Internet Engineering Task Force (IETF) J. Polk
Request for Comments: 6442 Cisco Systems
Category: Standards Track B. Rosen
ISSN: 2070-1721 J. Peterson
NeuStar
December 2011
Location Conveyance for the Session Initiation Protocol
Abstract
This document defines an extension to the Session Initiation Protocol
(SIP) to convey geographic location information from one SIP entity
to another SIP entity. The SIP extension covers end-to-end
conveyance as well as location-based routing, where SIP
intermediaries make routing decisions based upon the location of the
Location Target.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6442.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Polk, et al. Standards Track [Page 1]RFC 6442 Location Conveyance in SIP December 2011
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Table of Contents
1. Introduction ....................................................3
2. Conventions and Terminology Used in This Document ...............4
3. Overview of SIP Location Conveyance .............................4
3.1. Location Conveyed by Value .................................4
3.2. Location Conveyed as a Location URI ........................5
3.3. Location Conveyed though a SIP Intermediary ................6
3.4. SIP Intermediary Replacing Bad Location ....................7
4. SIP Extensions for Geolocation Conveyance .......................8
4.1. The Geolocation Header Field ...............................8
4.2. The Geolocation-Routing Header Field ......................11
4.2.1. Explaining Geolocation-Routing Header-Value
States .............................................12
4.3. 424 (Bad Location Information) Response Code ..............14
4.4. The Geolocation-Error Header Field ........................15
4.5. Location URIs in Message Bodies ...........................19
4.6. Location Profile Negotiation ..............................19
5. Geolocation Examples ...........................................20
5.1. Location-by-Value (in Coordinate Format) ..................20
5.2. Two Locations Composed in Same Location Object Example ....21
6. Geopriv Privacy Considerations .................................23
7. Security Considerations ........................................24
8. IANA Considerations ............................................26
8.1. IANA Registration for the SIP Geolocation Header Field ....26
8.2. IANA Registration for the SIP Geolocation-Routing
Header Field ..............................................26
8.3. IANA Registration for Location Profiles ...................27
8.4. IANA Registration for 424 Response Code ...................27
8.5. IANA Registration of New Geolocation-Error Header Field ...28
8.6. IANA Registration for the SIP Geolocation-Error Codes .....28
9. Acknowledgements ...............................................29
10. References ....................................................29
10.1. Normative References .....................................29
10.2. Informative References ...................................31
Appendix A. Requirements for SIP Location Conveyance ..............32
Polk, et al. Standards Track [Page 2]RFC 6442 Location Conveyance in SIP December 2011
1. Introduction
Session Initiation Protocol (SIP) [RFC3261] creates, modifies and
terminates multimedia sessions. SIP carries certain information
related to a session while establishing or maintaining calls. This
document defines how SIP conveys geographic location information of a
Target to a Location Recipient (LR). SIP acts as a Using Protocol of
location information, as defined in RFC 3693.
In order to convey location information, this document specifies
three new SIP header fields, Geolocation, Geolocation-Routing, and
Geolocation-Error, which carry a reference to a Location Object (LO),
grant permission to route a SIP request based on the location-value
and provide error notifications specific to location errors,
respectively. The Location Object (LO) may appear in a MIME body
attached to the SIP request, or it may be a remote resource in the
network.
A Target is an entity whose location is being conveyed, per RFC 3693.
Thus, a Target could be a SIP user agent (UA), some other IP device
(a router or a PC) that does not have a SIP stack, a non-IP device (a
person or a black phone), or even a non-communications device (a
building or store front). In no way does this document assume that
the SIP user agent client that sends a request containing a location
object is necessarily the Target. The location of a Target conveyed
within SIP typically corresponds to that of a device controlled by
the Target, for example, a mobile phone, but such devices can be
separated from their owners, and moreover, in some cases, the user
agent may not know its own location.
In the SIP context, a location recipient will most likely be a SIP
UA, but due to the mediated nature of SIP architectures, location
information conveyed by a single SIP request may have multiple
recipients, as any SIP proxy server in the signaling path that
inspects the location of the Target must also be considered a
Location Recipient. In presence-like architectures, an intermediary
that receives publications of location information and distributes
them to watchers acts as a Location Server per RFC 3693. This
location conveyance mechanism can also be used to deliver URIs
pointing to such Location Servers where prospective Location
Recipients can request Location Objects.
Polk, et al. Standards Track [Page 3]
RFC 6442 Location Conveyance in SIP December 2011
2. Conventions and Terminology 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 [RFC2119].
Furthermore, this document uses numerous terms defined in [RFC3693],
including: Location Object, Location Recipient, Location Server,
Target, Rule Maker, and Using Protocol.
3. Overview of SIP Location Conveyance
An operational overview of SIP location conveyance can be shown in
four basic diagrams, with most applications falling under one of the
following basic use cases. Each is separated into its own subsection
here in Section 3.
Each diagram has Alice and Bob as UAs. Alice is the Target, and Bob
is an LR. A SIP intermediary appears in some of the diagrams. Any
SIP entity that receives and inspects location information is an LR;
therefore, in any of the diagrams, the SIP intermediary that receives
a SIP request is potentially an LR -- though that does not mean such
an intermediary necessarily has to route the SIP request based on the
location information. In some use cases, location information passes
through the LS on the right of each diagram.
3.1. Location Conveyed by Value
We start with the simplest diagram of Location Conveyance, Alice to
Bob, where no other Layer 7 entities are involved.
Alice SIP Intermediary Bob LS
| | | |
| Request w/Location | |
|----------------------------------->| |
| | |
| Response | |
|<-----------------------------------| |
| | | |
Figure 1. Location Conveyed by Value
In Figure 1, Alice is both the Target and the LS that is conveying
her location directly to Bob, who acts as an LR. This conveyance is
point-to-point: it does not pass through any SIP-layer intermediary.
A Location Object appears by-value in the initial SIP request as a
MIME body, and Bob responds to that SIP request as appropriate.
There is a 'Bad Location Information' response code introduced within
this document to specifically inform Alice if she conveys bad
Polk, et al. Standards Track [Page 4]RFC 6442 Location Conveyance in SIP December 2011
location to Bob (e.g., Bob "cannot parse the location provided", or
"there is not enough location information to determine where Alice
is").
3.2. Location Conveyed as a Location URI
Here we make Figure 1 a little more complicated by showing a diagram
of indirect Location Conveyance from Alice to Bob, where Bob's entity
has to retrieve the location object from a third party server.
Alice SIP Intermediary Bob LS
| | | |
| Request w/Location URI | |
|----------------------------------->| |
| | Dereference |
| | Request |
| (To: Location URI) |
| |---------------->|
| | |
| | Dereference |
| | Response |
| (includes Location Object) |
| |<----------------|
| Response | |
|<-----------------------------------| |
| | | |
Figure 2. Location Conveyed as a Location URI
In Figure 2, location is conveyed indirectly, via a Location URI
carried in the SIP request (more of those details later). If Alice
sends Bob this Location URI, Bob will need to dereference the URI --
analogous to Content Indirection [RFC4483] -- in order to request the
location information. In general, the LS provides the location value
to Bob instead of Alice directly for conveyance to Bob. From a user
interface perspective, Bob the user won't know that this information
was gathered from an LS indirectly rather than culled from the SIP
request; practically, this does not impact the operation of location-
based applications.
The example given in this section is only illustrative, not
normative. In particular, applications can choose to dereference a
location URI at any time, possibly several times, or potentially not
at all. Applications receiving a Location URI in a SIP transaction
need to be mindful of timers used by different transactions. In
particular, if the means of dereferencing the Location URI might take
longer than the SIP transaction timeout (Timer C for INVITE
Polk, et al. Standards Track [Page 5]RFC 6442 Location Conveyance in SIP December 2011
transactions, Timer F for non-INVITE transactions), then it needs to
rely on mechanisms other than the transaction's response code to
convey location errors, if returning such errors are necessary.
3.3. Location Conveyed though a SIP Intermediary
In Figure 3, we introduce the idea of a SIP intermediary into the
example to illustrate the role of proxying in the location
architecture. This intermediary can be a SIP proxy or it can be a
back-to-back user agent (B2BUA). In this message flow, the SIP
intermediary could act as an LR, in addition to Bob. The primary use
case for intermediaries consuming location information is location-
based routing. In this case, the intermediary chooses a next hop for
the SIP request by consulting a specialized location service that
selects forwarding destinations based on the geographical location
information contained in the SIP request.
Alice SIP Intermediary Bob LS
| | | |
| Request | | |
| w/Location | | |
|--------------->| | |
| | Request | |
| | w/Location | |
| |------------------>| |
| | | |
| | Response | |
| |<------------------| |
| Response | | |
|<---------------| | |
| | | |
Figure 3. Location Conveyed though a SIP Intermediary
However, the most common case will be one in which the SIP
intermediary receives a request with location information (conveyed
either by-value or by-reference) and does not know or care about
Alice's location, or support this extension, and merely passes it on
to Bob. In this case, the intermediary does not act as a Location
Recipient. When the intermediary is not an LR, this use case is the
same as the one described in Section 3.1.
Note that an intermediary does not have to perform location-based
routing in order to be a Location Recipient. It could be the case
that a SIP intermediary that does not perform location-based routing
does care when Alice includes her location; for example, it could
care that the location information is complete or that it correctly
identifies where Alice is. The best example of this is
Polk, et al. Standards Track [Page 6]RFC 6442 Location Conveyance in SIP December 2011
intermediaries that verify location information for emergency
calling, but it could also be for any location based routing, e.g.,
contacting your favorite local pizza delivery service, making sure
that organization has Alice's proper location in the initial SIP
request.
There is another scenario in which the SIP intermediary cares about
location and is not an LR, one in which the intermediary inserts
another location of the Target, Alice in this case, into the request,
and forwards it. This secondary insertion is generally not advisable
because downstream SIP entities will not be given any guidance about
which location to believe is better, more reliable, less prone to
error, more granular, worse than the other location or just plain
wrong.
This document takes a "you break it, you bought it" approach to
dealing with second locations placed into a SIP request by an
intermediary entity. That entity becomes completely responsible for
all location within that SIP request (more on this in Section 4).
3.4. SIP Intermediary Replacing Bad Location
If the SIP intermediary rejects the message due to unsuitable
location information, the SIP response will indicate there was 'Bad
Location Information' in the SIP request and provide a location-
specific error code indicating what Alice needs to do to send an
acceptable request (see Figure 4 for this scenario).
Alice SIP Intermediary Bob LS
| | | |
| Request | | |
| w/Location | | |
|--------------->| | |
| | | |
| Rejected | | |
| w/New Location | | |
|<---------------| | |
| | | |
| Request | | |
| w/New Location | | |
|--------------->| | |
| | Request | |
| | w/New Location | |
| |------------------>| |
| | | |
Figure 4. SIP Intermediary Replacing Bad Location
Polk, et al. Standards Track [Page 7]RFC 6442 Location Conveyance in SIP December 2011
In this last use case, the SIP intermediary wishes to include a
Location Object indicating where it understands Alice to be. Thus,
it needs to inform her user agent of what location it will include in
any subsequent SIP request that contains her location. In this case,
the intermediary can reject Alice's request and, through the SIP
response, convey to her the best way to repair the request in order
for the intermediary to accept it.
Overriding location information provided by the user requires a
deployment where an intermediary necessarily knows better than an end
user -- after all, it could be that Alice has an on-board GPS, and
the SIP intermediary only knows her nearest cell tower. Which is
more accurate location information? Currently, there is no way to
tell which entity is more accurate or which is wrong, for that
matter. This document will not specify how to indicate which
location is more accurate than another.
As an aside, it is not envisioned that any SIP-based emergency
services request (i.e., IP-911 or 112 type of call attempt) will
receive a corrective 'Bad Location Information' response from an
intermediary. Most likely, in that scenario, the SIP intermediary
would act as a B2BUA and insert into the request by-value any
appropriate location information for the benefit of Public Safety
Answering Point (PSAP) call centers to expedite call reception by the
emergency services personnel; thereby, minimizing any delay in call
establishment time. The implementation of these specialized
deployments is, however, outside the scope of this document.
4. SIP Extensions for Geolocation Conveyance
The following sections detail the extensions to SIP for location
conveyance.
4.1. The Geolocation Header Field
This document defines "Geolocation" as a new SIP header field
registered by IANA, with the following ABNF [RFC5234]:
message-header =/ Geolocation-header
; (message-header from RFC 3261)
Geolocation-header = "Geolocation" HCOLON locationValue
*( COMMA locationValue )
locationValue = LAQUOT locationURI RAQUOT
*(SEMI geoloc-param)
locationURI = sip-URI / sips-URI / pres-URI
/ http-URI / https-URI
/ cid-url ; (from RFC 2392)
/ absoluteURI ; (from RFC 3261)
Polk, et al. Standards Track [Page 8]RFC 6442 Location Conveyance in SIP December 2011
geoloc-param = generic-param ; (from RFC 3261)
HCOLON, COMMA, LAQUOT, RAQUOT, and SEMI are defined in [RFC3261].
sip-URI, sips-URI, and absoluteURI are defined according to
[RFC3261].
The pres-URI is defined in [RFC3859].
http-URI and https-URI are defined according to [RFC2616] and
[RFC2818], respectively.
The cid-url is defined in [RFC2392] to locate message body parts.
This URI type is present in a SIP request when location is conveyed
as a MIME body in the SIP message.
GEO-URIs [RFC5870] are not appropriate for usage in the SIP
Geolocation header because it does not include retention and
re-transmission flags as part of the location information. Other URI
schemes used in the location URI MUST be reviewed against the
criteria in [RFC3693] for a Using Protocol. Section 4.6 discusses
how URI schemes are communicated using this SIP extension and what to
do if a URI scheme is received that cannot be supported.
The generic-param in the definition of locationValue is included as a
mechanism for future extensions that might require parameters. This
document defines no parameters for use with locationValue. If a
Geolocation header field is received that contains generic-params,
each parameter SHOULD be ignored, and SHOULD NOT be removed when
forwarding the locationValue. If a need arises to define parameters
for use with locationValue, a revision/extension to this document is
required.
The Geolocation header field MUST have at least one locationValue. A
SIP intermediary SHOULD NOT add location to a SIP request that
already contains location. This will quite often lead to confusion
within LRs. However, if a SIP intermediary adds location, even if
location was not previously present in a SIP request, that SIP
intermediary is fully responsible for addressing the concerns of any
424 (Bad Location Information) SIP response it receives about this
location addition and MUST NOT pass on (upstream) the 424 response.
A SIP intermediary that adds a locationValue MUST position the new
locationValue as the last locationValue within the Geolocation header
field of the SIP request.
Polk, et al. Standards Track [Page 9]
RFC 6442 Location Conveyance in SIP December 2011
This document defines the Geolocation header field as valid in the
following SIP requests:
INVITE [RFC3261] REGISTER [RFC3261]
OPTIONS [RFC3261] BYE [RFC3261]
UPDATE [RFC3311] INFO [RFC6086]
MESSAGE [RFC3428] REFER [RFC3515]
SUBSCRIBE [RFC3265] NOTIFY [RFC3265]
PUBLISH [RFC3903]
The Geolocation header field MAY be included in any one of the above
listed requests by a UA and a 424 response to any one of the requests
sent above. Fully appreciating the caveats/warnings mentioned above,
a SIP intermediary MAY add the Geolocation header field.
A SIP intermediary MAY add a Geolocation header field if one is not
present -- for example, when a user agent does not support the
Geolocation mechanism but their outbound proxy does and knows the
Target's location, or any of a number of other use cases (see Section
3).
The Geolocation header field MAY be present in a SIP request or
response without the presence of a Geolocation-Routing header
(defined in Section 4.2). As stated in Section 4.2, the default
value of Geolocation-Routing header-value is "no", meaning SIP
intermediaries MUST NOT view (i.e., process, inspect, or actively
dereference) any direct or indirect location within this SIP message.
This is for at least two fundamental reasons:
1) to make the possibility of retention of the Target's location
moot (because it was not viewed in the first place); and
2) to prevent a different treatment of this SIP request based on
the contents of the Location Information in the SIP request.
Any locationValue MUST be related to the original Target. This is
equally true for the location information in a SIP response, i.e.,
from a SIP intermediary back to the Target as explained in Section
3.4. SIP intermediaries SHOULD NOT modify or delete any existing
locationValue(s). A use case in which this would not apply would be
where the SIP intermediary is an anonymizer. The problem with this
scenario is that the geolocation included by the Target then becomes
useless for the purpose or service for which they wanted to use
(include) it. For example, 911/emergency calling or finding the
nearest (towing company/pizza delivery/dry cleaning) service(s) will
not yield intended results if the Location Information were to be
modified or deleted from the SIP request.
Polk, et al. Standards Track [Page 10]RFC 6442 Location Conveyance in SIP December 2011
4.2. The Geolocation-Routing Header Field
This document defines "Geolocation-Routing" as a new SIP header field
registered by IANA, with the following ABNF [RFC5234]:
message-header =/ Georouting-header
; (message-header from RFC 3261)
Georouting-header = "Geolocation-Routing" HCOLON
( "yes" / "no" / generic-value )
generic-value = generic-param; (from RFC 3261)
HCOLON is defined in [RFC3261].
The only defined values for the Geolocation-Routing header field are
"yes" or "no". When the value is "yes", the locationValue can be
used for routing decisions along the downstream signaling path by
intermediaries. Values other than "yes" or "no" are permitted for
future extensions. Implementations not aware of an extension MUST
treat any other received value the same as "no".
If no Geolocation-Routing header field is present in a SIP request, a
SIP intermediary MAY insert this header. Without knowledge from a
Rule Maker, the SIP intermediary inserting this header-value SHOULD
NOT set the value to "yes", as this may be more permissive than the
originating party intends. An easy way around this is to have the
Target always insert this header-value as "no".
When this Geolocation-Routing header-value is set to "no", this means
no locationValue (inserted by the originating User Agent Client (UAC)
or any intermediary along the signaling path) can be used by any SIP
intermediary to make routing decisions. Intermediaries that attempt
to use the location information for routing purposes in spite of this
counter indication could end up routing the request improperly as a
result. Section 4.4 gives the details on what a routing intermediary
does if it determines it needs to use the location in the SIP request
in order to process the message further. The practical implication
is that when the Geolocation-Routing header-value is set to "no", if
a cid:url is present in the SIP request, intermediaries MUST NOT view
the location (because it is not for intermediaries to consider when
processing the request); if a location URI is present, intermediaries
MUST NOT dereference it. UAs are allowed to view location in the SIP
request even when the Geolocation-Routing header-value is set to
"no". An LR MUST by default consider the Geolocation-Routing header-
value as set to "no", with no exceptions, unless the header field
value is set to "yes".
Polk, et al. Standards Track [Page 11]RFC 6442 Location Conveyance in SIP December 2011
A Geolocation-Routing header-value that is set to "no" has no special
security properties. At most, it is a request for behavior within
SIP intermediaries. That said, if the Geolocation-Routing header-
value is set to "no", SIP intermediaries are still to process the SIP
request and send it further downstream within the signaling path if
there are no errors present in this SIP request.
The Geolocation-Routing header field satisfies the recommendations
made in Section 3.5 of RFC 5606 [RFC5606] regarding indication of
permission to use location-based routing in SIP.
SIP implementations are advised to pay special attention to the
policy elements for location retransmission and retention described
in RFC 4119.
The Geolocation-Routing header field cannot appear without a header-
value in a SIP request or response (i.e., a null value is not
allowed). The absence of a Geolocation-Routing header-value in a SIP
request is always the same as the following header field:
Geolocation-Routing: no
The Geolocation-Routing header field MAY be present without a
Geolocation header field in the same SIP request. This concept is
further explored in Section 4.2.1.
4.2.1. Explaining Geolocation-Routing Header-Value States
The Geolocation header field contains a Target's location, and it
MUST NOT be present if there is no location information in this SIP
request. The location information is contained in one or more
locationValues. These locationValues MAY be contained in a single
Geolocation header field or distributed among multiple Geolocation
header fields. (See Section 7.3.1 of RFC 3261.)
The Geolocation-Routing header field indicates whether or not SIP
intermediaries can view and then route this SIP request based on the
included (directly or indirectly) location information. The
Geolocation-Routing header field MUST NOT appear more than once in
any SIP request, and MUST NOT lack a header-value. The default or
implied policy of a SIP request that does not have a Geolocation-
Routing header field is the same as if one were present and the
header-value were set to "no".
Polk, et al. Standards Track [Page 12]RFC 6442 Location Conveyance in SIP December 2011
There are only three possible states regarding the Geolocation-
Routing header field:
- "no"
- "yes"
- no header-field present in this SIP request
The expected results in each state are as follows:
If the Geolocation-Routing Only possible interpretations:
-------------------------- -----------------------------
"no" SIP intermediaries MUST NOT process
included geolocation information
within this SIP request.
SIP intermediaries inserting a
locationValue into a Geolocation
header field (whether adding to an
existing header-value or inserting the
Geolocation header field for the first
time) MUST NOT modify or delete the
received "no" header-value.
"yes" SIP intermediaries can process
included geolocation information
within this SIP request and can
change the policy to "no" for
intermediaries further downstream.
Geolocation-Routing absent If a Geolocation header field exists
(meaning a locationValue is already
present), a SIP intermediary MUST
interpret the lack of a
Geolocation-Routing header field as if
there were one present and the
header-value is set to "no".
If there is no Geolocation header
field in this SIP request, the default
Geolocation-Routing is open and can be
set by a SIP intermediary or not at
all.
Polk, et al. Standards Track [Page 13]RFC 6442 Location Conveyance in SIP December 2011
4.3. 424 (Bad Location Information) Response Code
This SIP extension creates a new location-specific response code,
defined as follows:
424 (Bad Location Information)
The 424 (Bad Location Information) response code is a rejection of
the request due to its location contents, indicating location
information that was malformed or not satisfactory for the
recipient's purpose or could not be dereferenced.
A SIP intermediary can also reject a location it receives from a
Target when it understands the Target to be in a different location.
The proper handling of this scenario, described in Section 3.4, is
for the SIP intermediary to include the proper location in the 424
response. This SHOULD be included in the response as a MIME message
body (i.e., a location value) rather than as a URI; however, in cases
where the intermediary is willing to share location with recipients
but not with a user agent, a reference might be necessary.
As mentioned in Section 3.4, it might be the case that the
intermediary does not want to chance providing less accurate location
information than the user agent; thus, it will compose its
understanding of where the user agent is in a separate <geopriv>
element of the same Presence Information Data Format Location Object
(PIDF-LO) [RFC4119] message body in the SIP response (which also
contains the Target's version of where it is). Therefore, both
locations are included -- each with different <method> elements. The
proper reaction of the user agent is to generate a new SIP request
that includes this composed location object, and send it towards the
original LR. SIP intermediaries can verify that subsequent requests
properly insert the suggested location information before forwarding
said requests.
SIP intermediaries that are forwarding (as opposed to generating) a
424 response MUST NOT add, modify, or delete any location appearing
in that response. This specifically applies to intermediaries that
are between the 424 response generator and the original UAC.
Geolocation and Geolocation-Error header fields and PIDF-LO body
parts MUST remain unchanged, never added to or deleted.
Section 4.4 describes a Geolocation-Error header field to provide
more detail about what was wrong with the location information in the
request. This header field MUST be included in the 424 response.
Polk, et al. Standards Track [Page 14]RFC 6442 Location Conveyance in SIP December 2011
It is only appropriate to generate a 424 response when the responding
entity needs a locationValue and there are no values in the request
that are usable by the responder, or when the responder has
additional location information to provide. The latter case is shown
in Figure 4 of Section 3.4. There, a SIP intermediary is informing
the upstream UA which location to include in the next SIP request.
A 424 response MUST NOT be sent in response to a request that lacks a
Geolocation header entirely, as the user agent in that case may not
support this extension at all. If a SIP intermediary inserted a
locationValue into a SIP request where one was not previously
present, it MUST take any and all responsibility for the corrective
action if it receives a 424 response to a SIP request it sent.
A 424 (Bad Location Information) response is a final response within
a transaction and MUST NOT terminate an existing dialog.
4.4. The Geolocation-Error Header Field
As discussed in Section 4.3, more granular error notifications
specific to location errors within a received request are required if
the location inserting entity is to know what was wrong within the
original request. The Geolocation-Error header field is used for
this purpose.
The Geolocation-Error header field is used to convey location-
specific errors within a response. The Geolocation-Error header
field has the following ABNF [RFC5234]:
message-header =/ Geolocation-Error
; (message-header from RFC 3261)
Geolocation-Error = "Geolocation-Error" HCOLON
locationErrorValue
locationErrorValue = location-error-code
*(SEMI location-error-params)
location-error-code = 1*3DIGIT
location-error-params = location-error-code-text
/ generic-param ; from RFC 3261
location-error-code-text = "code" EQUAL quoted-string
; from RFC 3261
HCOLON, SEMI, and EQUAL are defined in [RFC3261]. DIGIT is defined
in [RFC5234].
The Geolocation-Error header field MUST contain only one
locationErrorValue to indicate what was wrong with the locationValue
the Location Recipient determined was bad. The locationErrorValue
contains a 3-digit error code indicating what was wrong with the
Polk, et al. Standards Track [Page 15]RFC 6442 Location Conveyance in SIP December 2011
location in the request. This error code has a corresponding quoted
error text string that is human understandable. The text string is
OPTIONAL, but RECOMMENDED for human readability, similar to the
string phrase used for SIP response codes. That said, the strings
are complete enough for rendering to the user, if so desired. The
strings in this document are recommendations, and are not
standardized -- meaning an operator can change the strings -- but
MUST NOT change the meaning of the error code. Similar to how RFC
3261 specifies, there MUST NOT be more than one string per error
code.
The Geolocation-Error header field MAY be included in any response to
one of the SIP Methods mentioned in Section 4.1, so long as a
locationValue was in the request part of the same transaction. For
example, Alice includes her location in an INVITE to Bob. Bob can
accept this INVITE, thus creating a dialog, even though his UA
determined the location contained in the INVITE was bad. Bob merely
includes a Geolocation-Error header value in the 200 OK response to
the INVITE informing Alice the INVITE was accepted but the location
provided was bad.
If, on the other hand, Bob cannot accept Alice's INVITE without a
suitable location, a 424 (Bad Location Information) response is sent.
This message flow is shown in Figures 1, 2, or 3 in Sections 3.1,
3.2, and 3.3, respectively.
If Alice is deliberately leaving location information out of the LO
because she does not want Bob to have this additional information,
implementations should be aware that Bob could repeatedly error in
order to receive more location information about Alice in a
subsequent SIP request. Implementations MUST be on guard for this,
by not allowing continually more information to be revealed unless it
is clear that any LR is permitted by Alice to know all that Alice
knows about her location. A limit on the number of such rejections
to learn more location information SHOULD be configurable, with a
RECOMMENDED maximum of three times for each related transaction.
A SIP intermediary that requires Alice's location in order to
properly process Alice's INVITE also sends a 424 response with a
Geolocation-Error code. This message flow is shown in Figure 4 of
Section 3.4.
If more than one locationValue is present in a SIP request and at
least one locationValue is determined to be valid by the LR, the
location in that SIP request MUST be considered good as far as
location is concerned, and no Geolocation-Error is to be sent.
Polk, et al. Standards Track [Page 16]
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Here is an initial list of location-based error code ranges for any
SIP response, including provisional responses (other than 100 Trying)
and the new 424 (Bad Location Information) response. These error
codes are divided into three categories, based on how the response
receiver should react to these errors. There MUST be no more than
one Geolocation-Error code in a SIP response, regardless of how many
locationValues there are in the correlating SIP request. When more
than one locationValue is present in a SIP request, this mechanism
provides no indication to which one the Geolocation-Error code
corresponds. If multiple errors are present, the LR applies local
policy to select one.
o 1XX errors mean the LR cannot process the location within the
request:
A non-exclusive list of reasons for returning a 1XX is as follows:
- the location was not present or could not be found in the SIP
request,
- there was not enough location information to determine where the
Target was,
- the location information was corrupted or known to be
inaccurate.
o 2XX errors mean some specific permission is necessary to process
the included location information.
o 3XX errors mean there was trouble dereferencing the Location URI
sent.
Dereference attempts to the same request SHOULD be limited to 10
attempts within a few minutes. This number SHOULD be configurable,
but result in a Geolocation-Error: 300 error once reached.
It should be noted that for non-INVITE transactions, the SIP response
will likely be sent before the dereference response has been
received. This document does not alter that SIP protocol reality.
This means the receiver of any non-INVITE response to a request
containing location SHOULD NOT consider a 200 OK response to mean the
act of dereferencing has concluded and the dereferencer (i.e., the
LR) has successfully received and parsed the PIDF-LO for errors and
found none. The end of Section 3.2 discusses how transaction timing
considerations lead to this requirement.
Polk, et al. Standards Track [Page 17]RFC 6442 Location Conveyance in SIP December 2011
Additionally, if an LR cannot or chooses not to process location from
a SIP request, a 500 (Server Internal Error) SHOULD be used with or
without a configurable Retry-After header field. There is no special
location error code for what already exists within SIP today.
Within each of these ranges, there is a top-level error as follows:
Geolocation-Error: 100 ; code="Cannot Process Location"
Geolocation-Error: 200 ; code="Permission To Use Location
Information"
Geolocation-Error: 300 ; code="Dereference Failure"
If an error recipient cannot process a specific error code (such as
the 201 or 202 below), perhaps because it does not understand that
specific error code, the error recipient SHOULD process the error
code as if it originally were a top-level error code where the X in
X00 matches the specific error code. If the error recipient cannot
process a non-100 error code, for whatever reason, then the error
code 100 MUST be processed.
There are two specific Geolocation-Error codes necessary to include
in this document, both have to do with permissions necessary to
process the SIP request; they are
Geolocation-Error: 201 ; code="Permission To Retransmit Location
Information to a Third Party"
This location error is specific to having the PIDF-LO [RFC4119]
<retransmission-allowed> element set to "no". This location error is
stating it requires permission (i.e., PIDF-LO <retransmission-
allowed> element set to "yes") to process this SIP request further.
If the LS sending the location information does not want to give this
permission, it will not change this permission in a new request. If
the LS wants this message processed with the <retransmission-allowed>
element set to "yes", it MUST choose another logical path (if one
exists) for this SIP request.
Geolocation-Error: 202 ; code="Permission to Route based on Location
Information"
This location error is specific to having the Geolocation-Routing
header value set to "no". This location error is stating it requires
permission (i.e., the Geolocation-Routing header value set to "yes")
to process this SIP request further. If the LS sending the location
information does not want to give this permission, it will not change
this permission in a new request. If the LS wants this message
Polk, et al. Standards Track [Page 18]RFC 6442 Location Conveyance in SIP December 2011
processed with the <retransmission-allowed> element set to "yes", it
MUST choose another logical path (if one exists) for this SIP
request.
4.5. Location URIs in Message Bodies
In the case where an LR sends a 424 response and wishes to
communicate suitable location-by-reference rather than location-by-
value, the 424 response MUST include a content-indirection body per
RFC 4483.
4.6. Location Profile Negotiation
The following is part of the discussion started in Section 3, Figure
2, which introduced the concept of sending location indirectly.
If a location URI is included in a SIP request, the sending user
agent MUST also include a Supported header field indicating which
location profiles it supports. Two option tags for location profiles
are defined by this document: "geolocation-sip" and "geolocation-
http". Future specifications MAY define further location profiles
per the IANA policy described in Section 8.3.
The "geolocation-sip" option tag signals support for acquiring
location information via the presence event package of SIP [RFC3856].
A location recipient who supports this option can send a SUBSCRIBE
request and parse a resulting NOTIFY containing a PIDF-LO object.
The URI schemes supported by this option include "sip", "sips", and
"pres".
The "geolocation-http" option tag signals support for acquiring
location information via HTTP [RFC2616]. A location recipient who
supports this option can request location with an HTTP GET and parse
a resulting 200 response containing a PIDF-LO object. The URI
schemes supported by this option include "http" and "https". A
failure to parse the 200 response, for whatever reason, will return a
"Dereference Failure" indication to the original location sending
user agent to inform it that location was not delivered as intended.
If the location URI receiver does not understand the URI scheme sent
to it, it will return an Unsupported header value of the option tag
from the SIP request, and include the option tag of the preferred URI
scheme in the response's Supported header field.
See [GEO-FILTERS] or [HELD-DEREF] for more details on dereferencing
location information.
Polk, et al. Standards Track [Page 19]
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5. Geolocation Examples
5.1. Location-by-Value (in Coordinate Format)
This example shows an INVITE message with a coordinate location. In
this example, the SIP request uses a sips-URI [RFC3261], meaning this
message is protected using Transport Layer Security (TLS) on a hop-
by-hop basis.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...Session Description Protocol (SDP) goes here
--boundary1
Content-Type: application/pidf+xml
Content-ID: <target123@atlanta.example.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="target123-1">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
Polk, et al. Standards Track [Page 20]RFC 6442 Location Conveyance in SIP December 2011
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
</presence>
--boundary1--
The Geolocation header field from the above INVITE:
Geolocation: <cid:target123@atlanta.example.com>
... indicates the content-ID location [RFC2392] within the multipart
message body of where location information is. The other message
body part is SDP. The "cid:" eases message body parsing and
disambiguates multiple parts of the same type.
If the Geolocation header field did not contain a "cid:" scheme, for
example, it could look like this location URI:
Geolocation: <sips:target123@server5.atlanta.example.com>
... the existence of a non-"cid:" scheme indicates this is a
location URI, to be dereferenced to learn the Target's location. Any
node wanting to know where the target is located would subscribe to
the SIP presence event package [RFC3856] at:
sips:target123@server5.atlanta.example.com
(see Figure 2 in Section 3.2 for this message flow).
5.2. Two Locations Composed in Same Location Object Example
This example shows the INVITE message after a SIP intermediary
rejected the original INVITE (say, the one in Section 5.1). This
INVITE contains the composed LO sent by the SIP intermediary that
includes where the intermediary understands Alice to be. The rules
of RFC 5491 [RFC5491] are followed in this construction.
Polk, et al. Standards Track [Page 21]RFC 6442 Location Conveyance in SIP December 2011
This example is here, but ought not be taken as occurring very often.
In fact, this example is believed to be a corner case of location
conveyance applicability.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf0
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188512@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31863 INVITE
Contact: <sips:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...SDP goes here
--boundary1
Content-Type: application/pidf+xml
Content-ID: <target123@atlanta.example.com>
<?xml version="1.0" encoding="UTF-8"?>
<presence
xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
entity="pres:alice@atlanta.example.com">
<dm:device id="target123-1">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
Polk, et al. Standards Track [Page 22]RFC 6442 Location Conveyance in SIP December 2011
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
<dm:person id="target123">
<gp:geopriv>
<gp:location-info>
<cl:civicAddress>
<cl:country>US</cl:country>
<cl:A1>Texas</cl:A1>
<cl:A3>Colleyville</cl:A3>
<cl:RD>Treemont</cl:RD>
<cl:STS>Circle</cl:STS>
<cl:HNO>3913</cl:HNO>
<cl:FLR>1</cl:FLR>
<cl:NAM>Haley's Place</cl:NAM>
<cl:PC>76034</cl:PC>
</cl:civicAddress>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>triangulation</gp:method>
</gp:geopriv>
<dm:timestamp>2010-11-04T12:28:04Z</dm:timestamp>
</dm:person>
</presence>
--boundary1--
6. Geopriv Privacy Considerations
Location information is considered by most to be highly sensitive
information, requiring protection from eavesdropping and altering in
transit. [RFC3693] originally articulated rules to be followed by
any protocol wishing to be considered a "Using Protocol", specifying
how a transport protocol meets those rules. [RFC6280] updates the
guidance in RFC 3693 to include subsequently introduced entities and
concepts in the geolocation architecture.
Polk, et al. Standards Track [Page 23]RFC 6442 Location Conveyance in SIP December 2011
RFC 5606 explores the difficulties inherent in mapping the GEOPRIV
architecture onto SIP elements. In particular, the difficulties of
defining and identifying recipients of location information are given
in that document, along with guidance in Section 3.3.2 on the use of
location-by-reference mechanisms to preserve confidentiality of
location information from unauthorized recipients.
In a SIP deployment, location information may be added by any of
several elements, including the originating user agent or a proxy
server. In all cases, the Rule Maker associated with that location
information decides which entity adds location information and what
access control rules apply. For example, a SIP user agent that does
not support the Geolocation header may rely on a proxy server under
the direction of the Rule Maker adding a Geolocation header with a
reference to location information. The manner in which the Rule
Maker operates on these devices is outside the scope of this
document.
The manner in which SIP implementations honor the Rule Maker's
stipulations for access control rules (including retention and
retransmission) is application specific and not within the scope of
SIP protocol operations. Entities in SIP networks that fulfill the
architectural roles of the Location Server or Location Recipient
treat the privacy rules associated with location information per the
guidance in [RFC6280], Section 4.2.1. In particular, RFC 4119
(especially Section 2.2.2) gives guidance for handling access control
rules; SIP implementations should furthermore consult the
recommendations in RFC 5606.
7. Security Considerations
Conveyance of physical location of a UA raises privacy concerns, and
depending on use, there probably will be authentication and integrity
concerns. This document calls for conveyance to be accomplished
through secure mechanisms, like Secure/Multipurpose Internet Mail
Extensions (S/MIME) encrypting message bodies (although this is not
widely deployed), TLS protecting the overall signaling or conveyance
location-by-reference and requiring all entities that dereference
location to authenticate themselves. In location-based routing
cases, encrypting the location payload with an end-to-end mechanism
such as S/MIME is problematic because one or more proxies on the path
need the ability to read the location information to retarget the
message to the appropriate new destination User Agent Server (UAS).
Data can only be encrypted to a particular, anticipated target, and
thus if multiple recipients need to inspect a piece of data, and
those recipients cannot be predicted by the sender of data,
encryption is not a very feasible choice. Securing the location hop-
by-hop, using TLS, protects the message from eavesdropping and
Polk, et al. Standards Track [Page 24]
RFC 6442 Location Conveyance in SIP December 2011
modification in transit, but exposes the information to all proxies
on the path as well as the endpoint. In most cases, the UA has no
trust relationship with the proxy or proxies providing location-based
routing services, so such end-to-middle solutions might not be
appropriate either.
When location information is conveyed by reference, however, one can
properly authenticate and authorize each entity that wishes to
inspect location information. This does not require that the sender
of data anticipate who will receive data, and it does permit multiple
entities to receive it securely; however, it does not obviate the
need for pre-association between the sender of data and any
prospective recipients. Obviously, in some contexts, this pre-
association cannot be presumed; when it is not, effectively
unauthenticated access to location information MUST be permitted. In
this case, choosing pseudorandom URIs for location-by-reference,
coupled with path encryption like Session Initiation Protocol Secure
(SIPS), can help to ensure that only entities on the SIP signaling
path learn the URI, and thus restores rough parity with sending
location-by-value.
Location information is especially sensitive when the identity of its
Target is obvious. Note that there is the ability, according to
[RFC3693], to have an anonymous identity for the Target's location.
This is accomplished by the use of an unlinkable pseudonym in the
"entity=" attribute of the <presence> element [RFC4479]. Though,
this can be problematic for routing messages based on location
(covered in [RFC4479]). Moreover, anyone fishing for information
would correlate the identity at the SIP layer with that of the
location information referenced by SIP signaling.
When a UA inserts location, the UA sets the policy on whether to
reveal its location along the signaling path -- as discussed in
Section 4, as well as flags in the PIDF-LO [RFC4119]. UAC
implementations MUST make such capabilities conditional on explicit
user permission, and MUST alert the user that location is being
conveyed.
This SIP extension offers the default ability to require permission
to process location while the SIP request is in transit. The default
for this is set to "no". There is an error explicitly describing how
an intermediary asks for permission to view the Target's location,
plus a rule stating the user has to be made aware of this permission
request.
Polk, et al. Standards Track [Page 25]
RFC 6442 Location Conveyance in SIP December 2011
There is no end-to-end integrity on any locationValue or
locationErrorValue header field parameter (or middle-to-end if the
value was inserted by a intermediary), so recipients of either header
field need to implicitly trust the header field contents, and take
whatever precautions each entity deems appropriate given this
situation.
8. IANA Considerations
The following are the IANA considerations made by this SIP extension.
Modifications and additions to all these registrations require a
Standards Track RFC (Standards Action).
8.1. IANA Registration for the SIP Geolocation Header Field
The SIP Geolocation header field is created by this document, with
its definition and rules in Section 4.1 of this document, and it has
been added to the IANA sip-parameters registry as follows:
The Header Fields registry has been updated with:
Header Name Compact Reference
----------------- ------- ---------
Geolocation [RFC6442]
8.2. IANA Registration for the SIP Geolocation-Routing Header Field
The SIP Geolocation-Routing header field is created by this document,
with its definition and rules in Section 4.2 of this document, and it
has been added to the IANA sip-parameters registry as follows.
The Header Fields registry has been updated with:
Header Name Compact Reference
----------------- ------- ---------
Geolocation-Routing [RFC6442]
Polk, et al. Standards Track [Page 26]RFC 6442 Location Conveyance in SIP December 2011
8.3. IANA Registration for Location Profiles
This document defines two new SIP option tags: "geolocation-sip" and
"geolocation-http" that have been added to the IANA sip-parameters
Options Tags registry as follows.
Name Description Reference
----------- ------------------------------------------ ---------
geolocation-sip The "geolocation-sip" option tag signals [RFC6442]
support for acquiring location information
via the presence event package of SIP
(RFC 3856). A location recipient who
supports this option can send a SUBSCRIBE
request and parse a resulting NOTIFY
containing a PIDF-LO object. The URI
schemes supported by this option include
"sip", "sips", and "pres".
geolocation-http The "geolocation-http" option tag signals [RFC6442]
support for acquiring location information
via HTTP (RFC 2616). A location
recipient who supports this option can
request location with an HTTP GET and
parse a resulting 200 response containing
a PIDF-LO object. The URI schemes
supported by this option include "http"
and "https".
The names of profiles are SIP option tags, and the guidance in this
document does not supersede the option tag assignment guidance in
[RFC3261] (which requires a Standards Action for the assignment of a
new option tag). However, this document does stipulate that option
tags included to convey the name of a location profile per this
definition MUST begin with the string "geolocation" followed by a
dash. All such option tags should describe protocols used to acquire
location by reference: these tags have no relevance to location
carried in SIP requests by value, which use standard MIME typing and
negotiation.
8.4. IANA Registration for 424 Response Code
In the SIP Response Codes registry, the following is added
Reference: RFC 6442
Response code: 424 (recommended number to assign)
Default reason phrase: Bad Location Information
Polk, et al. Standards Track [Page 27]RFC 6442 Location Conveyance in SIP December 2011
Registry:
Response Code Reference
------------------------------------------ ---------
Request Failure 4xx
424 Bad Location Information [RFC6442]
This SIP Response code is defined in Section 4.3 of this document.
8.5. IANA Registration of New Geolocation-Error Header Field
The SIP Geolocation-Error header field is created by this document,
with its definition and rules in Section 4.4 of this document, to be
added to the IANA sip-parameters registry with two actions
1. Update the Header Fields registry with:
Registry:
Header Name Compact Reference
----------------- ------- ---------
Geolocation-Error [RFC6442]
2. In the portion titled "Header Field Parameters and Parameter
Values", add:
Predefined
Header Field Parameter Name Values Reference
----------------- ------------------- ---------- ---------
Geolocation-Error code yes [RFC6442]
8.6. IANA Registration for the SIP Geolocation-Error Codes
This document creates a new registry for SIP, called "Geolocation-
Error Codes". Geolocation-Error codes provide reason for the error
discovered by Location Recipients, categorized by action to be taken
by error recipient. The initial values for this registry are shown
below.
Registry Name: Geolocation-Error Codes
Reference: [RFC6442]
Registration Procedures: Specification Required
Code Default Reason Phrase Reference
---- --------------------------------------------------- ---------
100 "Cannot Process Location" [RFC6442]
200 "Permission To Use Location Information" [RFC6442]
201 "Permission To Retransmit Location Information
to a Third Party" [RFC6442]
Polk, et al. Standards Track [Page 28]RFC 6442 Location Conveyance in SIP December 2011
202 "Permission to Route based on Location Information" [RFC6442]
300 "Dereference Failure" [RFC6442]
Details of these error codes are in Section 4.4 of this document.
9. Acknowledgements
To Dave Oran for helping to shape this idea.
To Dean Willis for guidance of the effort.
To Allison Mankin, Dick Knight, Hannes Tschofenig, Henning
Schulzrinne, James Winterbottom, Jeroen van Bemmel, Jean-Francois
Mule, Jonathan Rosenberg, Keith Drage, Marc Linsner, Martin Thomson,
Mike Hammer, Ted Hardie, Shida Shubert, Umesh Sharma, Richard Barnes,
Dan Wing, Matt Lepinski, John Elwell, Thomas Stach, Jacqueline Lee,
and Adam Roach for constructive feedback and nit checking.
Special thanks to Paul Kyzivat for his help with the ABNF in this
document and to Robert Sparks for many helpful comments and the
proper construction of the Geolocation-Error header field.
And finally, to Spencer Dawkins for giving this document a good
scrubbing to make it more readable.
10. References
10.1. Normative References
[RFC3261] 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.
[RFC4119] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2392] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
[RFC3856] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
Polk, et al. Standards Track [Page 29]RFC 6442 Location Conveyance in SIP December 2011
[RFC3859] Peterson, J., "Common Profile for Presence (CPP)", RFC
3859, August 2004.
[RFC3428] Campbell, B., Ed., Rosenberg, J., Schulzrinne, H.,
Huitema, C., and D. Gurle, "Session Initiation Protocol
(SIP) Extension for Instant Messaging", RFC 3428, December
2002.
[RFC3311] Rosenberg, J., "The Session Initiation Protocol (SIP)
UPDATE Method", RFC 3311, October 2002.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC6086] Holmberg, C., Burger, E., and H. Kaplan, "Session
Initiation Protocol (SIP) INFO Method and Package
Framework", RFC 6086, January 2011.
[RFC3515] Sparks, R., "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003.
[RFC3903] Niemi, A., Ed., "Session Initiation Protocol (SIP)
Extension for Event State Publication", RFC 3903, October
2004.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January
2008.
[RFC4479] Rosenberg, J., "A Data Model for Presence", RFC 4479, July
2006.
[RFC4483] Burger, E., Ed., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483, May
2006.
[RFC5491] Winterbottom, J., Thomson, M., and H. Tschofenig, "GEOPRIV
Presence Information Data Format Location Object (PIDF-LO)
Usage Clarification, Considerations, and Recommendations",
RFC 5491, March 2009.
[RFC5870] Mayrhofer, A. and C. Spanring, "A Uniform Resource
Identifier for Geographic Locations ('geo' URI)", RFC
5870, June 2010.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
Polk, et al. Standards Track [Page 30]RFC 6442 Location Conveyance in SIP December 2011
10.2. Informative References
[RFC3693] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and
J. Polk, "Geopriv Requirements", RFC 3693, February 2004.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC5606] Peterson, J., Hardie, T., and J. Morris, "Implications of
'retransmission-allowed' for SIP Location Conveyance", RFC
5606, August 2009.
[GEO-FILTERS]
Mahy, R., Rosen, B., and H. Tschofenig, "Filtering
Location Notifications in SIP", Work in Progress, March
2010.
[HELD-DEREF]
Winterbottom, J., Tschofenig, H., Schulzrinne, H.,
Thomson, M., and M. Dawson, "A Location Dereferencing
Protocol Using HELD", Work in Progress, October 2011.
[RFC6280] Barnes, R., Lepinski, M., Cooper, A., Morris, J.,
Tschofenig, H., and H. Schulzrinne, "An Architecture for
Location and Location Privacy in Internet Applications",
BCP 160, RFC 6280, July 2011.
Polk, et al. Standards Track [Page 31]RFC 6442 Location Conveyance in SIP December 2011
Appendix A. Requirements for SIP Location Conveyance
The following subsections address the requirements placed on the UAC,
the UAS, as well as SIP proxies when conveying location. This text
is from a draft version of the location conveyance requirements that
has since evolved into this document (RFC 6442). It has been kept
for historical reasons.
If a requirement is not obvious in intent, a motivational statement
is included below it.
A.1. Requirements for a UAC Conveying Location
UAC-1 The SIP INVITE Method [RFC3261] must support location
conveyance.
UAC-2 The SIP MESSAGE method [RFC3428] must support location
conveyance.
UAC-3 SIP Requests within a dialog should support location
conveyance.
UAC-4 Other SIP Requests may support location conveyance.
UAC-5 There must be one, mandatory-to-implement means of
transmitting location confidentially.
Motivation:
To guarantee interoperability.
UAC-6 It must be possible for a UAC to update location conveyed at
any time in a dialog, including during dialog establishment.
Motivation:
If a UAC has moved prior to the establishment of a dialog
between UAs, the UAC must be able to send location
information. If location has been conveyed, and the UA moves,
the UAC must be able to update the location previously
conveyed to other parties.
UAC-7 The privacy and security rules established within [RFC3693]
that would categorize SIP as a 'Using Protocol' MUST be met.
UAC-8 The PIDF-LO [RFC4119] is a mandatory-to-implement format for
location conveyance within SIP.
Polk, et al. Standards Track [Page 32]RFC 6442 Location Conveyance in SIP December 2011
Motivation:
Interoperability with other IETF location protocols and
Mechanisms.
UAC-9 There must be a mechanism for the UAC to request the UAS send
its location.
UAC-9 has been DEPRECATED by the SIP WG, due to the many
problems this requirement would have caused if implemented.
The solution is for the above UAS to send a new request to the
original UAC with the UAS's location.
UAC-10 There must be a mechanism to differentiate the ability of the
UAC to convey location from the UACs lack of knowledge of its
location.
Motivation:
Failure to receive location when it is expected can happen
because the UAC does not implement this extension, or because
the UAC implements the extension, but does not know where the
Target is. This may be, for example, due to the failure of
the access network to provide a location acquisition mechanism
the UAC supports. These cases must be differentiated.
UAC-11 It must be possible to convey location to proxy servers along
the path.
Motivation:
Location-based routing.
A.2. Requirements for a UAS Receiving Location
The following are the requirements for location conveyance by a UAS:
UAS-1 SIP Responses must support location conveyance.
The SIPCORE WG reached consensus that this be allowed, but not
to communicate the UAS's location; rather for a SIP
intermediary to inform the UAC which location to include in
its next SIP request (as a matter of correcting what was
originally sent by the UAC).
UAS-2 There must be a unique 4XX response informing the UAC it did
not provide applicable location information.
In addition, requirements UAC-5, 6, 7, and 8 also apply to the UAS.
Polk, et al. Standards Track [Page 33]RFC 6442 Location Conveyance in SIP December 2011
A.3. Requirements for SIP Proxies and Intermediaries
The following are the requirements for location conveyance by a SIP
proxies and intermediaries:
Proxy-1 Proxy servers must be capable of adding a Location header
field during processing of SIP requests.
Motivation:
Provide network assertion of location when UACs are unable
to do so, or when network assertion is more reliable than
UAC assertion of location
Note: Because UACs connected to SIP signaling networks can have
widely varying access network arrangements, including VPN
tunnels and roaming mechanisms, it can be difficult for a
network to reliably know the location of the endpoint.
Proxies SHOULD NOT assert location of an endpoint unless the
SIP signaling network has reliable knowledge of the actual
location of the Targets.
Proxy-2 There must be a unique 4XX response informing the UAC it did
not provide applicable location information.
Polk, et al. Standards Track [Page 34]RFC 6442 Location Conveyance in SIP December 2011
Authors' Addresses
James Polk
Cisco Systems
3913 Treemont Circle
Colleyville, Texas 76034
33.00111N
96.68142W
Phone: +1-817-271-3552
EMail: jmpolk@cisco.com
Brian Rosen
NeuStar, Inc.
470 Conrad Dr.
Mars, PA 16046
40.70497N
80.01252W
Phone: +1 724 382 1051
EMail: br@brianrosen.net
Jon Peterson
NeuStar, Inc.
EMail: jon.peterson@neustar.biz
Polk, et al. Standards Track [Page 35]
