<configure_team> element for scenarios where the standard mixmode
settings do not provide sufficient control. The <configure_team>
element is a child of <configure_leg>.
To create personalized mixes, the client has to identify the
relationships among the participants. This is accomplished by
manipulating two MSCML objects. These objects are:
1. The list of team members (<teammate> elements), set using
<configure_team>
2. The mixmode attribute set through <configure_leg>
The media server uses the values of these objects to determine which
audio inputs to combine for output to the participant. In a normal
conference, each participant hears the conference mix minus their own
input if they are part of the mixed output. The team list enables
the client to specify other participants that the leg can hear in
addition to the normal mixed output. Note that personalized mix
settings apply only to audio media and do not affect video switching.
Team relationships are implicitly symmetric. If the client sets
participant A as a team member of participant B, then the media
server automatically sets participant B as a team member for A.
Van Dyke, et al. Informational [Page 18]RFC 4722 MSCML November 2006
The id attribute set through <configure_leg> is used to identify the
various participants. A unique ID MUST be assigned to each
participant included in a personalized mix. The IDs used MUST be
unique within the scope of the conference in which they appear.
By itself, the team list only defines those participants that the leg
can hear. The mixmode attribute of each team member determines
whether to include their audio input in the personalized mix. If the
client sets the teammate's mixmode to private, then it is part of the
mix. If the mixmode is set to any other value, it is not.
5.8.1. MSCML Elements and Attributes for Personalized Mixes
Control of personalized mixes rely on two major MSCML elements:
1. <configure_leg>, using the mixmode attribute setting
mixmode="private"
2. <configure_team>
The <configure_team> element allows the user to make the participants
members of a team within a specific conference. It is a child of the
<configure_leg> parent element.
The client sends the <configure_team> element in a <configure_leg>
request in either a SIP INVITE or SIP INFO.
o In an INVITE, to join a participant whose properties differ from
the properties established for the conference as a whole.
o In an INFO, to change the properties for an existing leg.
The two attributes of the configure_team element are "id" and
"action". The id attribute MUST contain the unique ID of the leg
being modified, as set in the original <configure_leg> request. The
action attribute can take on the values "add", "delete", "query", and
"set". The default value is "query". This attribute allows the user
to modify the team list. Table 1 describes the actions that can be
performed on the team list.
Van Dyke, et al. Informational [Page 19]RFC 4722 MSCML November 2006
+--------+----------------------------------------------------------+
| Action | Description |
+--------+----------------------------------------------------------+
| add | Adds a teammate to the mix. |
| delete | Deletes a teammate from the mix. |
| query | Returns the teammate list to the requestor. This is the |
| | default value. |
| set | Creates a team list when followed by <teammate id="n"> |
| | and also removes all the teammates from the team list |
| | for example, when the creator (originator) of the team |
| | list on that specific conference leg wants to remove all |
| | of the teammates from the team. If the set operation |
| | removes all teammates from a participant, that |
| | participant hears the full conference mix. |
+--------+----------------------------------------------------------+
Table 1: Configure Team Actions
5.8.2. Example Usage of Personalized Mixes
A common use of personalized mixing is to support coaching of one
participant by another. The coaching scenario includes three
participants:
1. The Supervisor, who coaches the agent.
2. The Agent, who interacts with the customer.
3. The Customer, who interacts with the agent.
Table 2 illustrates the details of the coached conference topology.
+-------------+------------+------------+---------+-----------------+
| Participant | ID | Team | Mixmode | Hears |
| | | Members | | |
+-------------+------------+------------+---------+-----------------+
| Supervisor | supervisor | Agent | Private | customer + |
| | | | | agent |
| Agent | agent | Supervisor | Full | customer + |
| | | | | supervisor |
| Customer | customer | none | Full | agent |
+-------------+------------+------------+---------+-----------------+
Table 2: Coached Conference Example
To create this topology, the client performs the following actions:
1. The client joins each leg to the conference, being certain to
include a unique ID in the <configure_leg> request. The leg ID
needs to be unique only within the scope of the conference to
which it belongs.
Van Dyke, et al. Informational [Page 20]RFC 4722 MSCML November 2006
2. The client configures the teammate list and mixmode of each
participant, as required.
Both actions (steps 1 and 2) may be combined in a single MSCML
request. The following sections detail these actions and their
corresponding MSCML payloads.
5.8.2.1. Create the Conference
Before joining any participants, the client must create the
conference by sending a SIP INVITE that contains an MSCML
<configure_conference> request with a unique conference identifier.
5.8.2.2. Joining and Configuring the Coach
Join the coach leg to the conference and configure its desired
properties by sending a SIP INVITE containing a <configure_leg>
request. The <configure_leg> element sets the leg's unique ID to
supervisor and its mixmode to private.
The corresponding MSCML request is as follows.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg id="supervisor" mixmode="private"/>
</request>
</MediaServerControl>
Figure 11: Join Coach Request
Note that the client cannot configure the teammate list for the coach
yet, as there are no other participants in the conference. One must
join a participant to the conference before one can add it as a
teammate for another leg.
5.8.2.3. Joining and Configuring the Agent
Join the agent leg to the conference and configure its desired
properties by sending a SIP INVITE containing a <configure_leg>
request. The <configure_leg> element sets the leg's unique ID to
"agent" and sets the supervisor as a team member of the agent.
Because team member relationships are symmetric, this action also
adds the agent as a team member for the coach.
Van Dyke, et al. Informational [Page 21]RFC 4722 MSCML November 2006
The corresponding MSCML request is as follows.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg id="agent">
<configure_team action="set">
<teammate id="supervisor"/>
</configure_team>
</configure_leg>
</request>
</MediaServerControl>
Figure 12: Join Agent Request
Because the desired mixmode for this leg is full, which is the
default value, there is no need to set it explicitly.
5.8.2.4. Joining and Configuring the Client
Join the client leg to the conference and configure its desired
properties by sending a SIP INVITE containing a <configure_leg>
request. The <configure_leg> element simply sets the leg's unique ID
to "customer". The media server does not need further configuration
because the desired mixmode, full, is the default and the customer
has no team members.
The corresponding MSCML request is as follows.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg id="customer"/>
</request>
</MediaServerControl>
Figure 13: Join Client Request
Strictly speaking, it is not a requirement that the client give the
customer leg a unique ID because it will not be a team member.
However, when using coached conferencing, we RECOMMEND that one
assign a unique ID to each leg in the initial INVITE request.
Assigning a unique ID eliminates the need to set it later by sending
a SIP INFO if one later desires personalized mixing for the customer
leg.
The conference is now in the desired configuration, shown previously
in Table 2.
Van Dyke, et al. Informational [Page 22]RFC 4722 MSCML November 2006
6. Interactive Voice Response (IVR)
In the IVR model, the media server acts as a media-processing proxy
for the UAC. This is particularly useful when the UAC is a media
gateway or other device with limited media processing capability.
The typical use case for MSCML is when there is an application server
that is the MSCML client. The client can use the SIP Service URI
concept (RFC 3087) to initiate a service. The client then uses RFC
4240 [2] to initiate a MSCML session on a media server. These
relationships are shown in Figure 14.
SIP +--------------+
Service URI | Application |
/----------------| Server |
/(e.g., RFC 3087) +--------------+
/ | MSCML
/ SIP | Session
/ +--------------+
+-----+/ RTP | |
| UAC |======================| Media Server |
+-----+ | |
+--------------+
Figure 14: IVR Model
The IVR service supports basic Interactive Voice Response functions,
playing announcements, collecting DTMF digits, and recording, based
on Media Server Control Markup Language (MSCML) directives added to
the message body of a SIP request. The major MSCML IVR requests are
<play>, <playcollect>, and <playrecord>.
Multifunction media servers MUST use the URI conventions described in
RFC 4240 [2]. The service indicator for MSCML IVR MUST be set to
"ivr", as shown in the following example:
sip:ivr@ms.example.net
The VoiceXML IVR service indicator is "dialog". This service
indicator MUST NOT be used for any other interactive voice response
control mechanism.
The media server MUST accept MSCML IVR payloads in INFO requests and
MUST NOT accept MSCML IVR payloads in the initial or subsequent
INVITEs. The INFO method reduces certain timing issues that occur
with INVITEs and requires less processing on both the client and
media server.
Van Dyke, et al. Informational [Page 23]RFC 4722 MSCML November 2006
The media server notifies the client that the command has completed
through a <response> message containing final status information and
associated data such as collected DTMF digits.
The media server does not queue IVR requests. If the media server
receives a new IVR request while another is in progress, the media
server stops the first operation and it carries out the new request.
The media server generates a <response> message for the first request
and returns any data collected up to that point. If a client wishes
to stop a request in progress but does not wish to initiate another
operation, it issues a <stop> request. This also causes the media
server to generate a <response> message.
The media server treats a SIP re-INVITE that modifies the established
SDP parameters as an implicit <stop> request. Examples of such SDP
modifications include receiving hold SDP or removing an audio or
video stream. When this occurs, the media server immediately
terminates the running <play>, <playcollect>, or <playrecord> request
and sends a <response> indicating "reason=stopped".
6.1. Specifying Prompt Content
The MSCML IVR requests support two methods of specifying content to
be delivered to the user. These are the <prompt> element and the
prompturl attribute. Clients MUST NOT utilize both methods in a
single IVR request. Clients SHOULD use the more flexible <prompt>
mechanism. Use of the prompturl attribute is deprecated and may not
be supported in future MSCML versions.
6.1.1. Use of the Prompt Element
The <prompt> element MAY be included in the body of a <play>,
<playcollect>, or <playrecord> request to specify a prompt sequence
to be delivered to the caller. The prompt sequence consists of one
or more references to physical content files, spoken variables, or
dynamic URLs that return a sub-sequence of files or variables. In
addition, the <prompt> element has several attributes that control
playback of the included content. These are described in the list
below.
Attributes of <prompt>:
o baseurl - optional, no default value: For notational convenience,
as well as reducing the MSCML payload size, the "baseurl"
attribute is used to specify a base URL that is prepended to any
other URLs in the sequence that are not fully qualified.
Van Dyke, et al. Informational [Page 24]RFC 4722 MSCML November 2006
o delay - optional, default value "0": The "delay" attribute to the
prompt element specifies the time to pause between repetitions of
the <prompt> sequence. It has no effect on the first iteration of
the sequence. Expressed as a time value (Section 4.2.1) from 0
onwards.
o duration - optional, default value "infinite": The "duration"
attribute to the prompt element controls the maximum amount of
time that may elapse while the media server repeats the sequence.
This allows the client to set an upper bound on the length of
play. Expressed as a time value (Section 4.2.1) from 1ms onwards
or the strings "immediate" and "infinite". "Immediate" directs
the media server to end play immediately, whereas "infinite"
indicates that the media server imposes no limit.
o gain - optional, default value "0": Sets the absolute gain to be
applied to the content contained in <prompt>. The value of this
attribute is specified in units of dB. The media server MAY
silently cap values that exceed the gain limits imposed by the
platform. The level reverts back to its original value when
playback of the content contained in <prompt> has been completed.
o gaindelta - optional, default value "0": Sets the relative gain to
be applied to the content contained in <prompt>. The value of
this attribute is specified in units of dB. The media server MAY
silently cap values which exceed the gain limits imposed by the
platform. The level reverts back to its original value when
playback of the content contained in <prompt> has been completed.
o rate - optional, default value "0": Specifies the absolute
playback rate of the content relative to normal as either a
positive percentage (faster) or a negative percentage (slower).
Any value that attempts to set the rate above the maximum allowed
or below the minimum allowed silently sets the rate to the maximum
or minimum. The rate reverts back to its original value when
playback of the content contained in <prompt> has been completed.
o ratedelta - optional, default value "0": Specifies the playback
rate of the content relative to it's current rate as either a
positive percentage (faster) or negative percentage (slower). Any
value that attempts to set the rate above the maximum allowed or
below the minimum allowed silently sets the rate to the maximum or
minimum. The rate reverts back to its original value when
playback of the content contained in <prompt> has completed.
Van Dyke, et al. Informational [Page 25]RFC 4722 MSCML November 2006
o locale - optional, no default value: Specifies the language and
country variant used for resolving spoken variables. The language
is defined as a two-letter code per ISO 639. The country variant
is also defined as a two-letter code per ISO 3166. These codes
are concatenated with a single underscore (%x5F) character.
o offset - optional, default value "0": A time value (Section 4.2.1)
which specifies the time from the beginning of the sequence at
which play is to begin. Offset only applies to the first
repetition; subsequent repetitions begin play at offset 0.
Allowable values are positive time values from 0 onwards. When
the sequence consists of multiple content files, the offset may
select any point in the sequence. If the offset value is greater
than the total time of the sequence, it will "wrap" to the
beginning and continue from there until the media server reaches
the specified offset.
o repeat - optional, default value "1": The "repeat" attribute to
the prompt element controls the number of times the media server
plays the sequence in the <prompt> element. Allowable values are
integers from 0 on and the string "infinite", which indicates that
repetition should occur indefinitely. For example, "repeat=2"
means that the sequence will be played twice, and "repeat=0",
which is allowed, means that the sequence is not played.
o stoponerror - optional, default value "no": Controls media server
handling and reporting of errors encountered when retrieving
remote content. If set to "yes", content play will end if a fetch
error occurs, and the response will contain details regarding the
failure. If set to "no", the media server will silently move on
to the next URL in the sequence if a fetch failure occurs.
Clients MUST NOT include both 'gain' and 'gaindelta' attributes
within a single <prompt> element.
When the client explicitly controls the output gain on a conference
leg, as described in Section 5.3, the 'gain' and 'gaindelta'
attributes SHOULD interact with the conference leg output gain
settings in the following manner.
o Conference leg output gain set to <fixed>: The operation of the
'gain' and 'gaindelta' attributes are unchanged. However, the
baseline gain value before any playback changes are applied is the
value specified for the conference leg.
o Conference leg output gain set to <auto>: When playback gain
controls are used, the automatic gain control settings for the leg
are suspended for the duration of the playback operation. The
Van Dyke, et al. Informational [Page 26]RFC 4722 MSCML November 2006
operation of the 'gain' and 'gaindelta' attributes are unchanged.
The automatic gain control settings are reinstated when playback
has finished.
Media servers SHOULD support rate controls for content. However,
media servers MAY silently ignore rate change requests if content
limitations do not allow the request to be honored. Clients MUST NOT
include both 'rate' and 'ratedelta' attributes within a single
<prompt> element.
Figure 16 shows a sample prompt block.
<prompt stoponerror="yes"
baseurl="file:////var/mediaserver/prompts/"
locale="en_US" offset="0" gain="0" rate="0"
delay="0" duration="infinite" repeat="1">
<audio url="num_dialed.raw" encoding="ulaw"/>
<variable type="dig" subtype="ndn" value="3014170700"/>
<audio url="num_invalid.wav"/>
<audio url="please_check.wav"/>
</prompt>
Figure 16: Prompt Block Example
6.1.1.1. <audio> and <variable> Elements
Clients compose prompt sequences using the <audio> and <variable>
elements. An <audio> element MAY refer to content that contains
audio, video, or both; the generic name is preserved for backwards
compatibility. The <audio> element has the attributes described in
the list below.
Attributes of <audio>:
o url - required, no default value: The URL of the content to be
retrieved and played. The target may be a local or remote (NFS)
"file://" scheme URL or an "http://" or "https://" scheme URL. If
the URL is not fully qualified and a "baseurl" attribute was set,
the value of the "baseurl" attribute will be prepended to this
value to generate the target URL.
o encoding - optional, default value "ulaw": Specifies the content
encoding for file formats that are not self-describing (e.g.,
.WAV). Allowable values are "ulaw", "alaw", and "msgsm". This
attribute only affects "file://" scheme URLs.
o gain - optional, default value "0": Sets the absolute gain to be
applied to the content URL. The value of this attribute is
Van Dyke, et al. Informational [Page 27]RFC 4722 MSCML November 2006
specified in units of dB. The media server MAY silently cap
values that exceed the gain limits imposed by the platform. The
level reverts back to its original value when playback of the
content URL has been completed.
o gaindelta - optional, default value "0": Sets the relative gain to
be applied to the content URL. The value of this attribute is
specified in units of dB. The media server MAY silently cap
values that exceed the gain limits imposed by the platform. The
level reverts back to its original value when playback of the
content URL has been completed.
o rate - optional, default value "0": Specifies the absolute
playback rate of the content relative to normal as either a
positive percentage (faster) or a negative percentage (slower).
Any value that attempts to set the rate above the maximum allowed
or below the minimum allowed silently sets the rate to the maximum
or minimum. The rate reverts back to its original value when
playback of the content URL has been completed.
o ratedelta - optional, default value "0": Specifies the playback
rate of the content relative to it's current rate as either a
positive percentage (faster) or a negative percentage (slower).
Any value that attempts to set the rate above the maximum allowed
or below the minimum allowed silently sets the rate to the maximum
or minimum. The rate reverts back to its original value when
playback of the content URL has been completed.
Clients MUST NOT include both 'gain' and 'gaindelta' attributes
within a single <audio> element.
When the client explicitly controls the output gain on a conference
leg, as described in Section 5.3, the 'gain' and 'gaindelta'
attributes SHOULD interact with the conference leg output gain
settings in the following manner.
o Conference leg output gain set to <fixed>: The operation of the
'gain' and 'gaindelta' attributes are unchanged. However, the
baseline gain value before any playback changes are applied is the
value specified for the conference leg.
o Conference leg output gain set to <auto>: When playback gain
controls are used, the automatic gain control settings for the leg
are suspended for the duration of the playback operation. The
operation of the 'gain' and 'gaindelta' attributes are unchanged.
The automatic gain control settings are reinstated when playback
has finished.
Van Dyke, et al. Informational [Page 28]RFC 4722 MSCML November 2006
Media servers SHOULD support rate controls for content. However,
media servers MAY silently ignore rate change requests if content
limitations do not allow the request to be honored. Clients MUST NOT
include both 'rate' and 'ratedelta' attributes within a single
<audio> element.
Media servers MUST support local and remote (NFS) "file://" scheme
URLs and "http://" and "https://" scheme URLs for content retrieval.
NOTE: The provisioning of NFS mount points and their mapping to
the "file://" schema is purely a local matter at the media server.
MSCML also supports "http://" and "https://" scheme URLS that return
a list of physical URLs using the "text/uri-list" MIME type. This
facility provides flexibility for applications to dynamically
generate prompt sequences at execution time and enables separation of
this function from the client and media server.
Spoken variables are specified using the <variable> element. This
element has the attributes described in the list below. MSCML's
spoken variables are based on those described in Audio Server
Protocol [17].
Attributes of <variable>:
o type - required, no default value: Specifies the major type format
of the spoken variable to be played. Allowable values are "dat"
(date), "dig" (digit), "dur" (duration), "mth" (month), "mny"
(money), "num" (number), "sil" (silence), "str" (string), "tme"
(time), and "wkd" (weekday).
o subtype - optional, no default value: Specifies the minor type
format of the spoken variable to be played. Allowable values
depend on the value of the corresponding "type" attribute.
Possible values are "mdy", "ymd", and "dmy" for dates, "t12" and
"t24" for times, "gen", "ndn", "crd", and "ord" for digits, and
"USD" for money.
o value - required, no default value: A string that will be
interpreted based on the formatting information specified in the
"type" and "subtype" attributes and the "locale" attribute of the
parent <prompt> element to render the spoken variable.
If the "locale" attribute was not specified in <prompt>, the media
server SHOULD make a selection based on platform configuration. If
the precise "locale" requested cannot be honored, the media server
SHOULD select the closest match based on the available content.
Van Dyke, et al. Informational [Page 29]RFC 4722 MSCML November 2006
IVR applications normally require specialized prompt content that is
authored by the application provider. To deliver a quality user
interaction, the specialized prompts and spoken variables must be
generated by the same speaker. Since the media server inherently
supports multiple simultaneous applications, it is extremely
difficult to provision all the necessary application prompts and
matching spoken variable content locally on the media server.
Therefore, we STRONGLY RECOMMEND that clients employ the dynamic URL
mechanism described earlier to generate spoken variables using an
external web server that returns "text/uri-list" content.
6.2. Multimedia Processing for IVR
MSCML IVR requests implicitly support multimedia content. Multimedia
capabilities are controlled by the audio and video media negotiated
for the dialog and the content specified by the client for play and
record operations. If the content specified for delivery contains
both audio and video tracks and the dialog has audio and video
streams, both tracks are streamed to the caller. Likewise, if the
dialog has both audio and video streams and the content format
specified supports both (e.g., .3gp files) the media server records
both streams to the file.
If there is a mismatch between the real time media and specified
content, the media server MUST play or record the appropriate content
tracks rather than failing the request. For example, if the client
has requested playback of content with audio and video tracks but
only audio media has been established for the dialog, the media
server should play the audio track. If the dialog has both audio and
video media but the content is audio-only, the media server MAY
stream a pre-provisioned video track to the caller. Media servers
SHOULD implement video transcoding functions to minimize
incompatibilities between real time media and content.
The media server MUST begin recording video media only when it
receives a refresh video frame. A refresh frame contains all the
video information required to decode that frame (i.e., there is no
dependency on data from previous video frames). Refresh frames are
large and generally sent infrequently to conserve network bandwidth.
The media server MUST implement standard mechanisms to request that
the caller (video encoder) transmit a refresh frame to ensure video
recording begins quickly. The media server MUST begin recording the
audio track immediately while waiting to receive the video refresh
frame.
Van Dyke, et al. Informational [Page 30]
RFC 4722 MSCML November 2006
6.3. Playing Announcements <play>
The client issues a <play> request to play an announcement without
interruption and with no digit collection. One use, for example, is
to announce the name of a new participant to the entire conference.
The <play> request has the attributes described in the list below.
Attributes of <play>:
o id - optional, no default value: Specifies a client-defined ID for
purposes of matching requests and responses.
o offset - optional, default value "0": Specifies the time from the
beginning of the URL specified in the 'prompturl' attribute at
which play will begin. Expressed as a time value (Section 4.2.1)
from 0 onwards. If the offset value is greater than the total
time of the content, it will "wrap" to the beginning and continue
from there until the media server reaches the specified offset.
NOTE: Use of this attribute is deprecated.
o promptencoding - optional, no default value: Specifies the content
encoding for file formats that are not self-describing (e.g.,
.WAV). Allowable values are "ulaw", "alaw", and "msgsm". This
attribute only affects "file://" scheme URLs. NOTE: Use of this
attribute is deprecated.
o prompturl - optional, no default value: The URL of the content to
be retrieved and played. The target may be a local or remote
(NFS) "file://" scheme URL or an "http://" or "https://" scheme
URL. NOTE: Use of this attribute is deprecated.
The <play> request has one child element defined, <prompt>. Use of
<prompt> is described in Section 6.1.1.
The client MUST NOT use both the <prompt> element and "prompturl"
attribute in a single request. As previously discussed, the
"prompturl" attribute is supported for backwards compatibility with
older MSCML applications, but its use is deprecated. The more
flexible <prompt> element SHOULD be used instead.
The following play request (Figure 17) example shows the delivery of
a complex prompt sequence consisting of content accessed via NFS and
spoken variables.
Van Dyke, et al. Informational [Page 31]RFC 4722 MSCML November 2006
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<play id="332985001">
<prompt stoponerror="yes"
baseurl="file:////var/mediaserver/prompts/"
locale="en_US" offset="0" gain="0" rate="0"
delay="0" duration="infinite" repeat="1">
<audio url="num_dialed.raw" encoding="ulaw"/>
<variable type="dig" subtype="ndn" value="3014170700"/>
<audio url="num_invalid.wav"/>
<audio url="please_check.wav"/>
</prompt>
</play>
</request>
</MediaServerControl>
Figure 17: <Play> Request Example
When the announcement has finished playing, the media server sends a
<response> payload to the client in a SIP INFO message. Details
regarding the format of <play> responses are provided in Section
10.4.
6.4. Prompt and Collect <playcollect>
The client issues a <playcollect> request to play an announcement
(optional) and collect digits. The <playcollect> request is executed
in two phases, prompt and collect. If the client specifies prompt
content to be played, using the <prompt> element or prompturl
attribute, the media server plays the content before starting the
collection phase. If no prompt content is specified, the collect
phase begins immediately.
The basic attributes of <playcollect> are the same as those of
<play>, which were described in Section 6.3. In addition to these
basic attributes, <playcollect> defines others which control digit
buffering and barge-in behavior, collection timers, special purpose
DTMF key functions, and logging of user DTMF input. Each functional
category and its attributes are described below.
Van Dyke, et al. Informational [Page 32]RFC 4722 MSCML November 2006
6.4.1. Control of Digit Buffering and Barge-In
Whenever the media server is processing a call that specifies an
MSCML service (i.e., "conf" and "ivr"), the media server continuously
looks for DTMF digits and places them in a quarantine buffer. The
quarantine buffer is examined when a <playcollect> request is
received. The media server compares any previously buffered digits
for barge-in, and to look for matches with DTMF grammars or special
purpose keys. This provides the type-ahead behavior for menu
traversal and other types of IVR interactions.
Attributes for Control of Digit Buffering and Barge-In:
o cleardigits - optional, default value "no": Specifies whether
previous user input should be considered or ignored for barge-in
purposes and DTMF matching. When it is set to "yes", any
previously buffered digits are removed, so prior user input is
ignored. If it is set to "no", previously buffered digits will be
considered. If "cleardigits" is set to "no" and barge-in is
enabled, previously buffered digits will immediately terminate the
prompt phase. In this case, the prompt is not played, and digit
collection begins immediately.
o barge - optional, default value "yes": Specifies whether user
input will barge the prompt and force transition to the collect
phase. When it is set to "yes", a DTMF input will barge the
prompt. When it is set to "no", the prompt phase cannot be
barged, and any user input during the prompt is placed in the
quarantine buffer for inspection during the collect phase. Note
that if the "barge" attribute is set to "no", the "cleardigits"
attribute implicitly has a value of "yes". This ensures that the
media server does not leave DTMF input that occurred prior to the
current collection in the quarantine buffer after the request is
completed.
6.4.2. Mapping DTMF Keys to Special Functions
The client can define mappings between DTMF digits and special
functions. The media server invokes the special function if the
associated DTMF digit is detected. MSCML has two attributes that
define mappings that affect termination of the collect phase. These
attributes are described in the list below.
Van Dyke, et al. Informational [Page 33]RFC 4722 MSCML November 2006
DTMF Key Mappings for <playcollect>:
o escapekey - optional, default value "*": Specifies a DTMF key that
indicates that the user wishes to terminate the current operation
without saving any input collected to that point. Detection of
the mapped DTMF key terminates the request immediately and
generates a response.
o returnkey - optional, default value "#": Specifies a DTMF key that
indicates that the user has completed input and wants to return
all collected digits to the client. When the media server detects
the returnkey, it immediately terminates collection and returns
the collected digits to the client in the <response> message.
MSCML defines three additional mappings to enable video cassette
recorder (VCR) type controls while playing a prompt sequence. Media
servers SHOULD support VCR controls. However, if the media server
does not support VCR controls, it MUST silently ignore DTMF inputs
mapped to VCR functions and complete the <playcollect> request. The
VCR control attributes are described in the list below.
Attributes for VCR Controls:
o skipinterval - optional, default value "6s": The "skipinterval"
attribute indicates how far the media server should skip backwards
or forwards when the rewind key (rwkey) or fast forward key
(ffkey) is pressed, specified as a time value (Section 4.2.1).
o ffkey - optional, no default value: The "ffkey" attribute maps a
DTMF key to a fast forward operation equal to the value of the
"skipinterval" attribute.
o rwkey - optional, no default value: The "rwkey" attribute maps a
DTMF key to a rewind action equal to the value of the
"skipinterval" attribute.
Clients MUST NOT map the same DTMF digit to both the "rwkey" and
"ffkey" attributes in a single <playcollect> request.
VCR control operations are bounded by the beginning and end of the
prompt sequence. A rewind action that moves the offset before the
beginning of the sequence results in playback starting at the
beginning of the sequence (i.e., offset=0). A fast forward action
that moves the offset past the end of the sequence results in the
media server's treating the sequence as complete.
Van Dyke, et al. Informational [Page 34]RFC 4722 MSCML November 2006
6.4.3. Collection Timers
MSCML defines several timer attributes that control how long the
media server waits for digits in the input sequence. All timer
settings are time values (Section 4.2.1). The list below describes
these attributes and their use.
Collection Timer Attributes:
o firstdigittimer - optional, default value "5000ms": Specifies how
long the media server waits for the initial DTMF input before
terminating the collection. Expressed as a time value (Section
4.2.1) from 1ms onwards or the strings "immediate" and "infinite."
The value "immediate" indicates that the timer should fire
immediately whereas "infinite" indicates that the timer will never
fire.
o interdigittimer - optional, default value "2000ms": Specifies how
long the media server waits between DTMF inputs. Expressed as a
time value (Section 4.2.1) from 1ms onwards or the strings
"immediate" and "infinite." The value "immediate" indicates that
the timer should fire immediately, whereas "infinite" indicates
that the timer will never fire.
o extradigittimer - optional, default value "1000ms": Specifies how
long the media server waits for additional user input after the
specified number of digits has been collected. Expressed as a
time value (Section 4.2.1) from 1ms onwards or the strings
"immediate" and "infinite." The value "immediate" indicates that
the timer should fire immediately, whereas "infinite" indicates
that the timer will never fire.
o interdigitcriticaltimer - optional, defaults to the value of the
interdigittimer attribute: Specifies how long the media server
waits after a grammar has been matched for a subsequent digit that
may cause a longer match. Expressed as a time value (Section
4.2.1) from 1ms onwards or the strings "immediate" and "infinite."
The value "immediate" results in "shortest match first" behavior,
whereas "infinite" means to wait indefinitely for additional
input. If not explicitly specified otherwise, this attribute is
set to the value of the 'interdigittimer' attribute.
The extradigittimer setting enables the "returnkey" input to be
associated with the current collection. For example, if maxdigits is
set to 3 and returnkey is set to #, the user may enter either "x#",
"xx#", or "xxx#", where x represents a DTMF digit.
Van Dyke, et al. Informational [Page 35]RFC 4722 MSCML November 2006
If the media server detects the "returnkey" pattern during the
"extradigit" interval, the media server returns the collected digits
to the client and removes the "returnkey" from the digit buffer.
If this were not the case, the example would return "xxx" to the
client and leave the terminating "#" in the digit buffer. At the
next <playcollect> request, the media server would process the '#'.
This might result in the termination of the following prompt, which
is clearly not what the user intended.
The extradigittimer has no effect unless returnkey has been set.
6.4.4. Logging Caller DTMF Input
Standard SIP mechanisms, such as those discussed in Security
Considerations (Section 14), protect MSCML protocol exchanges and the
information they contain. These protections do not apply to data
captured in media server log files. In general, media server logging
is platform specific and therefore is not covered by this
specification. However, one aspect of logging, the capture of
sensitive information (such as personal identification numbers or
credit card numbers), is relevant. The media server has no means to
determine whether the DTMF input it receives may be sensitive, as
that is in the purview of the client. Recognizing this, MSCML
includes a per- request mechanism to suppress logging of captured
DTMF to be enabled by clients as needed.
The "maskdigits" attribute controls whether detected DTMF digits
appear in the log output. Clients use this attribute when the media
server collects sensitive information that should not be accessible
through the log files.
Maskdigits Attribute:
o maskdigits - optional, default value "no": Controls whether user
DTMF inputs are captured in media server log files. The possible
values for this attribute are "yes" and "no".
6.4.5. Specifying DTMF Grammars
MSCML supports four methods for specifying DTMF grammars: the
"maxdigits" attribute, which provides a simple mechanism for
collecting any number of digits up to the maximum, regular
expressions, MGCP [5] digit maps, and H.248.1 [6] digit maps. A
media server MUST support the maxdigits and regular expression
methods for specifying DTMF grammars and SHOULD support MGCP and
H.248.1 methods. A client MUST NOT mix DTMF grammar types in a
single <playcollect> request.
Van Dyke, et al. Informational [Page 36]RFC 4722 MSCML November 2006
Following is a description of the "maxdigits" attribute.
Maxdigits Attribute:
o maxdigits - optional, no default value: Specifies the maximum
number of DTMF digits to be collected.
The <pattern> element specifies a digit pattern or patterns for the
media server to look for. This element may contain three different
child elements that specify the type of DTMF grammar used in the
expression. The <pattern> element has no attributes.
<regex> Use regular expressions to define DTMF patterns to match.
The complete regular expression syntax used in MSCML is described
in Appendix A.
<mgcpdigitmap> Use digit maps as specified in MGCP [5].
<megacodigitmap> Use digit maps as specified in H.248.1 [6].
At least one <regex> element MUST be present in <pattern> when regex
grammars are used. Multiple <regex> elements MAY be present. When
<mgcpdigitmap> or <megacodigitmap> grammars are used, <pattern> MUST
contain only one grammar element.
The DTMF grammar elements <regex>, <mgcpdigitmap>, and
<megacodigitmap> have the attributes described in the list below.
Attributes of DTMF Grammar Elements:
o value - required, no default value: Specifies a string
representing a DTMF grammar matching the parent element type
(e.g., regex). Regex values represent a single DTMF grammar.
MGCP and MEGACO digit maps allow multiple grammars to be described
in a single string.
o name - optional, no default value: Associates a client defined
name for the grammar that is sent back in the <playcollect>
response. This attribute is most useful with regex type grammars
as each grammar element can have a unique name.
6.4.6. Playcollect Response
When the <playcollect> has finished, the media server sends a
<response> payload to the client in a SIP INFO message.
Details of the <playcollect> response are described in Section 10.5.
Van Dyke, et al. Informational [Page 37]RFC 4722 MSCML November 2006
6.4.7. Playcollect Example
The following <playcollect> request (Figure 18) example depicts use
of the "maxdigits" attribute to control digit collection.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<playcollect id="332986004" maxdigits="6" firstdigittimer="10000"
interdigittimer="5000" extradigittimer="1000"
interdigitcriticaltimer="1000" returnkey="#" escapekey="*"
cleardigits="no" barge="yes" maskdigits="no">
<prompt baseurl="http://www.example.com/prompts/">
<audio url="generic/en_US/enter_pin.wav"/>
</prompt>
</playcollect>
</request>
</MediaServerControl>
Figure 18: <Playcollect> Request Example Using the Maxdigits
Attribute
6.5. Prompt and Record <playrecord>
The <playrecord> request directs the media server to convert and
possibly to transcode the RTP payloads it receives and store them to
the specified URL using the requested content codec(s) and file
format. This request proceeds in two phases; prompt and record.
The <playrecord> request shares the basic attributes of <play> and
<playcollect> as described in Section 6.3. MSCML also defines other
attributes that control the behavior of the prompt and recording
phases. These phases and the attributes that control them are
described in the text and tables below.
6.5.1. Prompt Phase
The presence or absence of a "prompturl" attribute or child <prompt>
element controls whether a prompt is played before recording begins.
As previously noted, use of the "prompturl" attribute is deprecated,
and clients SHOULD use <prompt> instead.
When the client requests that the media server prompt the caller
before recording audio, <playrecord> has two stages. The first is
equivalent to a <playcollect> operation. The client may set the
prompt phase to be interruptible by DTMF input (barge) and may
specify an escape key that will terminate the <playrecord> request
before the recording phase begins.
Van Dyke, et al. Informational [Page 38]RFC 4722 MSCML November 2006
The list below describes the attributes of <playrecord> that specify
the behavior of the prompt phase of the request.
Playrecord Attributes for the Prompt Phase:
o barge - optional, default value "yes": Specifies whether user
input will barge the prompt and force transition to the record
phase. When it is set to "yes", a DTMF input will barge the
prompt. When it is set to "no", the prompt phase cannot be
barged, and any user input during the prompt is placed in the
quarantine buffer for inspection during the collect phase. Note
that if the "barge" attribute is set to "no", the "cleardigits"
attribute implicitly has a value of "yes". This ensures that the
media server does not leave DTMF input that occurred prior to the
current collection in the quarantine buffer after the request
completes.
o cleardigits - optional, default value "no": Specifies whether
previous user input should be considered or ignored for barge-in
purposes. When it is set to "yes", any previously buffered digits
are removed, so prior user input is ignored. If it is set to
"no", previously buffered digits will be considered. If
"cleardigits" is set to "no" and barge-in is enabled, previously
buffered digits will terminate the prompt phase immediately. In
this case, the prompt is not played, and recording begins
immediately.
o escapekey - optional, default value "*": Specifies a DTMF key that
indicates the user wishes to terminate the current operation
without saving any input recorded to that point. Detection of the
mapped DTMF key terminates the request immediately and generates a
response.
Detection of the escape key generates a response message, and the
operation returns immediately. If the user presses any other keys
and if the prompt is interruptible (barge="yes"), then the play stops
immediately, and the recording phase begins.
6.5.2. Record Phase
If the request proceeds to the recording phase, the media server
discards any digits from the collect phase from the quarantine buffer
to eliminate unintended termination of the recording. The following
attributes control recording behavior.
Playrecord Attributes for the Record Phase:
Van Dyke, et al. Informational [Page 39]RFC 4722 MSCML November 2006
o recurl - required, no default value: Specifies the target URL for
the recorded content.
o recencoding - optional, default value "ulaw": Specifies the
encoding of the recorded content if it cannot be inferred from the
recurl. Possible values are "ulaw", "alaw", and "msgsm."
o mode - optional, default value "overwrite": Specifies whether the
recording should overwrite or be appended to the target URL.
Allowable values are "overwrite" and "append."
o duration - optional, default value "infinite": Specifies the
maximum allowable duration for the recording. Expressed as a time
value (Section 4.2.1) from 1 onwards or the strings "immediate"
and "infinite." The value "immediate" indicates that recording
will end immediately, whereas "infinite" indicates recording
should continue indefinitely. If the maximum duration is reached,
the <playrecord> request will terminate and generate a response.
o beep - optional, default value "yes": Specifies whether a beep
should be played to the caller immediately prior to the start of
the recording phase. Allowable values are "yes" and "no."
o initsilence - optional, default value "3000ms": Specifies how long
to wait for initial speech input before terminating (canceling)
the recording. Expressed as a time value (Section 4.2.1) from 1ms
onwards or the strings "immediate" and "infinite." The value
"immediate" indicates that the timer should fire immediately,
whereas "infinite" directs the media server to wait indefinitely.
o endsilence - optional, default value "4000ms": Specifies how long
the media server waits after speech has ended to stop the
recording. Expressed as a time value (Section 4.2.1) from 1ms
onwards or the strings "immediate" and "infinite." When set to
"infinite", the recording will continue indefinitely after speech
has ended and will only terminate due to a DTMF keypress or
because the input has reached the maximum desired duration.
o recstopmask - optional, default value "0123456789ABCD#*":
Specifies a list of individual DTMF characters that, if detected,
will cause the recording to be terminated. To ensure that the
input of a specific key does not cause the recording to stop,
remove the DTMF key from the list.
Media servers MUST support local and remote (NFS) "file://" scheme
URLs in the "recurl" attribute. MSCML supports "http://" and
"https://" scheme URLs indirectly through the <managecontent>
(Section 8) request.
Van Dyke, et al. Informational [Page 40]RFC 4722 MSCML November 2006
The media server buffers and returns any digits collected in the
prompt phase, with the exception of those contained in the
"recstopmask" attribute, in the response.
The media server compares digits detected during the recording phase
to the digits specified in the "recstopmask" to determine whether
they indicate a recording termination request.
The media server ignores digits not present in the recstopmask and
passes them into the recording. If DTMF input terminates the
recording, the media server returns the collected digit to the client
in the <response>.
Once recording has begun, the media server writes the received media
to the specified recurl URL no matter what DTMF events the media
server detects. It is the responsibility of the client to examine
the DTMF input returned in the <response> message to determine
whether the audio file should be saved or deleted and, potentially,
re-recorded.
If the endsilence timer expires, the media server trims the end of
the recorded audio by an amount equal to the value of the
"endsilence" attribute.
When the recording is finished, the media server generates a
<response> message and sends it to the client in a SIP INFO message.
Details of the <playrecord> response are described in Section 10.6.
6.5.3. Playrecord Example
The recording example (Figure 19) plays a prompt and records it to
the destination specified in the "recurl" attribute encoded as MS-GSM
in wave format.
Van Dyke, et al. Informational [Page 41]
RFC 4722 MSCML November 2006
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<playrecord id="5556123"
recurl="file:////nfs.example.com/rec/name.wav"
recencoding="msgsm"
initsilence="5000" endsilence="3000" duration="30000"
barge="yes"
beep="yes"
mode="overwrite"
cleardigits="no"
escapekey="*"
recstopmask="0123456789#*">
<prompt>
<audio url="http://www.example.com/prompts/recordname.wav"/>
</prompt>
</playrecord>
</request>
</MediaServerControl>
Figure 19: Recording Example
6.6. Stop Request <stop>
The client issues a <stop> request when the objective is to stop a
request in progress and not to initiate another operation. This
request generates a <response> message from the media server.
The only attribute is id, which is optional.
The client-defined request id correlates the asynchronous response
with its original request and echoes back to the client in the media
server's response.
The following MSCML payload (Figure 20) depicts an example <stop>
request.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<stop id="4578903"/>
</request>
</MediaServerControl>
Figure 20: Stop Example
The format of a response to a <stop> request is detailed in Section
10.2.
Van Dyke, et al. Informational [Page 42]RFC 4722 MSCML November 2006
As discussed previously, the media server treats a SIP re-INVITE that
modifies the established SDP parameters as an implicit <stop>
request. Examples of such SDP modifications include receiving hold
SDP or removing an audio or video stream. When this occurs, the
media server immediately terminates the running <play>,
<playcollect>, or <playrecord> request and sends a <response>
indicating "reason=stopped".
7. Call Leg Events
MSCML defines event notifications that are scoped to a specific SIP
dialog or call leg. These events allow a client to be notified of
individual, asynchronous DTMF keypresses, as well as of various call
progress signals. The subscription, event detection, and
notifications for call leg events occur in the same SIP dialog. This
is different from the conference level active talker events described
earlier. The subscription and notifications for active talker events
occur on the conference control leg, but the actual event detection
occurs on one or more participant legs.
Subscriptions for call leg events are made by sending an MSCML
<configure_leg> request on the desired SIP dialog. Call leg events
may be used with the MSCML conferencing or IVR services. When used
with the IVR service, the <configure_leg> request SHOULD NOT include
any conference-related attributes. The media server MUST ignore
these if present. Call leg event subscriptions MUST NOT be made on
the conference control leg, since it has no actual RTP media to
process for event detection. The media server MUST reject a
<configure_leg> request sent on the conference control leg.
The <configure_leg> request contains the child elements <subscribe>
and <events>. The <events> element may contain two child elements
that control subscriptions to call leg events. These are <keypress>
and <signal>. A <configure_leg> request MUST contain at most one
<keypress> element but MAY contain multiple <signal> elements that
request notification of different call progress events.
7.1. Keypress Events
Keypress events are used when the client wishes to receive
notifications of individual DTMF events that are not tied to a
specific <playcollect> request. One use of this facility is to
monitor conference legs for DTMF inputs that require application
intervention; for example, to notify the moderator that the caller
wishes to speak. Keypress events are also used when the application
desires complete control of grammars and timing constraints.
Van Dyke, et al. Informational [Page 43]
RFC 4722 MSCML November 2006
When used in a subscription context, the <keypress> element has two
attributes, 'report' and 'maskdigits', which are detailed in the list
below.
Keypress Subscription Attributes:
o report - required, no default value: Possible values are
'standard', 'long', 'both', and 'none'. 'Standard' means that
detected digits should be reported. 'Long' means that long digits
should be reported. 'Long' digits are defined as a single key
press held down for more than one second, or two distinct key
presses (a "double") of the same digit that occur within two
seconds of each other with no other intervening digits. 'Both'
means that both 'standard' and 'long' digit events should be
reported. As a 'long' digit consists of one or more "normal"
digits, a single long duration key press will generate one
standard event and one 'long' event. A "double" will produce two
standard events and one 'long' event. 'None' means that no
keypress events should be reported; it disables keypress event
reporting if enabled.
o maskdigits - optional, default value "no": Controls whether user
DTMF inputs are captured in media server log files. The possible
values for this attribute are "yes" and "no".
The media server sends an MSCML response to the subscription
immediately upon receiving the request. Notifications are sent to
the client when the specified events are detected.
When used in a notification context, the <keypress> element has
several attributes that are used to convey details of the event that
was detected. It also contains a child element, <status>, that
provides information on any MSCML request that was in progress when
the event occurred. The details of these notification attributes are
described in the list below.
Keypress Notification Attributes:
o digit - required, no default value: Specifies the DTMF digit
detected. Possible values are [0-9], [A-D], '#', or '*'.
o length - required, no default value: Specifies the duration class
of the DTMF input. Possible values are 'standard' or 'long'.
o method - required, no default value: Specifies the keypress
detection method that generated the notification. Possible values
are 'standard', 'long', and 'double'.
Van Dyke, et al. Informational [Page 44]RFC 4722 MSCML November 2006
o interdigittime - required, no default value: Specifies the elapsed
time, as a time value (Section 4.2.1), between the current event
detection and the previous one.
7.1.1. Keypress Subscription Examples
The following examples of MSCML payloads depict a subscription for
standard keypress events and disabling keypress reporting.
Figure 21 shows a subscription for standard keypress events.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg>
<subscribe>
<events>
<keypress report="standard"/>
</events>
</subscribe>
</configure_leg>
</request>
</MediaServerControl>
Figure 21: Standard Digit Events Subscription
Figure 22 shows a client disabling keypress event notifications.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg>
<subscribe>
<events>
<keypress report="none"/>
</events>
</subscribe>
</configure_leg>
</request>
</MediaServerControl>
Figure 22: Disabling Keypress Event Reporting
7.1.2. Keypress Notification Examples
The following MSCML payloads depict keypress event notifications
caused by various types of DTMF input.
Van Dyke, et al. Informational [Page 45]RFC 4722 MSCML November 2006
Figure 23 shows a notification generated by the detection of a
standard "4" DTMF digit. In this example, this is the first digit
detected. Thus, the 'interdigittime' attribute has a value of '0'.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<notification>
<keypress digit="4" length="standard" method="standard"
interdigittime="0">
<status command="play" duration="10"/>
</keypress>
</notification>
</MediaServerControl>
Figure 23: Standard Keypress Notification
Figure 24 shows a notification generated by detection of a long pound
(#).
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<notification>
<keypress digit="#" length="long" method="long"
interdigittime="200">
<status command="idle" duration="4"/>
</keypress>
</notification>
</MediaServerControl>
Figure 24: Long Keypress Notification
7.2. Signal Events
MSCML supports notification of certain call progress tones through
the <signal> element. When used in a subscription context, the
<signal> element has two attributes, 'type' and 'report', and no
child elements. These attributes are detailed in the list below.
Signal Subscription Attributes:
o report - required, no default value: Controls whether the
specified signal is reported. Possible values are 'yes' and 'no'.
When set to 'yes', the media server invokes the required signal
detection code and reports detected events. When it is set to
'no', the media server disables the associated signal detection
code and does not report events.
Van Dyke, et al. Informational [Page 46]RFC 4722 MSCML November 2006
o type - required, no default value: Specifies the type of call
progress signal to detect. Possible values are 'busy', 'ring',
'CED', 'CNG', and '400', which correspond to busy tone, ring tone,
fax CED, fax CNG, and 400 Hz tone, respectively.
NOTE: The details of media server provisioning required to support
country-specific variants of 'busy' and 'ring' is not covered by
this specification.
As stated previously, a single <configure_leg> request MAY contain
multiple <signal> elements that request notification of different
call progress tones. A single <configure_leg> request SHOULD NOT
contain multiple <signal> elements that have the same 'type'
attribute value. If the media server receives such a request, it
SHOULD honor the last element specifying that type that appears in
the request.
The media server generates an immediate response to the
<configure_leg> subscription request and sends notifications when the
specified signals are detected. A single notification is sent as
soon as the specified signal has been reliably detected. If the
signal persists continuously, additional notifications will not be
sent. If the signal is interrupted and then resumes, additional
notifications will be sent.
Signal notifications have a single attribute, "type", as described in
the list below.
Signal Notification Attribute:
o type - required, no default value: Specifies the type of call
progress signal that was detected. Possible values are 'busy',
'ring', 'CED', 'CNG', and '400', which correspond to busy tone,
ring tone, fax CED, fax CNG, and 400 Hz tone, respectively.
7.2.1. Signal Event Examples
The following MSCML payloads show a signal event subscription (Figure
25) and notification (Figure 26).
Van Dyke, et al. Informational [Page 47]RFC 4722 MSCML November 2006
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<configure_leg>
<subscribe>
<events>
<signal type="busy" report="yes"/>
</events>
</subscribe>
</configure_leg>
</request>
</MediaServerControl>
Figure 25: Signal Event Subscription
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<notification>
<signal type="busy"/>
</notification>
</MediaServerControl>
Figure 26: Signal Event Notification
8. Managing Content <managecontent>
MSCML uses the <managecontent> request to move recorded content from
the media server to remote locations using the HTTP protocol. This
is a store-and-forward model, which requires the completion of local
temporary recording before the media server can send it to the web
server. This facility is useful in applications such as voice
messaging, where a message may be reviewed by the caller prior to
being committed to persistent storage.
The <managecontent> request contains no child elements and has the
attributes described in the list below.
Managecontent Attributes:
o src - required, no default value: Specifies the local source URL
of the content. The URL scheme MUST be "file://".
o dest - required (see note), no default value: Specifies the
destination URL. The URL scheme MUST be "http://". Note: If the
selected action is 'delete', this attribute is optional; otherwise
it is required.
Van Dyke, et al. Informational [Page 48]RFC 4722 MSCML November 2006
o action - optional, default value "move": Specifies the operation
for the media server to execute. Values can be either 'move' or
'delete'. The 'delete' action operates on the local source file.
After a successful move or delete, the media server deletes the
source file from its local storage. If the request is
unsuccessful, the source file is not deleted, which gives the
client complete control of the retry strategy.
o httpmethod - optional, default value "post": HTTP protocol method
for the media server to use in the HTTP request. The only values
are 'post' or 'put'.
o name - required (see note), no default value: Specifies the field
name for the content in the form when using the 'post' method.
This is not to be confused with the "src" or "dest" attributes.
Note: This attribute is required when the "htttpmethod" has the
value "post" and is optional otherwise.
o fetchtimeout - optional, default value "10000ms": Specifies the
maximum time allowed for the transfer to complete. Expressed as a
time value (Section 4.2.1) from 1ms onwards.
o mimetype - required (see note), no default value: Specifies the
MIME type that the media server will use for the content transfer.
If it is not provided, the media server MUST try to infer it from
the content file extension based on a platform specific mapping
table. A non-normative, example mapping table is shown in Table
3. To avoid ambiguity, we RECOMMEND that clients explicitly set
this attribute. Note: If the MIME type of the content cannot be
inferred from the file extension, this attribute is required.
Table 3 shows common audio and video MIME types and possible file
extension mappings.
Van Dyke, et al. Informational [Page 49]RFC 4722 MSCML November 2006
+-----------+--------------------+
| Extension | MIME Type |
+-----------+--------------------+
| alaw | audio/x-alaw-basic |
| ulaw | audio/basic |
| msgsm | audio/ms-gsm |
| wav | audio/x-wav |
| tif | image/tiff |
| tiff | image/tiff |
| mov | video/quicktime |
| qt | video/quicktime |
| 3gp | video/3gpp |
| 3gpp | video/3gpp |
+-----------+--------------------+
Table 3: Example File Extension to MIME Type Mappings
<Managecontent> is purely a transport operation; the underlying
content is not changed by it. Therefore clients MUST ensure that the
source and destination file name extensions and MIME types are the
same. Failure to do so could result in content that is unreadable.
The ability to move or delete any local file presents a potential
risk to the security of the media server system. For this reason, we
STRONGLY RECOMMEND that implementers limit local file system access
when using <managecontent>. For example, we encourage limiting
access as based on file ownership and/or specific directories.
8.1. Managecontent Example
The following is an example (Figure 27) showing a local file on the
media server being transferred to an HTTP URL using the "put" method.
The client sends the following request.
<?xml version="1.0"?>
<MediaServerControl version="1.0">
<request>
<managecontent id="102"
src="file:////var/mediaserver/rec/6A5GH49B.ulaw"
dest="http://www.example.com/recordings/myrecording.ulaw"
mimetype="audio/basic" action="move" httpmethod="put"
fetchtimeout="5000"/>
</request>
</MediaServerControl>
Figure 27: Managecontent Example
Van Dyke, et al. Informational [Page 50]RFC 4722 MSCML November 2006
Note that the client can change the temporary file name assigned by
the media server as part of this operation as shown.
If the request is ambiguous, the media server MUST return a status
code of "400" and text "Bad Request." If the media server is unable
to execute a syntactically correct and unambiguous request, it MUST
return a "500" status code with the text "Server Error." For
example, the local file system access restrictions may prevent
deletion of the specified file. In this case, the "reason" attribute
in the response conveys additional details on the server error that
occurred. If there is a network or remote server error, the media
server provides detailed error information in the <error_info>
element contained in the media server response. Additional
information regarding <managecontent> responses is provided in
Section 10.7.
9. Fax Processing
9.1. Recording a Fax <faxrecord>
The <faxrecord> request directs the media server to process a fax in
answer mode. The reason for a request separate from <playrecord> is
that the media server needs to know to process the T.30 [18] or T.38
[19] fax protocols.
The <faxrecord> request has multiple attributes and one child
element, <prompt>. Its attributes are described in the list below.
Attributes of <faxrecord>:
o lclid - optional, default value "" (the empty string): A string
that identifies the called station.
o prompturl - optional, no default value: The URL of the fax content
to be retrieved and played. The target may be a local or remote
(NFS) "file://" scheme URL or an "http://" or "https://" scheme
URL. NOTE: Use of this attribute is deprecated.
o promptencoding - optional, no default value: Specifies the content
encoding for files that do not have a 'tif' or 'tiff' extension.
The only allowable value is 'tiff'. This attribute only affects
"file://" scheme URLs. NOTE: Use of this attribute is deprecated.
o recurl - optional, no default value: Specifies the target URL for
the recorded content.
o rmtid - optional, no default value: Specifies the calling station
identifier of the remote terminal. If present, the media server
Van Dyke, et al. Informational [Page 51]RFC 4722 MSCML November 2006
MUST reject transactions with the remote terminal if the remote
terminal's identifier does not match the value of 'rmtid'.
Clients SHOULD use the more flexible <prompt> mechanism for
specifying fax content. Use of the 'prompturl' attribute is
deprecated and may not be supported in future MSCML versions. The
<prompt> element is described in Section 6.1.1. A <prompt> element
sent in a <faxrecord> request MUST NOT contain <variable> elements.
Media servers MUST support local and remote (NFS) "file://" scheme
URLs in the "recurl" attribute. MSCML supports "http://" and
"https://" scheme URLs indirectly through the <managecontent>
(Section 8) request.
The <faxrecord> request operates in one of three modes: receive,
poll, and turnaround poll. The combination of <prompt> or
'prompturl' attribute and 'recurl' attribute define the mode. Table
4 describes these modes in detail. The 'prompt' column in the table
has the value 'yes' if the request has either a <prompt> element or a
'prompturl' attribute.
+--------+--------+---------+---------------------------------------+
| prompt | recurl | Mode | Operation |
+--------+--------+---------+---------------------------------------+
| no | no | Invalid | Request fails. |
| no | yes | Receive | Record the fax to the target URL |
| | | | specified in 'recurl'. |
| yes | no | Poll | Send fax from source specified in the |
| | | | <prompt> element or 'prompturl' |
| | | | attribute. If there is a 'rmtid', it |
| | | | MUST match the remote terminal's |
| | | | identifier, or the request will fail. |
| yes | yes | TP | Turnaround Poll (TP) mode. If the |
| | | | remote terminal wishes to transmit, |
| | | | the media server records the fax to |
| | | | the target URL specified in 'recurl'. |
| | | | If the remote terminal wishes to |
| | | | receive, the media server sends the |
| | | | fax from the source URL contained in |
| | | | <prompt> or 'prompturl'. If there is |
| | | | a 'rmtid', it MUST match remote |
| | | | terminal's identifier, or the send |
| | | | request will fail. A receive |
| | | | operation will still succeed, |
| | | | however. |
+--------+--------+---------+---------------------------------------+
Table 4: Fax Receive Modes
Van Dyke, et al. Informational [Page 52]RFC 4722 MSCML November 2006
In receive mode, the media server receives the fax and writes the fax
data to the target URL specified by the 'recurl' attribute.
In poll mode, the media server sends a fax, but as a polled (called)
device.
In turnaround poll mode, the media server will record a fax that the
remote machine sends. If the remote machine requests a transmission,
then the media server will send the fax.
When transmitting a fax, the media server will advertise that it can
receive faxes in the DIS message. Likewise, when receiving a fax,
the media server will advertise that it can send faxes in the DIS
message.
The media server MUST flush any quarantined digits when it receives a
<faxrecord> request.
9.2. Sending a Fax <faxplay>
The <faxplay> request directs the media server to process a fax in
originate mode. The reason for a request separate from <play> is
that the media server needs to know to process the T.30 [18] or T.38
[19] fax protocols.
The <faxplay> request has multiple attributes and one child element,
<prompt>. Its attributes are described in the list below.
Attributes of <faxplay>:
o lclid - optional, default value "" (the empty string): A string
that identifies the called station.
o prompturl - optional, no default value: The URL of the content to
be retrieved and played. The target may be a local or remote
(NFS) "file://" scheme URL or an "http://" or "https://" scheme
URL. NOTE: Use of this attribute is deprecated.
o promptencoding - optional, no default value: Specifies the content
encoding for files that do not have a 'tif' or 'tiff' extension.
The only allowable value is 'tiff'. This attribute only affects
"file://" scheme URLs. NOTE: Use of this attribute is deprecated.
o recurl - optional, no default value: Specifies the target URL for
the recorded content.
o rmtid - optional, no default value: Specifies the calling station
identifier of the remote terminal. If present, the media server
Van Dyke, et al. Informational [Page 53]RFC 4722 MSCML November 2006
MUST reject transactions with the remote terminal if the remote
terminal's identifier does not match the value of 'rmtid'.
Clients SHOULD use the more flexible <prompt> mechanism for
specifying fax content. Use of the 'prompturl' attribute is
deprecated and may not be supported in future MSCML versions. The
<prompt> element is described in Section 6.1.1. A <prompt> element
sent in a <faxrecord> request MUST NOT contain <variable> elements.
Media servers MUST support local and remote (NFS) "file://" scheme
URLs in the "recurl" attribute. MSCML supports "http://" and
"https://" scheme URLs indirectly through the <managecontent>
(Section 8) request.
The <faxplay> request operates in one of three modes: send, remote
poll, and turnaround poll. The combination of <prompt> or
'prompturl' attribute and 'recurl' attribute define the mode. Table
5 describes these modes in detail. The 'prompt' column in the table
has the value 'yes' if the request has either a <prompt> element or a
'prompturl' attribute.
Van Dyke, et al. Informational [Page 54]RFC 4722 MSCML November 2006
+--------+--------+---------+---------------------------------------+
| prompt | recurl | Mode | Operation |
+--------+--------+---------+---------------------------------------+
| no | no | Invalid | Request fails. |
| yes | no | Send | Send fax from source specified in the |
| | | | <prompt> element or 'prompturl' |
| | | | attribute. If there is a 'rmtid', it |
| | | | MUST match the remote terminal's |
| | | | identifier, or the request will fail. |
| no | yes | Poll | Send fax from source specified in the |
| | | | <prompt> element or 'prompturl' |
| | | | attribute, assuming the remote |
| | | | terminal specifies it can receive a |
| | | | fax in its DIS message. If the remote |
| | | | terminal does not support reverse |
| | | | polling, the request will fail. If |
| | | | 'rmtid' is specified, it MUST match |
| | | | remote terminal's identifier, or the |
| | | | request will fail. |
| yes | yes | TP | Turnaround Poll (TP) mode. If the |
| | | | remote terminal wishes to transmit, |
| | | | the media server records the fax to |
| | | | the target URL specified in 'recurl'. |
| | | | If the remote terminal wishes to |
| | | | receive, the media server sends the |
| | | | fax from the source URL contained in |
| | | | <prompt> or 'prompturl'. If there is |
| | | | a 'rmtid', it MUST match remote |
| | | | terminal's identifier, or the send |
| | | | request will fail. A receive |
| | | | operation will still succeed, |
| | | | however. |
+--------+--------+---------+---------------------------------------+
Table 5: Fax Send Modes
In send mode, the media server sends the fax.
In remote poll mode, the client places a call on behalf of the media
server. The media server requests a fax transmission from the remote
fax terminal.
In turnaround poll mode, the media server will record a fax that the
remote machine sends. If the remote machine requests a transmission,
then the media server will send the fax.
When transmitting a fax, the media server will advertise that it can
receive faxes in the DIS message. Likewise, when receiving a fax,
Van Dyke, et al. Informational [Page 55]RFC 4722 MSCML November 2006
the media server will advertise that it can send faxes in the DIS
message.
The media server MUST flush any quarantined digits when it receives a
<faxplay> request.
10. MSCML Response Attributes and Elements
10.1. Mechanism
The media server acknowledges receipt of a client MSCML request sent
in a SIP INVITE by sending a response of either 200 OK or 415 Bad
Media Type. The media server responds with 415 when the SIP request
contains a content type other than "application/sdp" or "application/
mediaservercontrol+xml".
The media server acknowledges receipt of a client MSCML request sent
in a SIP INFO with a 200 OK or 415 Bad Media Type. The media server
responds with 415 if the INFO request contains a content type other
than "application/mediaservercontrol+xml".
The media server transports the MSCML <response> message in a SIP
INFO request.
If there is an error in the request or the media server cannot
complete the request, the media server sends the <response> message
very shortly after receiving the request. If the request is able to
proceed, the <response> contains final status information as
described below.
10.2. Base <response> Attributes
All MSCML responses have the basic attributes defined in the list
below.
Basic MSCML Response Attributes:
o id - optional, no default value: Echoes the client-defined ID
contained in the request.
o request - required, no default value: Specifies the MSCML request
type that generated the response. Allowable values are
"configure_conference", "configure_leg", "play", "playcollect",
"playrecord", "stop", "faxplay", "faxrecord", and "managecontent".
Van Dyke, et al. Informational [Page 56]RFC 4722 MSCML November 2006
o code - required, no default value: The final status code for the
request. MSCML uses a subset of the status classes defined in RFC
3261 [4]. In MSCML, 2XX responses indicate success, 4XX responses
indicate client error, and 5XX responses indicate an error on the
media server. There are no 1XX, 3XX, or 6XX status codes in
MSCML.
o text - required, no default value: The human readable reason
phrase associated with the status code.
Responses to <configure_conference> and <stop> requests contain only
the attributes above. MSCML responses to other requests MAY contain
additional request-specific attributes and elements. These are
described in the following sections.
10.3. Response Attributes and Elements for <configure_leg>
Responses to <configure_leg> requests have only the base response
attributes defined in Section 10.2. However, when the request
contains a <configure_team> element, the response includes a <team>
element describing the teammate configuration for that leg. The
attributes of the <team> element are shown in the list below.
Attributes of <team>:
o id - required, no default value: The client-defined unique
identifier for the conference leg.
o numteam - required, no default value: The number of team members
for the leg.
Additional information on each team member is conveyed by child
<teammate> elements contained within <team>. Each teammate is
represented by a single element in the list. The <teammate> element
has a single attribute, as described below.
Attributes of <teammate>:
o id - required, no default value: The client-defined unique
identifier for the teammate leg.
10.4. Response Attributes and Elements for <play>
In addition to the base response attributes defined in Section 10.2,
responses to <play> requests have the additional attributes described
in the list below.
Van Dyke, et al. Informational [Page 57]RFC 4722 MSCML November 2006
MSCML Response Attributes for <play>:
o reason - optional, no default value: For requests that are not
completed immediately, the "reason" attribute conveys additional
information regarding why the command was completed. Possible
values are "stopped", indicating that an explicit or implicit
<stop> request was received, and "EOF", indicating that the end of
the specified sequence of URLs was reached.
o playduration - required, no default value: A time value (Section
4.2.1) that returns the duration of the associated content
playout.
o playoffset - required, no default value: A time value (Section
4.2.1) that returns the time offset into the specified content
sequence where play was terminated. If the initial "offset" value
in the sequence was "0", then "playduration" and "playoffset" are
equal. However, if the initial offset had some other value,
"playoffset" serves as a bookmark for the client to resume play in
a subsequent request.
10.4.1. Reporting Content Retrieval Errors
If the associated request set "stoponerror=yes" in <prompt> and an
error occurred while retrieving the specified content the response
will include an <error_info> element detailing the problem. This
element contains the response information received from the remote
content server. The <error_info> element has the attributes
described in the list below.
Attributes of <error_info>:
o code - required, no default value: The status code returned by the
remote content server. For example, a web server might return 404
to indicate that the requested content was not found.
o text - required, no default value: The human-readable reason
phrase returned by the remote content server. For example, the
reason phrase "Not Found" would be returned if the requested
content was not found.
o context - required, no default value: Contains the content URL
that was being fetched when the retrieval error occurred. This
enables the client to know precisely which URL in a sequence
caused the problem.
An <error_info> element MAY be present in the response to any request
that contains a child <prompt> element.
Van Dyke, et al. Informational [Page 58]RFC 4722 MSCML November 2006
10.5. Response Attributes and Elements for <playcollect>
In addition to the base response attributes defined in Section 10.2,
responses to <playcollect> requests have the additional attributes
described in the list below.
MSCML Response Attributes for <playcollect>:
o reason - optional, no default value: For requests that are not
completed immediately, the "reason" attribute conveys additional
information regarding why the command was completed. Possible
values are "stopped", indicating that an explicit or implicit
<stop> request was received; "match", meaning that a DTMF grammar
was matched; "timeout", indicating that no DTMF input was received
before one of the collection timers expired; and "returnkey" or
"escapekey", meaning the DTMF digit mapped to that key was
detected and the return key or escape key terminated the
operation, respectively.
o playduration - required, no default value: A time value (Section
4.2.1) that returns the duration of the associated content
playout. If the caller barged the prompt, this value will reflect
the play duration up to that event.
o playoffset - required, no default value: A time value (Section
4.2.1) that returns the time offset into the specified content
sequence where play was terminated. If the initial "offset" value
in the sequence was "0", then "playduration" and "playoffset" are
equal. However, if the initial offset had some other value,
"playoffset" serves as a bookmark for the client to resume play in
a subsequent request. If the caller barged the prompt this value
will reflect the time offset at which barge-in occurred.
o digits - required, no default value: Contains the collected DTMF
input characters. If no DTMF input was collected, this attribute
is set to the empty string ("").
o name - required (see note), no default value: The client-defined
name of the DTMF grammar that was matched. Note: This attribute
is required if the "name" attribute was set in the matching DTMF
grammar.
Responses to <playcollect> requests MAY include an <error_info>
element, as described in Section 10.4.1.
Van Dyke, et al. Informational [Page 59]RFC 4722 MSCML November 2006
10.6. Response Attributes and Elements for <playrecord>
In addition to the base response attributes defined in Section 10.2,
responses to <playrecord> requests have the additional attributes
described in the list below.
o reason - optional, no default value: For requests that are not
completed immediately, the "reason" attribute conveys additional
information regarding why the command was completed. Possible
values are "stopped", indicating that an explicit or implicit
<stop> request was received; "digit", meaning that a DTMF digit
was detected and that the prompt phase was barged; "init_silence",
meaning the recording terminated because of no input;
"end_silence", meaning that the recording was terminated because
the "endsilence" timer elapsed; "max_duration", indicating that
the maximum time for the recording was reached; "escapekey",
indicating that the DTMF input mapped to "escapekey" was detected,
thus terminating the recording; and "error", indicating a general
operation failure.
o playduration - required, no default value: A time value (Section
4.2.1) that returns the duration of the associated content
playout. If the caller barged the prompt, this value will reflect
the play duration up to that event.
o playoffset - required, no default value: A time value (Section
4.2.1) that returns the time offset into the specified content
sequence where play was terminated. If the initial "offset" value
in the sequence was "0", then "playduration" and "playoffset" are
equal. However, if the initial offset had some other value,
"playoffset" serves as a bookmark for the client to resume play in
a subsequent request. If the caller barged the prompt this value
will reflect the time offset at which barge-in occurred.
o digits - required, no default value: Contains the DTMF digit that
terminated the recording. If no DTMF input was detected, this
attribute is set to the empty string ("").
o reclength - required, no default value: The length of the recorded
content, in bytes.
o recduration - required, no default value: A time value (Section
4.2.1) indicating the elapsed duration of the recording.
Responses to <playrecord> requests MAY include an <error_info>
element, as described in Section 10.4.1.
Van Dyke, et al. Informational [Page 60]RFC 4722 MSCML November 2006
10.7. Response Attributes and Elements for <managecontent>
Responses to <managecontent> requests have only the base response
attributes defined in Section 10.2. If a content transfer error
occurs while executing the request the response will also contain an
<error_info> element as described in Section 10.4.1.
10.8. Response Attributes and Elements for <faxplay> and <faxrecord>
In addition to the base response attributes defined in Section 10.2,
responses to <faxplay> and <faxrecord> requests have the additional
attributes described in the list below.
o reason - required, no default value: For requests that are not
completed immediately, the "reason" attribute conveys additional
information regarding why the command was completed. Possible
values are "stopped", indicating that an explicit or implicit
<stop> request was received; "complete", indicating successful
completion, even if there were bad lines or minor negotiation
problems (e.g., a DCN was received); "disconnect", meaning that
the session was disconnected; and "notfax", indicating that no DIS
or DCS was received on the connection.
o pages_received - required (see note), no default value: Indicates
the number of fax pages received. Note: This attribute is
required if any pages were received.
o pages_sent - required (see note), no default value: Indicates the
number of fax pages sent. Note: This attribute is required if any
pages were sent.
o faxcode - required, no default value: The value of the "faxcode"
attribute is the binary-or of the bit patterns defined in Table 6.
Van Dyke, et al. Informational [Page 61]RFC 4722 MSCML November 2006
+------+--------------------------------------+
| Mask | description |
+------+--------------------------------------+
| 0 | Operation Failed |
| 1 | Operation Succeeded |
| 2 | Partial Success |
| 4 | Image received and placed in recurl |
| 8 | Image sent from specified source URL |
| 16 | rmtid did not match |
| 32 | Error reading source URL |
| 64 | Error writing recurl |
| 128 | Negotiation failure on send phase |
| 256 | Negotiation failure on receive phase |
| 512 | Reserved |
| 1024 | Irrecoverable IP packet loss |
| 2048 | Line errors in received image |
+------+--------------------------------------+
Table 6: Faxcode Mask
Responses to <faxplay> and <faxrecord> requests MAY include an
<error_info> element, as described in Section 10.4.1.
11. Formal Syntax
The following syntax specification uses XML Schema as described in
XML [7].
11.1. Schema
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified">
<xs:element name="MediaServerControl">
<xs:complexType>
<xs:choice>
<xs:element name="request">
<xs:complexType>
<xs:choice>
<xs:element name="configure_conference"
type="configure_conferenceRequestType"/>
<xs:element name="configure_leg"
type="configure_legRequestType"/>
<xs:element name="play" type="playRequestType"/>
<xs:element name="playcollect"
type="playcollectRequestType"/>
<xs:element name="playrecord"
type="playrecordRequestType"/>
Van Dyke, et al. Informational [Page 62]RFC 4722 MSCML November 2006
<xs:element name="managecontent"
type="managecontentRequestType"/>
<xs:element name="faxplay"
type="faxRequestType"/>
<xs:element name="faxrecord"
type="faxRequestType"/>
<xs:element name="stop" type="stopRequestType"/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:element name="response" type="responseType"/>
<xs:element name="notification">
<xs:complexType>
<xs:choice>
<xs:element name="conference"
type="conferenceNotificationType"/>
<xs:element name="keypress"
type="keypressNotificationType"/>
<xs:element name="signal"
type="signalNotificationType"/>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:choice>
<xs:attribute name="version" use="required"/>
</xs:complexType>
</xs:element>
<!-- Definitions for base and concrete MSCML requests -->
<!-- and embedded types. -->
<xs:complexType name="base_requestType" abstract="true">
<xs:attribute name="id" type="xs:string"/>
</xs:complexType>
<xs:complexType name="playRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:sequence>
<xs:element name="prompt" type="promptType"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="prompturl" type="xs:string"/>
<xs:attribute name="offset" type="xs:string"/>
<xs:attribute name="promptencoding" type="xs:string"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="configure_conferenceRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
Van Dyke, et al. Informational [Page 63]RFC 4722 MSCML November 2006
<xs:sequence>
<xs:element name="subscribe"
type="conference_eventsubscriptionType" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="reservedtalkers"
type="xs:positiveInteger"/>
<xs:attribute name="reserveconfmedia" type="yesnoType"
default="yes"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="configure_legRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:sequence>
<xs:element name="inputgain" type="gainType"
minOccurs="0"/>
<xs:element name="outputgain" type="gainType"
minOccurs="0"/>
<xs:element name="configure_team"
type="configure_teamType" minOccurs="0"/>
<xs:element name="subscribe"
type="leg_eventsubscriptionType" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="type">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="talker"/>
<xs:enumeration value="listener"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="mixmode">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="full"/>
<xs:enumeration value="mute"/>
<xs:enumeration value="preferred"/>
<xs:enumeration value="parked"/>
<xs:enumeration value="private"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="dtmfclamp" type="yesnoType"/>
<xs:attribute name="toneclamp" type="yesnoType"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
Van Dyke, et al. Informational [Page 64]RFC 4722 MSCML November 2006
<xs:complexType name="configure_teamType">
<xs:sequence>
<xs:element name="teammate" type="teammateType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="id" type="xs:string"/>
<xs:attribute name="action" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="add"/>
<xs:enumeration value="delete"/>
<xs:enumeration value="query"/>
<xs:enumeration value="set"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:complexType>
<xs:complexType name="teammateType">
<xs:attribute name="id" type="xs:string" use="required"/>
</xs:complexType>
<xs:complexType name="playcollectRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:sequence>
<xs:element name="prompt" type="promptType"
minOccurs="0"/>
<xs:element name="pattern" type="dtmfGrammarType"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="prompturl" type="xs:string"/>
<xs:attribute name="offset" type="xs:string"/>
<xs:attribute name="barge" type="yesnoType" default="yes"/>
<xs:attribute name="promptencoding" type="xs:string"/>
<xs:attribute name="cleardigits" type="yesnoType"
default="no"/>
<xs:attribute name="maxdigits" type="xs:string"/>
<xs:attribute name="firstdigittimer" type="xs:string"
default="5000ms"/>
<xs:attribute name="interdigittimer" type="xs:string"
default="2000ms"/>
<xs:attribute name="extradigittimer" type="xs:string"
default="1000ms"/>
<xs:attribute name="interdigitcriticaltimer"
type="xs:string"/>
<xs:attribute name="skipinterval" type="xs:string"
default="6s"/>
<xs:attribute name="ffkey" type="DTMFkeyType"/>
<xs:attribute name="rwkey" type="DTMFkeyType"/>
Van Dyke, et al. Informational [Page 65]RFC 4722 MSCML November 2006
<xs:attribute name="returnkey" type="DTMFkeyType"
default="#"/>
<xs:attribute name="escapekey" type="DTMFkeyType"
default="*"/>
<xs:attribute name="maskdigits" type="yesnoType"
default="no"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="playrecordRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:sequence>
<xs:element name="prompt" type="promptType"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="prompturl" type="xs:string"/>
<xs:attribute name="promptencoding" type="xs:string"/>
<xs:attribute name="offset" type="xs:string" default="0"/>
<xs:attribute name="barge" type="yesnoType" default="yes"/>
<xs:attribute name="cleardigits" type="yesnoType"
default="no"/>
<xs:attribute name="escapekey" type="xs:string" default="*"/>
<xs:attribute name="recurl" type="xs:string" use="required"/>
<xs:attribute name="mode" default="overwrite">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="append"/>
<xs:enumeration value="overwrite"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="recencoding" type="xs:string"/>
<xs:attribute name="initsilence" type="xs:string"/>
<xs:attribute name="endsilence" type="xs:string"/>
<xs:attribute name="duration" type="xs:string"/>
<xs:attribute name="beep" type="yesnoType" default="yes"/>
<xs:attribute name="recstopmask" type="xs:string"
default="01234567890*#"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="managecontentRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:attribute name="fetchtimeout" type="xs:string"
default="10000"/>
<xs:attribute name="mimetype" type="xs:string"/>
Van Dyke, et al. Informational [Page 66]RFC 4722 MSCML November 2006
<xs:attribute name="name" type="xs:string"/>
<xs:attribute name="httpmethod">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="put"/>
<xs:enumeration value="post"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="action">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="move"/>
<xs:enumeration value="delete"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="dest" type="xs:string"/>
<xs:attribute name="src" type="xs:string" use="required"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="stopRequestType">
<xs:complexContent>
<xs:extension base="base_requestType"/>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="faxRequestType">
<xs:complexContent>
<xs:extension base="base_requestType">
<xs:sequence>
<xs:element name="prompt" type="promptType" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="lclid" type="xs:string"/>
<xs:attribute name="prompturl" type="xs:string"/>
<xs:attribute name="recurl" type="xs:string"/>
<xs:attribute name="rmtid" type="xs:string"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="dtmfGrammarType">
<xs:choice>
<xs:element name="regex" type="dtmfPatternType"
maxOccurs="unbounded"/>
<xs:element name="mgcpdigitmap" type="dtmfPatternType"/>
<xs:element name="megacodigitmap" type="dtmfPatternType"/>
</xs:choice>
</xs:complexType>
Van Dyke, et al. Informational [Page 67]RFC 4722 MSCML November 2006
<xs:complexType name="dtmfPatternType">
<xs:attribute name="value" type="xs:string" use="required"/>
<xs:attribute name="name" type="xs:string"/>
</xs:complexType>
<!-- Definitions for base and concrete MSCML responses -->
<!-- and embedded types. -->
<xs:complexType name="base_responseType" abstract="true">
<xs:attribute name="request" use="required">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="configure_conference"/>
<xs:enumeration value="configure_leg"/>
<xs:enumeration value="play"/>
<xs:enumeration value="playcollect"/>
<xs:enumeration value="playrecord"/>
<xs:enumeration value="managecontent"/>
<xs:enumeration value="faxplay"/>
<xs:enumeration value="faxrecord"/>
<xs:enumeration value="stop"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="id" type="xs:string"/>
<xs:attribute name="code" type="xs:string" use="required"/>
<xs:attribute name="text" type="xs:string" use="required"/>
</xs:complexType>
<xs:complexType name="responseType">
<xs:complexContent>
<xs:extension base="base_responseType">
<xs:sequence>
<xs:element name="error_info"
type="stoponerrorResponseType" minOccurs="0"/>
<xs:element name="team" type="configure_teamResponseType"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="reason" type="xs:string"/>
<xs:attribute name="reclength" type="xs:string"/>
<xs:attribute name="recduration" type="xs:string"/>
<xs:attribute name="digits" type="xs:string"/>
<xs:attribute name="name" type="xs:string"/>
<xs:attribute name="playduration" type="xs:string"/>
<xs:attribute name="playoffset" type="xs:string"/>
<xs:attribute name="faxcode" type="xs:string"/>
<xs:attribute name="pages_sent" type="xs:string"/>
<xs:attribute name="pages_recv" type="xs:string"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
Van Dyke, et al. Informational [Page 68]RFC 4722 MSCML November 2006
<xs:complexType name="stoponerrorResponseType">
<xs:attribute name="code" type="xs:string" use="required"/>
<xs:attribute name="text" type="xs:string" use="required"/>
<xs:attribute name="context" type="xs:string" use="required"/>
</xs:complexType>
<xs:complexType name="configure_teamResponseType">
<xs:sequence>
<xs:element name="teammate" type="teammateType" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:attribute name="numteam" type="xs:integer" use="required"/>
</xs:complexType>
<!-- Definitions for MSCML event subscriptions and -->
<!-- embedded types -->
<xs:complexType name="conference_eventsubscriptionType">
<xs:sequence>
<xs:element name="events">
<xs:complexType>
<xs:sequence>
<xs:element name="activetalkers"
type="activetalkersSubscriptionType"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:complexType name="activetalkersSubscriptionType">
<xs:attribute name="report" type="yesnoType" use="required"/>
<xs:attribute name="interval" type="xs:string" default="60s"/>
</xs:complexType>
<xs:complexType name="leg_eventsubscriptionType">
<xs:sequence>
<xs:element name="events">
<xs:complexType>
<xs:sequence>
<xs:element name="keypress"
type="keypressSubscriptionType" minOccurs="0"
maxOccurs="1"/>
<xs:element name="signal" type="signalSubscriptionType"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:complexType name="keypressSubscriptionType">
<xs:attribute name="report" use="required">
Van Dyke, et al. Informational [Page 69]RFC 4722 MSCML November 2006
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="standard"/>
<xs:enumeration value="long"/>
<xs:enumeration value="both"/>
<xs:enumeration value="none"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="maskdigits" type="yesnoType" default="no"/>
</xs:complexType>
<xs:complexType name="signalSubscriptionType">
<xs:attribute name="type" type="xs:NMTOKEN" use="required"/>
<xs:attribute name="report" type="yesnoType" use="required"/>
</xs:complexType>
<!-- Definitions for MSCML event notifications and -->
<!-- embedded types. -->
<xs:complexType name="conferenceNotificationType">
<xs:sequence>
<xs:element name="activetalkers"
type="activetalkersNotificationType" minOccurs="0"/>
</xs:sequence>
<xs:attribute name="uniqueid" type="xs:string" use="required"/>
<xs:attribute name="numtalkers" type="xs:string"
use="required"/>
</xs:complexType>
<xs:complexType name="activetalkersNotificationType">
<xs:sequence minOccurs="0">
<xs:element name="talker" maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="callid" type="xs:string"
use="required"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
<xs:complexType name="keypressNotificationType">
<xs:sequence>
<xs:element name="status" type="statusType"/>
</xs:sequence>
<xs:attribute name="digit" type="DTMFkeyType" use="required"/>
<xs:attribute name="length" use="required">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="standard"/>
<xs:enumeration value="long"/>
</xs:restriction>
</xs:simpleType>
Van Dyke, et al. Informational [Page 70]RFC 4722 MSCML November 2006
</xs:attribute>
<xs:attribute name="method" use="required">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="standard"/>
<xs:enumeration value="long"/>
<xs:enumeration value="double"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="interdigittime" type="xs:string"
use="required"/>
</xs:complexType>
<xs:complexType name="statusType">
<xs:attribute name="command" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="idle"/>
<xs:enumeration value="play"/>
<xs:enumeration value="collect"/>
<xs:enumeration value="record"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="duration" type="xs:string" use="required"/>
</xs:complexType>
<xs:complexType name="signalNotificationType">
<xs:attribute name="type" use="required" fixed="busy"/>
</xs:complexType>
<!-- Definitions for miscellaneous embedded, helper data types -->
<xs:complexType name="promptType">
<xs:choice maxOccurs="unbounded">
<xs:element name="audio" type="promptcontentType"/>
<xs:element name="variable" type="spokenvariableType"/>
</xs:choice>
<xs:attribute name="locale" type="xs:string"/>
<xs:attribute name="baseurl" type="xs:string"/>
<xs:attribute name="stoponerror" type="yesnoType" default="no"/>
<xs:attribute name="gain" type="xs:string" default="0"/>
<xs:attribute name="gaindelta" type="xs:string" default="0"/>
<xs:attribute name="rate" type="xs:string" default="0"/>
<xs:attribute name="ratedelta" type="xs:string" default="0"/>
<xs:attribute name="repeat" type="xs:string" default="1"/>
<xs:attribute name="duration" type="xs:string"
default="infinite"/>
<xs:attribute name="offset" type="xs:string" default="0"/>
<xs:attribute name="delay" type="xs:string" default="0"/>
</xs:complexType>
Van Dyke, et al. Informational [Page 71]RFC 4722 MSCML November 2006
<xs:complexType name="promptcontentType">
<xs:attribute name="url" type="xs:string" use="required"/>
<xs:attribute name="encoding" type="xs:string"/>
<xs:attribute name="gain" type="xs:string" default="0"/>
<xs:attribute name="gaindelta" type="xs:string" default="0"/>
<xs:attribute name="rate" type="xs:string" default="0"/>
<xs:attribute name="ratedelta" type="xs:string" default="0"/>
</xs:complexType>
<xs:complexType name="spokenvariableType">
<xs:attribute name="type" use="required">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="dat"/>
<xs:enumeration value="dig"/>
<xs:enumeration value="dur"/>
<xs:enumeration value="mth"/>
<xs:enumeration value="mny"/>
<xs:enumeration value="num"/>
<xs:enumeration value="sil"/>
<xs:enumeration value="str"/>
<xs:enumeration value="tme"/>
<xs:enumeration value="wkd"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="subtype">
<xs:simpleType>
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="mdy"/>
<xs:enumeration value="dmy"/>
<xs:enumeration value="ymd"/>
<xs:enumeration value="ndn"/>
<xs:enumeration value="t12"/>
<xs:enumeration value="t24"/>
<xs:enumeration value="USD"/>
<xs:enumeration value="gen"/>
<xs:enumeration value="ndn"/>
<xs:enumeration value="crd"/>
<xs:enumeration value="ord"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
<xs:attribute name="value" type="xs:string" use="required"/>
</xs:complexType>
<xs:simpleType name="yesnoType">
<xs:restriction base="xs:NMTOKEN">
<xs:enumeration value="yes"/>
<xs:enumeration value="no"/>
Van Dyke, et al. Informational [Page 72]RFC 4722 MSCML November 2006
<xs:enumeration value="1"/>
<xs:enumeration value="0"/>
<xs:enumeration value="true"/>
<xs:enumeration value="false"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="DTMFkeyType">
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]"/>
<xs:pattern value="[A-D]"/>
<xs:pattern value="[a-d]"/>
<xs:pattern value="#"/>
<xs:pattern value="\*"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="gainType">
<xs:choice>
<xs:element name="auto" type="autogainType"/>
<xs:element name="fixed" type="fixedgainType"/>
</xs:choice>
</xs:complexType>
<xs:complexType name="autogainType">
<xs:attribute name="startlevel" type="xs:string"/>
<xs:attribute name="targetlevel" type="xs:string"/>
<xs:attribute name="silencethreshold" type="xs:string"/>
</xs:complexType>
<xs:complexType name="fixedgainType">
<xs:attribute name="level" type="xs:string"/>
</xs:complexType>
</xs:schema>
12. IANA Considerations
12.1. IANA Registration of MIME Media Type application/
mediaservercontrol+xml
MIME media type name: application
MIME subtype name: mediaservercontrol+xml
Required parameters: none
Optional parameters: charset
charset This parameter has identical semantics to the charset
parameter of the "application/xml" media type, as specified in
XML Media Types [8].
Encoding considerations: See RFC 3023 [8].
Interoperability considerations: See RFC 2023 [8] and RFC 4722.
Published specification: RFC 4722
Van Dyke, et al. Informational [Page 73]RFC 4722 MSCML November 2006
Applications that use this media type: Multimedia, enhanced
conferencing and interactive applications.
Personal and email address for further
information: eburger@cantata.com [31]
Intended usage: COMMON
13. Security Considerations
Because media flows through a media server in a conference, the media
server itself MUST protect the integrity, confidentiality, and
security of the sessions. It should not be possible for a conference
participant, on her own behalf, to be able to "tap in" to another
conference without proper authorization.
Because conferencing is a high-value application, the media server
SHOULD implement appropriate security measures. This includes, but
is not limited to, access lists for application servers. That is,
the media server only allows a select list of application or proxy
servers to create conferences, to invite participants to sessions,
etc. Note that the mechanisms for such security, like private
networks, shared certificates, MAC white/black lists, are beyond the
scope of this document.
Security concerns are one important reason MSCML limits requests with
conference scope to a separate control leg per conference. MSCML
uses the simple, proven, Internet-scale security model of SIP to
determine if a client is who they say they are (authentication) and
if they are allowed to create and manipulate a conference. However,
the security model to enable a control leg to manipulate arbitrary
conferences on the media server is extremely difficult. Not only
would one need to authenticate and authorize the basic conference
primitives, but privacy considerations require policies for one
client to access another client's conferences, even if the two
clients are on the same host. For example, if the media server
allowed any control leg to control any conference, an authorized but
unrelated client could maliciously attach itself to an existing
session and record or tap the conversation without the participant's
knowledge or consent.
Participants give implicit authorization to their applications by
virtue of the INVITE to the application. However, there is no trust,
explicit or implicit, between the users of one service and a distinct
client of another service.
All MSCML messages are sent within an INVITE-created SIP dialog. As
a result, it would be difficult for an entity other than the original
requestor to interfere with an established MSCML session, as this
would require detailed information on the dialog state. This allows
Van Dyke, et al. Informational [Page 74]RFC 4722 MSCML November 2006
multiple applications to utilize the resources of a single media
server simultaneously without interfering with one another.
Because of the sensitive nature of collected data, such as credit
card numbers or other identifying information, the media server MUST
support sips: and TLS. Clients, who presumably know the value of the
information they collect, as well as the privacy expectations of
their users, are free to use clear text signaling or encrypted secure
signaling, depending on the application's needs. Likewise, the media
server SHOULD support Secure Realtime Transport Protocol (SRTP) [9].
Again, the clients are free to negotiate the appropriate level of
media security.
The media management facilities of MSCML, such as the <managecontent>
(Section 8) request, assume a trust relationship between the media
server and file server. This scenario is similar to the one
addressed by URLAUTH [20]. Namely, the media server is acting on
behalf of a given user, yet the media server does not have
credentials for that user. One might be tempted to use the user:pass
facility of the HTTP URI to offer per-user security, but that also
requires that the media server be secure, as the media server would
need to know the user credentials in a form that is easily
compromised (clear text passwords).
The IETF is investigating methods for providing per-user or per-
instance authorization of third-party http writing, as is needed for
other protocols as well, such as WEBDAV [21]. However, until that
work is completed, media server implementations MUST be prepared to
authenticate themselves to file and web servers using appropriate
authentication means. At a minimum, the media server MUST support
HTTPS basic authentication. Implementers should note that the media
server will need to respond appropriately to whatever authentication
mechanism the file server requires.
As this is an XML markup, all the security considerations of RFC 3023
[8] apply.
14. References
14.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Burger, E., Van Dyke, J., and A. Spitzer, "Basic Network Media
Services with SIP", RFC 4240, December 2005.
[3] Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.
Van Dyke, et al. Informational [Page 75]RFC 4722 MSCML November 2006
[4] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[5] "Network call signalling protocol for the delivery of time-
critical services over cable television networks using cable
modems", ITU-T J.162, March 2001.
[6] Groves, C., Pantaleo, M., Anderson, T., and T. Taylor, "Gateway
Control Protocol Version 1", RFC 3525, June 2003.
[7] Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn, "XML
Schema Part 1: Structures", W3C REC REC-xmlschema-1-20010502,
May 2001.
[8] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.
[9] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC
3711, March 2004.
14.2. Informative References
[10] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol (SIP)", RFC 4353, February 2006.
[11] Carter, J., Danielsen, P., Hunt, A., Ferrans, J., Lucas, B.,
Porter, B., Rehor, K., Tryphonas, S., McGlashan, S., and D.
Burnett, "Voice Extensible Markup Language (VoiceXML) Version
2.0", W3C REC REC-voicexml20-20040316, March 2004.
[12] International Packet Communications Consortium, "IPCC Reference
Architecture V2", June 2002.
[13] European Telecommunications Standards Institute, "Digital
cellular telecommunications system (Phase 2+); Universal Mobile
Telecommunications System (UMTS); IP Multimedia Subsystem
(IMS); Stage 2 (3GPP TS 23.228 version 7.2.0 Release 7)",
December 2005.
[14] Hollenbeck, S., Rose, M., and L. Masinter, "Guidelines for the
Use of Extensible Markup Language (XML) within IETF Protocols",
BCP 70, RFC 3470, January 2003.
[15] Jacobs, I., Lie, H., Bos, B., and C. Lilley, "Cascading Style
Sheets, level 2 (CSS2) Specification", W3C REC REC-CSS2-
19980512, May 1998.
Van Dyke, et al. Informational [Page 76]RFC 4722 MSCML November 2006
[16] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference State",
RFC 4575, August 2006.
[17] Cable Television Laboratories, Inc., "Audio Server Protocol",
January 2005.
[18] "Procedures for document facsimile transmission in the general
switched telephone network", Recommendation T.30, April 1999.
[19] "Procedures for real-time Group 3 facsimile communication over
IP networks", Recommendation T.38, March 2002.
[20] Crispin, M., "Internet Message Access Protocol (IMAP) - URLAUTH
Extension", RFC 4467, May 2006.
[21] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV",
RFC 2518, February 1999.
[22] Institute of Electrical and Electronics Engineers, "Information
Technology - Portable Operating System Interface (POSIX) - Part
1: Base Definitions, Chapter 9", IEEE Standard 1003.1, June
2001.
[23] Burger, E. and M. Dolly, "A Session Initiation Protocol (SIP)
Event Package for Key Press Stimulus (KPML)", RFC 4730,
November 2006.
[24] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April
2001.
[25] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed., "The
Message Session Relay Protocol", Work in Progress, June 2006.
URIs
[26] <http://www.ietf.org/html.charters/sip-charter.html>
[27] <http://www.ietf.org/html.charters/sipping-charter.html>
[28] <http://www.ietf.org/html.charters/mmusic.html>
[29] <http://www.ietf.org/html.charters/xcon-charter.html>
[30] <http://www.3gpp.org/ftp/Specs/html-info/23228.htm>
[31] <mailto:eburger@cantata.com>
Van Dyke, et al. Informational [Page 77]RFC 4722 MSCML November 2006
Appendix A. Regex Grammar Syntax
The regular expression syntax used in MSCML is a telephony-oriented
subset of POSIX Extended Regular Expressions (ERE) [22] termed Digit
REGular EXpression (DRegex). This syntax was first described in KPML
[23].
DRegex includes ordinary characters, special characters, bracket
expressions, and interval expressions. These entities are defined in
the list below.
character matches digits 0-9, *, #, and A-D (case insensitive)
* matches the * character
# matches the # character
[character selector] matches any character in selector
[range1-range2] matches any character in range from range1 to range2,
inclusive
x matches any digit 0-9
{m} matches m repetitions of the previous pattern
{m,} matches m or more repetitions of the previous pattern
{,n} matches at most n (including zero) repetitions of the previous
pattern
{m,n} at least m and at most n repetitions of the previous pattern
L the presence of 'L' in any regex expression causes the media
server to enable "long" digit detection mode. See Section 7.1 for
the definition of "long" digits.
Table 7 illustrates DRegex usage through examples.
+--------------+--------------------------------------------+
| Example | Description |
+--------------+--------------------------------------------+
| 1 | Matches the digit 1 |
| [179] | Matches 1, 7, or 9 |
| [2-9] | Matches 2, 3, 4, 5, 6, 7, 8, 9 |
| [02-46-9A-D] | Matches 0, 2, 3, 4, 6, 7, 8, 9, A, B, C, D |
| x | Matches 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 |
| *6[179#] | Matches *61, *67, *69, or *6# |
| x{10} | Ten digits (0-9) |
| 011x{7,15} | 011 followed by seven to fifteen digits |
| L* | Long star |
+--------------+--------------------------------------------+
Table 7: DRegex Examples
Van Dyke, et al. Informational [Page 78]RFC 4722 MSCML November 2006
Appendix B. Contributors
Jeff Van Dyke and Andy Spitzer did the concept, development,
documentation, and execution for MSCML at SnowShore Networks, Inc.,
which is now part of Cantata Technology, Inc. Andy Spitzer's
original work at The Telephone Connection, Inc., influenced the IVR
implementation. Mary Ann Leekley implemented the personalized mix
feature and several other enhancements.
Cliff Schornak of Commetrex and Jeff Van Dyke developed the facsimile
service.
Jai Cauvet, Rolando Herrero, Srinivas Motamarri, and Ashish Patel
contributed greatly by testing MSCML.
Appendix C. Acknowledgements
The following individuals provided valuable assistance in the
direction, development, or debugging of MSCML:
o Brian Badger and Phil Crable from Verizon Business
o Stephane Bastien from BroadSoft
o Peter Danielsen of Lucent Technologies
o Kevin Flemming, formerly of SnowShore Networks, Inc.
o Wesley Hicks and Ravindra Kabre, formerly from Sonus Networks
o Jon Hinckley from SkyWave/Sestro
o Terence Lobo, formerly of SnowShore Networks, Inc.
o Kunal Nawale, formerly of SnowShore Networks, Inc.
o Edwina Nowicki, formerly of SnowShore Networks, Inc.
o Diana Rawlins and Sharadha Vijay, formerly of WorldCom
o Gaurav Srivastva and Subhash Verma from BayPackets
o Kevin Summers from Sonus Networks
o Tim Wong from at&t
The authors would like to thank Cullen Jennings and Dan Wing from
Cisco Systems for their helpful review comments.
The authors would also like to thank Scotty Farber for applying her
technical writing expertise to the documentation of MSCML.
Van Dyke, et al. Informational [Page 79]
RFC 4722 MSCML November 2006
Authors' Addresses
Jeff Van Dyke
Cantata Technology, Inc.
18 Keewaydin Dr.
Salem, NH 03079
USA
EMail: jvandyke@cantata.com
Eric Burger (editor)
Cantata Technology, Inc.
18 Keewaydin Dr.
Salem, NH 03079
USA
EMail: eburger@cantata.com
Andy Spitzer
Pingtel Corporation
400 West Cummings Park
Woburn, MA 01801
USA
EMail: woof@pingtel.com
Van Dyke, et al. Informational [Page 80]
RFC 4722 MSCML November 2006
Full Copyright Statement
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Van Dyke, et al. Informational [Page 81]
