Internet Engineering Task Force James Polk Internet Draft Subha Dhesikan Expiration: April 18th, 2005 Cisco Systems File: draft-polk-tsvwg-rsvp-bw-reduction-00.txt A Resource Reservation Extension for the Reduction of Bandwidth of a Reservation Flow October 18th, 2004 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document proposes an extension to the Resource Reservation Protocol (RSVPv1) to reduce the guaranteed bandwidth allocated to a reservation. This mechanism can be used to affect individual reservations, aggregate reservations or other forms of RSVP tunnels. Polk & Dhesikan [Page 1]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Changes From Previous Version . . . . . . . . . . . . . 4 2. Individual Reservation Reduction Scenario . . . . . . . . . . 4 3. RSVP Aggregation Overview . . . . . . . . . . . . . . . . . . 6 3.1 RSVP Aggregation Reduction Scenario . . . . . . . . . . . 7 4. Requirements for Reservation Reduction . . . . . . . . . . . 8 5. RSVP Bandwidth Reduction Solution . . . . . . . . . . . . . . 9 5.1 Partial Preemption Error Code . . . . . . . . . . . . . 10 5.2 Error Flow Descriptor . . . . . . . . . . . . . . . . . 10 5.3 Individual Reservation Flow Reduction . . . . . . . . . . 10 5.4 Aggregation Reduction of Individual Flows . . . . . . . . 11 5.5 RSVP Flow Reduction involving IPsec Tunnels . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . 12 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 Appendix. Walking Through the Solution . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1 Normative References . . . . . . . . . . . . . . . . . . 15 9.2 Informational References . . . . . . . . . . . . . . . . 16 10. Author Information . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction This document proposes an extension to the Resource Reservation Protocol (RSVP) [1] to allow an existing reservation to be reduced in allocated bandwidth in lieu of tearing that reservation down. Several examples exist in which this mechanism may be utilized. The bandwidth allotted to an individual reservation may be reduced due to a variety of reasons such as preemption, etc. In such cases, when the entire bandwidth allocated to a reservation is not required, the reservation need not be torn down. The solution described in this document can allow endpoints to negotiate a new (lower) bandwidth that falls at or below the specified bandwidth allocated by the network. Using a voice session as an example, this indication in RSVP could lead endpoints, using another protocol such as Session Initiation Protocol (SIP) [9], to signal for a lower bandwidth codec. With RSVP aggregation [2], two aggregate flows with differing priority levels may traverse the same router interface. If that router interface reaches bandwidth capacity and is then asked to establish a new reservation or increase an existing reservation then the router has to make a choice: deny the new request (because all resources have been utilized) or preempt an existing lower priority reservation to make room for the new or expanded reservation. If the flow being preempted is an aggregate of many individual Polk & Dhesikan [Page 2]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 flows, this has greater consequences. While [2] clearly does not terminate all the individual flows if an aggregate is denied, this event will cause packets to be discarded. This document describes a method where only the minimum required bandwidth is taken away from the lower-priority aggregated reservation and the entire reservation is not preempted. This has the advantage that only some of the microflows making up the aggregate are affected. Without this extension, all individual flows are affected and the deaggregator will have to attempt the reservation request with a reduced bandwidth. RSVP tunnels utilizing IPsec [8] also requires an indication that the reservation must be reduced to a certain amount (or less). Note that when this document refers to a router interface being "full" or "at capacity", this does not imply that all of the bandwidth has been used, but rather that all of the bandwidth available for reservation via RSVP under the applicable policy has been used. Policies for real-time traffic routinely reserve capacity for routing and inelastic applications, and may distinguish between voice, video, and other real time applications. Explicit Congestion notification (ECN) [10] is an indication that the transmitting endpoint must reduce its transmission. It does not provide sufficient indication to tell the endpoint by how much the reduction should be. Hence the application may have to attempt multiple times before it is able to drop its bandwidth utilization below the available limit. Therefore, while we consider ECN to be very useful for elastic applications it is not sufficient for the purpose of inelastic application where an indication of bandwidth availability is useful for codec selection. Section 2 will discuss the individual reservation flow problem while Section 3 will discuss the aggregate reservation flow problem space. Section 4 lists the requirements for this extension. Section 5 details the protocol changes necessary in RSVP to create a reservation reduction indication. And finally, there is an appendix with a walk-through example of how this extension modifies RSVP functionality in an aggregate scenario. This document is intended to be classified as an 'update' to RFC 3181 [3] if published as an RFC. The previous version of this document had a different filename, as that effort only focused on solving reservation reduction of an aggregate. That filename was: draft-polk-tsvwg-rsvp-aggregate-reduction-00 This note will be removed in the next version of the effort. Polk & Dhesikan [Page 3]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 1.1 Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [4]. 1.2 Changes from the previous version to this version This is a listing of the changes that have taken place to this Internet Draft since the previous version: o Changed the filename to remove "aggregation" as the focus of the draft to open up this solution to a wider applicability o Reduced text in the introductory section to be more succinct o Added the use-case for this mechanism with individual reservations o Added the use-case for this mechanism with reservations of IPsec data flows o Opened up the text in the document body for this wider applicability o Mentioned why ECN is inappropriate for reducing bandwidth allocations of RSVP reservations. 2. Individual Reservation Reduction Scenario Figure 1 is a network topology that is used to describe the benefit of bandwidth reduction in an individual reservation. +--------------+ +--------------+ | |Int 1 | |Int 7 | | Flow 1===> | +----- | |------+ | Flow 1===> | Rtr1 |Int 2 |===========>|Int 8 | Rtr2 | | | |:::::::::::>| | | Flow 2:::> | +----- | |------+ | Flow 2:::> | |Int 3 | |Int 9 | | +--------------+ +--------------+ Figure 1. Simple Reservation Flows Figure 1. Legend/Rules: - Flow 1 priority = 300 - Flow 2 priority = 100 - Both flows are shown in the same direction (left to right). Corresponding flows in the reverse direction are not shown for diagram simplicity Polk & Dhesikan [Page 4]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 RSVP is a reservation establishment protocol in one direction only. This split path philosophy is because the routed path from one device to the other in one direction might not be the routed path for communicating between the same two endpoints in the reverse direction. End-systems must request 2 one-way reservations if that is what is needed for a particular application (like voice calls). Please refer to [1] for the details on how this functions. This example only describes the reservation scenario in one direction for simplicity sake. Figure 1. depicts 2 routers, (Rtr1 and Rtr2) initially with only one flow (Flow 1). The flows are forwarded from Rtr1 to Rtr2 via interface 2. For this example, let us say that flow 1 and flow 2 each require 80 units of bandwidth (such as for the codec G.711 with no silence suppression). Let us also say that the RSVP bandwidth limit for interface 2 of Rtr1 is 100 units. As described in [3], a priority indication is established for each flow. In fact, there are two priority indications: 1) one to establish the reservation, and 2) one to defend the reservation. In this example, flow 1 and flow 2 have an 'establishing' and a 'defending' priority of 300 and 100 respectively. Flow 2 will have a higher establishing priority than flow 1 has for its defending priority. This means that when flow 2 is signaled, and if no bandwidth is available at the interface, flow 1 will have to relinquish bandwidth in favor of the higher priority request of flow 2. The priorities assigned to a reservation are always end-to-end, and not altered by any routers in transit. Without the benefit of this specification, flow 1 will be preempted. This specification makes it possible for the ResvErr message to indicate that 20 units are still available for a reservation to remain up (the interface's 100 units maximum minus flow 2's 80 units). The reservation initiating node (router or end-system) for Flow 1 has the opportunity to re-negotiate (via call signaling) for acceptable parameters within the existing and available bandwidth for the flow (for example, it may decide to change to using a codec such as G.729) The problems avoided with the partial failure of the flow are: - Reduced packet loss which is resulted as flow 1 attempts to re-establish the reservation for a lower bandwidth. - Inefficiency caused by multiple attempts until flow 1 is able to request bandwidth equal to or lower than what is available. If flow 1 is established with much less than what is available then Polk & Dhesikan [Page 5]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 it leads to inefficient use of available bandwidth. 3. RSVP Aggregation Overview The following network overview is to help visualize the concerns that this specification addresses in RSVP Aggregates. Figure 2 consists of 10 routers (the boxes) and 11 flows (1, 2, 3, 4, 5, 9, A, B, C, D, and E). Initially there will 5 flows per aggregate (flow 9 will be introduced to cause the problem we are addressing in this document),with 2 aggregates (A & B); (1 through 5) in aggregate A and (A through E) in aggregate B. These 2 aggregates will cross one router interface utilizing all available capacity (in this example). RSVP aggregation [per 2] is no different from an individual reservation with respect to being unidirectional. Aggregator of A Deaggregator of A | | V V +------+ +------+ +------+ +------+ Flow 1-->| | | | | | | |--> Flow 1 Flow 2-->| | | | | | | |--> Flow 2 Flow 3-->| |==>| | | |==>| |--> Flow 3 Flow 4-->| | ^ | | | | ^ | |--> Flow 4 Flow 5-->| | | | | | | | | |--> Flow 5 Flow 9 | Rtr1 | | | Rtr2 | | Rtr3 | | | Rtr4 | Flow 9 +------+ | +------+ +------+ | +------+ | || || | Aggregate A-->|| Aggregate A ||<--Aggregate A || | || +--------------+ | +--------------+ | |Int 7 | | |Int 1 | | | +----- | V |------+ | | Rtr10 |Int 8 |===========>|Int 2 | Rtr11 | | | |:::::::::::>| | | | +----- | ^ |------+ | | |Int 9 | | |Int 3 | | +--------------+ | +--------------+ .. | .. Aggregate B--->.. Aggregate B ..<---Aggregate B | .. .. | +------+ | +------+ +------+ | +------+ Flow A-->| | | | | | | | | |--> Flow A Flow B-->| | V | | | | V | |--> Flow B Flow C-->| |::>| | | |::>| |--> Flow C Flow D-->| | | | | | | |--> Flow D Flow E-->| Rtr5 | | Rtr6 | | Rtr7 | | Rtr8 |--> Flow E +------+ +------+ +------+ +------+ ^ ^ | | Aggregator of B Deaggregator of B Polk & Dhesikan [Page 6]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 Figure 2. Generic RSVP Aggregate Topology Figure 2 legend/rules: - Aggregate A priority = 100 - Aggregate B priority = 200 - All boxes are Routers - Both aggregates are shown in the same direction (left to right). Corresponding aggregates in the reverse direction are not shown for diagram simplicity The path for aggregate A is: Rtr1 => Rtr2 => Rtr10 => Rtr11 => Rtr3 => Rtr4 where aggregate A starts in Rtr1, and deaggregates in Rtr4. Flows 1, 2, 3, 4, 5 and 9 communicate through aggregate A The path for aggregate B is: Rtr5 ::> Rtr6 ::> Rtr10 ::> Rtr11 ::> Rtr7 ::> Rtr8 where aggregate B starts in Rtr5, and deaggregates in Rtr8. Flows A, B, C, D and E communicate through aggregate B Both aggregates share one leg or physical link: between Rtr10 and Rtr11, thus they share one outbound interface: Int8 of Rtr10, where contention of resources may exist. That link has an RSVP capacity of 800kbps. RSVP signaling (messages) is outside this 800kbps in this example, as is any session signaling protocol like SIP. 3.1 RSVP Aggregation Reduction Scenario Figure 2 shows an established aggregated reservation (aggregate A) between the routers rtr1 and rtr4. This aggregated reservation consists of 5 microflows (flow 1, 2, 3, 4, 5). For the sake of this discussion, let us assume that each flow represents a voice call and requires 80kb (such as for the codec G.711 with no silence suppression). Aggregate A request is for 400kbps (80kbps * 5 flows). The priority of the aggregate is derived from the individual microflows that it is made up of. In the simple case, all flows of a single priority are bundled as a single aggregate (another priority level would be in another aggregate, even if traversing the same path through the network). There may be other ways in which the priority of the aggregate is derived, but for this discussion it is sufficient to note that each aggregate contains a priority (both hold and defending priority). The means of deriving the priority is out of scope for this discussion. Polk & Dhesikan [Page 7]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 Aggregate B, in Figure 2, consists of flows A, B, C, D and E and requires 400kbps (80kbps * 5 flows), and starts at rtr5 and ends rtr8. This means there are two aggregates occupying all 800kbps of the RSVP capacity. When Flow 9 is added into aggregate A, this will occupy 80kbps more than Int8 on rtr10 has available (880k offered vs. 800k capacity) [1] and [2] create a behavior in RSVP to deny the entire aggregate B and all its individual flows because aggregate A has a higher priority. This situation is where this document focuses its requirements and calls for a solution. There should be some means to signal to all affected routers of aggregate B that only 80kbps is needed to accommodate another (higher priority) aggregate. A solution that accomplishes this reduction instead of a failure could: - reduce significant packet loss of all flows within aggregate B During the re-reservation request period of time no packets will traverse the aggregate until it is reestablished. - reduces the chances that the reestablishment of the aggregate will reserve an inefficient amount of bandwidth, causing the likely preemption of more individual flows at the aggregator than would be necessary had the aggregator had more information (that RSVP does not provide at this time) During reestablishment of the aggregation in Figure 2. (without any modification to RSVP), rtr8 would guess at how much bandwidth to ask for in the new RESV message. It could request too much bandwidth, and have to wait for the error that not that much bandwidth was available; it could request too little bandwidth and have that aggregation accepted, but this would meant that more individual flows would need to be preempted outside the aggregate than were necessary, leading to inefficiencies in the opposite direction. 4. Requirements for Reservation Reduction The following are the requirements to reduce the bandwidth of a reservation. This applies to both individual and aggregate reservations: Req#1 - MUST have the ability to differentiate one reservation from another. In the case of aggregates, it MUST distinguish one aggregate from other flows. Req#2 - MUST have the ability to indicate within an RSVP error message (generated at the router with the congested interface) that a specific reservation (individual or aggregate) is to be reduced in bandwidth. Polk & Dhesikan [Page 8]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 Req#3 - MUST have the ability to indicate within the same error message the new maximum amount of bandwidth that is available to be utilized within the existing reservation, but no more. Req#4 - MUST NOT produce a case in which retransmitted reduction indications further reduce the bandwidth of a reservation. Any additional reduction in bandwidth for a specified reservation MUST be signaled in a new message. RSVP messages are unreliable and can get lost. This specification should not compound any error in the network. If a reduction message were lost, another one needs to be sent. If the receiver ends up receiving two copies to reduce the bandwidth of a reservation by some amount, it is likely the router will reduce the bandwidth by twice the amount than was actually called for. This will be in error. 5. RSVP Bandwidth Reduction Solution When a reservation is partially failed, a ResvErr (Reservation Error) message is generated just as it is done currently with preemptions. The error spec object and the preemption pri policy object are included as well. Very few additions/changes are needed to the ResvErr message to support partial preemptions. A new error sub code is required and is defined in section 5.1. The error flowspec contained in the ResvErr message indicates the flowspec that is reserved and this flowspec may not match or be less than the original reservation request. This is defined in section 5.2. A comment about RESV message not using a reliable transport. This document recommends that ResvErr message be made reliable by implementing mechanisms in [6]. The current behavior in RSVP requires a ResvTear message to be transmitted upstream when the ResvErr message is transmitted downstream (per 1). This ResvTear message terminates the reservation in all routers upstream of the router where the failure occurred. This document requires that the ResvTear is only generated when the reservation is to be completely removed. In cases where the reservation is only to be reduced, routers compliant with this specification requires that the ResvTear message MUST NOT be sent. An appendix has been written to walk through the overall solution to the problems presented in sections 2 and 3. There is mention of this ResvTear transmission behavior within the appendix. Polk & Dhesikan [Page 9]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 5.1 Partial Preemption Error Code The ResvErr message generated due to preemption includes the Error Spec object as well as the Preemption Priority Policy object. The format of Error-spec objects is defined in [1]. The error code listed in the ERROR_SPEC object for preemption [5] currently is as follows: Errcode = 2 (Policy Control Failure) and ErrSubCode = 5 (ERR_PREEMPT) The following error code is suggested in the Error_spec object for partial preemption: Errcode = 2 (Policy Control Failure) and ErrSubCode = X (ERR_PARTIAL_PREEMPT) Where 'X' is the number assigned by IANA for this error code There is also an error code in the preemption-pri policy object. This error code takes a value of 1 to indicate that the admitted flow was preempted [3]. The same error value of 1 may be used for the partial preemption case as well. 5.2 Error Flow Descriptor The error flow descriptor is defined in [1] & [7]. In the case of partial failure, the flowspec contained in the error flow descriptor indicates the highest average and peak rates that the preempting system can accept in the next RESV message. The deaggregator must reduce its reservation to a number less than or equal to that, whether by changing codecs, by dropping reservations, or some other mechanism. 5.3 Individual Reservation Flow Reduction When a router requires part of the bandwidth that has been allocated to a reservation be used for another flow, the router engages in the partial-reduction of bandwidth as described in this document. The router sends a ResvErr downstream to indicate the partial error with the error code and sub code as described in section 5.1. The flowspec contained in the ResvErr message will be used to indicate the bandwidth that is currently allocated. The requesting endpoint that receives the ResvErr can then negotiate with the transmitting endpoint to lower the bandwidth requirement (by selecting another lower bandwidth codec, for example). After the negotiations, both endpoints will issue the RSVP PATH and RESV message with the new, lowered bandwidth. Polk & Dhesikan [Page 10]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 5.4 Aggregation Reduction of Individual Flows When a partial-failure occurs in a aggregation scenario, the deaggregator receives the ResvErr message with the reduction indication from a router in the path of the aggregate. It then decides whether one or more individual flows from the aggregate are to be affected by this ResvErr message. The following choices are possible: o If that (deaggregator) router determines one or more individual flow(s) are to partially failed, then it sends a ResvErr message with a reduced bandwidth indication to those individual flow(s). This is as per the descriptions in the previous section (5.3). o If that (deaggregator) router determines one individual flow is to be preempted to satisfy the aggregate ResvErr, it determines which flow is affected. That router transmits a new ResvErr message downstream per [3]. That same router transmits a ResvTear message upstream. This ResvTear message of an individual flow does not tear down the aggregate. Only the individual flow is affected. o If that (deaggregator) router determines multiple individual flows are to be preempted to satisfy the aggregate ResvErr, it chooses which flows are affected. That router transmits a new ResvErr message downstream as per [3] to each individual flow. The router also transmits ResvTear messages upstream for the same individual flows. These ResvTear messages of an individual flow do not tear down the aggregate. Only the individual flows are affected. In all cases, the Deaggregator lowers the bandwidth requested in the Aggregate Resv message to reflect the change. Which particular flow or series of flows within an aggregate are picked by the deaggregator for bandwidth reduction or preemption is outside the scope of this document. 5.5 RSVP Flow Reduction involving IPsec Tunnels RFC 2207 (per [8]) specifies how RSVP reservations function in IPsec data flows. The nodes initiating the IPsec flow can be an end- system like a computer, or it can router between two end-systems, or it can be an in-line bulk encryption device immediately adjacent to a router interface. The methods of identification of an IPsec with reservation flow are different than non-encrypted flows, but how the reduction mechanism specified within this document functions is not. An IPsec with reservation flow is, for all intents and purposes, considered an individual flow with regard to how to reduce the bandwidth of the flow. Obviously an IPsec with reservation flow can Polk & Dhesikan [Page 11]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 be a series of individual flows or disjointed best effort packets between two systems. But to this specification, this tunnel is an individual RSVP reservation. Anywhere within this specification that mentions an individual reservation flow, the same rules of bandwidth reduction and preemption MUST apply. 6. Security Considerations This document does not lessen the overall security of RSVP or of reservation flows through an aggregate. If this specification is implemented poorly - which is never intended, but is a consideration - the following issue may arise: 1) If the ResvTear messages are transmitted initially (at the same time as the ResvErr messages indicating a reduction in bandwidth is necessary), all upstream routers will tear down the entire reservation. This will free up the total amount of bandwidth of this reservation inadvertently. This may cause the re- establishment of an otherwise good reservation to fail. This has the most severe affects on an aggregate that has many individual flows that would have remained operational. 7. IANA Considerations IANA is to assign the following from RFC [XXXX] (this document): The following error code is to be defined in the Error_spec object for partial reservation failure under "Errcode = 2 (Policy Control Failure)": ErrSubCode = X (ERR_PARTIAL_PREEMPT) Where 'X' is assigned by IANA for this error code The behavior of this ErrSubCode is defined in this document. 8. Acknowledgements The authors would like to thank Fred Baker for contributing text and guidance in this effort and to Roger Levesque for helpful comments. Polk & Dhesikan [Page 12]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 Appendix 1. Walking Through the Solution Here is a concise explanation of roughly how RSVP behaves with the solution to the problems presented in sections 2 & 3 of this document. There is no normative text in this appendix. Here is a duplicate of Figure 2 from section 3 of the document body (to bring it closer to the detailed description of the solution). Aggregator of A Deaggregator of A | | V V +------+ +------+ +------+ +------+ Flow 1-->| | | | | | | |--> Flow 1 Flow 2-->| | | | | | | |--> Flow 2 Flow 3-->| |==>| | | |==>| |--> Flow 3 Flow 4-->| | ^ | | | | ^ | |--> Flow 4 Flow 5-->| | | | | | | | | |--> Flow 5 Flow 9-->| Rtr1 | | | Rtr2 | | Rtr3 | | | Rtr4 |--> Flow 9 +------+ | +------+ +------+ | +------+ | || || | Aggregate A--->|| Aggregate A ||<--Aggregate A || | || +--------------+ | +--------------+ | |Int 7 | | |Int 1 | | | +----- | V |------+ | | Rtr10 |Int 8 |===========>|Int 2 | Rtr11 | | | |:::::::::::>| | | | +----- | ^ |------+ | | |Int 9 | | |Int 3 | | +--------------+ | +--------------+ .. | .. Aggregate B--->.. Aggregate B ..<---Aggregate B | .. .. | +------+ | +------+ +------+ | +------+ Flow A-->| | | | | | | | | |--> Flow A Flow B-->| | V | | | | V | |--> Flow B Flow C-->| |::>| | | |::>| |--> Flow C Flow D-->| | | | | | | |--> Flow D Flow E-->| Rtr5 | | Rtr6 | | Rtr7 | | Rtr8 |--> Flow E +------+ +------+ +------+ +------+ ^ ^ | | Aggregator of B Deaggregator of B Duplicate of Figure 2. Generic RSVP Aggregate Topology Looking at Figure 2., aggregate A (with five 80kbps flows) traverses: Rtr1 ==> Rtr2 ==> Rtr10 ==> Rtr11 ==> Rtr3 ==> Rtr4 Polk & Dhesikan [Page 13]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 And aggregate B (with five 80kbps flows) traverses: Rtr5 ::> Rtr6 ::> Rtr10 ::> Rtr11 ::> Rtr7 ::> Rtr8 Both aggregates are 400kbps. This totals 800kbps at Interface-7 in Rtr10, which is the maximum bandwidth RSVP has access to at this interface. Signaling messages still traverse the interface without problem. Aggregate A is at a higher relative priority than aggregate B. Local policy in this example is for higher relative priority flows to preempt lower priority flows during times of congestion. The following points describe the flow when aggregate A is increased to include flow 9. o When flow 9 (at 80kbps) is added to aggregate A, Rtr1 will initiate the PATH message towards the destination endpoint of the flow. This hop-by-hop message will take it through Rtr2, Rtr10, Rtr11, Rtr3 and Rtr4 which is the aggregate A path (that was built per [2] from the aggregate's initial set up) to the endpoint node. o In response, Rtr4 will generate the RESV (reservation) message [defined behavior per 1]. This RESV from the deaggregator indicates an increase bandwidth sufficient to accommodate the existing 5 flows (1,2,3,4,5) and the new flow (9) [as stated in 2]. o As mentioned before, in this example, Int8 in RTR 10 can only accommodate 800kbps, and aggregates A and B have each already established 400kbps flows comprised of five 80kbps individual flows. Therefore, Rtr10 (the interface that detects a congestion event in this example) must make a decision about this new congestion generating condition in regard to the RESV message received at Int8. o Local Policy in this scenario is to preempt lower priority reservations to place higher priority reservations. This would normally cause all of aggregate B to be preempted just to accommodate aggregate A's request for an additional 80kbps. o This document defines how aggregate B is not completely preempted, but reduced in bandwidth by 80kbps. This is contained in the ResvErr message that Rtr10 generates (downstream) towards Rtr11, Rtr7 and Rtr8. See section 5 for the details of the error message. o Normal operation of RSVP is to have the router that generates a ResvErr message downstream to also generate a ResvTear message upstream (in the opposite direction towards Rtr5). The ResvTear message terminates an individual flow or aggregate flow. This document calls for that message to not be sent on any partial failure of reservation. Polk & Dhesikan [Page 14]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 o Rtr8 is the deaggregator of aggregate B. The deaggregator controls all the parameters of an aggregate reservation. This will be the node that reduces the necessary bandwidth of the aggregate as a response to the reception of an ResvErr message (from Rtr10) indicating such an action is called for. In this example, bandwidth reduction is accomplished by preempting an individual flow within the aggregate (perhaps picking on Flow D for individual preemption by generating a ResvErr downstream on that individual flow). o At the same time, a ResvTear message is transmitted upstream on that individual flow (Flow D) by Rtr8. This will not affect the aggregate directly, but is an indication to the routers (and the source end-system) which individual flow is to be preempted. o Once Rtr8 preempts whichever individual flow (or 'bandwidth' at the aggregate ingress), it transmits a new RESV message for that aggregate (B), not for a new aggregate. This RESV from the deaggregator indicates an decrease in bandwidth sufficient to accommodate the remaining 4 flows (A,B,C,E), which is now 320kbps (in this example). o This RESV message travels the entire path of the reservation, resetting all routers to this new aggregate bandwidth value. This should be what is necessary to prevent a ResvTear message from being generated by Rtr10 towards Rtr6 and Rtr5. Rtr5 will not know through this RESV message which individual flow was preempted. If in this example, Rtr8 was given more bandwidth to keep, it might have transmitted a bandwidth reduction ResvErr indication towards the end-system of Flow D. In that case, a voice signaling protocol (such as SIP) could have attempted a renegotiation of that individual flow to a reduced bandwidth (say, but changing the voice codec from G.711 to G. 729). This could have saved Flow D from preemption. 9. References 9.1 Normative References [1] R. Braden, Ed., L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997 [2] F. Baker, C. Iturralde, F. Le Faucheur, B. Davie, "Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175, September 2001 [3] S. Herzog, "Signaled Preemption Priority Policy Element", RFC 3181, October 2001 Polk & Dhesikan [Page 15]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 [4] Bradner S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997 [5] S. Herzog, "RSVP Extensions for Policy Control", RFC 2750, January 2000 [6] L. Berger, D. Gan, G. Swallow, P. Pan, F. Tommasi, S. Molendini, "RSVP Refresh Overhead Reduction Extensions" RFC 2961, April 2001 [7] J. Wroclawski, "The Use of RSVP with IETF Integrated Services", RFC 2210, September 1997 [8] L. Berger, T. O'Malley, "RSVP Extensions for IPSEC Data Flows", RFC 2207, September 1997 9.2 Informational References [9] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, May 2002. [10] K. Ramakrishnan, S. Floyd, D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, September 2001 10. Author Information James M. Polk Cisco Systems 2200 East President George Bush Turnpike Richardson, Texas 75082 USA Email: jmpolk@cisco.com Subha Dhesikan Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA Email: sdhesika@cisco.com Intellectual Property Statement 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. Polk & Dhesikan [Page 16]
Internet Draft RSVP Bandwidth Reduction Oct 13th, 2004 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. 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. 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. Copyright Statement Copyright (C) The Internet Society (2004). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. The Expiration date for this Internet Draft is: April 13th, 2005 Polk & Dhesikan [Page 17]