One document matched: draft-lefaucheur-emergency-rsvp-01.txt
Differences from draft-lefaucheur-emergency-rsvp-00.txt
RSVP Extensions for Emergency Services March 2006
Internet Draft Francois Le Faucheur
James Polk
Cisco Systems, Inc.
Ken Carlberg
G11
draft-lefaucheur-emergency-rsvp-01.txt
Expires: March 2006 February 2006
RSVP Extensions for Emergency Services
Status of this Memo
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Abstract
An Emergency Telecommunications Service (ETS) requires the ability to
provide an elevated probability of call completion to an authorized
user in times of network congestion (typically, during a crisis).
When supported over the Internet Protocol suite, this may be achieved
through an admission control solution which supports admission
priority capabilities and possibly session preemption capabilities
Le Faucheur, et al. [Page 1]
RSVP Extensions for Emergency Services March 2006
(depending on policies and deployed implementations). Admission
priority involves setting aside some resources (e.g. bandwidth) out
of the engineered capacity limits for the emergency services only, or
alternatively involves allowing the emergency sessions to seize
additional resources beyond the engineered capacity limits applied to
normal calls.
This document specifies RSVP extensions necessary for supporting such
admission priority capabilities.
Copyright Notice
Copyright (C) The Internet Society (2006)
Specification of Requirements
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].
1. Introduction
[EMERG-RQTS] and [EMERG-TEL] detail requirements for an Emergency
Telecommunications Service (ETS), which is an umbrella term
identifying those networks and specific services used to support
emergency communications. An underlying goal of these documents is to
present requirements that elevate the probability of session
establishment from an authorized user in times of network congestion
(presumably because of a crisis condition). To that end, some of
these types of services require that the network be capable of
preempting sessions; others do not involve preemption but instead
rely on another network mechanism which we refer throughout this
document as "admission priority", in order to obtain a high
probability of session completion for those. Admission priority
involves setting aside some resources (e.g. bandwidth) out of the
engineered capacity limits for the emergency services only, or
alternatively involves allowing the emergency related sessions to
seize additional resources beyond the engineered capacity limits
applied to normal calls.
Note: Below, this document references several examples of IP
telephony and its use of "calls", which is one form of the term
"sessions" (Video over IP and Instant Messaging being other examples
that rely on session establishment). For the sake of simplicity, we
shall use the widely known term "call" for the remainder of this
document.
Le Faucheur, et al. [Page 2]
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[EMERG-IMP] describes the call and admission control procedures (at
initial call set up, as well as after call establishment through
maintenance of a continuing call model of the status of all calls)
which allow support of an Emergency Telecommunications Service.
[EMERG-IMP] also describes how these call and admission control
procedures can be realized using the Resource reSerVation Protocol
[RSVP] along with its associated protocol suite and extensions,
including those for policy based admission control ([FW-POLICY],
[RSVP-POLICY]), for user authentication and authorization ([RSVP-ID])
and for integrity and authentication of RSVP messages ([RSVP-CRYPTO-
1], [RSVP-CRYPTO-2]).
Furthermore, [EMERG-IMP] describes how the RSVP Signaled Preemption
Priority Policy Element specified in [RSVP-PREEMP] can be used to
enforce the call preemption needed by some emergency services.
This document specifies RSVP extensions, which can be used to enforce
the "admission priority" required by an RSVP capable ETS network. 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 selective bandwidth admission
control decision based on the call admission priority. This document
also provides three examples of a bandwidth allocation model which
can be used by RSVP-routers to enforce such admission priority on
every link.
1.1. Changes from previous versions
1.1.1. Changes from -00 to -01
The most significant changes are:
o adding a second RSVP Policy Element that contains the
application-level resource priority requirements (for example as
communicated in the SIP Resource-Priority Header) for scenarios
where priority calls transits through multiple administrative
domains.
o adding description of a third bandwidth allocation model
example: the Priority Bypass Model
o adding discussion on policies for mapping the various bandwidth
allocation model over the engineered capacity limits.
2. Overview of RSVP extensions and Operations
Let us consider the case where a call requiring ETS type service is
to be established, and more specifically that the preference to be
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granted to this call is in terms of "admission priority" (as opposed
to preference granted through preemption of existing calls). By
"admission priority" we mean allowing that priority call to seize
resources from the engineered capacity that have been set-aside and
not made available to normal calls, or alternatively by allowing that
call to seize additional resources beyond the engineered capacity
limits applied to normal calls.
As described in [EMERG-IMP], the session establishment can be
conditioned to resource-based and policy-based admission control
achieved via RSVP signaling. In the case where the session control
protocol is SIP, the use of RSVP-based admission control by SIP is
specified in [SIP-RESOURCE].
Devices involved in the session establishment are expected to be
aware of the application-level priority requirements of emergency
calls. Again considering the case where the session control protocol
is SIP, the SIP user agents can be made aware of the resource
priority requirements in the case of an emergency call using the
Resource-Priority Header mechanism specified in [SIP-PRIORITY].
Where, as per our considered case, the application-level priority
requirement of the emergency call involves admission priority, the
devices involved in the upper-layer session establishment simply need
to:
(1) map the application-level priority requirements of the
emergency call into an RSVP "admission priority" level and
convey this information in the relevant RSVP messages used
for admission control. The admission priority is encoded
inside the new Admission Priority Policy Element defined in
this document. This way, the RSVP-based admission control
can take this information into account at every RSVP-enabled
network hop.
(2) Copy the application-level resource priority requirements
(e.g. as communicated in SIP Resource-Priority Header)
inside the new RSVP Application-Level Resource-Priority
Header Policy Element defined in this document. Conveying
the application-level resource priority requirements inside
the RSVP message allows this application level requirement
to be remapped into a different RSVP "admission priority" at
every administrative domain boundary based on the policy
applicable in that domain.
For example, the first domain may honor the resource
priority requirement and map it into a high RSVP admission
control priority while the second domain may decide to not
honor that resource priority requirement and map it into the
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default (lowest) RSVP admission control priority. As another
example, we can consider the case where the resource
priority header enumerates several namespaces, as explicitly
allowed by [SIP-PRIORITY], for support of scenarios where
calls traverse multiple administrative domains using
different namespace. In that case, the relevant namespace
can be used at the domain boundary to map into an RSVP
Admission priority. 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
administrative domain. It is expected to be used at
administrative domain boundaries only in order to set/reset
the RSVP Admission Priority Policy Element.
Note: The existence of pre-established inter-domain policy
agreements or Service Level Agreements may preclude the need
to take real-time action on step (2) at domain boundaries.
Also, step (2) may be applied to boundaries between various
signaling protocols, such as those advanced by the NSIS
working group.
Note that this operates in a very similar manner to the case where
the priority requirement of the emergency call involves preemption
priority. In that case, the devices involved in the session
establishment map the emergency call requirement into an RSVP
"preemption priority" level (or more accurately into both a setup
preemption level and a defending preemption priority level) and
convey this information in the relevant RSVP messages used for
admission control. This preemption priority information is encoded
inside the Preemption Priority Policy Element of [RSVP-PREEMP] and
thus, can be taken into account at every RSVP-enabled network hop.
2.1. Operations of Admission Priority
The RSVP Admission Priority policy element defined in this document
allows admission bandwidth to be allocated selectively to an
authorized priority service. Multiple models of bandwidth allocation
MAY be used to that end. However, the bandwidth allocation model MUST
ensure that it is possible to limit admission of non-priority traffic
[Respectively, lower priority traffic] to a maximum bandwidth which
can be configured below the link capacity (or below the bandwidth
granted by the scheduler to the relevant Diffserv PHB) thereby
ensuring that some capacity is effectively set aside for admission of
priority traffic [Respectively, higher priority traffic].
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.
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Those include the Maximum Allocation Model (MAM) defined in [DSTE-
MAM] and the Russian Dolls Model (RDM) specified in [DSTE-RDM]. These
same models MAY however be applied for allocation of bandwidth across
different levels of admission priority as defined in this document.
Sections 2.1.1 and 2.1.2 respectively illustrate how MAM and RDM can
indeed be used for support of admission priority. Section 2.1.3
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 charts below:
x represents a non-priority session
o represents a priority session
2.1.1.
Illustration of Admission Priority with Maximum Allocation Model
This section illustrates operations of admission priority when a
Maximum Allocation Model is used for bandwidth allocation across non-
priority traffic and priority traffic. A property of the Maximum
Allocation Model is that priority traffic can not 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
-------------------------
Chart 1. MAM Bandwidth Allocation
Chart 1 shows a link within a routed network conforming to this
document. On this link are two amounts of bandwidth available to two
types of traffic: non-priority and priority.
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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 currently fully utilized.
With the Maximum Allocation Model, in the case where the priority
load reaches the maximum bandwidth reserved for priority calls, no
additional priority sessions can be accepted.
As illustrated in Chart 1, an operator may map the MAM model onto 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 calls. This policy illustrated as (1) in Chart 1. 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
calls from using the full engineered capacity, even when there is no
or little priority load, which is the majority of time. This policy
illustrated as (3) in Chart 1. 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 illustrated as (2) in Chart 1.
Chart 2 shows some of the non-priority capacity of this link being
used.
-----------------------
^ ^ ^ | | ^
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RSVP Extensions for Emergency Services March 2006
. . . | | .
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
-------------------------
Chart 2. Partial load of non-priority calls
Chart 3 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
-------------------------
Chart 3. Partial load of non-priority calls
& partial load of priority calls
Chart 4 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
Le Faucheur, et al. [Page 8]
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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
-------------------------
Chart 4. Full non-priority load
& partial load of priority calls
Although this is not expected to occur in practice (or to occur
extremely rarely) because of proper allocation of bandwidth to
priority traffic, Chart 5 shows for completeness 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 calls 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).
-----------------------
^ ^ ^ |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
-------------------------
Chart 5. Partial non-priority load & Full priority load
2.1.2.
Illustration of Admission Priority with Russian Dolls Model
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This section illustrates operations of admission priority when a
Russian Dolls Model is used for bandwidth allocation across non-
priority traffic and priority traffic. A property of the Russian
Dolls Model is that priority traffic can use the bandwidth which is
not currently used by non-priority traffic.
As with the MAM model, an operator may map the RDM model 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.
Chart 6 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
---------------------------------------
Chart 6. Partial non-priority load & Partial Aggregate load
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Chart 7 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
---------------------------------------
Chart 7. Full non-priority load & Partial Aggregate load
Chart 8 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 Chart 7, priority calls 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
---------------------------------------
Chart 8. Partial non-priority load & Heavy Aggregate load
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Chart 9 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. In that situation 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). This is not expected to occur (or to occur extremely
rarely) in practice because of proper allocation of bandwidth to
priority traffic (or more precisely because of proper sizing of the
difference in bandwidth allocated to non-priority traffic and
bandwidth allocated to non-priority & priority traffic).
--------------------------------------
|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
---------------------------------------
Chart 9. Full non-priority load & Full Aggregate load
2.1.3.
Illustration of Admission Priority with Priority Bypass Model
This section illustrates operations of admission priority when a
simple Priority Bypass Model is used for bandwidth allocation across
non-priority traffic and priority traffic. With the Priority Bypass
Model, non-priority traffic is subject to resource based admission
control while priority traffic simply bypasses the resource based
admission control. In other words:
- when a non-priority call arrives, this call 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.
- when a priority call arrives, this call is admitted regardless
of the current load.
A property of this model is that a priority call is never rejected.
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The rationale for this simple scheme is that, in practice in some
networks:
- the volume of priority calls is very low for the vast majority
of time, so it may not be economical to completely set aside
bandwidth for priority calls and preclude the utilization of
this bandwidth by normal calls in normal situations
- even in emergency periods where priority calls are more heavily
used, those always still represent a fairly small proportion of
the overall load which can be absorbed within the 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 model, an operator may map the Priority
Bypass model 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 limits; 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 Priority Bypass Model.
Chart 10 shows illustrates the bandwidth allocation with the Priority
Bypass Model.
-----------------------
^ ^ | | ^
. . | | .
Total . . | | . Bandwidth Limit
(1) (2) | | . (on non-priority + priority)
Engi- . . | | . for admission
neered . or . | | . of non-priority traffic
. . | | .
Capacity. . | | .
v . | | v
. |--------------| ---
. | |
v | |
| |
Le Faucheur, et al. [Page 13]
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Chart 10. Priority Bypass Model Bandwidth Allocation
Chart 11 shows some of the non-priority capacity of this link being
used. In this situation, both new non-priority and new priority calls
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 | |
| |
Chart 11. Partial load of non-priority calls
Chart 12 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 calls 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 | |
| |
Chart 12. Partial load of non-priority calls
& partial load of priority calls
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Chart 13 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 call is rejected
while any new priority call 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 | |
| |
Chart 13. Full non-priority load
3. New Policy Elements
3.1. Admission Priority Policy Element
[RSVP-POLICY] 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 of Policy Elements, each
representing a different (and perhaps orthogonal) policy. As an
example, [RSVP-PREEMP] specifies the Preemption Priority Policy
Element.
This document defines a new Policy Element called the Admission
Priority Policy Element.
The format of Admission Priority policy element is as follows:
+-------------+-------------+-------------+-------------+
| Length | P-Type = ADMISSION_PRI |
+-------------+-------------+-------------+-------------+
| Flags | M. Strategy | Error Code | Reserved |
+-------------+-------------+-------------+-------------+
| Rvd | Pri| Reserved |
+---------------------------+---------------------------+
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Length: 16 bits
Always 12. The overall length of the policy element, in bytes.
P-Type: 16 bits
ADMISSION_PRI = To be allocated by IANA
(see "IANA Considerations" section)
Flags: 8 bits
Reserved (always 0).
Merge Strategy: 8 bit (only applicable to multicast flows)
1 Take priority of highest QoS: recommended
2 Take highest priority: aggressive
3 Force Error on heterogeneous merge
Error code: 8 bits (only applicable to multicast flows)
0 NO_ERROR Value used for regular ADMISSION_PRI elements
2 HETEROGENEOUS This element encountered heterogeneous merge
Reserved: 8 bits
Always 0.
Reserved: 5 bits
Always 0.
Pri. (Admission Priority): 3 bits (unsigned)
The admission control priority of the flow, in terms of access
to network bandwidth in order to provide higher probability of
call completion to selected flows. Lower values represent higher
Priority. 0 represents the highest priority. A reservation
established without an Admission Priority policy element is
equivalent to a reservation established with the lowest
supported admission priority.
Bandwidth allocation models such as those described in section
2.1 are to be used by the RSVP router to achieve such increased
probability of call completion. The admission priority value
indicates the bandwidth constraint(s) of the bandwidth
constraint model in use which is(are) applicable to admission of
this RSVP reservation.
Reserved: 16 bits
Always 0.
Note that the Admission Priority Policy Element does NOT indicate
that this RSVP reservation is to preempt any call. If a priority
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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.
It has been identified that some ETS emergency type sessions would
need:
- to benefit from elevated admission priority
- to be able to preempt other ETS emergency type sessions (the
ones with lower preemption priorities)
- to not be able to preempt non-emergency sessions.
One approach to address this requirement is to add a new Flag in the
Preemption Priority Policy Element in order to reduce the scope of
the RSVP preemption mechanism to emergency sessions. Feedback is
sought on this requirement and potential solution. This will be
addressed further in next revisions of this document.
3.1.1.
Admission Priority Merging Rules
This session discusses alternatives for dealing with RSVP admission
priority in case of merging of reservations. As merging is only
applicable to multicast, this section also only applies to multicast
sessions.
3.1.1.1 Admission Priority Merging Strategies
In merging situations Local Decision Points (LDPs) may receive
multiple admission priority elements and must compute the admission
priority of the merged flow according to the following rules:
a. Participating admission priority elements are selected.
All admission priority elements are examined according to their
merging strategy to decide whether they should participate in the
merged result (as specified below).
b. The highest admission priority of all participating admission
priority elements is computed.
The remainder of this section describes the different merging
strategies the can be specified in the ADMISSION_PRI element.
3.1.1.2 Take priority of highest QoS
The ADMISSION_PRI element would participate in the merged reservation
only if it belongs to a flow that contributed to the merged QoS level
(i.e., that its QoS requirement does not constitute a subset of
another reservation.) A simple way to determine whether a flow
contributed to the merged QoS result is to compute the merged QoS
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with and without it and to compare the results (although this is
clearly not the most efficient method).
The reasoning for this approach is that the highest QoS flow is the
one dominating the merged reservation and as such its priority should
dominate it as well.
3.1.1.3 Take highest priority
All ADMISSION_PRI elements participate in the merged reservation.
This strategy disassociates priority and QoS level, and therefore is
highly subject to free-riders and its inverse image, denial of
service.
3.1.1.4 Force error on heterogeneous merge
A ADMISSION_PRI element may participate in a merged reservation only
if all other flows in the merged reservation have the same QoS level
(homogeneous flows).
The reasoning for this approach assumes that the heterogeneous case
is relatively rare and too complicated to deal with, thus it better
be prohibited.
This strategy lends itself to denial of service, when a single
receiver specifying a non-compatible QoS level may cause denial of
service for all other receivers of the merged reservation.
Note: The determination of heterogeneous flows applies to QoS level
only (FLOWSPEC values), and is a matter for local (LDP) definition.
Other types of heterogeneous reservations (e.g. conflicting
reservation styles) are handled by RSVP and are unrelated to this
ADMISSION_PRI element.
3.1.2.
Modifying Admission Priority Elements
When POLICY_DATA objects are protected by integrity, LDPs should not
attempt to modify them. They must be forwarded as-is or else their
security envelope would be invalidated. In other cases, LDPs may
modify and merge incoming ADMISSION _PRI elements to reduce their
size and number according to the following rule:
Merging is performed for each merging strategy separately.
There is no known algorithm to merge ADMISSION_PRI element of
different merging strategies without losing valuable information that
may affect OTHER nodes.
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- For each merging strategy, the highest QoS of all participating
ADMISSION _PRI elements is taken and is placed in an outgoing
ADMISSION _PRI element of this merging strategy.
- This approach effectively compresses the number of forwarded
ADMISSION _PRI elements to at most to the number of different
merging strategies, regardless of the number of receivers.
3.1.3.
Merging Error Processing
An Error Code is sent back (inside the Admission Priority Policy
Element) toward the appropriate receivers when an error involving
ADMISSION_PRI elements occur.
Heterogeneity
When a flow F1 with "Force Error on heterogeneous merge" merging
strategy set in its ADMISSION_PRI element encounters
heterogeneity, the ADMISSION_PRI element is sent back toward
receivers with the Heterogeneity error code set.
3.2. Application-Level Resource Priority Policy Element
This document defines another new Policy Element called the
Application-Level Resource Priority Element.
The format of Admission Priority policy element is as follows:
+-------------+-------------+-------------+-------------+
| Length | P-Type = APP_RESOURCE_PRI |
+-------------+-------------+-------------+-------------+
| Flags | M. Strategy | Error Code | Reserved |
+-------------+-------------+-------------+-------------+
| ARP Namespace | ARP Priority| Reserved |
+---------------------------+---------------------------+
Length: 16 bits
Always 12. The overall length of the policy element, in bytes.
P-Type: 16 bits
APP_RESOURCE_PRI = To be allocated by IANA
(see "IANA Considerations" section)
Flags: 8 bits
Reserved (always 0).
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Merge Strategy: 8 bit (only applicable to multicast flows)
TBD
Error code: 8 bits (only applicable to multicast flows)
TBD
Reserved: 8 bits
Always 0.
ARP Namespace (Application-Level Resource Priority Namespace):
16 bits (unsigned)
Contains the namespace of the application-level resource
priority. This is encoded as a numerical value which represents
the position of the namespace in the "Resource-Priority
Namespace" IANA registry, starting with 0. Creation of this
registry has been requested to IANA in [SIP-PRIORITY].
For example, as "dsn", "drsn", "q735", "ets" and "wps" are
currently the first, second, third, fourth and fifth namespaces
defined in the "Resource-Priority Namespace" registry, those are
respectively encoded as value 0, 1, 2, 3 and 4.
ARP Priority: (Application-Level Resource Priority Priority):
8 bits (unsigned)
Contains the priority value within the namespace of the
application-level resource priority.
This is encoded as a numerical value which represents the
priority defined in the "Resource-Priority Namespace" IANA
registry for the considered namespace, starting from 0 for the
highest priority and increasing as priority decreases.
For example, as "flash-override", "flash", "immediate",
"priority" and "routine" are the priorities in decreasing order
of priority registered for the "dsn" namespace, those are
respectively encoded as value 0, 1, 2, 3 and 4.
Reserved: 16 bits
Always 0.
Multiple instances of Application-Level Resource Priority Policy
Elements may appear in a POLICY_DATA object or in different
POLICY_DATA objects. This can be used to convey application-level
resource priority requirements in multiple namespaces in a single
RSVP message (in a similar manner to how multiple namespace
priorities can be conveyed in the SIP Resource-Priority Header of
[SIP-PRIORITY]). As discussed earlier, this is useful for calls which
transit through multiple administrative domains.
3.2.1.
Application-Level Resource Priority Merging Rules
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This session discusses alternatives for dealing with RSVP
application-level resource priority in case of merging of
reservations. As merging is only applicable to multicast, this
section also only applies to multicast sessions.
This will be discussed in the next revision of this document.
[Editor's note: One approach could be to ensure that the reunion of
all the namespaces is included in the merge (ie if one receiver
includes namespace1.prio1 and another one includes namespace2.prio2,
the merged reservation will contain both namespace1.prio1 and
namespace2.prio2. Feedback on that is sought]
4. Security Considerations
The integrity of ADMISSION_PRI and APP_RESOURCE_PRI is guaranteed, as
any other policy element, by the encapsulation into a Policy Data
object [RSVP-POLICY]. The two optional security mechanisms discussed
in section 6 of [RSVP-POLICY] can be used to protect the
ADMISSION_PRI and APP_RESOURCE_PRI policy elements.
5. IANA Considerations
As specified in [POLICY-RSVP], Standard RSVP Policy Elements (P-type
values) are to be assigned by IANA as per "IETF Consensus" following
the policies outlined in [IANA-CONSIDERATIONS].
IANA needs to allocate two P-Types from the Standard RSVP Policy
Element range:
- one P-Type to the Admission Priority Policy Element
- one P-Type to the Application-Level Resource Priority
Policy Element
6. 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 Preemption Priority Policy
Element [RSVP-PREEMP]. Dave Oran and Janet Gunn provided useful input
into this document.
7. Normative References
[EMERG-RQTS] Carlberg, K. and R. Atkinson, "General Requirements for
Emergency Telecommunication Service (ETS)", RFC 3689, February 2004.
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RSVP Extensions for Emergency Services March 2006
[EMERG-TEL] Carlberg, K. and R. Atkinson, "IP Telephony Requirements
for Emergency Telecommunication Service (ETS)", RFC 3690, February
2004.
[EMERG-IMP] F. Baker & J. Polk, "Implementing an Emergency
Telecommunications Service for Real Time Services in the Internet
Protocol Suite", draft-ietf-tsvwg-mlpp-that-works-04, Work in
Progress
[RSVP] Braden, R., ed., et al., "Resource ReSerVation Protocol
(RSVP)- Functional Specification", RFC 2205, September 1997.
[FW-POLICY] Yavatkar, R., Pendarakis, D., and R. Guerin, "A
Framework for Policy-based Admission Control", RFC 2753, January 2000.
[RSVP-POLICY] Herzog, S., "RSVP Extensions for Policy Control", RFC
2750, January 2000.
[RSVP-PREEMP] Herzog, S., "Signaled Preemption Priority Policy
Element", RFC 3181, October 2001.
[DSTE-MAM] Le Faucheur & Lai, "Maximum Allocation Bandwidth
Constraints Model for Diffserv-aware MPLS Traffic Engineering",
RFC 4125, June 2005.
[DSTE-RDM] Le Faucheur et al, Russian Dolls Bandwidth Constraints
Model for Diffserv-aware MPLS Traffic Engineering, RFC 4127, June
2005
[SIP-PRIORITY] H. Schulzrinne & J. Polk. Communications Resource
Priority for the Session Initiation Protocol (SIP), RFC4412, February
2006.
8. Informative References
[RSVP-ID] Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore, T.,
Herzog, S., and R. Hess, "Identity Representation for RSVP", RFC 3182,
October 2001.
[RSVP-CRYPTO-1] Baker, F., Lindell, B., and M. Talwar, "RSVP
Cryptographic Authentication", RFC 2747, January 2000.
[RSVP-CRYPTO-2] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value", RFC 3097, April 2001.
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[SIP-RESOURCE] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session Initiation Protocol
(SIP)", RFC 3312, October 2002.
9. Authors Address:
Francois Le Faucheur
Cisco Systems, Inc.
Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille
06410 Biot Sophia-Antipolis
France
Email: flefauch@cisco.com
James Polk
Cisco Systems, Inc.
2200 East President George Bush Turnpike
Richardson, Texas 75082
USA
Email: jmpolk@cisco.com
Ken Carlberg
G11
123a Versailles Circle
Towson, MD. 21204
USA
email: carlberg@g11.org.uk
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Le Faucheur, et al. [Page 23]
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Le Faucheur, et al. [Page 24]
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