Internet Engineering Task Force (IETF) F. Le Faucheur
Request for Comments: 6401 J. Polk
Category: Standards Track Cisco
ISSN: 2070-1721 K. Carlberg
G11
October 2011
RSVP Extensions for Admission Priority
Abstract
Some applications require the ability to provide an elevated
probability of session establishment to specific sessions in times of
network congestion. When supported over the Internet Protocol suite,
this may be facilitated through a network-layer admission control
solution that supports prioritized access to resources (e.g.,
bandwidth). These resources may be explicitly set aside for
prioritized sessions, or may be shared with other sessions. This
document specifies extensions to the Resource reSerVation Protocol
(RSVP) that can be used to support such an admission priority
capability at the network layer.
Based on current security concerns, these extensions are intended for
use in a single administrative domain.
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/rfc6401.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Le Faucheur, et al. Standards Track [Page 1]RFC 6401 RSVP Extensions for Admission Priority October 2011
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 4
3. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
4. Overview of RSVP Extensions and Operations . . . . . . . . . . 4
4.1. Operations of Admission Priority . . . . . . . . . . . . . 6
5. New Policy Elements . . . . . . . . . . . . . . . . . . . . . 7
5.1. Admission Priority Policy Element . . . . . . . . . . . . 8
5.1.1. Admission Priority Merging Rules . . . . . . . . . . . 9
5.2. Application-Level Resource Priority Policy Element . . . . 10
5.2.1. Application-Level Resource Priority Modifying and
Merging Rules . . . . . . . . . . . . . . . . . . . . 11
5.3. Default Handling . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6.1. Use of RSVP Authentication between RSVP Neighbors . . . . 13
6.2. Use of INTEGRITY object within the POLICY_DATA Object . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Examples of Bandwidth Allocation Model for
Admission Priority . . . . . . . . . . . . . . . . . 19
A.1. Admission Priority with Maximum Allocation Model (MAM) . . 19
A.2. Admission Priority with Russian Dolls Model (RDM) . . . . 23
A.3. Admission Priority with Priority Bypass Model (PrBM) . . . 26
Appendix B. Example Usages of RSVP Extensions . . . . . . . . . . 29
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1. Introduction
Some applications require the ability to provide an elevated
probability of session establishment to specific sessions in times of
network congestion.
Solutions to meet this requirement for elevated session establishment
probability may involve session-layer capabilities prioritizing
access to resources controlled by the session control function. As
an example, entities involved in session control (such as SIP user
agents, when the Session Initiation Protocol (SIP) [RFC3261], is the
session control protocol in use) can influence their treatment of
session establishment requests (such as SIP requests). This may
include the ability to "queue" session establishment requests when
those can not be immediately honored (in some cases with the notion
of "bumping", or "displacement", of less important session
establishment requests from that queue). It may include additional
mechanisms such as alternate routing and exemption from certain
network management controls.
Solutions to meet the requirement for elevated session establishment
probability may also take advantage of network-layer admission
control mechanisms supporting admission priority. Networks usually
have engineered capacity limits that characterize the maximum load
that can be handled (say, on any given link) for a class of traffic
while satisfying the quality-of-service (QoS) requirements of that
traffic class. Admission priority may involve setting aside some
network resources (e.g., bandwidth) out of the engineered capacity
limits for the prioritized sessions only. Or alternatively, it may
involve allowing the prioritized sessions to seize additional
resources beyond the engineered capacity limits applied to normal
sessions. This document specifies the necessary extensions to
support such admission priority when network-layer admission control
is performed using the Resource reSerVation Protocol (RSVP)
[RFC2205].
[RFC3181] specifies the Signaled Preemption Priority Policy Element
that can be signaled in RSVP so that network node may take into
account this policy element in order to preempt some previously
admitted low-priority sessions in order to make room for a newer,
higher-priority session. In contrast, this document specifies new
RSVP extensions to increase the probability of session establishment
without preemption of existing sessions. This is achieved by
engineered capacity techniques in the form of bandwidth allocation
models. In particular, this document specifies two new RSVP policy
elements allowing the admission priority to be conveyed inside RSVP
signaling messages so that RSVP nodes can enforce a selective
bandwidth admission control decision based on the session admission
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RFC 6401 RSVP Extensions for Admission Priority October 2011
priority. Appendix A of this document also provides examples of
bandwidth allocation models that can be used by RSVP-routers to
enforce such admission priority on every link. A given reservation
may be signaled with the admission priority extensions specified in
the present document, with the preemption priority specified in
[RFC3181], or with both.
1.1. Terminology
This document assumes the terminology defined in [RFC2753]. For
convenience, the definitions of a few key terms are repeated here:
o Policy Decision Point (PDP): The point where policy decisions are
made.
o Local Policy Decision Point (LPDP): The PDP local to the network
element.
o Policy Enforcement Point (PEP): The point where the policy
decisions are actually enforced.
o Policy Ignorant Node (PIN): A network element that does not
explicitly support policy control using the mechanisms defined in
[RFC2753].
2. Applicability Statement
A subset of RSVP messages are signaled with the Router Alert Option
(RAO) ([RFC2113], [RFC2711]). The security aspects and common
practices around the use of the current IP Router Alert Option and
consequences on the use of IP Router Alert by applications such as
RSVP are discussed in [RFC6398]. Based on those, the extensions
defined in this document are intended for use within a single
administrative domain. Thus, in particular, the extensions defined
in this document are not intended for end-to-end use on the Internet.
3. Requirements Language
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 [RFC2119].
4. Overview of RSVP Extensions and Operations
Let us consider the case where a session requires elevated
probability of establishment, and more specifically that the
preference to be granted to this session is in terms of network-layer
"admission priority" (as opposed to preference granted through
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preemption of existing sessions). By "admission priority" we mean
allowing the priority session to seize network-layer resources from
the engineered capacity that has been set aside for priority sessions
(and not made available to normal sessions) or, alternatively,
allowing the priority session to seize additional resources beyond
the engineered capacity limits applied to normal sessions.
Session establishment can be made conditional on resource-based and
policy-based network-layer admission control achieved via RSVP
signaling. In the case where the session control protocol is SIP,
the use of RSVP-based admission control in conjunction with SIP is
specified in [RFC3312].
Devices involved in the session establishment are expected to be
aware of the application-level priority requirements of prioritized
sessions. For example, considering the case where the session
control protocol is SIP, the SIP user agents may be made aware of the
resource priority requirements of a given session using the
"Resource-Priority" header mechanism specified in [RFC4412]. The
end-devices involved in the upper-layer session establishment simply
need to copy the application-level resource priority requirements
(e.g., as communicated in the SIP "Resource-Priority" header) inside
the new RSVP Application-Level Resource Priority Policy Element
defined in this document.
Conveying the application-level resource priority requirements inside
the RSVP message allows this application-level requirement to be
mapped/remapped into a different RSVP "admission priority" at a
policy boundary based on the policy applicable in that policy area.
In a typical model (see [RFC2753]) where PDPs control PEPs at the
periphery of the policy area (e.g., on the first hop router), PDPs
would interpret the RSVP Application-Level Resource Priority Policy
Element and map the requirement of the prioritized session into an
RSVP "admission priority" level. Then, PDPs would convey this
information inside the new Admission Priority Policy Element defined
in this document. This way, the RSVP admission priority can be
communicated to downstream PEPs (i.e., RSVP routers) of the same
policy domain that have LPDPs but no controlling PDP. In turn, this
means the necessary RSVP Admission priority can be enforced at every
RSVP hop, including all the (possibly many) hops that do not have any
understanding of application-level resource priority semantics. It
is not expected that the RSVP Application-Level Resource Priority
Header Policy Element would be taken into account at RSVP hops within
a given policy area. It is expected to be used at policy area
boundaries only in order to set/reset the RSVP Admission Priority
Policy Element.
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RFC 6401 RSVP Extensions for Admission Priority October 2011
Remapping by PDPs of the Admission Priority Policy Element from the
Application-Level Resource Priority Policy Element may also be used
at boundaries with other signaling protocols, such as the NSIS
Signaling Layer Protocol (NSLP) for QoS Signaling [RFC5974].
As can be observed, the framework described above for mapping/
remapping application-level resource priority requirements into an
RSVP admission priority can also be used together with [RFC3181] for
mapping/remapping application-level resource priority requirements
into an RSVP preemption priority (when preemption is indeed deemed
necessary by the prioritized session handling policy). In that case,
when processing the RSVP Application-Level Resource Priority Policy
Element, the PDPs at policy boundaries (or between various QoS
signaling protocols) can map it into an RSVP "preemption priority"
information. This preemption priority information comprises a setup
preemption level and a defending preemption priority level that can
then be encoded inside the Preemption Priority Policy Element of
[RFC3181].
Appendix B provides examples of various hypothetical policies for
prioritized session handling, some of them involving admission
priority, some of them involving both admission priority and
preemption priority. Appendix B also identifies how the application-
level resource priority needs to be mapped into RSVP policy elements
by the PDPs to realize these policies.
4.1. Operations of Admission Priority
The RSVP Admission Priority Policy Element defined in this document
allows admission bandwidth to be allocated preferentially to
prioritized sessions. Multiple models of bandwidth allocation MAY be
used to that end.
A number of bandwidth allocation models have been defined in the IETF
for allocation of bandwidth across different classes of traffic
trunks in the context of Diffserv-aware MPLS Traffic Engineering.
Those include the Maximum Allocation Model (MAM) defined in
[RFC4125], the Russian Dolls Model (RDM) specified in [RFC4127], and
the Maximum Allocation model with Reservation (MAR) defined in
[RFC4126]. However, these same models MAY be applied for allocation
of bandwidth across different levels of admission priority as defined
in this document. Appendix A provides an illustration of how these
bandwidth allocation models can be applied for such purposes and also
introduces an additional bandwidth allocation model that we term the
Priority Bypass Model (PrBM). It is important to note that the
models described and illustrated in Appendix A are only informative
and do not represent a recommended course of action.
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We can see in these examples how the RSVP Admission Priority can be
used by RSVP routers to influence their admission control decision
(for example, by determining which bandwidth pool is to be used by
RSVP for performing its bandwidth allocation) and therefore to
increase the probability of reservation establishment. In turn, this
increases the probability of application-level session establishment
for the corresponding session.
5. New Policy Elements
The Framework document for policy-based admission control [RFC2753]
describes the various components that participate in policy decision
making (i.e., PDP, PEP, and LPDP).
As described in Section 4 of the present document, the Application-
Level Resource Priority Policy Element and the Admission Priority
Policy Element serve different roles in this framework:
o The Application-Level Resource Priority Policy Element conveys
application-level information and is processed by PDPs.
o The emphasis of Admission Priority Policy Element is to be simple,
stateless, and lightweight such that it can be processed
internally within a node's LPDP. It can then be enforced
internally within a node's PEP. It is set by PDPs based on
processing of the Application-Level Resource Priority Policy
Element.
[RFC2750] defines extensions for supporting generic policy-based
admission control in RSVP. These extensions include the standard
format of POLICY_DATA objects and a description of RSVP handling of
policy events.
The POLICY_DATA object contains one or more policy elements, each
representing a different (and perhaps orthogonal) policy. As an
example, [RFC3181] specifies the Preemption Priority Policy Element.
This document defines two new policy elements called:
o the Admission Priority Policy Element
o the Application-Level Resource Priority Policy Element
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5.1. Admission Priority Policy Element
The format of the Admission Priority Policy Element is as shown in
Figure 1:
0 0 0 1 1 2 2 3
0 . . . 7 8 . . . 5 6 . . . 3 4 . . . 1
+-------------+-------------+-------------+-------------+
| Length | P-Type = ADMISSION_PRI |
+-------------+-------------+-------------+-------------+
| Flags | M. Strategy | Error Code | Reserved |
+-------------+-------------+-------------+-------------+
| Reserved |Adm. Priority|
+---------------------------+---------------------------+
Figure 1: Admission Priority Policy Element
where:
o Length: 16 bits
* Always 12. The overall length of the policy element, in bytes.
o P-Type: 16 bits
* ADMISSION_PRI = 0x05 (see the "IANA Considerations" section).
o Flags: Reserved
* SHALL be set to zero on transmit and SHALL be ignored on
reception.
o Merge Strategy: 8 bits (applicable to multicast flows)
* values are defined in the corresponding registry maintained by
IANA (see the "IANA Considerations" section).
o Error code: 8 bits (applicable to multicast flows)
* values are defined in the corresponding registry maintained by
IANA (see the "IANA Considerations" section).
o Reserved: 8 bits
* SHALL be set to zero on transmit and SHALL be ignored on
reception.
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o Reserved: 24 bits
* SHALL be set to zero on transmit and SHALL be ignored on
reception
o Adm. Priority (Admission Priority): 8 bits (unsigned)
* The admission control priority of the flow, in terms of access
to network bandwidth in order to provide higher probability of
session completion to selected flows. Higher values represent
higher priority. Bandwidth allocation models such as those
described in Appendix A are to be used by the RSVP router to
achieve increased probability of session establishment. The
admission priority value effectively indicates which bandwidth
constraint(s) of the bandwidth constraint model in use is/are
applicable to admission of this RSVP reservation.
Note that the Admission Priority Policy Element does NOT indicate
that this RSVP reservation is to preempt any other RSVP reservation.
If a priority session justifies both admission priority and
preemption priority, the corresponding RSVP reservation needs to
carry both an Admission Priority Policy Element and a Preemption
Priority Policy Element. The Admission Priority and Preemption
Priority are handled by LPDPs and PEPs as separate mechanisms. They
can be used one without the other, or they can be used both in
combination.
5.1.1. Admission Priority Merging Rules
This section discusses alternatives for dealing with RSVP admission
priority in case of merging of reservations. As merging applies to
multicast, this section also applies to multicast sessions.
The rules for merging Admission Priority Policy Elements are defined
by the value encoded inside the Merge Strategy field in accordance
with the corresponding IANA registry. This registry applies both to
the Merge Strategy field of the Admission Priority Policy Element
defined in the present document and to the Merge Strategy field of
the Preemption Priority Policy Element defined in [RFC3181]. The
registry initially contains the values already defined in [RFC3181]
(see the "IANA Considerations" section).
The only difference from [RFC3181] is that this document does not
recommend a given merge strategy over the others for Admission
Priority, while [RFC3181] recommends the first of these merge
strategies for Preemption Priority. Note that with the Admission
Priority (as is the case with the Preemption Priority), "take highest
priority" translates into "take the highest numerical value".
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5.2. Application-Level Resource Priority Policy Element
The format of the Application-Level Resource Priority Policy Element
is as shown in Figure 2:
0 0 0 1 1 2 2 3
0 . . . 7 8 . . . 5 6 . . . 3 4 . . . 1
+-------------+-------------+-------------+-------------+
| Length | P-Type = APP_RESOURCE_PRI |
+-------------+-------------+-------------+-------------+
// ALRP List //
+---------------------------+---------------------------+
Figure 2: Application-Level Resource Priority Policy Element
where:
o Length:
* The length of the policy element (including the Length and
P-Type) is in number of octets (MUST be a multiple of 4) and
indicates the end of the ALRP list.
o P-Type: 16 bits
* APP_RESOURCE_PRI = 0x06 (see the "IANA Considerations"
section).
o ALRP List:
* List of ALRPs where each ALRP is encoded as shown in Figure 3.
ALRP:
0 0 0 1 1 2 2 3
0 . . . 7 8 . . . 5 6 . . . 3 4 . . . 1
+---------------------------+-------------+-------------+
| ALRP Namespace | Reserved |ALRP Value |
+---------------------------+---------------------------+
Figure 3: Application-Level Resource Priority
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where:
o ALRP Namespace (Application-Level Resource Priority Namespace): 16
bits (unsigned)
* Contains a numerical value identifying the namespace of the
application-level resource priority. This value is encoded as
per the "Resource Priority Namespaces" IANA registry. (See the
"IANA Considerations" section; IANA has extended the registry
to include this numerical value).
o Reserved: 8 bits
* SHALL be set to zero on transmit and SHALL be ignored on
reception.
o ALRP Value (Application-Level Resource Priority Value): 8 bits
(unsigned)
* Contains the priority value within the namespace of the
application-level resource priority. This value is encoded as
per the "Resource Priority Priority-Value" IANA registry. (See
the "IANA Considerations" section; IANA has extended the
registry to include this numerical value).
5.2.1. Application-Level Resource Priority Modifying and Merging Rules
When POLICY_DATA objects are protected by integrity, LPDPs should not
attempt to modify them. They MUST be forwarded without modification
to ensure their security envelope is not invalidated.
In case of multicast, when POLICY_DATA objects are not protected by
integrity, LPDPs MAY merge incoming Application-Level Resource
Priority Elements to reduce their size and number. When they do
merge those elements, LPDPs MUST do so according to the following
rule:
o The ALRP List in the outgoing APP_RESOURCE_PRI element MUST
contain all the ALRPs appearing in the ALRP List of an incoming
APP_RESOURCE_PRI element. A given ALRP MUST NOT appear more than
once. In other words, the outgoing ALRP List is the union of the
incoming ALRP Lists that are merged.
As merging applies to multicast, this rule also applies to multicast
sessions.
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5.3. Default Handling
As specified in Section 4.2 of [RFC2750], Policy Ignorant Nodes
(PINs) implement a default handling of POLICY_DATA objects ensuring
that those objects can traverse PINs in transit from one PEP to
another. This applies to the situations where POLICY_DATA objects
contain the Admission Priority Policy Element and the ALRP Policy
Element specified in this document, so that those objects can
traverse PINs.
Section 4.2 of [RFC2750] also defines a similar default behavior for
policy-capable nodes that do not recognize a particular policy
element. This applies to the Admission Priority Policy Element and
the ALRP Policy Element specified in this document, so that those
elements can traverse policy-capable nodes that do not support these
extensions defined in the present document.
6. Security Considerations
As this document defines extensions to RSVP, the security
considerations of RSVP apply. Those are discussed in [RFC2205],
[RFC4230], and [RFC6411]. Approaches for addressing those concerns
are discussed further below.
A subset of RSVP messages are signaled with the Router Alert Option
(RAO) ([RFC2113], [RFC2711]). The security aspects and common
practices around the use of the current IP Router Alert Option and
consequences on the use of IP Router Alert by applications such as
RSVP are discussed in [RFC6398]. As discussed in Section 2, the
extensions defined in this document are intended for use within a
single administrative domain.
[RFC6398] discusses router alert protection approaches for service
providers. These approaches can be used to protect a given network
against the potential risks associated with the leaking of router
alert packets resulting from the use of the present extensions in
another domain. Also, where RSVP is not used, by simply not enabling
RSVP on the routers of a given network, generally that network can
isolate itself from any RSVP signaling that may leak from another
network that uses the present extensions (since the routers will then
typically ignore RSVP messages). Where RSVP is to be used internally
within a given network, the network operator can activate, on the
edge of his network, mechanisms that either tunnel or, as a last
resort, drop incoming RSVP messages in order to protect the given
network from RSVP signaling that may leak from another network that
uses the present extensions.
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The ADMISSION_PRI and APP_RESOURCE_PRI Policy Elements defined in
this document are signaled by RSVP through encapsulation in a
POLICY_DATA object as defined in [RFC2750]. Therefore, like any
other policy elements, their integrity can be protected as discussed
in Section 6 of [RFC2750] by two optional security mechanisms. The
first mechanism relies on RSVP authentication as specified in
[RFC2747] and [RFC3097] to provide a chain of trust when all RSVP
nodes are policy capable. With this mechanism, the INTEGRITY object
is carried inside RSVP messages. The second mechanism relies on the
INTEGRITY object within the POLICY_DATA object to guarantee integrity
between RSVP PEPs that are not RSVP neighbors.
6.1. Use of RSVP Authentication between RSVP Neighbors
RSVP authentication can be used between RSVP neighbors that are
policy capable. RSVP authentication (defined in [RFC2747] and
[RFC3097]) SHOULD be supported by an implementation of the present
document.
With RSVP authentication, the RSVP neighbors use shared keys to
compute the cryptographic signature of the RSVP message. [RFC6411]
discusses key types and key provisioning methods as well as their
respective applicabilities.
6.2. Use of INTEGRITY object within the POLICY_DATA Object
The INTEGRITY object within the POLICY_DATA object can be used to
guarantee integrity between non-neighboring RSVP PEPs. This is
useful only when some RSVP nodes are Policy Ignorant Nodes (PINs).
The INTEGRITY object within the POLICY_DATA object MAY be supported
by an implementation of the present document.
Details for computation of the content of the INTEGRITY object can be
found in Appendix B of [RFC2750]. This states that the Policy
Decision Point (PDP), at its discretion, and based on the destination
PEP/PDP or other criteria, selects an Authentication Key and the hash
algorithm to be used. Keys to be used between PDPs can be
distributed manually or via a standard key management protocol for
secure key distribution.
Note that where non-RSVP hops may exist in between RSVP hops, as well
as where RSVP-capable PINs may exist in between PEPs, it may be
difficult for the PDP to determine what is the destination PDP for a
POLICY_DATA object contained in some RSVP messages (such as a Path
message). This is because in those cases the next PEP is not known
at the time of forwarding the message. In this situation, key shared
across multiple PDPs may be used. This is conceptually similar to
the use of a key shared across multiple RSVP neighbors as discussed
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RFC 6401 RSVP Extensions for Admission Priority October 2011
in [RFC6411]. We observe also that this issue may not exist in some
deployment scenarios where a single (or low number of) PDP is used to
control all the PEPs of a region (such as an administrative domain).
In such scenarios, it may be easy for a PDP to determine what is the
next-hop PDP, even when the next-hop PEP is not known, simply by
determining what is the next region that will be traversed (say,
based on the destination address).
7. IANA Considerations
As specified in [RFC2750], standard RSVP policy elements (P-type
values) are to be assigned by IANA as per "IETF Consensus" policy as
outlined in [RFC2434] (this policy is now called "IETF Review" as per
[RFC5226]) .
IANA has allocated two P-Types from the standard RSVP policy element
range:
o 0x05 ADMISSION_PRI for the Admission Priority Policy Element
o 0x06 APP_RESOURCE_PRI for the Application-Level Resource Priority
Policy Element
In Section 5.1, the present document defines a Merge Strategy field
inside the Admission Priority Policy Element. This registry is to be
specified as also applicable to the Merge Strategy field of the
Preemption Priority Policy Elements defined in [RFC3181]. Since it
is conceivable that, in the future, values will be added to the
registry that only apply to the Admission Priority Policy Element or
to the Preemption Priority Policy Element (but not to both), IANA has
listed the applicable documents for each value. IANA has allocated
the following values:
o 0: Reserved
o 1: Take priority of highest QoS [RFC3181] [RFC6401]
o 2: Take highest priority [RFC3181] [RFC6401]
o 3: Force Error on heterogeneous merge [RFC3181] [RFC6401]
Following the policies outlined in [RFC5226], numbers in the range
0-127 are allocated according to the "IETF Review" policy, numbers in
the range 128-240 as "First Come First Served", and numbers in the
range 241-255 are "Reserved for Private Use".
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In Section 5.1, the present document defines an Error Code field
inside the Admission Priority Policy Element. IANA has created a
registry for this field and allocate the following values:
o 0: NO_ERROR - Value used for regular ADMISSION_PRI elements
o 2: HETEROGENEOUS - This element encountered heterogeneous merge
Following the policies outlined in [RFC5226], numbers in the range
0-127 are allocated according to the "IETF Review" policy, numbers in
the range 128-240 as "First Come First Served", and numbers in the
range 241-255 are "Reserved for Private Use". Value 1 is Reserved
(for consistency with [RFC3181] Error Code values).
The present document defines an ALRP Namespace field in Section 5.2
that contains a numerical value identifying the namespace of the
application-level resource priority. The IANA already maintains the
Resource-Priority Namespaces registry (under the SIP Parameters)
listing all such namespaces. That registry has been updated to
allocate a numerical value to each namespace. To be exact, the IANA
has extended the Resource-Priority Namespaces registry in the
following ways:
o A new column has been added to the registry.
o The title of the new column is "Namespace Numerical Value *".
o In the Legend, a line has been added stating "Namespace Numerical
Value = the unique numerical value identifying the namespace".
o In the Legend, a line has been added stating "* : [RFC6401]".
o An actual numerical value has been allocated to each namespace in
the registry and is listed in the new "Namespace Numerical Value
*" column.
A numerical value has been allocated by IANA for all existing
namespaces. In the future, IANA should automatically allocate a
numerical value to any new namespace added to the registry.
The present document defines an ALRP Priority field in Section 5.2
that contains a numerical value identifying the actual application-
level resource priority within the application-level resource
priority namespace. The IANA already maintains the Resource-Priority
Priority-Values registry (under the SIP Parameters) listing all such
priorities. That registry has been updated to allocate a numerical
value to each priority-value. To be exact, the IANA has extended the
Resource-Priority Priority-Values registry in the following ways:
Le Faucheur, et al. Standards Track [Page 15]RFC 6401 RSVP Extensions for Admission Priority October 2011
o For each namespace, the registry is structured with two columns.
o The title of the first column is "Priority Values (least to
greatest)".
o The first column lists all the values currently defined in the
registry (e.g., for the drsn namespace: "routine", "priority",
"immediate", "flash", "flash-override", and "flash-override-
override")
o The title of the second column is "Priority Numerical Value *".
o At the bottom of the registry, a "Legend" has been added with a
line stating "Priority Numerical Value = the unique numerical
value identifying the priority within a namespace".
o In the Legend, a line has been added stating "* : [RFC6401]".
o An actual numerical value has been allocated to each priority
value and is listed in the new "Priority Numerical Value *"
column.
A numerical value has been allocated by IANA to all existing
priorities. In the future, IANA should automatically allocate a
numerical value to any new namespace added to the registry. The
numerical value must be unique within each namespace. Within each
namespace, values should be allocated in decreasing order ending with
0 (so that the greatest priority is always allocated value 0). For
example, in the drsn namespace, "routine" is allocated numerical
value 5, and "flash-override-override" is allocated numerical value
0.
8. Acknowledgments
We would like to thank An Nguyen for his encouragement to address
this topic and ongoing comments. Also, this document borrows heavily
from some of the work of S. Herzog on the Preemption Priority Policy
Element [RFC3181]. Dave Oran and Janet Gunn provided useful input
for this document. Ron Bonica, Magnus Westerlund, Cullen Jennings,
Ross Callon and Tim Polk provided specific guidance for the
applicability statement of the mechanisms defined in this document.
Le Faucheur, et al. Standards Track [Page 16]RFC 6401 RSVP Extensions for Admission Priority October 2011
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205, September 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
Authentication", RFC 2747, January 2000.
[RFC2750] Herzog, S., "RSVP Extensions for Policy Control", RFC
2750, January 2000.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097,
April 2001.
[RFC3181] Herzog, S., "Signaled Preemption Priority Policy Element",
RFC 3181, October 2001.
[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.
[RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session Initiation
Protocol (SIP)", RFC 3312, October 2002.
[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource
Priority for the Session Initiation Protocol (SIP)", RFC
4412, February 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, October 2011.
Le Faucheur, et al. Standards Track [Page 17]RFC 6401 RSVP Extensions for Admission Priority October 2011
9.2. Informative References
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113, February
1997.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, October 1999.
[RFC2753] Yavatkar, R., Pendarakis, D., and R. Guerin, "A Framework
for Policy-based Admission Control", RFC 2753, January
2000.
[RFC4125] Le Faucheur, F. and W. Lai, "Maximum Allocation Bandwidth
Constraints Model for Diffserv-aware MPLS Traffic
Engineering", RFC 4125, June 2005.
[RFC4126] Ash, J., "Max Allocation with Reservation Bandwidth
Constraints Model for Diffserv-aware MPLS Traffic
Engineering & Performance Comparisons", RFC 4126, June
2005.
[RFC4127] Le Faucheur, F., "Russian Dolls Bandwidth Constraints
Model for Diffserv-aware MPLS Traffic Engineering", RFC
4127, June 2005.
[RFC4230] Tschofenig, H. and R. Graveman, "RSVP Security
Properties", RFC 4230, December 2005.
[RFC4495] Polk, J. and S. Dhesikan, "A Resource Reservation Protocol
(RSVP) Extension for the Reduction of Bandwidth of a
Reservation Flow", RFC 4495, May 2006.
[RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS
Signaling Layer Protocol (NSLP) for Quality-of-Service
Signaling", RFC 5974, October 2010.
[RFC6411] Behringer, M., Le Faucheur, F., and B. Weis,
"Applicability of Keying Methods for RSVP Security", RFC
6411, October 2011.
Le Faucheur, et al. Standards Track [Page 18]RFC 6401 RSVP Extensions for Admission Priority October 2011
Appendix A. Examples of Bandwidth Allocation Model for Admission
Priority
Appendices A.1 and A.2 respectively illustrate how the Maximum
Allocation Model (MAM) [RFC4125] and the Russian Dolls Model (RDM)
[RFC4127] can be used for support of admission priority. The Maximum
Allocation model with Reservation (MAR) [RFC4126] can also be used in
a similar manner for support of admission priority. Appendix A.3
illustrates how a simple "Priority Bypass Model" can also be used for
support of admission priority.
For simplicity, operations with only a single "priority" level
(beyond non-priority) are illustrated here; however, the reader will
appreciate that operations with multiple priority levels can easily
be supported with these models.
In all the figures below:
"x" represents a non-priority session
"o" represents a priority session
A.1. Admission Priority with Maximum Allocation Model (MAM)
This section illustrates operations of admission priority when a
Maximum Allocation Model (MAM) is used for bandwidth allocation
across non-priority traffic and priority traffic. A property of the
Maximum Allocation Model is that priority traffic cannot use more
than the bandwidth made available to priority traffic (even if the
non-priority traffic is not using all of the bandwidth available for
it).
-----------------------
^ ^ ^ | | ^
. . . | | .
Total . . . | | . Bandwidth
(1)(2)(3) | | . available
Engi- . . . | | . for non-priority use
neered .or.or. | | .
. . . | | .
Capacity. . . | | .
v . . | | v
. . |--------------| ---
v . | | ^
. | | . Bandwidth available for
v | | v priority use
-------------------------
Figure 4: MAM Bandwidth Allocation
Le Faucheur, et al. Standards Track [Page 19]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 4 shows a link that is within a routed network and conforms to
this document. On this link are two amounts of bandwidth available
to two types of traffic: non-priority and priority.
If the non-priority traffic load reaches the maximum bandwidth
available for non-priority, no additional non-priority sessions can
be accepted even if the bandwidth reserved for priority traffic is
not fully utilized currently.
With the Maximum Allocation Model, in the case where the priority
load reaches the maximum bandwidth reserved for priority sessions, no
additional priority sessions can be accepted.
As illustrated in Figure 4, an operator may map the MAM to the
engineered capacity limits according to different policies. At one
extreme, where the proportion of priority traffic is reliably known
to be fairly small at all times and where there may be some safety
margin factored in the engineered capacity limits, the operator may
decide to configure the bandwidth available for non-priority use to
the full engineered capacity limits, effectively allowing the
priority traffic to ride within the safety margin of this engineered
capacity. This policy can be seen as an economically attractive
approach as all of the engineered capacity is made available to non-
priority sessions. This policy is illustrated as (1) in Figure 4.
As an example, if the engineered capacity limit on a given link is X,
the operator may configure the bandwidth available to non-priority
traffic to X, and the bandwidth available to priority traffic to 5%
of X. At the other extreme, where the proportion of priority traffic
may be significant at times and the engineered capacity limits are
very tight, the operator may decide to configure the bandwidth
available to non-priority traffic and the bandwidth available to
priority traffic such that their sum is equal to the engineered
capacity limits. This guarantees that the total load across non-
priority and priority traffic is always below the engineered capacity
and, in turn, guarantees there will never be any QoS degradation.
However, this policy is less attractive economically as it prevents
non-priority sessions from using the full engineered capacity, even
when there is no or little priority load, which is the majority of
time. This policy is illustrated as (3) in Figure 4. As an example,
if the engineered capacity limit on a given link is X, the operator
may configure the bandwidth available to non-priority traffic to 95%
of X, and the bandwidth available to priority traffic to 5% of X. Of
course, an operator may also strike a balance anywhere in between
these two approaches. This policy is illustrated as (2) in Figure 4.
Le Faucheur, et al. Standards Track [Page 20]
RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 5 shows some of the non-priority capacity of this link being
used.
-----------------------
^ ^ ^ | | ^
. . . | | .
Total . . . | | . Bandwidth
. . . | | . available
Engi- . . . | | . for non-priority use
neered .or.or. |xxxxxxxxxxxxxx| .
. . . |xxxxxxxxxxxxxx| .
Capacity. . . |xxxxxxxxxxxxxx| .
v . . |xxxxxxxxxxxxxx| v
. . |--------------| ---
v . | | ^
. | | . Bandwidth available for
v | | v priority use
-------------------------
Figure 5: Partial Load of Non-Priority Calls
Figure 6 shows the same amount of non-priority load being used at
this link and a small amount of priority bandwidth being used.
-----------------------
^ ^ ^ | | ^
. . . | | .
Total . . . | | . Bandwidth
. . . | | . available
Engi- . . . | | . for non-priority use
neered .or.or. |xxxxxxxxxxxxxx| .
. . . |xxxxxxxxxxxxxx| .
Capacity. . . |xxxxxxxxxxxxxx| .
v . . |xxxxxxxxxxxxxx| v
. . |--------------| ---
v . | | ^
. | | . Bandwidth available for
v |oooooooooooooo| v priority use
-------------------------
Figure 6: Partial Load of Non-Priority Calls and Partial Load of
Priority Calls
Le Faucheur, et al. Standards Track [Page 21]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 7 shows the case where non-priority load equates or exceeds
the maximum bandwidth available to non-priority traffic. Note that
additional non-priority sessions would be rejected even if the
bandwidth reserved for priority sessions is not fully utilized.
-----------------------
^ ^ ^ |xxxxxxxxxxxxxx| ^
. . . |xxxxxxxxxxxxxx| .
Total . . . |xxxxxxxxxxxxxx| . Bandwidth
. . . |xxxxxxxxxxxxxx| . available
Engi- . . . |xxxxxxxxxxxxxx| . for non-priority use
neered .or.or. |xxxxxxxxxxxxxx| .
. . . |xxxxxxxxxxxxxx| .
Capacity. . . |xxxxxxxxxxxxxx| .
v . . |xxxxxxxxxxxxxx| v
. . |--------------| ---
v . | | ^
. | | . Bandwidth available for
v |oooooooooooooo| v priority use
-------------------------
Figure 7: Full Non-Priority Load and Partial Load of Priority Calls
Figure 8 shows the case where the priority traffic equates or exceeds
the bandwidth reserved for such priority traffic.
In that case, additional priority sessions could not be accepted.
Note that this does not mean that such sessions are dropped
altogether: they may be handled by mechanisms, which are beyond the
scope of this particular document (such as establishment through
preemption of existing non-priority sessions or such as queueing of
new priority session requests until capacity becomes available again
for priority traffic).
Le Faucheur, et al. Standards Track [Page 22]RFC 6401 RSVP Extensions for Admission Priority October 2011
-----------------------
^ ^ ^ |xxxxxxxxxxxxxx| ^
. . . |xxxxxxxxxxxxxx| .
Total . . . |xxxxxxxxxxxxxx| . Bandwidth
. . . |xxxxxxxxxxxxxx| . available
Engi- . . . |xxxxxxxxxxxxxx| . for non-priority use
neered .or.or. |xxxxxxxxxxxxxx| .
. . . |xxxxxxxxxxxxxx| .
Capacity. . . | | .
v . . | | v
. . |--------------| ---
v . |oooooooooooooo| ^
. |oooooooooooooo| . Bandwidth available for
v |oooooooooooooo| v priority use
-------------------------
Figure 8: Partial Non-Priority Load and Full Priority Load
A.2. Admission Priority with Russian Dolls Model (RDM)
This section illustrates operations of admission priority when a
Russian Dolls Model (RDM) is used for bandwidth allocation across
non-priority traffic and priority traffic. A property of the RDM is
that priority traffic can use the bandwidth that is not currently
used by non-priority traffic.
As with the MAM, an operator may map the RDM onto the engineered
capacity limits according to different policies. The operator may
decide to configure the bandwidth available for non-priority use to
the full engineered capacity limits. As an example, if the
engineered capacity limit on a given link is X, the operator may
configure the bandwidth available to non-priority traffic to X, and
the bandwidth available to non-priority and priority traffic to 105%
of X.
Alternatively, the operator may decide to configure the bandwidth
available to non-priority and priority traffic to the engineered
capacity limits. As an example, if the engineered capacity limit on
a given link is X, the operator may configure the bandwidth available
to non-priority traffic to 95% of X, and the bandwidth available to
non-priority and priority traffic to X.
Finally, the operator may decide to strike a balance in between. The
considerations presented for these policies in the previous section
in the MAM context are equally applicable to RDM.
Le Faucheur, et al. Standards Track [Page 23]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 9 shows the case where only some of the bandwidth available to
non-priority traffic is being used, and a small amount of priority
traffic is in place. In that situation, both new non-priority
sessions and new priority sessions would be accepted.
--------------------------------------
|xxxxxxxxxxxxxx| . ^
|xxxxxxxxxxxxxx| . Bandwidth .
|xxxxxxxxxxxxxx| . available for .
|xxxxxxxxxxxxxx| . non-priority .
|xxxxxxxxxxxxxx| . use .
|xxxxxxxxxxxxxx| . . Bandwidth
| | . . available for
| | v . non-priority
|--------------| --- . and priority
| | . use
| | .
|oooooooooooooo| v
---------------------------------------
Figure 9: Partial Non-Priority Load and Partial Aggregate Load
Figure 10 shows the case where all of the bandwidth available to non-
priority traffic is being used and a small amount of priority traffic
is in place. In that situation, new priority sessions would be
accepted, but new non-priority sessions would be rejected.
--------------------------------------
|xxxxxxxxxxxxxx| . ^
|xxxxxxxxxxxxxx| . Bandwidth .
|xxxxxxxxxxxxxx| . available for .
|xxxxxxxxxxxxxx| . non-priority .
|xxxxxxxxxxxxxx| . use .
|xxxxxxxxxxxxxx| . . Bandwidth
|xxxxxxxxxxxxxx| . . available for
|xxxxxxxxxxxxxx| v . non-priority
|--------------| --- . and priority
| | . use
| | .
|oooooooooooooo| v
---------------------------------------
Figure 10: Full Non-Priority Load and Partial Aggregate Load
Le Faucheur, et al. Standards Track [Page 24]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 11 shows the case where only some of the bandwidth available
to non-priority traffic is being used, and a heavy load of priority
traffic is in place. In that situation, both new non-priority
sessions and new priority sessions would be accepted. Note that, as
illustrated in Figure 10, priority sessions use some of the bandwidth
currently not used by non-priority traffic.
--------------------------------------
|xxxxxxxxxxxxxx| . ^
|xxxxxxxxxxxxxx| . Bandwidth .
|xxxxxxxxxxxxxx| . available for .
|xxxxxxxxxxxxxx| . non-priority .
|xxxxxxxxxxxxxx| . use .
| | . . Bandwidth
| | . . available for
|oooooooooooooo| v . non-priority
|--------------| --- . and priority
|oooooooooooooo| . use
|oooooooooooooo| .
|oooooooooooooo| v
---------------------------------------
Figure 11: Partial Non-Priority Load and Heavy Aggregate Load
Figure 12 shows the case where all of the bandwidth available to non-
priority traffic is being used, and all of the remaining available
bandwidth is used by priority traffic. In that situation, new non-
priority sessions would be rejected, and new priority sessions could
not be accepted right away. Those priority sessions may be handled
by mechanisms, which are beyond the scope of this particular document
(such as established through preemption of existing non-priority
sessions or such as queueing of new priority session requests until
capacity becomes available again for priority traffic).
Le Faucheur, et al. Standards Track [Page 25]RFC 6401 RSVP Extensions for Admission Priority October 2011
--------------------------------------
|xxxxxxxxxxxxxx| . ^
|xxxxxxxxxxxxxx| . Bandwidth .
|xxxxxxxxxxxxxx| . available for .
|xxxxxxxxxxxxxx| . non-priority .
|xxxxxxxxxxxxxx| . use .
|xxxxxxxxxxxxxx| . . Bandwidth
|xxxxxxxxxxxxxx| . . available for
|xxxxxxxxxxxxxx| v . non-priority
|--------------| --- . and priority
|oooooooooooooo| . use
|oooooooooooooo| .
|oooooooooooooo| v
---------------------------------------
Figure 12: Full Non-Priority Load and Full Aggregate Load
A.3. Admission Priority with Priority Bypass Model (PrBM)
This section illustrates operations of admission priority when a
simple Priority Bypass Model (PrBM) is used for bandwidth allocation
across non-priority traffic and priority traffic. With the PrBM,
non-priority traffic is subject to resource-based admission control,
while priority traffic simply bypasses the resource-based admission
control. In other words:
o when a non-priority session arrives, this session is subject to
bandwidth admission control and is accepted if the current total
load (aggregate over non-priority and priority traffic) is below
the engineered/allocated bandwidth.
o when a priority session arrives, this session is admitted
regardless of the current load.
A property of this model is that a priority session is never
rejected.
The rationale for this simple scheme is that, in practice, in some
networks:
o The volume of priority sessions is very low for the vast majority
of time, so it may not be economical to completely set aside
bandwidth for priority sessions and preclude the utilization of
this bandwidth by normal sessions in normal situations.
o Even in congestion periods where priority sessions may be more
heavily used, those sessions always still represent a fairly small
proportion of the overall load that can be absorbed within the
Le Faucheur, et al. Standards Track [Page 26]RFC 6401 RSVP Extensions for Admission Priority October 2011
safety margin of the engineered capacity limits. Thus, even if
they are admitted beyond the engineered bandwidth threshold, they
are unlikely to result in noticeable QoS degradation.
As with the MAM and RDM, an operator may map the PrBM onto the
engineered capacity limits according to different policies. The
operator may decide to configure the bandwidth limit for admission of
non-priority traffic to the full engineered capacity limit. As an
example, if the engineered capacity limit on a given link is X, the
operator may configure the bandwidth limit for non-priority traffic
to X. Alternatively, the operator may decide to configure the
bandwidth limit for non-priority traffic to below the engineered
capacity limits (so that the sum of the non-priority and priority
traffic stays below the engineered capacity). As an example, if the
engineered capacity limit on a given link is X, the operator may
configure the bandwidth limit for non-priority traffic to 95% of X.
Finally, the operator may decide to strike a balance in between.
The considerations presented for these policies in the previous
sections in the MAM and RDM contexts are equally applicable to the
PrBM.
Figure 13 illustrates the bandwidth allocation with the PrBM.
-----------------------
^ ^ | | ^
. . | | .
Total . . | | . Bandwidth limit
(1) (2) | | . (on non-priority + priority)
Engi- . . | | . for admission
neered . or . | | . of non-priority traffic
. . | | .
Capacity. . | | .
v . | | v
. |--------------| ---
. | |
v | |
| |
Figure 13: Priority Bypass Model Bandwidth Allocation
Le Faucheur, et al. Standards Track [Page 27]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 14 shows some of the non-priority capacity of this link being
used. In this situation, both new non-priority and new priority
sessions would be accepted.
-----------------------
^ ^ |xxxxxxxxxxxxxx| ^
. . |xxxxxxxxxxxxxx| .
Total . . |xxxxxxxxxxxxxx| . Bandwidth limit
(1) (2) |xxxxxxxxxxxxxx| . (on non-priority + priority)
Engi- . . | | . for admission
neered . or . | | . of non-priority traffic
. . | | .
Capacity. . | | .
v . | | v
. |--------------| ---
. | |
v | |
| |
Figure 14: Partial Load of Non-Priority Calls
Figure 15 shows the same amount of non-priority load being used at
this link and a small amount of priority bandwidth being used. In
this situation, both new non-priority and new priority sessions would
be accepted.
-----------------------
^ ^ |xxxxxxxxxxxxxx| ^
. . |xxxxxxxxxxxxxx| .
Total . . |xxxxxxxxxxxxxx| . Bandwidth limit
(1) (2) |xxxxxxxxxxxxxx| . (on non-priority + priority)
Engi- . . |oooooooooooooo| . for admission
neered . or . | | . of non-priority traffic
. . | | .
Capacity. . | | .
v . | | v
. |--------------| ---
. | |
v | |
| |
Figure 15: Partial Load of Non-Priority Calls and Partial Load of
Priority Calls
Le Faucheur, et al. Standards Track [Page 28]RFC 6401 RSVP Extensions for Admission Priority October 2011
Figure 16 shows the case where aggregate non-priority and priority
load exceeds the bandwidth limit for admission of non-priority
traffic. In this situation, any new non-priority session is
rejected, while any new priority session is admitted.
-----------------------
^ ^ |xxxxxxxxxxxxxx| ^
. . |xxxxxxxxxxxxxx| .
Total . . |xxxxxxxxxxxxxx| . Bandwidth limit
(1) (2) |xxxxxxxxxxxxxx| . (on non-priority + priority)
Engi- . . |oooooooooooooo| . for admission
neered . or . |xxxooxxxooxxxo| . of non-priority traffic
. . |xxoxxxxxxoxxxx| .
Capacity. . |oxxxooooxxxxoo| .
v . |xxoxxxooxxxxxx| v
. |--------------| ---
. |oooooooooooooo|
v | |
| |
Figure 16: Full Non-Priority Load
Appendix B. Example Usages of RSVP Extensions
This section provides examples of how RSVP extensions defined in this
document can be used (in conjunction with other RSVP functionality
and SIP functionality) to enforce different hypothetical policies for
handling prioritized sessions in a given administrative domain. This
appendix does not provide additional specification. It is only
included in this document for illustration purposes.
We assume an environment where SIP is used for session control and
RSVP is used for resource reservation.
We refer here to "Session Queueing" as the set of "session-layer"
capabilities that may be implemented by SIP user agents to influence
their treatment of SIP requests. This may include the ability to
"queue" session requests when those cannot be immediately honored (in
some cases with the notion of "bumping", or "displacement", of less
important session requests from that queue). It may include
additional mechanisms such as alternate routing and exemption from
certain network management controls.
We only mention below the RSVP policy elements that are to be
enforced by PEPs. It is assumed that these policy elements are set
at a policy area boundary by PDPs. The Admission Priority and
Le Faucheur, et al. Standards Track [Page 29]RFC 6401 RSVP Extensions for Admission Priority October 2011
Preemption Priority RSVP policy elements are set by PDPs as a result
of processing the Application-Level Resource Priority Policy Element
(which is carried in RSVP messages).
If one wants to implement a prioritized service purely based on
Session Queueing, one can achieve this by signaling prioritized
sessions:
o using the "Resource-Priority" header in SIP
o not using the Admission-Priority Policy Element in RSVP
o not using the Preemption Policy Element in RSVP
If one wants to implement a prioritized service based on Session
Queueing and "prioritized access to network-layer resources", one can
achieve this by signaling prioritized sessions:
o using the "Resource-Priority" header in SIP
o using the Admission-Priority Policy Element in RSVP
o not using the Preemption Policy Element in RSVP
Establishment of prioritized sessions will not result in preemption
of any session. Different bandwidth allocation models can be used to
offer different "prioritized access to network-layer resources".
Just as examples, this includes setting aside capacity exclusively
for prioritized sessions as well as simple bypass of admission limits
for prioritized sessions.
If one wants to implement a prioritized service based on Session
Queueing and "prioritized access to network-layer resources", and
wants to ensure that (say) "Prioritized-1" sessions can preempt
"Prioritized-2" sessions, but non-prioritized sessions are not
affected by preemption, one can do that by signaling prioritized
sessions:
o using the "Resource-Priority" header in SIP
o using the Admission-Priority Policy Element in RSVP
o using the Preemption Policy Element in RSVP with:
* setup (Prioritized-1) > defending (Prioritized-2)
* setup (Prioritized-2) <= defending (Prioritized-1)
Le Faucheur, et al. Standards Track [Page 30]RFC 6401 RSVP Extensions for Admission Priority October 2011
* setup (Prioritized-1) <= defending (Non-Prioritized)
* setup (Prioritized-2) <= defending (Non-Prioritized)
If one wants to implement a prioritized service based on Session
Queueing and "prioritized access to network-layer resources", and
wants to ensure that prioritized sessions can preempt regular
sessions, one could do that by signaling Prioritized sessions:
o using the "Resource-Priority" header in SIP
o using the Admission-Priority Policy Element in RSVP
o using the Preemption Policy Element in RSVP with:
* setup (Prioritized) > defending (Non-Prioritized)
* setup (Non-Prioritized) <= defending (Prioritized)
If one wants to implement a prioritized service based on Session
Queueing and "prioritized access to network-layer resources", and
wants to ensure that prioritized sessions can partially preempt
regular sessions (i.e., reduce their reservation size), one could do
that by signaling prioritized sessions:
o using the "Resource-Priority" header in SIP
o using the Admission-Priority Policy Element in RSVP
o using the Preemption Policy Element in RSVP with:
* setup (Prioritized) > defending (Non-Prioritized)
* setup (Non-Prioritized) <= defending (Prioritized)
o activate [RFC4495] RSVP bandwidth reduction mechanisms
Le Faucheur, et al. Standards Track [Page 31]RFC 6401 RSVP Extensions for Admission Priority October 2011
Authors' Addresses
Francois Le Faucheur
Cisco Systems
Greenside, 400 Avenue de Roumanille
Sophia Antipolis 06410
France
Phone: +33 4 97 23 26 19
EMail: flefauch@cisco.com
James Polk
Cisco Systems
2200 East President George Bush Highway
Richardson, TX 75082-3550
United States
Phone: +1 972 813 5208
EMail: jmpolk@cisco.com
Ken Carlberg
G11
123a Versailles Circle
Towson, MD 21204
United States
EMail: carlberg@g11.org.uk
Le Faucheur, et al. Standards Track [Page 32]
