One document matched: draft-lefaucheur-emergency-rsvp-00.txt
Admission Priority Policy Element October 2005
Internet Draft Francois Le Faucheur
James Polk
Cisco Systems, Inc.
draft-lefaucheur-emergency-rsvp-00.txt
Expires: March 2006 October 2005
RSVP Admission Priority Policy Element 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 crisis. When supported over the Internet Protocol
suite, this may be achieved through an admission control solution
which supports call preemption capabilities as well as admission
priority capabilities, whereby some resources (e.g. bandwidth) are
reserved for emergency services only.
Le Faucheur, et al. [Page 1]
Admission Priority Policy Element October 2005
This document specifies RSVP extensions necessary for supporting such
admission priority capabilities.
Copyright Notice
Copyright (C) The Internet Society. (2005)
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). The key requirement is to guarantee
superior probability of call completion from an authorized user in
times of crisis. To that end, some of these types of services require
that the network be capable of preempting calls; others do not
involve preemption but instead rely on another network mechanism
which we refer throughout this document as "admission priority"
whereby some resources (e.g. bandwidth) is set aside for the
emergency services only, in order to obtain a high probability of
call completion for those.
[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 services of the ETS.
This document specifies RSVP extensions which can be used to enforce
the "admission priority" required by other services of the ETS.
1.1. Changes from previous versions
Le Faucheur, et al. [Page 2]
Admission Priority Policy Element October 2005
This is the initial version of the document
2. Overview of RSVP extensions and Operations
Let us consider the case where a call requiring Internet Emergency
Preference Service is to be established, and more specifically that
the preference to be granted to this call is in terms of admission
priority (i.e. by allowing that call to seize resources that have
been set-aside and not made available to normal calls) and that the
preference to be granted to this new call does not involve preempting
existing 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 priority requirements of emergency calls. Again, in the
case where the session control protocol is SIP, the SIP user agents
can be aware of the resource priority requirements in the case of an
emergency call using mechanisms specified in [SIP-PRIORITY].
Where, as per our considered case, the priority requirement of the
emergency call involves admission priority, the devices involved in
the session establishment simply need to map the 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.
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
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Admission Priority Policy Element October 2005
The RSVP admission priority defined in this document allows admission
bandwidth to be allocated for use by 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.
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.
This section illustrates how MAM and RDM can indeed be used for
support of admission priority. For simplicity, operations with only a
single "priority" level (beyond non-priority) is 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 reserved for priority traffic (even if the non-priority
traffic is not using all of the bandwidth available for it).
-----------------------
^ | | ^
. | | .
Total . | | . Bandwidth
. | | . Available
Avail . | | . for non-priority use
. | | .
BW . | | .
. | | .
. | | v
. |--------------| ---
Le Faucheur, et al. [Page 4]
Admission Priority Policy Element October 2005
. | | ^
. | | . Bandwidth reserved for
v | | v priority use
-------------------------
Chart 1. Overall Link Capacity
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. The aggregate of the
two amounts equals the total link capacity (or the total capacity
granted to the corresponding Diffserv Per Hop Behavior).
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 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.
Chart 2 shows some of the non-priority capacity of this link being
used.
----------------------
^ | | ^
. | | .
Total . | | . Bandwidth
. | | . Available
Avail . |xxxxxxxxxxxxxx| . for non-priority use
. |xxxxxxxxxxxxxx| .
BW . |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| v
. |--------------| ---
. | | ^
. | | . Bandwidth reserved 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.
----------------------
^ | | ^
. | | .
Le Faucheur, et al. [Page 5]
Admission Priority Policy Element October 2005
Total . | | . Bandwidth
. | | . Available
Avail . |xxxxxxxxxxxxxx| . for non-priority use
. |xxxxxxxxxxxxxx| .
BW . |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| v
. |--------------| ---
. | | ^
. | | . Bandwidth reserved 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
Avail . |xxxxxxxxxxxxxx| . for non-priority use
. |xxxxxxxxxxxxxx| .
BW . |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| .
. |xxxxxxxxxxxxxx| v
. |--------------| ---
. | | ^
. | | . Bandwidth reserved 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 because of proper
allocation of bandwidth to priority traffic, for completeness Chart 5
shows the case where there priority traffic equates or exceeds the
bandwidth reserved for such priority traffic.
In that case additional priority sessions could not be accepted. They
may be handled by mechanisms which are beyond the scope of this
particular document (such as established through preemption of
Le Faucheur, et al. [Page 6]
Admission Priority Policy Element October 2005
existing non-priority sessions, or new priority session requests
could be queues until capacity becomes available again for priority
traffic).
----------------------
^ |xxxxxxxxxxxxxx| ^
. |xxxxxxxxxxxxxx| .
Total . |xxxxxxxxxxxxxx| . Bandwidth
. |xxxxxxxxxxxxxx| . Available
Avail . |xxxxxxxxxxxxxx| . for non-priority use
. |xxxxxxxxxxxxxx| .
BW . |xxxxxxxxxxxxxx| .
. | | .
. | | v
. |--------------| ---
. |oooooooooooooo| ^
. |oooooooooooooo| . Bandwidth reserved 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
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.
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
Le Faucheur, et al. [Page 7]
Admission Priority Policy Element October 2005
---------------------------------------
Chart 6. Partial non-priority load & Partial Aggregate load
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
---------------------------------------
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Admission Priority Policy Element October 2005
Chart 8. Partial non-priority load & Heavy Aggregate load
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 new priority session requests
could be queues until capacity becomes available again for priority
traffic). This is not expected to occur 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 8. Full non-priority load & Full Aggregate load
3. 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.
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Admission Priority Policy Element October 2005
This document defines a new Policy Element called the Admission
Priority Policy Element.
The format of Admission Priority policy element is as follows:
+-------------+-------------+-------------+-------------+
| Length (12) | P-Type = ADMISSION_PRI |
+-------------+-------------+-------------+-------------+
| Flags | M. Strategy | Error Code | Reserved(0) |
+-------------+-------------+-------------+-------------+
| Admission Priority | Reserved (0) |
+---------------------------+---------------------------+
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
1 Take priority of highest QoS: recommended
2 Take highest priority: aggressive
3 Force Error on heterogeneous merge
Error code: 8 bits
0 NO_ERROR Value used for regular ADMISSION_PRI elements
2 HETEROGENEOUS This element encountered heterogeneous merge
Reserved: 8 bits
Always 0.
Admission Priority: 16 bit (unsigned)
The admission control priority of the flow, in terms of access
to resources set aside in order to provide higher probability of
call completion to selected flows. Higher values represent
higher Priority. A reservation established without an Admission
Priority policy element is equivalent to a reservation
established with an Admission Priority policy element whose
Admission Priority value is 0.
Reserved: 16 bits
Always 0.
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Admission Priority Policy Element October 2005
4. 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.
4.1. Admission Priority Merging Strategies
In merging situations Local Decision Points (LDPs) may receive
multiple preemption 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.
4.1.1.
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
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.
4.1.2.
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.
4.1.3.
Force error on heterogeneous merge
A ADMISSION_PRI element may participate in a merged reservation only
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Admission Priority Policy Element October 2005
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.
4.2. 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.
- 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.
5. 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
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Admission Priority Policy Element October 2005
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.
6. Security Considerations
The integrity of ADMISSION_PRI is guaranteed, as any other policy
element, by the encapsulation into a Policy Data object [RSVP-POLICY].
7. 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 a P-Type from the Standard RSVP Policy Element
range to the Admission Priority Policy Element.
8. Acknowledgments
We would like to thank An Nguyen for his encouragement to address
this topic and comments. Also, this document borrows heavily from
some of the work of S. Herzog on Preemption Priority Policy Element
[RSVP-PREEMP].
9. Normative References
[EMERG-RQTS] Carlberg, K. and R. Atkinson, "General Requirements for
Emergency Telecommunication Service (ETS)", RFC 3689, February 2004.
[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-02, 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.
Le Faucheur, et al. [Page 13]
Admission Priority Policy Element October 2005
[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
10. 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.
[SIP-RESOURCE] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session Initiation Protocol
(SIP)", RFC 3312, October 2002.
[SIP-PRIORITY] H. Schulzrinne & J. Polk. Communications Resource
Priority for the Session Initiation Protocol (SIP), draft-ietf-sip-
resource-priority-10, work in progress
11. 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
Le Faucheur, et al. [Page 14]
Admission Priority Policy Element October 2005
Richardson, Texas 75082
USA
Email: jmpolk@cisco.com
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14. Copyright Notice
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to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Le Faucheur, et al. [Page 15]
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