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 By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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]
RSVP Extensions for Emergency Services March 2006 [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 Le Faucheur, et al. [Page 3]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 4]
RSVP Extensions for Emergency Services March 2006 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. Le Faucheur, et al. [Page 5]
RSVP Extensions for Emergency Services March 2006 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. Le Faucheur, et al. [Page 6]
RSVP Extensions for Emergency Services March 2006 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. ----------------------- ^ ^ ^ | | ^ Le Faucheur, et al. [Page 7]
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]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 9]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 10]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 11]
RSVP Extensions for Emergency Services March 2006 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. Le Faucheur, et al. [Page 12]
RSVP Extensions for Emergency Services March 2006 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]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 14]
RSVP Extensions for Emergency Services March 2006 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 | +---------------------------+---------------------------+ Le Faucheur, et al. [Page 15]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 16]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 17]
RSVP Extensions for Emergency Services March 2006 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. Le Faucheur, et al. [Page 18]
RSVP Extensions for Emergency Services March 2006 - 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). Le Faucheur, et al. [Page 19]
RSVP Extensions for Emergency Services March 2006 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 Le Faucheur, et al. [Page 20]
RSVP Extensions for Emergency Services March 2006 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. Le Faucheur, et al. [Page 21]
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. Le Faucheur, et al. [Page 22]
RSVP Extensions for Emergency Services March 2006 [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 10. IPR Statements The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. Le Faucheur, et al. [Page 23]
RSVP Extensions for Emergency Services March 2006 The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. 11. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 12. Copyright Notice Copyright (C) The Internet Society (2006). This document is subject 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 24]
