Internet Draft INTERNET-DRAFT Lan Wang Expires: September 2000 Andreas Terzis <draft-ietf-rsvp-state-compression-03.txt> Lixia Zhang UCLA March 2000 RSVP Refresh Overhead Reduction by State CompressionStatus of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 As a soft-state protocol, RSVP specifies that each RSVP node sends peri- odic RSVP messages for each existing RSVP session. The overhead due to such periodic state refreshes goes up linearly with the number of active RSVP sessions. One can reduce the overhead by using a longer refresh period, which unfortunately leads to longer delays in re-synchronizing RSVP state in face of packet losses. To overcome the dilemma, this specification describes the use of a "state-compression" approach to soft-state protocol refreshes. In the absence of state changes this compression mechanism has a constant message overhead while retaining the soft-state nature of RSVP. draft-wang-rsvp-state-compression-03.txt [Page 1] INTERNET-DRAFT March 2000 Changes Below is a list of changes from the previous version of this draft <draft-wang-rsvp-state-compression-02.txt>. - Paragraphs that describe the MessageID extension are revised to be consistent with draft-ietf-rsvp-refresh-reduct-03.txt where the extension is defined. - Section 9 is added to compare our state compression scheme with other proposals on RSVP refresh overhead reduction. 1. Introduction As a soft-state setup protocol, RSVP specifies that each RSVP node sends control messages for each active RSVP session to each of its neighbors serving the same session. These control messages are sent immediately whenever a change of state occurs, for example when a new session starts, when the TSPEC or RSPEC parameters of an existing session change, or when a route change occurs that affects the paths of existing RSVP sessions. In addition, an RSVP node also sends periodic refresh messages to its neighbors about all existing sessions. Such periodic refreshes serve the purpose of keeping consistent RSVP reservation state along data flow paths. There are potentially a number of causes that can make the reservation state between neighbor RSVP nodes out-of-syn- chronization. For example: - An RSVP message that carries state-change information gets lost. - A rare local event inadvertently changed RSVP state values. - Other locally induced state changes occur, for example when the current Kerberos key expires, a new key is obtained which needs to be carried to the next hop by the POLICY_DATA object in the next refresh. Instead of attempting to identify all the potential causes of changes and handle them individually, RSVP simply uses periodic refreshes to persistently re-synchronize the reservation state along the path. This approach assures consistent reservation state along the data flow path, without the routers being informed of an exhaustive list of all the pos- sible causes of state inconsistency or how to correct them individually. The drawback of this simple and effective approach is the associated protocol overhead which grows linearly with the number of active RSVP sessions. A common mechanism to reduce the periodic refresh overhead is by using a longer refresh period, e.g. RTCP reports [1] and SDP announcements [2]. A longer refresh period, however, leads to longer delays in re-synchronizing state if some RSVP update messages get lost. draft-wang-rsvp-state-compression-03.txt [Page 2] INTERNET-DRAFT March 2000 In this draft we propose a "state compression" mechanism for refresh overhead reduction. Our goal is to improve the efficiency of soft-state protocols in their communication behavior. Our design applies compres- sion algorithms to the protocol state information so that the number of refresh messages is reduced from being proportional to the number of sessions to being proportional to the number of neighboring nodes, while retaining the soft-state nature of RSVP. Section 7 presents a detailed overhead analysis of our compression mechanism. 2. Refresh Overhead Reduction Even in the absence of new control information generated by sources or destinations, an RSVP node sends one message per refresh period to its neighboring nodes for each of all the RSVP sessions. One way to reduce this refresh overhead is to compress the state of all RSVP sessions to a single digest message, which can then be sent to neighboring nodes in place of all the "raw" refresh messages. All we need is an algorithm that can produce a mapping from the given set of RSVP state to a digest with a low probability of collision. Two compression algorithms have been suggested so far, CRC-32 and MD5 algorithm [3]. Section 8 presents a brief comparison of the two algo- rithms. In the following discussion we assume either one can be used for the purpose and simply refer to it as "the compression algorithm". Whenever state inconsistency is detected (the digests of two neighbors disagree), raw RSVP messages are transmitted to re-synchronize the state. Our state compression scheme is designed in accordance with the Mes- sageID extension of RSVP described in [4]. The MessageID extension enables nodes to request an ACK for each raw RSVP message that carries state-change information. Our design requires that every digest message be acknowledged either by an ACK message when the neighbor node has a matching digest value or otherwise by a DigestErr message. It is impor- tant to note that the use of ACKs in the MessageID extension is to assure quick delivery of time-sensitive information; RSVP still relies on periodic refreshes to correct any potential state inconsistency that may occur even when critical messages are acknowledged, for example state inconsistency due to undetected bit errors, or due to RSVP state changes made at local nodes. 2.1. Definitions - Input Message draft-wang-rsvp-state-compression-03.txt [Page 3] INTERNET-DRAFT March 2000 The input to the compression function. In this document an input message contains some portion of the RSVP state stored at the local node. - Signature The result of compression function on an input message. - Digest A set of Signatures that represents a compressed version of the RSVP state shared between two neighboring RSVP nodes. The following definitions are taken from RFC 2209. - PSB Path State Block. Each PSB holds path state for a particular (ses- sion, sender) pair, defined by SESSION and SENDER_TEMPLATE objects, respectively. -RSB Reservation State Block. Each RSB holds a reservation request that arrived in a particular RESV message, corresponding to the triple: (session, next hop, Filter_spec_list). 2.2. Benefits and Constraints of the New Scheme The design of the new scheme aims at the following features - efficient state re-synchronization when two RSVP neighbors discover state inconsistency. - choice of individual nodes to use either original RSVP refreshes or the compressed refresh with overhead reduction, or switch in between over time to achieve the best tradeoff. - backward compatibility with the current RSVP specification. - incremental digest computation when only part of the session(s) changes state. We also recognize the necessary cost and constraints of the new scheme. First, to assure RSVP state consistency over reserved paths, the digest must be computed over the RSVP session state rather than over the mes- sages that are exchanged. Those messages represent partial, but not all causes of state changes, two neighbor nodes may end up in inconsistent draft-wang-rsvp-state-compression-03.txt [Page 4] INTERNET-DRAFT March 2000 state even when RSVP messages are all acknowledged. Secondly, to reduce the refresh overhead to one refresh message per refresh period per neighbor, a digest must represent the compressed state of aggregate sessions. Thus an RSVP node must first group all RSVP sessions by each neighbor, compute the digest, and then send to the corresponding neighbor node. On the other hand, the paths of individual RSVP sessions may change over time. In the current design, RSVP PATH messages carry the destination address of the session, thus all refresh messages automatically follow the latest unicast or multicast routing changes (including multicast group membership changes). Although RSVP has an interface to the local routing module for prompt notification of route changes to minimize the adaptation delay, all RSVP reservations eventually converge on new paths even in the absence of such notifica- tions. When routers stop sending individual PATH refresh messages, however, RSVP loses its ability to automatically adjust reservations according to route changes. The proposed scheme relies on explicit notifications to any routing changes. We consider this the major constraint of the new scheme. When two neighbor nodes of a unicast RSVP session are directly con- nected, RSVP can expect to receive notification of route changes through the interface to the local routing module. When the two nodes are interconnected through a non-RSVP cloud, however, there seems no known way to reliably detect all routing changes without the per session peri- odic refreshes. Multicast sessions present a similar problem, namely that the list of neighbors for a given session may not be known and may change dynamically as receivers leave and join the session. Further complications associated with multicast sessions also arise when a router is attached to a broadcast LAN. For example there can be both compression-capable and compression-incapable downstream neighbors on the LAN, in which case RSVP must fall back to per session periodic refreshes. Furthermore, it remains an open issue whether a router can reliably detect all changes in the downstream neighbors when a down- stream router on the broadcast LAN joins or leaves a group without affecting the list of outgoing interfaces of the associated RSVP state. Therefore we limit the problem space to handling unicast sessions whose paths do not cross non-RSVP clouds. An RSVP node resorts to the current refresh scheme for all sessions that have the "non_RSVP_cloud" bit set, or that have a multicast destination address. draft-wang-rsvp-state-compression-03.txt [Page 5] INTERNET-DRAFT March 2000 3. Digest Mechanism Description 3.1. Session Signatures RSVP maintains path state and reservation state for each active session [5]. A session is uniquely identified by a session object which con- tains the IP destination address, protocol ID and optionally a destina- tion port number of the associated data packets. A Path State Block (PSB) is comprised of a sender template (i.e. IP address and port number of the sender), a Tspec that describes the sender's traffic characteris- tics, and possibly objects for policy control and advertisements. A Reservation State Block (RSB) contains filterspecs (i.e. sender tem- plates) of the senders for which the reservation is intended, the reser- vation style and a flowspec that quantifies the reservation. It may also contain objects for policy control and confirmation. As the first step in computing a digest, an RSVP node computes a signa- ture for each session. Table 1 shows the objects that should be included in the digest computation. These objects must be fed into the computation procedure in the order as presented in the table. Although PSBs and RSBs also contain a few other fields such as incoming interface and outgoing interfaces, those fields have local meaning and may have different values at different nodes. Therefore they must be excluded from the digest computation. RSVP Structure || Objects to Include _________________||_______________________________________ || Session || session object _________________||_______________________________________ || PSB || sender template, sender tspec, || adspec, policy _________________||_______________________________________ || RSB || filterspec, flowspec, style, policy _________________||_______________________________________ Table 1. Objects to Include in Digest Computation 3.2. State Organization for Digest Computation As a second step to efficient refresh exchanges, an RSVP node organizes all the sessions shared with each neighbor node in a hash table. draft-wang-rsvp-state-compression-03.txt [Page 6] INTERNET-DRAFT March 2000 Assuming the hash table has M slots, each RSVP session is hashed into one of the M slots. The hashing is done over some fixed session fields (e.g the session ID). If multiple sessions hash to the same slot, they create an ordered linked list, following the increasing order of IP address, protocol ID and port number in session objects. Figure 1 shows the hash table created for each neighbor. In this Figure, slot i contains a pointer to the head of the linked list of all RSVP sessions that hash to i. Assuming the total number of RSVP sessions is T, the average length of this linked list will be T/M. Slot i also con- tains a Signature that is computed by applying the compression algorithm over the concatenation of the signatures of all the sessions in the linked list. If the slot is empty, the signature is zero. Whenever any of the sessions in the list changes state, the signature of the slot must also be recomputed. <--------T/M--------> +---+ +---+ +---+ +---+ | 1 |--->| |-->| |-->| | +---+ +---+ +---+ +---+ | . | | . | | . | +---+ +---+ +---+ | i |--->| |-->|D_1| +---+ +---+ +---+ | . | | . | | . | +---+ | M | +---+ Figure 1. Session Hash Table As a third step towards efficient refresh exchanges, we propose to com- pute the digest in a structured way. To illustrate this need, suppose there are 100,000 sessions and we can transmit 80 signatures in each digest message. With a hash table size (M) of 4,000 (25 sessions in each slot on average), if we periodically exchange all the 4,000 signa- tures(one for each slot), the overhead will be 50 digest messages per refresh period. When session state changes relatively infrequently, it would be desirable if we can further reduce this refresh overhead. Therefore, we build a N-ary tree on top of the hash table to compress the M signatures to no more than N signatures, where N is the number of signatures that can fit inside a single IP packet. This set of draft-wang-rsvp-state-compression-03.txt [Page 7] INTERNET-DRAFT March 2000 signatures is called a digest. Whenever two neighbor nodes disagree on the digest value, they can walk down specific branches of the N-ary tree to locate the portion of inconsistent state in an efficient way. The digest computation tree is shown in Figure 2. ^ o o o digest | /|\ /|\ /|\ h y_1 o o o o o o o o o level-1 signature | /|\ ......... /|\ v o o o ..........o o o level-0 signatures x_1...x_N Figure 2. A Digest Tree with N=3 A node constructs the digest computation tree in the following way. The leaves of the tree are the signatures stored in the slots of the hash table. The signatures of N slots are concatenated and the compression function is applied on the compound message. The result is stored at the parent node on the tree. Looking at Figure 2, Signatures x_1, ..., x_N are concatenated and the result of the compression function is stored in node y_1. This grouping results in Ceiling[M/N] level-1 signatures. If the number of level-1 signatures is still larger than N, the node con- tinues on to group level-1 signatures to compute Ceiling[M/N^2] level-2 signatures. If C_i is the number of level-i signatures, we repeat the grouping until C_i is smaller or equal to N. The top level signatures represent the digest of the total RSVP state. In our previous example N is 80 and M is 4,000, so we have 50 level-1 signatures and the final digest is comprised of these signatures. We choose the degree of the tree to be the same as the maximum number of Signatures in a digest object to simplify the data structure and the partial rollback process when two nodes detect inconsistent state. Note that all RSVP session insertions and deletions are done in the hash table; the purpose of the digest computation tree is simply to compress the session signatures to fit them into one packet. It is important that neighboring RSVP nodes use the same hash table size M and digest size N (the maximum number of signatures in a single mes- sage); inconsistency in either of these two values will lead to the failure of the compression scheme. Therefore, two neighboring nodes need to choose the M and N to be used before starting exchanging digest mes- sages. Ideally, these two constants should be selected based on the link MTU and the expected number of active sessions. This specification assumes that neighbors have reached consensus on the value of N and M for simplicity. draft-wang-rsvp-state-compression-03.txt [Page 8] INTERNET-DRAFT March 2000 A digest needs to be recomputed when the following events occur: o a new session is added; o an existing session is changed, i.e. a state is added to a session, or a state is modified or deleted from a session; o an existing session is deleted. The cost of digest computation is summarized in section 7. An RSVP node needs to compute two digests for each neighbor, i.e. OutDi- gest and InDigest. OutDigest is computed on the state for which this node sends refresh messages to that neighbor and it will be included in the Digest messages sent to the neighbor. InDigest is computed on the state that is refreshed by messages from the neighbor. It will match the digest value received from the neighbor if the local node is synchro- nized with the neighbor. 3.3. An Example of Digest Computation In this section, we use a simple example to illustrate how we compute and update a digest tree. T_20 T_21 / \ / \ digest tree (N = 2) T_10 T_11 T_12 T_13 / \ / \ / \ / \ +----+----+----+----+----+----+----+----+ |T_00 T_01 T_02 T_03 T_04 T_05 T_06 T_07| hash table (8 slots) +----+----+----+----+----+----+----+----+ SS10 SS19 SS12 SS13 SS14 SS25 SS16 SS17 sessions hashed to each slot SS18 SS22 Figure 3. A Digest Tree on top of a Hash Table Suppose a node currently shares 10 sessions with a neighbor and it uses a small hash table with 8 slots. For simplicity, the sessions' addresses are of the format 1.2.3.j (j = 10, 12, 13, 14, 16, 17, 18, 19, 22, 25) and we call the signature of session j SSj. The node first maps the sessions into the hash table (Figure 3 shows the result of the map- ping). It then computes a signature for each slot over the session sig- natures contained in that slot. For example, T_00 is obtained by com- pressing the concatenation of SS10 and SS18. Now we have signatures T_00 to T_07, but our goal is to reduce these eight signatures to two signatures assuming N is 2. Therefore, we separate them into groups of 2 and compute a signature for each group. This procedure is repeated twice to produce the final digest (T_20 and T_21). draft-wang-rsvp-state-compression-03.txt [Page 9] INTERNET-DRAFT March 2000 Now we look at the procedure to update this structure when this node receives a path message with a destination address of 1.2.3.15 which creates a new path state. In addition to forward this path message to its neighbor, the node calculates the signature of this session (SS15) and inserts the new session into the hash table. Let's assume this ses- sion is mapped to slot 5. Since the new session's address is smaller than that of session 25, it's inserted before session 25. Next, the node recalculates T_05, T_12 and T_21, i.e. all the signatures on the path from the leaf signature (slot 5's signature) to the corresponding root. To delete a session, the node first needs to locate the session's slot and remove it from the slot. The procedure to update the digest tree is the same as that of adding a session. 3.4. Neighbor Data Structure To avoid having to traverse all the RSVP sessions to compute the digest for a specific neighbor, a router maintains a Neighbor data structure containing pointers to all the sessions shared with the neighbor. In addition to the data structures used in digest computation, the Neighbor structure holds all the information needed to send and receive digests to/from a neighboring RSVP node, such as address information of the neighbor and timers for digest exchanges. An example of the per neigh- bor structure is shown in Figure 4. Below is a non-exhaustive list of the fields in the Neighbor structure. IP Address Holds the IP address of the interface this neighbor uses to communi- cate with the local node. OutSession This field points to the hash table holding the sessions to be included in the computation of the digest that the local node is sending to this neighbor. The sessions included are those that have PSBs whose next downstream hop is the neighbor in question and RSBs that have the neighbor as the immediate upstream hop. OutDigest A set of pointers that point to the top level signatures of the Out- Digest tree for the neighbor. RefreshOutTimer draft-wang-rsvp-state-compression-03.txt [Page 10] INTERNET-DRAFT March 2000 Contains the next time a digest should be sent to this neighbor. Neighbor Struct +----------------- + | IP Address | +----------------- + | OutSession |--->Hash table for outgoing sessions +----------------- + | OutDigest | +----------------- + | RefreshOutTimer | +----------------- + | IDLastSent | +------------------+ | OutDigestTimeout | +------------------+ | InSession |--->Hash table for incoming sessions +------------------+ | InDigest | +------------------+ | CleanupInTimer | +------------------+ | ... | +------------------+ Figure 4. Neighbor Structure IDLastSent Contains the Message_ID of the latest digest sent to this neighbor. OutDigestTimeout Contains the timeout period in milliseconds for the latest digest sent to this neighbor. If an acknowledgment is not received by the end of this period, the digest should be retransmitted. InSession This field points to the hash table holding the sessions that are refreshed by digests received from this neighbor. Specifically, the table includes sessions whose PSBs have this neighbor as previous hop draft-wang-rsvp-state-compression-03.txt [Page 11] INTERNET-DRAFT March 2000 and sessions whose RSBs have this neighbor as next hop. InDigest A set of pointers that point to the top level signatures of the InDi- gest tree for the neighbor. CleanupInTimer If no digest is received from this neighbor by the time contained in the CleanupInTimer field, all associated state should be cleaned up. 3.4.1. SessDigest Structure The SessDigest structure contains information about a session that has a specific neighbor as a Next Hop. The SessDigest structure has the fol- lowing fields: Session* A pointer to the RSVP session represented by this structure. Next SessDigest When multiple sessions map to the same hash table bin, this field is used to point to the next object in the linked list of SessDigest objects. Otherwise this field SHOULD be NULL. P/R This field indicates whether the PSB or the RSB of a Session will be used in the signature operation. Signature Contains the computed Signature for this session. draft-wang-rsvp-state-compression-03.txt [Page 12] INTERNET-DRAFT March 2000 Session Struct ^ | | +-----------------+ | Session* | +-----------------+ | Next SessDigest |---->.. +-----------------+ | P/R | +-----------------+ | Signature | +-----------------+ Figure 5. The SessDigest structure 3.5. Neighbor Discovery To use the state compression scheme, a router needs to discover all the neighbors that are capable of exchanging digests (state compression capable). We add a D bit to the common RSVP header for this purpose (see below). If a node receives a raw RSVP message with the D bit turned on from a neighbor, that neighbor is assumed to be state compres- sion capable. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Vers | Flags | Msg Type | RSVP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Send_TTL | (Reserved) | RSVP Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags: 4 bits bb1b: state compression capable (D-bit set to 1) bb0b: state compression incapable (D-bit set to 0) When a non-RSVP cloud exists between two RSVP neighboring nodes, the upstream node may not be able to detect a change of the downstream neighbor caused by a unicast route change. As shown in Figure 6, node A originally has a downstream neighbor B for a particular unicast RSVP session. After a route change, node C becomes A's downstream neighbor. However, since A's outgoing interface is unchanged, A will not notice the route change, hence it will continue to include the path state of sender S when calculating the digest to B. Node B will not be aware of draft-wang-rsvp-state-compression-03.txt [Page 13] INTERNET-DRAFT March 2000 the change either as long as A sends B the same digest. C may never get a path message from A. Therefore, the digest scheme cannot be used crossing non-RSVP clouds until an effective way of detecting route changes is found. RSVP routers can detect the existence of non-RSVP clouds between neighbors by comparing the TTL value in the IP header with the Send_TTL in the RSVP common header, as described in [6]. original route ___________ ---> -> ->| |-- B ----| -> S - - --- A --| non-RSVP | |------- D | cloud | | |___________|-- C ----| new route ---> Figure 6. An RSVP Session with a non-RSVP cloud 3.6. Digest Refreshes RSVP state is refreshed by regular RSVP messages as well as by Digest messages. A digest message usually carries multiple signatures, each representing the compressed state of multiple sessions. If any signa- ture in the received digest matches the corresponding local value, all the RSVP state covered by that signature should be refreshed. That is, the local node should carry out the same operation as if one refresh message for each of the covered sessions has been received. The refresh rate of digest messages can be different from the refresh rate of the individual sessions covered by that digest. For digest mes- sages, the default refresh rate is 30 seconds as suggested by RFC 2205. If a different refresh rate is used, it SHOULD be carried in the TIME_VALUES object of the digest message. 4. New RSVP Message Types and Objects In this section, we define Digest object, Digest message and DigestErr message. Since the digest mechanism uses the MessageID objects and ACK message defined in the MessageID extension [4], we first review the for- mat and usage of these objects and message to help readers better under- stand our scheme. draft-wang-rsvp-state-compression-03.txt [Page 14] INTERNET-DRAFT March 2000 4.1. MessageID Extension There are three types of MessageID objects, i.e. MESSAGE_ID, MES- SAGE_ID_ACK and MESSAGE_ID_NACK. MESSAGE_ID object is used to identify messages that carry state-changing information. MESSAGE_ID_ACK and MES- SAGE_ID_NACK are included in ACK messages to acknowledge the correspond- ing messages. Their definitions are taken from [4]. 4.1.1. MESSAGE_ID Objects MESSAGE_ID Class = Value to be assigned by IANA of form 0bbbbbbb MESSAGE_ID object Class = MESSAGE_ID Class, C_Type = 1 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Epoch | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message_Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags: 8 bits 0x01 = ACK_Desired flag Indicates that the sender requests the receiver to send an acknowl- edgment for the message. Epoch: 24 bits A value that indicates when the Message_Identifier sequence has been reset. SHOULD be randomly generated each time a node reboots. This value MUST NOT be changed during normal operation. Message_Identifier: 32 bits When combined with the message generator's IP address, the Mes- sage_Identifier field uniquely identifies a message. The value placed in this field changes incrementally and only decreases when the Epoch changes or when the value wraps. draft-wang-rsvp-state-compression-03.txt [Page 15] INTERNET-DRAFT March 2000 4.1.2. MESSAGE_ID_ACK and MESSAGE_ID_NACK Objects MESSAGE_ID_ACK Class = Value to be assigned by IANA of form 0bbbbbbb MESSAGE_ID_ACK object Class = MESSAGE_ID_ACK Class, C_Type = 1 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Epoch | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message_Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Flags: 8 bits No flags are currently defined. This field MUST be zero on transmis- sion and ignored on receipt. Epoch: 24 bits The Epoch field copied from the message being acknowledged. Message_Identifier: 32 bits The Message_Identifier field copied from the message being acknowl- edged. MESSAGE_ID_NACK object Class = MESSAGE_ID_ACK Class, C_Type = 2 Definition is the same as the MESSAGE_ID_ACK object. 4.1.3. Ack Message Format The Ack message format is as follows: draft-wang-rsvp-state-compression-03.txt [Page 16] INTERNET-DRAFT March 2000 ::= [ ] | [ [ | ] ... ] For Ack messages, the Msg Type field of the Common Header MUST be set to 13 (This is a suggested value, the permanent value is to be assigned by IANA). 4.2. DIGEST Object DIGEST Class = Value to be assigned by IANA of form 10bbbbbb DIGEST object Class = DIGEST Class, C_Type = 1 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |S| Level/Slot | Index | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Number of Signatures | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // signature list // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ S: 1 bit When the S-bit is set to 1, this digest message carries the signa- tures of the individual sessions inside a hash slot. Level/Slot: 15 bits When S is set to 1, this is the index of the hash slot that this set of signatures belong to. When S is set to 0, this is the level of this set of signatures in the corresponding digest tree. The level of a signature is defined as follows: 1. Leaf signatures are assigned level 0; 2. The level of a non-leaf signature is (1 + the level of its imme- diate children). draft-wang-rsvp-state-compression-03.txt [Page 17] INTERNET-DRAFT March 2000 Index: 16 bits This is the index of the first signature in this digest message. The index of a signature is defined as follows: 1. For the signatures of individual sessions, the signature of the first session in a linked list of sessions contained in the same hash slot has index 0 and the following sessions are numbered increasingly. 2. The signatures at the same level of a digest tree are numbered increasingly from left to right and the left-most signature is assigned index 0. Level and index uniquely identify the loca- tion of a signature in a digest tree. Reserved: 16 bits This field is reserved. It MUST be set to zero on transmission and MUST be ignored on receipt. Number of Signatures: 16 bits Number of Signatures contained in this object. Signature List: A set of signatures that is the compressed state of a group of ses- sions. It may be the final digest of a node or some intermediate level digest in the digest tree or a set of session signatures. 4.3. Digest Message The format of a Digest message is as follows: ::= [ ] [ ] A Digest message has a common RSVP header with the message type set to 16 (This is a suggested value, the permanent value is to be assigned by IANA). It MUST contain a MESSAGE_ID object with the ACK_Requested flag set and a digest object. The optional TIME_VALUES object contains the refresh timer value of the Digest message. draft-wang-rsvp-state-compression-03.txt [Page 18] INTERNET-DRAFT March 2000 4.4. DigestErr Message A DigestErr message has the following format: ::= [ ] The message type of DigestErr message is 17 (This is a suggested value, the permanent value is to be assigned by IANA). It MUST contain a MES- SAGE_ID_NACK object and a DIGEST object. A DigestErr message acts as a negative acknowledgment to a Digest message. The MESSAGE_ID_NACK object identifies the Digest message being acknowledged. The DIGEST object carries the local digest value of the sender of the DigestErr message. 4.5. Backward Compatibility Regarding Digest messages, a node should start sending Digest messages only when it discovers that its particular peer is compression-capable using the procedure outlined in Section 3.5. 5. RSVP Message Operations 5.1. Digest Message Once a compression-capable node discovers a compression-capable neigh- bor, instead of sending one refresh message for each PATH/RESV state, it sends a digest, in one RSVP message per refresh period to each of the neighbors. Special treatments for RSVP state containing ADSPEC and POL- ICY_DATA objects are discussed in section 5.3. Each digest MUST carry a MESSAGE_ID object with the ACK_Requested flag set. When the neighbor receives the Digest message, it first locates the cor- responding set of signatures in the local digest tree and then performs a binary comparison between each signature in the message and that in the local digest tree. o If there is a mismatch between any of the signatures received and the corresponding local signatures, the node should respond with a DigestErr message containing the local digest value. Note that if there is any matching signature, RSVP state represented by that signature should be refreshed. o Otherwise, the receiver is in a consistent state with the sender, draft-wang-rsvp-state-compression-03.txt [Page 19] INTERNET-DRAFT March 2000 so it sends an ACK message and refreshes all the state shared with the sender. Digest messages are also retransmitted for a maximum number of times in the absence of ACK or DigestErr messages. However, following the origi- nal RSVP design where an RSVP node never stops sending refresh messages for each active session, a node should not stop sending digest refreshes even if it fails to receive an acknowledgment in the previous refresh interval. If the peer node crashed and becomes alive again, it will find the digest value different from its own and the two routers will start the re-synchronization process. When the digest value is changed, the node needs to cancel any pending retransmission of the obsolete Digest message and promptly send a Digest message with the new digest value. 5.2. Refresh of ADSPEC and POLICY_DATA An RSVP message may carry an ADSPEC object that contains resource infor- mation used by receivers to predict the end-to-end service. This object is updated hop-by-hop to gather information along a route. Since it is opaque to RSVP, RSVP simply records the received ADSPEC in the corre- sponding state and, whenever it needs to send a refresh message for a state, it calls the traffic control module with the recorded ADSPEC to get an updated ADSPEC object. Therefore, the ADSPEC object sent by a node may be different from that received by the node. POLICY_DATA object is handled in the same way except that it is submitted to the policy control module. To handle ADSPEC or POLICY_DATA objects correctly with the digest scheme, we need to solve the following two problems. First, for each session with ADSPEC or POLICY_DATA object, we must trigger periodic updates of ADSPEC or POLICY_DATA objects. Second, since ADSPEC and POL- ICY_DATA are opaque to RSVP, RSVP cannot tell whether the objects returned by the traffic control (or policy control) module changes after each call. For the first problem, we treat digest refreshes the same way as regular RSVP refresh messages. In other words, before a node sends a digest, the node calls corresponding modules to update these objects. If the traffic and/or policy control modules provide trigger mechanisms that asyn- chronously notify the RSVP module when changes occur then this step will be avoided. There are three possible solutions to the second problem. First, a node can simply assume that the object returned by the traffic control (or policy control) module changes after each call at refresh period, which represents a change in RSVP state and hence a regular RSVP PATH state should be sent to carry the new object value to the next hop. This draft-wang-rsvp-state-compression-03.txt [Page 20] INTERNET-DRAFT March 2000 approach requires no changes to RSVP specification but it essentially falls back to the original RSVP refresh mechanism whenever ADSPEC or POLICY_DATA object exists in an RSVP session. The second option is to modify the RSVP/traffic control and RSVP/policy control interfaces so that they return a change bit that indicates whether the updated object is different from the previously returned one. The previously returned object can be an argument passed to the interface. For example, the original RSVP/traffic control interface for ADSPEC is Call: TC_Advertise( Interface, Adspec, Non_RSVP_Hop_flag ) -> New_Adspec, where Adspec is the ADSPEC from received RSVP messages. We can change it to Call: TC_Advertise( Interface, Adspec, Old_Adspec Non_RSVP_Hop_flag ) -> New_Adspec, change bit, and Old_Adspec is the ADSPEC object returned by the previous call. When the changed bit is set, a regular RSVP refresh must be sent. The third option is to let RSVP perform a binary comparison between the previously and newly returned objects after each call to traffic control (policy control) module to find out whether the object has changed. This third option can be a short-term fix while we work on the proposed changes in RSVP interfaces to other modules. If POLICY_DATA objects are encoded, for replay attack prevention reasons, in a way that makes iden- tical POLICY_DATA objects look as different binary objects this third option will deteriorate to the first option, i.e. a refresh message will be sent, for every POLICY_DATA object returned by the policy control module. 6. RSVP State Re-synchronization Two RSVP neighbors may become out-of-sync due to a number of reasons. - A state-changing RSVP message is lost, and the sender did not ask for ACK. - A neighbor crashed and lost part or all of its state. - Other unknown reasons. draft-wang-rsvp-state-compression-03.txt [Page 21] INTERNET-DRAFT March 2000 Receipt of a DigestErr message indicates inconsistency between two nodes. The MESSAGE_ID and digest value in the DigestErr message help the two neighbors to localize the problem. o If the Message_ID acknowledged is smaller than the Message_ID of the last Digest message sent (IDLastSent), this error message is for an obsolete message. This message should be ignored since it may not represent the current state of the neighbor. o If the Message_IDs are equal, the node should start the recovery process we describe next. The node then compares the signatures contained in the DigestErr mes- sage. When it finds the first mismatching signature (call it S_1), it sends a Digest message containing the lower level signatures in the digest tree used to compute S_1. A DigestErr is expected for this Digest message since at least one of the children signatures does not match. The node again looks for the first mismatching signature (S_2) in the second DigestErr message and sends the children of S_2 in a Digest message. This procedure is repeated until the leaf signature (S_h) (h=log_N(M), see Figure 2) causing the problem is found. Now, the node knows that one or more of the sessions in that hash table slot (represented by S_h) must be inconsistent with those in the neighbor. It can then either locate these sessions by exchanging the session signa- tures with the receiver or it can simply send raw refreshes for all the sessions in that particular bin. After refreshing these sessions, the node re-examines S_(h-1) (the parent of S_h) for other inconsistencies and continues to traverse the tree until all the mismatching sessions are located and refreshed. Notice there is a tradeoff between the latency of the recovery procedure and the transmission efficiency. For example, if the tree has many lev- els, many RTTs are needed to exchange the digests at all the tree levels in order to find the leaf-level sessions that contribute to the incon- sistency. However, if speed of convergence is more important than effi- ciency, one can stop at an intermediate tree level and refresh all the state represented by the mismatching signature at that level. 7. Computation Costs We have presented in Section 3.2 the structure used to support efficient and incremental computation of digests. This structure consists of two parts: a hash table that stores the Signatures of sessions shared with a particular neighbor and an N-ary tree used to reduce the number of sig- natures to a number that can be sent inside a single packet. In this section we focus on the operations applied to these data structures and analyze their requirements in terms of processing. draft-wang-rsvp-state-compression-03.txt [Page 22] INTERNET-DRAFT March 2000 We begin with some definitions. Let the number of sessions be T, the size of the hash table be M and the number of Signatures inside the digest message be N. Let's further define the cost of computing the com- pression function on a message of size x to be f(x). To determine the behavior of f(x), we have to study each algorithm's behavior. Summariz- ing the description in RFC 1321 [3], the MD5 algorithm divides the input message to 64-byte blocks and applies a four-step process to each one of these 64-byte blocks. In each of the four steps, sixty-four bit-wise logical operations are applied to that 64-byte block. The results of the computation on the n-th block are used as input for the computation of the (n+1)-th block. After all the blocks have been processed, the mes- sage's digest is produced. From this description, one can see that f(x) is a linear function of x, the size of the input message measured in bytes. A similar analysis applies for CRC-32, so the cost of computing the CRC-32 checksum of a message with size x is also linear on the size of x but with smaller constants. When a session is modified, a new signature for that session as well as a new digest has to be computed. To illustrate this procedure, imagine that we want to update session D_1 inside the hash table of Figure 1. First, we look up the session inside the hash table (a possible opti- mization here is to store the hash table index where the session is stored rather than re-computing the hash function every time the session is modified). In our example, we would come up with the index i. If mul- tiple sessions map to the same hash table slot, we traverse the linked list of sessions until we find the session in question. Once the session is found and its new Signature is computed, we have to compute the new Signature stored at the base of the linked list which represents all the sessions mapped to that hash table slot. On the average Ceiling[T/M] sessions will occupy the same slot. The total time needed for this oper- ation is therefore f(D* Ceiling[T/M]), where D is the size of the signa- ture (16 bytes for MD5 and 4 bytes for CRC-32). We assume that the linked-list lookup time which is O(Ceiling[T/M]) is small compared to the time needed to update the Signatures and therefore we don't include it in our calculations. The next step is to update the values on the digest tree. We begin by computing the Signature of the contents of slot i concatenated with its N-1 siblings which will be stored in their par- ent node on the digest tree. We continue this procedure until we reach the top of the tree. Since there are log_N(M) levels on the tree and at each level we apply the compression algorithm on a message of size D*N (the combined size of N Signatures), the time spent during this step is N*(log_N(M)-1)*f(D). Notice that the term is log_N(M)-1 since we do not calculate a Signature out of the N topmost Signatures. Also f(D*N) = N*f(D) since f(x) is linear on x. From the discussion above, we can conclude that the total time needed to calculate the new digest after a session is modified is given by the following formula, where S is the size of a session in bytes: draft-wang-rsvp-state-compression-03.txt [Page 23] INTERNET-DRAFT March 2000 f(S) + f(D * Ceiling[T/M]) + N*(log_N(M)-1) * f(D) (1) When a new session has to be inserted in the hash table, we locate the slot this session hashes to and insert the session to that slot's linked list, if one exists. Given that the list is ordered, the new session has to be inserted in order inside the list, which means traversing the list until we find a session whose destination address is larger than the destination address of the session we want to add and inserting the new session before that session. Deleting a session, involves finding the slot it hashes to, searching for it inside the linked list, and ``splic- ing'' its predecessor to its successor on the list. The computation cost for the creation of the new digest after an inser- tion or deletion operation, is almost identical to the update cost. The only difference is that in the case of deletion we don't calculate the Signature of the session (since we are deleting it) but only calculate the combined Signature of the rest of the sessions on the list. Equa- tions 2 and 3 respectively, show the insertion and deletion costs. f(S) + f(D * Ceiling[T/M]) + N*(log_N(M)-1) * f(D) (2) f(D * Ceiling[T/M]) + N*(log_N(M)-1) * f(D) (3) We can see from Equations 1, 2 and 3 that when the size M of the hash table is small compared to the number of sessions T, the cost of updat- ing the linked list of sessions will be linear to T. In this case, updating the linked list becomes the most expensive operation, forcing the total cost to also be linear to T. The size M of the hash table should therefore be comparable to the expected T to avoid increased update times. 8. Compression Mechanism Comparison We mentioned earlier that two possible candidates for the compression function are the CRC-32 checksum algorithm and the MD-5 digest algorithm [3]. The main task of the compression function is to produce a one-to- one mapping between sets of sessions and digests. It is therefore important that the probability of two different configurations producing the same digest (collision probability) is negligible. The compression scheme fails when the digest trees created at the two neighbors contain different sessions but produce the same digest, i.e the same set of N top level Signatures. In this section we compute the probability of failure as a function of draft-wang-rsvp-state-compression-03.txt [Page 24] INTERNET-DRAFT March 2000 the size of signatures produced by the compression algorithm. Specifi- cally we compute the probability a single bit difference in the RSVP state shared between the two neighbors is not detected. Let's assume that the maximum packet size that can be sent un-fragmented is L bits. Then if the size of the signature is x bits, N, the number of Signatures in a digest, is L/x. As before, let's further assume that the size of the hash table is M. To make the calculations easier we actu- ally compute the probability that the error will be detected, P(suc- cess). The failure probability is of course 1-P(success). The probability that the error will be detected is the probability that the modified session will produce a different Signature AND the list of other sessions contained in the same slot with the modified session will create a different Signature AND all the nodes on the path of the digest tree from that hash table bin to one of the roots of the digest tree will create different Signatures. Let's calculate each of these proba- bilities first. Assuming that the compression function is perfect, i.e. it distributes messages evenly over the set of Signatures, the probability that the changed session will create a different Signature is (1-1/2^x). In a similar fashion the probability that at each level of the digest tree a different Signature will be produced is again (1-1/2^x). (Note: one might observe that CRC-32 detects all single bit differences and there- fore in this case the probability of detection in the first step is one. While this is correct, the goal of our simplified analysis is to compare the relative performance of the two schemes without focusing on the specifics of each compression algorithm.) Since the compression function produces a (pseudo-)random set of bits, the events described above are independent and therefore to compute the desired probability we take their product. Hence the probability that the error will be detected is: P(success) = (1-1/2^x)^(h+1) (4) and P(failure) = 1 -P(success) = 1 - (1-1/2^x)^(h+1) (5) Where h is the height of the digest tree, h = log_N(M). To get a better understanding, we substitute the parameters in Equation 5 with some values. For M=10000, L=10000 bits and x=32 (CRC-32), P(fail- ure) = 3.74*10^-9 while for x=128 (MD5) P(failure)=0. draft-wang-rsvp-state-compression-03.txt [Page 25] INTERNET-DRAFT March 2000 From this numerical example we can see that for single-bit differences, MD5 has infinitesimal probability of failure while at the same time CRC-32 provides high assurance that errors will be detected. Multiple bit changes present a slightly different picture. While the detection probability in the case of MD5 is independent of the number of changed bits, for CRC-32 the probability of detection decreases when the number of changed bits increases. The conjecture is therefore that CRC-32 will perform worse than MD5 for multiple bit differences. On the other hand the smaller size of the CRC-32 Signature means that N will be larger and the height h of the digest tree will be significantly shorter. Finally, computing the CRC-32 checksum is a lot faster than the MD5 computation. 9. Comparison with Other Schemes This section compares our Digest mechanism with the Summary Refresh and Periodic Checksum mechanisms proposed by Lou Berger et. al. [4]. Both proposals aim to reduce RSVP's refresh message overhead, but our scheme can achieve a higher degree of state consistency and higher message overhead reduction. The Summary Refresh mechanism uses the message identifier contained in the MESSAGE_ID object of a trigger message to represent the state infor- mation that the message carries. To refresh a state, a node can send the latest message identifier of the particular state in a Summary Refresh (SRefresh) message. Upon receiving the message, the receiver will look up the state that corresponds to the identifier and refresh the state as if a normal refresh message was received. Multiple message identifiers can be sent in one SRefresh message to refresh multiple state. The Summary Refresh mechanism looks similar to our Digest mechanism in that both use some "number" to represent a state, i.e. message identi- fier and signature respectively. However, they differ in the following fundamental ways: - State Consistency Since message identifier is just a random number associated with a mes- sage, it is not a true representation of a state. Suppose the message contains undetected bit errors or either end has made a local state change after processing the message, then the resulting inconsistency cannot be detected via the message identifier. On the other hand, since the Digest mechanism computes the signature from the RSVP state, any state inconsistency between two nodes can be easily discovered. - Message Overhead Reduction draft-wang-rsvp-state-compression-03.txt [Page 26] INTERNET-DRAFT March 2000 Recall that we use a hash table and a digest tree to reduce the size of a digest so that it can be contained in a single message. Therefore, our mechanism can reduce the number of refresh messages to one per refresh period. The Summary Refresh mechanism, on the other hand, does not fur- ther compress the message identifiers, which means the refresh message overhead still goes up linearly as the number of state increases. - Message Processing Overhead The Summary Refresh mechanism requires checking the message identifiers of all the state in each refresh period regardless of whether two nodes are consistent, while the Digest mechanism only needs one comparison of the Digest value when two nodes have consistent state. When a state needs to be repaired, the Digest mechanism requires more Digest message exchanges to identify the state with error. Nonetheless, as you can see, the digest tree is usually quite shallow, so the number of messages exchanged during state recovery should be very small. Given that Summary Refresh mechanism only provides a limited degree of state consistency, the Periodic Checksum mechanism was introduced to solve the problem. A checksum is computed for every state and when a state is changed, its checksum is recomputed. A node also periodically checks if there are unnoticed changes by computing a new checksum over the state and comparing it with the existing one. If the two checksums are different, this node will refresh the corresponding state. In this way, the node can ensure that valid changes to the state can propagate to other nodes even though they were previously undetected by RSVP at the time of change. However, like the Summary Refresh mechanism, the Periodic Checksum can- not protect against all forms of errors. If a state is corrupted inter- nally, which cannot be distinguished from unnoticed valid changes, the incorrect state information will also be propagated by this mechanism. What's more, this inconsistency will persist until the node that has the corrupted state gets refresh messages from its upstream node. Our digest mechanism does not have this problem, however, since every node is "forced" to synchronize with its upstream node periodically and all the nodes will eventually be consistent with the sources of state informa- tion, e.g. senders for path state and receivers for reservation state. One may argue that the Digest mechanism has higher storage and computa- tion overhead because of the need to compute and store digest trees and hash tables. However, we would like to point out that the Digest mecha- nism can operate without using the digest tree and hash table. Nodes can exchange the plain session signatures without reducing them to a single digest. Although this will result in a message overhead comparable to that of the Summary Refresh mechanism, the digest mechanism can still achieve a higher state consistency than the combination of the Summary draft-wang-rsvp-state-compression-03.txt [Page 27] INTERNET-DRAFT March 2000 Refresh and Periodic Checksum mechanism. Another concern about the Digest mechanism is that it may require stan- dard internal representation of data. A simple solution for this prob- lem is to store the data in a machine dependent format and then convert the data to a standard format before computing its signature. 10. Summary Due to the scaling requirements from setting up large numbers of RSVP reservations, such as the case in MPLS traffic engineering, a few recent proposals suggested to slow down or eliminate periodic state refreshes in RSVP. We believe that elimination of refreshes represents a funda- mental departure from the soft-state approach adopted in RSVP design. As we have argued in this draft, reliable RSVP message delivery alone is insufficient for assuring consistent reservation state inside the net- work; it merely brings the benefit of quick synchronization whenever RSVP state changes. The state compression mechanism described in this draft makes the over- head of the RSVP soft-state refreshes independent from the number of RSVP sessions by paying the cost of computing and maintaining a tree of session signatures. When sessions or session parameters change, updat- ing the tree of session signatures has a computational overhead propor- tional to T/M (T is the total number of sessions and M is a constant comparable to T). When large numbers of RSVP sessions exist in a network, we believe that the proposed scheme brings substantial performance gain from reduced refresh overhead, especially when most of the sessions are relatively stable. The feasibility of using this approach in a highly dynamic envi- ronment where many sessions are constantly added and deleted remains an open issue. 11. IANA Considerations IANA must provide two new Msg Types for the two new messages defined in this draft: Digest and DigestErr. Also IANA must provide Class Numbers for the Digest object defined here. The DIGEST object requires a a Class-Num value of the form 10bbbbbb. 12. Security Considerations No new security issues are raised in this document. See [5] for a gen- eral discussion on RSVP security issues. draft-wang-rsvp-state-compression-03.txt [Page 28] INTERNET-DRAFT March 2000 13. Acknowledgments The phrase "overhead reduction by state compression" was suggested by Van Jacobson of cisco. Vern Paxson suggested the use of hashing to sim- plify Digest computation. Our design also benefited from discussion with Steve McCanne of UC Berkeley regarding the roles of acknowledgment in soft-state protocol design. We thank Hilarie Orman for her insight- ful comments on MD5 and CRC-32. We also received valuable feedback from Bob Braden and Steven Berson of ISI. 14. References [1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996. [2] Handley, M., and V. Jacobson, "SDP: Session Description Proto- col", RFC 2327, April 1998. [3] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [4] Berger, L., Gan, D., et al, "RSVP Refresh Overhead Reduction Extensions", draft-ietf-rsvp-refresh-reduct-03.txt, March 2000. [5] Braden, R. Ed., Zhang, L., et al, "Resource ReserVation Protocol -- Version 1 Functional Specification", RFC 2205, September 1997. [6] Braden, R. and Zhang, L., "Resource ReSerVation Protocol (RSVP) -- Version 1 Message Processing Rules", RFC 2209, September 1997. 15. Authors' Addresses Lan Wang UCLA 4805 Boelter Hall Los Angeles, CA 90095 Phone: 310-267-2190 Email: lanw@cs.ucla.edu Andreas Terzis UCLA 4677 Boelter Hall Los Angeles, CA 90095 draft-wang-rsvp-state-compression-03.txt [Page 29] INTERNET-DRAFT March 2000 Phone: 310-267-2190 Email: terzis@cs.ucla.edu Lixia Zhang UCLA 4531G Boelter Hall Los Angeles, CA 90095 Phone: 310-825-2695 Email: lixia@cs.ucla.edu draft-wang-rsvp-state-compression-03.txt [Page 30]