Network Working Group Ghyslain Pelletier, Editor, Ericsson AB INTERNET-DRAFT Lars-Erik Jonsson, Ericsson AB Expires: April 2004 Mark A West, Siemens/Roke Manor Richard Price, Siemens/Roke Manor October 27, 2003 RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP) Status 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 cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Abstract This document specifies a ROHC (Robust Header Compression) profile for compression of TCP/IP packets. The profile, called ROHC-TCP, is a robust header compression scheme for TCP/IP that provides improved compression efficiency and enhanced capabilities for compression of various header fields including TCP options. Existing TCP/IP header compression schemes do not work well when used over links with significant error rates and long round-trip times. For many bandwidth limited links where header compression is essential, such characteristics are common. In addition, existing schemes [RFC-1144, RFC-2507] have not addressed how to compress TCP options such as SACK (Selective Acknowledgements) [RFC-2018, RFC- 2883] and Timestamps [RFC-1323]. Pelletier, et al. [Page 1] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Table of contents 1. Introduction....................................................3 2. Terminology.....................................................4 3. Background......................................................5 3.1. Existing TCP/IP header compression schemes................5 3.2. Classification of TCP/IP header fields....................6 3.3. Characteristics of short-lived TCP transfers..............7 4. Overview of the TCP/IP profile..................................8 4.1. General concepts..........................................8 4.2. Context replication.......................................8 4.3. State machines and profile operation......................8 4.4. Packet formats and encoding methods.......................8 5. Compression and decompression state machines....................9 5.1. Compressor states and logic...............................9 5.1.1. Initialization and Refresh (IR) state...................9 5.1.2. Compression (CO) state..................................9 5.1.3. Feedback logic.........................................10 5.1.4. State transition logic.................................10 5.1.4.1. Optimistic approach, upward transition...............10 5.1.4.2. Optional acknowledgements (ACKs), upward transition..10 5.1.4.3. Timeouts, downward transition........................11 5.1.4.4. Negative ACKs (NACKs), downward transition...........11 5.1.4.5. Need for updates, downward transition................11 5.1.5. State machine supporting context replication...........11 5.2. Decompressor states and logic............................12 5.2.1. No Context (NC) state..................................12 5.2.2. Static Context (SC) state..............................12 5.2.3. Full Context (FC) state................................13 5.2.4. Allowing decompression.................................13 5.2.5. Reconstruction and verification........................14 5.2.6. Actions upon CRC failure...............................14 5.2.7. Feedback logic.........................................14 6. ROHC-TCP - TCP/IP compression (Profile 0x0006).................15 6.1. Feedback channel considerations..........................15 6.2. Master Sequence Number (MSN).............................16 6.3. Initialization...........................................16 6.4. Packet types.............................................17 6.4.1. Initialization and Refresh packets (IR)................17 6.4.2. Context replication packets (IR-CR)....................18 6.4.3. Compressed packets (CO)................................20 Pelletier, et al. [Page 2] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.5. Packet formats...........................................20 6.5.1. Uncompressed TCP/IP packet.............................21 6.5.2. Default encoding methods...............................22 6.5.3. Compressed TCP Options using list encoding.............25 6.5.4. Packet type IR and IR-DYN..............................29 6.5.5. Compressed TCP/IP packets..............................31 6.5.5.1. Packet type IR-CR....................................31 6.5.5.2. Packet type CO.......................................37 6.6. Feedback formats and options.............................55 6.6.1. Feedback formats.......................................55 6.6.2. Feedback options.......................................56 7. Security considerations........................................57 8. IANA considerations............................................57 9. Acknowledgements...............................................58 10. References....................................................58 10.1. Normative references.....................................58 10.2. Informative references...................................58 11. Authors' addresses............................................60 Full Copyright Statement...........................................61 1. Introduction There are several reasons to perform header compression on low- or medium-speed links for TCP/IP traffic, and these have already been discussed in [RFC-2507]. [TCP-REQ] introduces additional considerations making robustness an important objective for a TCP compression scheme. Finally, existing TCP/IP header compression schemes [RFC-1144, RFC-2507] are limited in their handling of the TCP options field and cannot compress the headers of handshaking packets (SYNs and FINs). It is thus desirable for a header compression scheme to be able to handle loss on the link between the compression and decompression point as well as loss before the compression point. The header compression scheme also needs to consider how to efficiently compress short-lived TCP transfers and TCP options, such as SACK [RFC-2018, RFC-2883] and Timestamps [RFC-1323]. The ROHC WG has developed a header compression framework on top of which various profiles can be defined for different protocol sets, or for different compression strategies. This document defines a TCP/IP compression profile for the ROHC framework [RFC-3095], compliant with the requirements on ROHC TCP/IP header compression [TCP-REQ]. Pelletier, et al. [Page 3] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Specifically, it describes a header compression scheme for TCP/IP header compression (ROHC-TCP) that is robust against packet loss and that offers enhanced capabilities, in particular for the compression of header fields including TCP options. The profile identifier for TCP/IP compression is 0x0006. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119. This document reuses some of the terminology found in [RFC-3095]. In addition, this document defines the following terms: Base context The base context is a context that has been validated by both the compressor and the decompressor. A base context can be used as the reference when building a new context using replication. Base CID The Base Context Identifier is the CID used to identify the Base Context, where information needed for context replication can be extracted from. Context replication Context replication is the mechanism that establishes and initializes a new context based on another existing valid context (a base context). This mechanism is introduced to reduce the overhead of the context establishment procedure, and is especially useful for compression of multiple short-lived TCP connections that may be occurring simultaneously or near-simultaneously. Short-lived TCP Transfer Short-lived TCP transfers refer to the TCP connections transmitting only small amounts of data for each single connection. Short TCP flows seldom need to operate beyond the slow-start phase of TCP to complete their transfer, which also means that the transmission ends before any significant increase of the TCP congestion window may occur. Pelletier, et al. [Page 4] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 3. Background This chapter provides some background information on TCP/IP header compression. The fundamentals of general header compression may be found in [RFC-3095]. In the following sections, two existing TCP/IP header compression schemes are first described along with a discussion of their limitations, followed by the classification of TCP/IP header fields. Finally, some of the characteristics of short- lived TCP transfers are summarized. The behavior analysis of TCP/IP header fields among multiple short- lived connections may be found in [TCP-BEH]. 3.1. Existing TCP/IP header compression schemes Compressed TCP (CTCP) and IP Header Compression (IPHC) are two different schemes that may be used to compress TCP/IP headers. Both schemes transmit only the differences from the previous header in order to reduce the large overhead of the TCP/IP header. The CTCP [RFC-1144] compressor detects transport-level retransmissions and sends a header that updates the context completely when they occur. While CTCP works well over reliable links, it is vulnerable when used over less reliable links as even a single packet loss results in loss of synchronization between the compressor and the decompressor. This in turn leads to the TCP receiver discarding all remaining packets in the current window because of a checksum error. This effectively prevents the TCP Fast Retransmit algorithm [RFC-2001] from being triggered. In such case, the compressor must wait until the TCP timeout to resynchronize. To reduce the errors due to the inconsistent contexts between compressor and decompressor when compressing TCP, IPHC [RFC-2507] improves somewhat on CTCP by augmenting the repair mechanism of CTCP with a local repair mechanism called TWICE and with a link-level nacking mechanism to request a header that updates the context. The TWICE algorithm assumes that only the Sequence Number field of TCP segments are changing with the deltas between consecutive packets being constant in most cases. This assumption is however not always true, especially when TCP Timestamps and SACK options are used. The full header request mechanism requires a feedback channel that may be unavailable in some circumstances. This channel is used to explicitly request that the next packet be sent with an uncompressed header to allow resynchronization without waiting for a TCP timeout. In addition, this mechanism does not perform well on links with long round-trip time. Both CTCP and IPHC are also limited in their handling of the TCP options field. For IPHC, any change in the options field (caused by Pelletier, et al. [Page 5] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 timestamps or SACK, for example) renders the entire field uncompressible, while for CTCP such a change in the options field effectively disables TCP/IP header compression altogether. Finally, existing TCP/IP compression schemes do not compress the headers of handshaking packets (SYNs and FINs). Compressing these packets may greatly improve the overall header compression ratio for the cases where many short-lived TCP connections share the same link. 3.2. Classification of TCP/IP header fields Header compression is possible due to the fact that there is much redundancy between header field values within packets, especially between consecutive packets. To utilize these properties for TCP/IP header compression, it is important to understand the change patterns of the various header fields. All fields of the TCP/IP packet header have been classified in detail in [TCP-BEH]. The main conclusion is that most of the header fields can easily be compressed away since they never or seldom change. The following fields do however require more sophisticated mechanisms: - IPv4 Identification (16 bits) - IP-ID - TCP Sequence Number (32 bits) - SN - TCP Acknowledgement Number (32 bits) - ACKN - TCP Reserved (4 bits) - TCP ECN flags (2 bits) - ECN - TCP Window (16 bits) - WINDOW - TCP Options - Maximum Segment Size (4 octets) - MSS - Window Scale (3 octets) - WSopt - SACK Permitted (2 octets) - TCP SACK - SACK - TCP Timestamp (32 bits) - TS The assignment of IP-ID values can be done in various ways, which are Sequential jump, Random, and Sequential, respectively. However, designers of IPv4 stacks for cellular terminals should use an assignment policy close to Sequential. In [RFC-3095], the IP-ID is generally inferred from the RTP Sequence Number. However, with regard to TCP compression, the analysis in [TCP-BEH] reveals that there is no obvious candidate to this purpose among the TCP fields. The change pattern of several TCP fields (Sequence Number, Acknowledgement Number, Window, etc.) are very hard to predict and differs entirely from the behavior of RTP fields discussed in [RFC- 3095]. Of particular importance to a TCP/IP header compression scheme is the understanding of the sequence and acknowledgement number [TCP- BEH]. Specifically, at any point on the path (i.e. wherever a compressor might be deployed), the sequence number can be anywhere within a range defined by the TCP window. Missing packets or Pelletier, et al. [Page 6] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 retransmissions can cause the TCP sequence number to fluctuate within the limits of this window. The jumps in acknowledgement number are also bounded by this TCP window. Another important behavior of the TCP/IP header is the dependency between the sequence number and the acknowledgment number. It is well-known that most TCP connections only have one-way traffic (web browsing and FTP downloading, for example). This means that on the forward path (from server to client), only the sequence number is changing while the acknowledgement number remains constant for most packets; on the backward path (from client to server), only the sequence number is changing and the acknowledgement number remains constant for most packets. With respect to TCP options, it is noted that most options (such as MSS, WSopt, SACK-permitted, etc.) may appear only on a SYN segment. Every implementation should (and we expect most will) ignore unknown options on SYN segments. Headers specific to Mobile IP (for IPv4 or IPv6) do not receive any special treatment in this document, for similar reasons as those described in [RFC-3095]. 3.3. Characteristics of short-lived TCP transfers Recent studies shows that the majority of TCP flows are short-lived transfers with an average and a median size no larger than 10KB. Short-lived TCP transfers will degrade the performance of header compression schemes that establish a new context by initially sending full headers. It is hard to improve the performance for a single, unpredictable, short-lived connection. However, there are common cases where there will be multiple TCP connections between the same pair of hosts. A mobile user browsing several web pages from the same web server (this is more the case with HTTP/1.0 than HTTP/1.1) is one example. In such case, multiple short-lived TCP/IP flows occur simultaneously or near simultaneously within a relatively short time interval. It may be expected that most (if not all) of the IP header of the these connections will be almost identical to each other, with only small relative jumps for the IP-ID field. Furthermore, a subset of the TCP fields may also be very similar from one connection to another. For example, one of the port numbers may be reused (the service port) while the other (the ephemeral port) may be changed only by a small amount relative to the just-closed connection. With regard to header compression, this means that parts of a compression context used for a TCP connection may be reusable for Pelletier, et al. [Page 7] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 another TCP connection. A mechanism supporting context replication, where a new context is initialized from an existing one, provide useful optimizations for a sequence of short-lived TCP connections. Context replication is possible due to the fact that there is much similarity in header field values and context values among multiple simultaneous or near simultaneous connections. All header fields and related context values have been classified in detail in [TCP-BEH]. The main conclusion is that most part of the IP sub-context, some TCP fields, and some context values can easily be replicated since they seldom change or change with only a small jump. 4. Overview of the TCP/IP profile 4.1. General concepts Many of the concepts behind the ROHC-TCP profile are similar to those described in [RFC-3095]. Like for other ROHC profiles, ROHC-TCP makes use of the ROHC protocol as described in [RFC-3095, sections 5.1 to 5.2.6]. This include data structures, reserved packet types, general packet formats, segmentation and initial decompressor processing. 4.2. Context replication For ROHC-TCP, context replication may be particularly useful for short-lived TCP flows [TCP-REQ]. ROHC-TCP therefore supports context replication as defined in [ROHC-CR]. 4.3. State machines and profile operation Header compression with ROHC can be characterized as an interaction between two state machines, one compressor machine and one decompressor machine, each instantiated once per context. For ROHC-TCP compression, the compressor has two states and the decompressor has three states. The two compressor states are the Initialization and Refresh (IR) state, and the Compression (CO) state. The three states of the decompressor are No Context (NC), Static Context (SC) and Full Context (FC). The compressor may also implement a third state, the Context Replication (CR) state, to support context replication [ROHC-CR]. Transitions need not be synchronized between the two state machines. 4.4. Packet formats and encoding methods The packet formats used for ROHC-TCP and found in this document are defined using the formal notation [ROHC-FN]. The formal notation is used to provide an unambiguous representation of the packet formats and a clear definition of the encoding methods. The encoding methods used in the packet formats for ROHC-TCP are defined in [ROHC-FN]. Pelletier, et al. [Page 8] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 5. Compressor and decompressor state machines The header compression state machines and their associated logic as specified in this section are a simplified version of the ones found in [RFC-3095]. 5.1. Compressor states and logic The two compressor states are the Initialization and Refresh (IR) state, and the Compression (CO) state. The compressor always start in the lower compression state (IR). The compressor will normally operate in the higher compression state (CO), under the constraint that the compressor is sufficiently confident that the decompressor has the information necessary to reconstruct a header compressed according to this state. The figure below shows the state machine for the compressor. The details of each state, state transitions, and compression logic are given in sub-sections following the figure. Optimistic approach / ACK ACK +------>------>------>------+ +->-+ | | | | | v | v +----------+ +----------+ | IR State | | CO State | +----------+ +----------+ ^ | | Timeout / NACK / STATIC-NACK | +-------<-------<-------<--------+ The transition from IR state to CO state is based on the following principles: the need for update and the optimistic approach principle or, if a feedback channel is established, feedback received from the decompressor. 5.1.1. Initialization and Refresh (IR) state The purpose of the IR state is to initialize the static parts of the context at the decompressor or to recover after failure. In this state, the compressor sends complete header information. This includes static and non-static fields in uncompressed form plus some additional information. The compressor stays in the IR state until it is fairly confident that the decompressor has received the static information correctly. 5.1.2. Compression (CO) state The purpose of the CO state is to efficiently communicate irregularities in the packet stream when needed while maintaining the Pelletier, et al. [Page 9] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 most optimal compression ratio. When operating in this state, the compressor normally sends most or all of the information in a compressed form. 5.1.3. Feedback logic The compressor state machine makes use of feedback from decompressor to compressor for transitions in the backward direction, and optionally to improve the forward transition. The reception of either positive feedback (ACKs) or negative feedback (NACKs) establishes the feedback channel from the decompressor. Once there is an established feedback channel, the compressor makes use of this feedback for optionally improving the transitions among different states. This helps increasing the compression efficiency by providing the information needed for the compressor to achieve the necessary confidence level. When the feedback channel is established, it becomes superfluous for the compressor to send periodic refreshes. 5.1.4. State transition logic Decisions about transitions between the IR and the CO states are taken by the compressor on the basis of: - variations in the packet headers - positive feedback from decompressor (Acknowledgements -- ACKs) - negative feedback from decompressor (Negative ACKS -- NACKs) - confidence level regarding error-free decompression of a packet 5.1.4.1. Optimistic approach, upward transition Transition to the CO state is carried out according to the optimistic approach principle. This means that the compressor transits to the CO state when it is fairly confident that the decompressor has received enough information to correctly decompress packets sent according to the higher compression state. In general, there are many approaches where the compressor can obtain such information. A simple and general approach can be achieved by sending uncompressed or partial full headers periodically. 5.1.4.2. Optional acknowledgements (ACKs), upward transition The compressor can also transit to the CO state based on feedback received by the decompressor. If a feedback channel is available, the decompressor MAY use positive feedback (ACKs) to acknowledge successful decompression of packets. Upon reception of an ACK for a context updating packet, the compressor knows that the decompressor has received the acknowledged packet and the transition to the CO state can be carried out immediately. Pelletier, et al. [Page 10] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 This functionality is optional, so a compressor MUST NOT expect to get such ACKs initially or during normal operation, even if a feedback channel is available or established. 5.1.4.3. Timeouts, downward transition When the optimistic approach is used (i.e. until a feedback channel is established), there will always be a possibility of failure since the decompressor may not have received sufficient information for correct decompression. Therefore, unless a feedback channel has been established by the decompressor, the compressor MUST periodically transit to the IR state. 5.1.4.4. Negative ACKs (NACKs), downward transition Negative acknowledgments (NACKs) are also called context requests. Upon reception of a NACK, the compressor transits back to the IR state and sends updates (such as IR-DYN or IR) to the decompressor. 5.1.4.5. Need for updates, downward transition When the header to be compressed does not conform to the established pattern or when the compressor is not confident whether the decompressor has the synchronized context, the compressor will transit to the IR state. 5.1.5. State machine supporting context replication For a profile supporting context replication, the additional compressor logic (including corresponding state transition and feedback logic) found in [ROHC-CR] must be added to the compressor state machine described above. The following figure shows the resulting state machine: Optimistic approach / ACK +--->------>------>------>------>------>------>---+ | | | BCID Selection Optimistic approach / ACK | ACK | +------>----->------+ +----->----->----->-----+ | +->-+ | | | | | | | | | | v | v v | v +---------+ +---------+ +---------+ | IR | | CR | | CO | | State | | State | | State | +---------+ +---------+ +---------+ ^ ^ | | | | NACK / STATIC-NACK | | | +---<-----<-----<----+ | | | | Timeout / NACK / STATIC-NACK | +-----<-------<-------<-------<-------<-------<----+ Pelletier, et al. [Page 11] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 5.2. Decompressor states and logic The three states of the decompressor are No Context (NC), Static Context (SC) and Full Context (FC). The decompressor starts in its lowest compression state, the NC state. Successful decompression will always move the decompressor to the FC state. The decompressor state machine normally never leaves the FC state once it has entered this state; only repeated decompression failures will force the decompressor to transit downwards to a lower state. Below is the state machine for the decompressor. Details of the transitions between states and decompression logic are given in the sub-sections following the figure. Success +-->------>------>------>------>------>--+ | | No Static | No Dynamic Success | Success +-->--+ | +-->--+ +--->----->---+ +-->--+ | | | | | | | | | | v | | v | v | v +-----------------+ +---------------------+ +-------------------+ | No Context (NC) | | Static Context (SC) | | Full Context (FC) | +-----------------+ +---------------------+ +-------------------+ ^ | ^ | | k_2 out of n_2 failures | | k_1 out of n_1 failures | +-----<------<------<-----+ +-----<------<------<-----+ 5.2.1. No Context (NC) state Initially, while working in the NC state, the decompressor has not yet successfully decompressed a packet. Upon receiving an IR or an IR-DYN packet, the decompressor will verify the correctness of this packet by validating its header using the CRC check. If the decompressed packet is successfully verified, the decompressor will update the context and use this packet as the reference packet. Once a packet has been decompressed correctly, the decompressor can transit to the FC state, and only upon repeated failures will it transit back to a lower state. 5.2.2. Static Context (SC) state In the SC state, the decompressor assumes static context damage when the CRC check of k_2 out of the last n_2 decompressed packets have failed. The decompressor moves to the NC state and discards all packets until a packet (e.g. IR or IR-DYN packet) that successfully passes the verification check is received. The decompressor may send feedback (see section 5.2.7.) when assuming static context damage. Pelletier, et al. [Page 12] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Note that appropriate values for k and n, are related to the residual error rate of the link. When the residual error rate is close to zero, k = n = 1 may be appropriate. 5.2.3. Full Context (FC) state In the FC state, the decompressor assumes context damage when the CRC check of k_1 out of the last n_1 decompressed packets have failed, (where k and n are related to the residual error rate of the link as in section 5.2.2.). The decompressor moves to the SC state and discards all packets until a packet carrying a 7- or 8-bit CRC that successfully passes the verification check is received. The decompressor may send feedback (see section 5.2.7.) when assuming context damage. Upon receiving an IR or an IR-DYN packet, the decompressor SHOULD verify the correctness of its header using CRC validation. If the verification succeeds, the decompressor will update the context and use this packet as the reference packet. Consequently, the decompressor will convert the packet into the original packet and pass it to the network layer of the system. Upon receiving other types of packet, the decompressor will decompress it. The decompressor MUST verify the correctness of the decompressed packet by CRC check. If this verification succeeds, the decompressor passes the decompressed packet to the system's network layer. The decompressor will then use this packet as the reference value, if it is not older than the current reference packet (based on sequence numbers in the compressed packet or in the uncompressed header). 5.2.4. Allowing decompression <# Editor's Note: #> <# Open issue : Should some of the CO packets, such as packets #> <# containing a large amount of context-updating #> <# information, use additional CRC protection #> <# (7- or 8-bit CRC) in their format? #> In the No Context state, only packets carrying sufficient information on the static fields (i.e. IR packets) can be decompressed. In the Static Context state, only packets carrying a 7- or 8-bit CRC may be decompressed (i.e. IR, IR-DYN and some CO packets). In the Full Context state, decompression may be attempted regardless of the type of packet received. If decompression may not be performed, the packet is discarded. As per [ROHC-CR], IR-CR packets may be decompressed in any state. Pelletier, et al. [Page 13] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 5.2.5. Reconstruction and verification <# Editor's Note: #> <# Should the definition of the CRC #> <# polynomials be included in the ROHC-FN #> <# library of encoding methods or in the #> <# profile definition? #> The CRC carried within compressed headers MUST be used to verify decompression. When the decompression is verified and successful, the decompressor updates the context with the information received in the current header; otherwise if the reconstructed header fails the CRC check, these updates MUST NOT be performed. 5.2.6. Actions upon CRC failure When a CRC check fails, the decompressor MUST discard the packet. The actions to be taken when a CRC verification fails following the decompression of an IR-CR packet are specified in [ROHC-CR]. For other packet types carrying a CRC, if feedback is used the logic specified in section 5.2.7 must be followed when a CRC verification fails. Note: Decompressor implementations may attempt corrective or repair measures prior to performing the above actions, and the result of any attempt MUST be verified using the CRC check. 5.2.7. Feedback logic The decompressor may send positive feedback (ACKs) to initially establish the feedback channel for a particular flow. Either positive feedback (ACKs) or negative feedback (NACKs) will establish this channel. The feedback channel will then be used by the decompressor to send error recovery requests and (optionally) acknowledgements of significant context updates. Once a feedback channel is established by the decompressor, the compressor will operate using an optimistic logic. In particular, this means that the compressor will rely on a specific decompressor feedback logic: - the decompressor will send negative acknowledgements in case when context damage is assumed or in other failure situations; - the decompressor is not strictly expected to send feedback upon successful decompression, other than for the purpose of improving the forward state transition. Once the feedback channel is established, the decompressor is REQUIRED to continue sending feedback for the lifetime of the packet stream as follow: Pelletier, et al. [Page 14] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 In NC state: The decompressor SHOULD send a STATIC-NACK if a packet of a type other than IR is received, or if an IR packet has failed the CRC check. In SC state: The decompressor SHOULD send a STATIC-NACK when decompression of an IR, an IR-DYN or a CO packet carrying a 7-bit CRC fails and if static context damage is assumed (see also section 5.2.2.). If any other packet type is received, the decompressor SHOULD treat it as a CRC mismatch when deciding if feedback is to be sent. In FC state: The decompressor SHOULD send a NACK when decompression of any packet type fails and if context damage is assumed (see also section 5.2.3.). When decompression fails, feedback should be sent only when decompression of several consecutive packets have failed, and when this occurs, the feedback rate should be limited. In addition, the decompressor should also limit the rate at which feedback is sent on successful decompression, if sent at all. The decompressor may limit the feedback rate by sending feedback for one out of a number of packets providing the same type of feedback. The decompressor MAY optionally send ACKs upon successful decompression of any packet type. In particular, when an IR, an IR- DYN or any CO packet carrying a 7- or 8-bit CRC is correctly decompressed, the compressor may optionally send an ACK. 6. ROHC-TCP - TCP/IP compression (Profile 0x0006) This section describes a ROHC profile for TCP/IP compression. The profile identifier for ROHC-TCP is 0x0006. 6.1. Feedback channel considerations The ROHC-TCP profile may be used in environments with or without feedback capabilities from decompressor to compressor. ROHC-TCP however assumes that if a ROHC feedback channel is available and is used at least once by the decompressor, this channel will be present during the entire compression operation. Otherwise, if the connection is broken and the channel disappears, header compression should be restarted. Pelletier, et al. [Page 15] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 To parallel [RFC-3095], this is similar to allowing only one mode transition per compressor: from the initial unidirectional mode to the bi-directional mode of operation, with the transition being triggered by the reception of the first packet containing feedback from the decompressor. This effectively means that ROHC-TCP does not explicitly define any operational modes. 6.2. Master Sequence Number (MSN) Feedback packets of types ACK and NACK carry information about sequence number or acknowledgement number from decompressor to compressor. Unfortunately, there is no guarantee that sequence number and acknowledgement number fields will be used by every IP protocol stack. In addition, the combined size of the sequence number field and the acknowledgement number field is rather large, and they can therefore not be carried efficiently within the feedback packet. To overcome this problem, ROHC-TCP introduces a control field called the Master Sequence Number (MSN) field. The MSN field is created at the compressor, rather than using one of the fields already present in the uncompressed header. It has the following two functions: 1. Differentiating between packets when sending feedback data. 2. Inferring the value of incrementing fields such as the IP-ID. The MSN field is present in every packets sent by the compressor. The MSN is LSB encoded within the CO packets, and the 16-bit MSN is sent in full in IR/IR-DYN packets. The decompressor always sends the MSN as part of the feedback information. The MSN can later be used by the compressor to infer which packet is being acknowledged by the decompressor. 6.3. Initialization The static context of ROHC TCP streams can be initialized in either two ways: 1) By using an IR packet as in section 5.4.1, where the profile is six (6) and the static chain ends with the static part of a TCP packet. At the compressor, the MSN is initialized to a value of zero when the initial IR packet is sent. 2) By replicating an existing context using the mechanism defined in [ROHC-CR]. This is done with an IR-CR packet as in section 5.4.3, where the profile number is six (6) and the static replication chain ends with the static part of a TCP packet. At the compressor, the MSN is then reinitialized to a value of zero when the initial IR-CR packet is sent. Pelletier, et al. [Page 16] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.4. Packet types ROHC-TCP defines two different packet types: the Initialization and Refresh (IR) packet type, and the Compressed packet type (CO). Each type correspond to one of the possible states of the compressor. Each packet type also define a number of packet formats: 30 packet formats are defined for compressed headers (CO), and two for initialization and refresh (IR). Finally, the profile-specific part of the IR-CR packet [ROHC-CR] is also defined in this section. 6.4.1. Initialization and Refresh packets (IR) The ROHC-TCP IR packet follows the general format of the ROHC IR packet, as defined in [RFC-3095, section 5.2.3]. Packet type: IR This packet type communicates the static part and the dynamic part of the context. The ROHC-TCP IR packet has the following format: 0 1 2 3 4 5 6 7 --- --- --- --- --- --- --- --- : Add-CID octet : if for small CIDs and (CID != 0) +---+---+---+---+---+---+---+---+ | 1 1 1 1 1 1 0 0 | IR type octet +---+---+---+---+---+---+---+---+ : : / 0-2 octets of CID / 1-2 octets if for large CIDs : : +---+---+---+---+---+---+---+---+ | Profile | 1 octet +---+---+---+---+---+---+---+---+ | CRC | 1 octet +---+---+---+---+---+---+---+---+ | | / profile_specific_part / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - CRC: 8-bit CRC, computed according to [RFC-3095, section 5.9.1.]. Pelletier, et al. [Page 17] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 profile_specific_part: The format of this field is defined using the formal notation in section 6.5.4. Payload: The payload of the corresponding original packet, if any. The presence of a payload is inferred from the packet length. Packet type: IR-DYN This packet type communicates the dynamic part of the context. The ROHC-TCP IR-DYN packet has the following format: 0 1 2 3 4 5 6 7 --- --- --- --- --- --- --- --- : Add-CID octet : if for small CIDs and (CID != 0) +---+---+---+---+---+---+---+---+ | 1 1 1 1 1 0 0 0 | IR-DYN type octet +---+---+---+---+---+---+---+---+ : : / 0-2 octets of CID / 1-2 octets if for large CIDs : : +---+---+---+---+---+---+---+---+ | Profile | 1 octet +---+---+---+---+---+---+---+---+ | CRC | 1 octet +---+---+---+---+---+---+---+---+ | | / profile_specific_part / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - CRC: 8-bit CRC, computed according to [RFC-3095, section 5.9.1.]. profile_specific_part: The format of this field is defined using the formal notation in section 6.5.4. Payload: The payload of the corresponding original packet, if any. The presence of a payload is inferred from the packet length. 6.4.2. Context Replication packets (IR-CR) ROHC-TCP supports the context replication mechanism defined in [ROHC- CR]. Context replication requires a dedicated IR packet format that uniquely identifies the IR-CR packet for this profile. Pelletier, et al. [Page 18] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Packet type: IR-CR This packet type communicates a reference to a base context along with the static and dynamic parts of the replicated context that differs from the base context. The ROHC-TCP IR-CR packet follows the general format of the ROHC CR packet, as defined in [ROHC-CR, section 3.4.2.]. With consideration to the extensibility of the IR packet type defined in [RFC-3095], the ROHC-TCP profile supports context replication through the profile specific part of the IR packet. This is achieved using the bit (x) left in the IR packet header for "Profile specific information". For ROHC-TCP, this bit is defined as a flag indicating whether this packet is an IR packet or an IR-CR packet. For the ROHC-TCP IR-CR packet, the value of the x bit must be set to one. The ROHC-TCP IR-CR has the following format: 0 1 2 3 4 5 6 7 --- --- --- --- --- --- --- --- : Add-CID octet : if for small CIDs and (CID != 0) +---+---+---+---+---+---+---+---+ | 1 1 1 1 1 1 0 1 | IR-CR type octet +---+---+---+---+---+---+---+---+ : : / 0-2 octets of CID / 1-2 octets if for large CIDs : : +---+---+---+---+---+---+---+---+ | Profile | 1 octet +---+---+---+---+---+---+---+---+ | CRC | 1 octet +---+---+---+---+---+---+---+---+ | B | CRC7 | 1 octet +---+---+---+---+---+---+---+---+ | | present if B = 1, / Base CID / 1 octet if for small CIDs, or | | 1-2 octets if for large CIDs +---+---+---+---+---+---+---+---+ | | | replicate_common / variable length | | +---+---+---+---+---+---+---+---+ | | / replicate_formats / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - Pelletier, et al. [Page 19] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 B: B = 1 indicates that the Base CID field is present. CRC7: The CRC over the original, uncompressed, header. This 7-bit CRC is computed according to [ROHC-CR, section 3.4.1.1]. replicate_common: Static and dynamic subheader information used for replication common to all IR-CR packet types. The format of this field is defined using the formal notation in section 6.5.4.2. replicate_formats: Static and dynamic subheader information used for replication. What information is present is inferred from the discriminator of the IR-CR. The format of this field is defined using the formal notation in section 6.5.4.2. Payload: The payload of the corresponding original packet, if any. The presence of a payload is inferred from the packet length. 6.4.3. Compressed packets (CO) The ROHC-TCP CO packets communicates irregularities in the packet header. All CO packets carry a CRC and can update the context. 6.5. Packet formats <# #> <# Editor's Note: Formatting should be improved. #> <# Some explanatory text improving clarity should #> <# be added throughout this section. #> <# #> <# #> <# Open issue : Should the fields in the packet formats follow #> <# the order of their corresponding fields in the #> <# uncompressed format, or should they be aligned? #> <# #> This section describes the set of compressed TCP/IP packet formats. The normative description of the packet formats is given using the Formal Notation for Robust Header Compression [ROHC-FN]. The ROHC-FN description of the packet formats specifies all of the information needed to compress and decompress a header relative to the context. In particular, it provides a list of all the fields present in the uncompressed and compressed TCP/IP headers, and defines how to map from each uncompressed packet to its compressed equivalent and vice versa. See [ROHC-FN] for an explanation of the Formal Notation itself, and the encoding methods used to compress each of the fields in the TCP/IP header. Pelletier, et al. [Page 20] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 The following constants are defined to improve readability of the packet formats in this section: sequential_ip_id ::= constant(0), random_ip_id ::= constant(1), zero_ip_id ::= constant(0), nonzero_ip_id ::= constant(1), tcp_ecn_used ::= constant(0), tcp_ecn_unused ::= constant(1), 6.5.1. Uncompressed TCP/IP packet The uncompressed format of the TCP/IP header specified using the formal notation is as follow: tcp_ip ::= multiple_packet_formats, uncompressed_format ::= ip_version, % 4 bits ip_header_length, % 4 bits ip_tos, % 6 bits ip_ecn, % 2 bits ip_length, % 16 bits ip_id, % 16 bits ip_reserved, % 1 bit ip_dont_frag, % 1 bit ip_more_fragments, % 1 bit ip_offset, % 13 bits ip_ttl, % 8 bits ip_protocol, % 8 bits ip_checksum, % 16 bits ip_src_addr, % 32 bits ip_dest_addr, % 32 bits tcp_src_port, % 16 bits tcp_dest_port, % 16 bits tcp_seq_number, % 32 bits tcp_ack_number, % 32 bits tcp_data_offset, % 4 bits tcp_reserved, % 4 bits tcp_flags_ecn, % 2 bits tcp_flags_urg, % 1 bit tcp_flags_ack, % 1 bit tcp_flags_psh, % 1 bit tcp_flags_rsf, % 3 bits tcp_window, % 16 bits tcp_checksum, % 16 bits tcp_urg_point, % 16 bits tcp_options, % data_offset * 32 % - 160 bits <# Editor's Note: Explanatory text regarding tcp options should #> <# be added #> Pelletier, et al. [Page 21] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.5.2. Default encoding methods The following notation defines a set of default encoding methods for fields in the TCP/IP header. If a particular CO packet format does not specify how to encode a field, then it is assumed to use the default encoding method. default_methods ::= ... , { ip_version ::= value(4, 4), ip_header_length ::= value(4, 5), ip_tos ::= static, ip_ecn ::= derived_value, { field_length ::= constant(2), field_value ::= expression((uncomp(tcp_ip.tcp_ecn_and_reserved) // 16) mod 4) }, ip_length ::= inferred_size(16, 0), ip_id ::= multiple_packet_formats, { uncompressed_format ::= ip_id, % 16 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 0 bit ip_id, % 16 bits { discriminator ::= '', discriminator.format ::= same_as(nonzero_ip_id), ip_id ::= irregular(16) }, co_format_1 ::= discriminator, % 0 bit ip_id, % 0 bit { discriminator ::= '', discriminator.format ::= same_as(zero_ip_id), ip_id ::= value(16, 0) } }, ip_reserved ::= static, ip_dont_frag ::= static, ip_more_fragments ::= value(1, 0), ip_offset ::= value(13, 0), ip_ttl ::= static, ip_protocol ::= value(8, 6), ip_checksum ::= inferred_ip_checksum, ip_src_addr ::= static, ip_dest_addr ::= static, Pelletier, et al. [Page 22] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_src_port ::= static, tcp_dest_port ::= static, tcp_seq_number ::= derived_value, { field_length ::= constant(32), field_value ::= expression(uncomp(tcp_seq_number_scaled) * uncomp(tcp_payload_size) + uncomp(tcp_seq_number_residue)) }, tcp_ack_number ::= static, tcp_data_offset ::= derived_value, { field_length ::= constant(4), field_value ::= expression((uncomp(tcp_ip.tcp_options.list_length) + 160) // 32) }, tcp_reserved ::= derived_value, { field_length ::= constant(4), field_value ::= expression(uncomp(tcp_ip.tcp_ecn_and_reserved) mod 16) }, tcp_flags_ecn ::= derived_value, { field_length ::= constant(2), field_value ::= expression(uncomp(tcp_ip.tcp_ecn_and_reserved) // 64) }, tcp_flags_urg ::= value(1, 0), tcp_window ::= static, tcp_urg_point ::= static, tcp_ecn_and_reserved ::= control_field, { base_field ::= group, { field_list ::= tcp_ip.tcp_flags_ecn, tcp_ip.ip_ecn, tcp_ip.tcp_reserved }, compressed_method ::= multiple_packet_formats, { uncompressed_format ::= tcp_ecn_and_reserved, % 8 bits co_num_formats ::= constant(2), Pelletier, et al. [Page 23] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 co_format_0 ::= discriminator, % 0 bit tcp_ecn_and_reserved, % 0 bit { discriminator ::= '', discriminator.format ::= same_as(tcp_ecn_unused), tcp_ecn_and_reserved ::= value(8, 0) }, co_format_1 ::= discriminator, % 0 bit tcp_ecn_and_reserved, % 8 bits { discriminator ::= '', discriminator.format ::= same_as(tcp_ecn_used), tcp_ecn_and_reserved ::= irregular(8) } } }, tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= static }, tcp_seq_number_residue ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) mod uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= static }, order_flag ::= control_field, { base_field ::= same_as(tcp_ip.tcp_options.order_flag), compressed_method ::= value(1, 0) }, presence_flag ::= control_field, { base_field ::= same_as(tcp_ip.tcp_options.presence_flag), compressed_method ::= value(1, 0) }, Pelletier, et al. [Page 24] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.5.3. Compressed TCP Options using list encoding The following notation defines how to compress the TCP options: tcp_options ::= list_of_known_length, { list_length ::= expression(uncomp(tcp_ip.tcp_data_offset) * 32 - 160), list_items ::= mss, wsopt, sack, timestamp, nop, eol, sack, generic, order_flag ::= from_list(tcp_ip.order_flag), presence_flag ::= from_list(tcp_ip.presence_flag), mss ::= single_packet_format, { uncompressed_data ::= kind, % 8 bits length, % 8 bits mss, % 16 bits compressed_data ::= mss, % 16 bits kind ::= value(8, 2), length ::= value(8, 4), mss ::= irregular(16) }, wsopt ::= single_packet_format, { uncompressed_data ::= kind, % 8 bits length, % 8 bits scale, % 8 bits compressed_data ::= wscale, % 8 bits kind ::= value(8, 3), length ::= value(8, 3), wscale ::= irregular(8) }, eol ::= value(8, 0), nop ::= value(8, 1), Pelletier, et al. [Page 25] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 sack ::= single_packet_format, { uncompressed_data ::= kind, % 8 bits length, % 8 bits sack_blocks, % list_length bits compressed_data ::= sack_blocks, kind ::= value(8, 5), length ::= static, sack_blocks ::= list_of_known_length, { list_length ::= expression(uncomp(length) * 8 - 16), list_items ::= sack_block, sack_block, sack_block, sack_block, sack_block ::= multiple_packet_formats, { uncompressed_data ::= block_start, % 32 bits block_end, % 32 bits co_format_count ::= constant(3), co_format_0 ::= discriminator, % 2 bits block_start, % 32 bits block_end.offset, % 14 bits { discriminator ::= '00', block_start ::= irregular(32), block_end ::= inferred_offset(32), { base_field ::= same_as(block_start), offset ::= irregular(14) } }, co_format_1 ::= discriminator, % 2 bits block_start, % 32 bits block_end.offset, % 22 bits { discriminator ::= '01', block_start ::= irregular(32), block_end ::= inferred_offset(32), { base_field ::= same_as(block_start), offset ::= irregular(22) } Pelletier, et al. [Page 26] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 }, co_format_2 ::= discriminator, % 2 bits block_start, % 32 bits block_end.offset, % 30 bits { discriminator ::= '10', block_start ::= irregular(32), block_end ::= inferred_offset(32), { base_field ::= same_as(block_start), offset ::= irregular(30) } } } } }, timestamp ::= multiple_packet_formats, { co_num_formats ::= constant(5), uncompressed_format ::= kind, % 8 bits length, % 8 bits value, % 32 bits echo_reply, % 32 bits co_format_0 ::= discriminator, % 4 bits value, % 14 bits echo_reply, % 14 bits { discriminator ::= '0000', kind ::= value(8, 8), length ::= value(8, 10), value ::= lsb(14, 0), echo_reply ::= lsb(14, 0) }, co_format_1 ::= discriminator, % 4 bits value, % 14 bits echo_reply, % 22 bits { discriminator ::= '0001', kind ::= value(8, 8), length ::= value(8, 10), value ::= lsb(14, 0), echo_reply ::= lsb(22, 0) }, co_format_2 ::= discriminator, % 4 bits Pelletier, et al. [Page 27] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 value, % 22 bits echo_reply, % 14 bits { discriminator ::= '0010', kind ::= value(8, 8), length ::= value(8, 10), value ::= lsb(22, 0), echo_reply ::= lsb(14, 0) }, co_format_3 ::= discriminator, % 4 bits value, % 22 bits echo_reply, % 22 bits { discriminator ::= '0011', kind ::= value(8, 8), length ::= value(8, 10), value ::= lsb(22, 0), echo_reply ::= lsb(22, 0) }, co_format_4 ::= discriminator, % 8 bits value, % 32 bits echo_reply, % 32 bits { discriminator ::= '10000000', kind ::= value(8, 8), length ::= value(8, 10), value ::= irregular(32), echo_reply ::= irregular(32) } }, generic ::= single_packet_format, { uncompressed_data ::= kind, % 8 bits length, % 8 bits data_item, % data_size bits compressed_data ::= data_item, kind ::= static, length ::= static, data_item ::= uncompressible(tcp_ip.tcp_options.generic.length, 8, 1, -16) } } } }. Pelletier, et al. [Page 28] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.5.4. Packet type IR and IR-DYN <# Editor's Note: Is the coverage part of the definition of the #> <# CRC encoding method in the formal notation? #> <# Editor's Note: This section attempts to make a binding #> <# between the packet format using the formal #> <# notation and the notation in rfc-3095. #> ROHC-TCP uses the basic structure of the ROHC IR and IR-DYN packets as defined in [RFC-3095, section 5.2.3. and 5.2.4. respectively]. The 8-bit CRC is computed according to [RFC-3095, section 5.9.1.]. For the ROHC-TCP IR packet, the value of the x bit must be set to zero. The profile-specific information of the IR packet consists of the static chain, the dynamic chain and TCP options, as follow: profile_specific_part ::= ir_static_part, ir_dynamic_part, tcp_ip:options. For the ROHC-TCP IR-DYN packet, the profile-specific information of the IR-DYN packet consists of the dynamic chain and TCP options only, as follow: profile_specific_part ::= ir_dynamic_part, tcp_ip:options . The static and dynamic parts have the following format: ir_static_part ::= ip_src_addr, % 32 bits ip_dest_addr, % 32 bits tcp_src_port, % 16 bits tcp_dest_port, % 16 bits { ip_src_addr ::= irregular(32), ip_dest_addr ::= irregular(32), tcp_src_port ::= irregular(16), tcp_dest_port ::= irregular(16) }, ir_dynamic_part ::= discriminator, % 2 bits format, % 1 bit ip_id.discriminator, % 1 bit tcp_ecn_and_reserved.discriminator, % 1 bit order_flag, % 1 bit presence_flag, % 1 bit ip_reserved, % 1 bit msn, % 16 bits ip_tos, % 6 bits ip_dont_frag, % 1 bit Pelletier, et al. [Page 29] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_flags_ack, % 1 bit ip_ttl, % 8 bits tcp_seq_number, % 32 bits tcp_ack_number % 32 bits tcp_window, % 16 bits tcp_checksum, % 16 bits tcp_urg_point, % 16 bits tcp_data_offset, % 4 bits tcp_flags_psh, % 1 bit tcp_flags_rsf, % 3 bits ip_id, % 0 or 16 bits tcp_ecn_and_reserved,% 0 or 8 bits tcp_options,% variable no. of bits { discriminator ::= '00', { num_formats ::= constant(2) }, discriminator.format ::= irregular(1), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= irregular(16) }, ip_tos ::= irregular(6), ip_id ::= multiple_packet_formats, { uncompressed_format ::= ip_id, % 16 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_id, % 16 bits { discriminator ::= '0', discriminator.format ::= value(1, 0), % non-zero IP ID ip_id ::= irregular(16) }, co_format_1 ::= discriminator, % 1 bit ip_id, % 0 bit { discriminator ::= '1', discriminator.format ::= value(1, 1), % zero IP ID ip_id ::= value(16, 0) } } ip_reserved ::= irregular(1), ip_dont_frag ::= irregular(1), ip_ttl ::= irregular(8), tcp_seq_number ::= irregular(32), tcp_ack_number ::= irregular(32), tcp_data_offset ::= irregular(4), tcp_flags_ack ::= irregular(1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= irregular(3), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16), tcp_urg_point ::= irregular(16), tcp_ecn_and_reserved ::= control_field, { base_field ::= group, { field_list ::= tcp_ip.tcp_flags_ecn, tcp_ip.ip_ecn, Pelletier, et al. [Page 30] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_ip.tcp_reserved }, compressed_method ::= multiple_packet_formats, { uncompressed_format ::= tcp_ecn_and_reserved, % 8 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit tcp_ecn_and_reserved, % 0 bit { discriminator ::= '0', discriminator.format ::= value(1, 0), % ECN/reserved % unused tcp_ecn_and_reserved ::= value(8, 0) }, co_format_1 ::= discriminator, % 1 bit tcp_ecn_and_reserved,% 8 bits { discriminator ::= '1', discriminator.format ::= value(1, 1), % ECN/reserved % used tcp_ecn_and_reserved ::= irregular(8) } } }, order_flag ::= control_field, { base_field ::= same_as(tcp_ip.default_methods.tcp_options.order_flag), compressed_method ::= irregular(1) }, presence_flag ::= control_field, { base_field ::= same_as(tcp_ip.default_methods.tcp_options.presence_flag), compressed_method ::= irregular(1) } }, 6.5.5. Compressed TCP/IP packets 6.5.5.1. Packet type IR-CR The profile-specific information of the IR-CR packet consists of a replicated part common to all IR-CR formats along with fields specific to the particular format, as follow: profile_specific_part ::= multiple_replicate_formats, tcp_ip:options. Pelletier, et al. [Page 31] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 The following notation describes the IR-REPLICATE packet. Note that options are as per IR/IR-DYNAMIC packets. replicate_format_0 ::= discriminator, % 4 bits format, % 1 bit ip_id.discriminator, % 1 bit ip_src_addr.discriminator, % 1 bit ip_dst_addr.discriminator, % 1 bit ip_tos.discriminator, % 1 bit ip_ttl.discriminator, % 1 bit tcp_src_port.discriminator, % 2 bits tcp_dst_port.discriminator, % 2 bits tcp_ack_number.discriminator, % 1 bit tcp_ecn_and_reserved.discriminator,% 1 bit order_flag, % 1 bit presence_flag, % 1 bit ip_dont_frag, % 1 bit tcp_flags_urg, % 1 bit tcp_flags_ack, % 1 bit tcp_flags_psh, % 1 bit tcp_flags_rsf, % 2 bits header_crc, % 8 bits msn, % 16 bits tcp_seq_number, % 32 bits ip_src_addr, % 0 or 32 bits ip_dst_addr, % 0 or 32 bits ip_id, % 0 or 16 bits tcp_src_port, % 0, 8 or 16 bits tcp_dst_port, % 0, 8 or 16 bits tcp_ack_number, % 0 or 32 bits tcp_ecn_and_reserved, % 0 or 8 bits tcp_options, % variable no. of bits { discriminator ::= '0000', discriminator.format ::= irregular(1), ip_dont_frag ::= irregular(1), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= irregular(16) }, ip_id ::= multiple_packet_formats, { uncompressed_format ::= ip_id, % 16 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_id, % 16 bits { discriminator ::= '0', discriminator.format ::= value(1, 0), % non-zero IP ID theoretically replicable, but only saves 1 bit Pelletier, et al. [Page 32] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 ip_id ::= irregular(16) }, co_format_1 ::= discriminator, % 1 bit ip_id, % 0 bit { discriminator ::= '1', discriminator.format ::= value(1, 1), % zero IP ID theoretically replicable, but only saves 1 bit ip_id ::= value(16, 0) } }, header_crc ::= crc(8), ip_src_addr ::= multiple_packet_formats, { uncompressed_format ::= ip_src_addr, % 32 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_src_addr, % 0 bit { discriminator ::= '0', ip_src_addr ::= static }, co_format_1 ::= discriminator, % 1 bit ip_src_addr, % 32 bits { discriminator ::= '1', ip_src_addr ::= irregular(32) } }, ip_dst_addr ::= multiple_packet_formats, { uncompressed_format ::= ip_dst_addr, % 32 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_dst_addr, % 0 bit { discriminator ::= '0', ip_dst_addr ::= static }, co_format_1 ::= discriminator, % 1 bit ip_dst_addr, % 32 bits { discriminator ::= '1', ip_dst_addr ::= irregular(32) } }, ip_tos ::= multiple_packet_formats, { uncompressed_format ::= ip_tos, % 8 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_tos, % 0 bit { discriminator ::= '0', Pelletier, et al. [Page 33] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 ip_tos ::= static }, co_format_1 ::= discriminator, % 1 bit ip_tos, % 8 bits { discriminator ::= '1', ip_tos ::= irregular(8) } }, ip_ttl ::= multiple_packet_formats, { uncompressed_format ::= ip_ttl, % 8 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit ip_ttl, % 0 bit { discriminator ::= '0', ip_ttl ::= static }, co_format_1 ::= discriminator, % 1 bit ip_ttl, % 8 bits { discriminator ::= '1', ip_ttl ::= irregular(8) } }, tcp_flags_urg ::= irregular(1) tcp_flags_ack ::= irregular(1) tcp_flags_psh ::= irregular(1) tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_ecn_and_reserved ::= control_field, { base_field ::= group, { field_list ::= tcp_ip.tcp_flags_ecn, tcp_ip.ip_ecn, tcp_ip.tcp_reserved }, compressed_method ::= multiple_packet_formats, { uncompressed_format ::= tcp_ecn_and_reserved,% 8 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bits tcp_ecn_and_reserved,% 0 bit { discriminator ::= '0', discriminator.format ::= value (1, 0), tcp_ecn_and_reserved ::= value(8, 0) Pelletier, et al. [Page 34] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 }, co_format_1 ::= discriminator, % 1 bit tcp_ecn_and_reserved,% 8 bits { discriminator ::= '1', discriminator.format ::= value (1, 1), tcp_ecn_and_reserved ::= irregular(8) } } }, tcp_src_port ::= multiple_packet_formats, { uncompressed_format ::= tcp_src_port, % 32 bits co_num_formats ::= constant(3), co_format_0 ::= discriminator, % 2 bits tcp_src_port, % 0 bit { discriminator ::= '00', tcp_src_port ::= static }, co_format_1 ::= discriminator, % 2 bits tcp_src_port, % 8 bits { discriminator ::= '01', tcp_src_port ::= lsb(8,64) }, co_format_1 ::= discriminator, % 2 bits tcp_src_port, % 16 bits { discriminator ::= '10', tcp_src_port ::= irregular(16) }, }, tcp_dst_port ::= multiple_packet_formats, { uncompressed_format ::= tcp_dst_port, % 32 bits co_num_formats ::= constant(3), co_format_0 ::= discriminator, % 2 bits tcp_dst_port, % 0 bit { discriminator ::= '00', tcp_dst_port ::= static }, co_format_1 ::= discriminator, % 2 bits tcp_dst_port, % 8 bits { discriminator ::= '01', tcp_dst_port ::= lsb(8,64) }, co_format_1 ::= discriminator, % 2 bits tcp_dst_port, % 16 bits { discriminator ::= '10', tcp_dst_port ::= irregular(16) }, }, Pelletier, et al. [Page 35] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_seq_number ::= irregular(32), tcp_ack_number ::= multiple_packet_formats, { uncompressed_format ::= tcp_ack_number % 32 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit tcp_ack_number, % 0 bit { discriminator ::= '0', tcp_ack_number ::= value(32,0) }, co_format_1 ::= discriminator, % 1 bit tcp_ack_number, % 32 bits { discriminator ::= '1', tcp_ack_number ::= irregular(32) } }, tcp_window ::= multiple_packet_formats, { uncompressed_format ::= tcp_window, % 16 bits co_num_formats ::= constant(2), co_format_0 ::= discriminator, % 1 bit tcp_window, % 0 bit { discriminator ::= '0', tcp_window ::= static }, co_format_1 ::= discriminator, % 1 bit tcp_window, % 16 bits { discriminator ::= '1', tcp_window ::= irregular(16) } }, tcp_urg_point ::= value(16, 0) order_flag ::= control_field, { base_field ::= same_as(tcp_ip.default_methods.tcp_options.order_flag), compressed_method ::= irregular(1) }, presence_flag ::= control_field, { base_field ::= same_as(tcp_ip.default_methods.tcp_options.presence_flag), compressed_method ::= irregular(1) } } Pelletier, et al. [Page 36] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 6.5.5.2. Packet type CO The ROHC-TCP compressed header has the following format: % The following notation describes all of the 31 compressed (CO) packet formats % for the basic TCP/IP header (excluding TCP options, which are handled separately). % Open issue: Is this a sensible number of packet formats? co_num_formats ::= constant(31), co_format_0 ::= discriminator, % 3 bits msn, % 1 bit tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_checksum, % 16 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '100', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_1 ::= discriminator, % 8 bits tcp_checksum, % 16 bits msn, % 1 bit tcp_seq_number_scaled, % 7 bits tcp_seq_number_residue, % 0 bit tcp_flags_psh, % 1 bit ip_id, % 2 bits tcp_ack_number, % 2 bits header_crc, % 3 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '11001100', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), Pelletier, et al. [Page 37] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(2, 1) }, tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(7, 63) } }, co_format_2 ::= discriminator, % 2 bits tcp_ack_number, % 14 bits tcp_checksum, % 16 bits msn, % 1 bit tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_seq_number_scaled, % 3 bits tcp_seq_number_residue, % 0 bit tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '01', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(3, 3) } }, co_format_3 ::= discriminator, % 6 bits msn, % 2 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit tcp_ack_number, % 2 bits header_crc, % 3 bits ip_id, % 3 bits Pelletier, et al. [Page 38] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 4 bits tcp_seq_number_residue, % 0 bit tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '110000', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(3, 3) }, tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(4, 3) } }, co_format_4 ::= discriminator, % 3 bits msn, % 1 bit tcp_seq_number, % 12 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_ack_number, % 12 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '101', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_seq_number ::= lsb(12, 1023), tcp_ack_number ::= lsb(12, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) Pelletier, et al. [Page 39] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 }, co_format_5 ::= discriminator, % 8 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit msn, % 2 bits tcp_seq_number, % 13 bits tcp_ack_number, % 2 bits header_crc, % 3 bits ip_id, % 3 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '11001111', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(3, 3) }, tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 1), tcp_checksum ::= irregular(16) }, co_format_6 ::= discriminator, % 8 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit msn, % 2 bits tcp_seq_number, % 13 bits tcp_ack_number, % 2 bits header_crc, % 3 bits ip_id, % 3 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '11001001', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(3, 3) }, Pelletier, et al. [Page 40] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_7 ::= discriminator, % 4 bits tcp_seq_number_scaled, % 4 bits tcp_seq_number_residue, % 0 bit tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 7 bits msn, % 2 bits tcp_ack_number, % 14 bits ip_id, % 3 bits tcp_window, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '1101', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(3, 3) }, tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_window ::= lsb(13, 2047), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(4, 3) } }, co_format_8 ::= discriminator, % 2 bits msn, % 1 bit tcp_window, % 13 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 7 bits Pelletier, et al. [Page 41] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_seq_number, % 12 bits tcp_ack_number, % 12 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '00', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), tcp_seq_number ::= lsb(12, 1023), tcp_ack_number ::= lsb(12, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_window ::= lsb(13, 2047), tcp_checksum ::= irregular(16) }, co_format_9 ::= discriminator, % 9 bits msn, % 1 bit tcp_flags_psh, % 1 bit tcp_seq_number, % 2 bits header_crc, % 3 bits tcp_ack_number, % 32 bits tcp_checksum, % 16 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '110010001', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_seq_number ::= lsb(2, 0), tcp_ack_number ::= irregular(32), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_10 ::= discriminator, % 8 bits ip_id, % 16 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit msn, % 2 bits tcp_seq_number, % 13 bits tcp_ack_number, % 2 bits Pelletier, et al. [Page 42] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 header_crc, % 3 bits tcp_flags_rsf, % 3 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '11001110', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= irregular(16) }, tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_checksum ::= irregular(16) }, co_format_11 ::= discriminator, % 7 bits tcp_flags_psh, % 1 bit tcp_window, % 16 bits tcp_checksum, % 16 bits msn, % 2 bits tcp_ack_number, % 14 bits ip_id, % 3 bits tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 3 bits tcp_seq_number_residue, % 0 bit header_crc, % 7 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '1100101', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= lsb(3, 3) }, tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), Pelletier, et al. [Page 43] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(3, 3) } }, co_format_12 ::= discriminator, % 6 bits tcp_ack_number, % 2 bits ip_id, % 16 bits ip_ttl, % 8 bits tcp_checksum, % 16 bits msn, % 1 bit header_crc, % 7 bits tcp_flags_psh, % 1 bit tcp_flags_rsf, % 3 bits tcp_seq_number, % 12 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '110001', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= irregular(16) }, ip_ttl ::= irregular(8), tcp_seq_number ::= lsb(12, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_checksum ::= irregular(16) }, co_format_13 ::= discriminator, % 9 bits header_crc, % 7 bits ip_id, % 16 bits ip_ttl, % 8 bits tcp_window, % 16 bits tcp_checksum, % 16 bits ip_dont_frag, % 1 bit tcp_flags_psh, % 1 bit ip_tos, % 6 bits msn, % 2 bits Pelletier, et al. [Page 44] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_ack_number, % 14 bits tcp_flags_rsf, % 3 bits tcp_seq_number, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '110010000', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_tos ::= irregular(6), ip_id ::= inferred_offset(16), { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= irregular(16) }, ip_dont_frag ::= irregular(1), ip_ttl ::= irregular(8), tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16) }, co_format_14 ::= discriminator, % 8 bits ip_id, % 16 bits ip_ttl, % 8 bits tcp_ack_number, % 32 bits tcp_window, % 16 bits tcp_checksum, % 16 bits msn, % 1 bit header_crc, % 7 bits tcp_flags_ack, % 1 bit tcp_flags_psh, % 1 bit tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 3 bits tcp_seq_number_residue, % 0 bit tcp_ecn_and_reserved, % 0 or 8 bits { discriminator ::= '11001101', discriminator.format ::= same_as(sequential_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), ip_id ::= inferred_offset(16), Pelletier, et al. [Page 45] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 { base_field ::= expression(uncomp(tcp_ip.msn)), compressed_method ::= irregular(16) }, ip_ttl ::= irregular(8), tcp_ack_number ::= irregular(32), tcp_flags_ack ::= irregular(1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(3, 3) } }, co_format_15 ::= discriminator, % 3 bits msn, % 1 bit tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_checksum, % 16 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '100', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_16 ::= discriminator, % 3 bits msn, % 1 bit tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_checksum, % 16 bits tcp_ack_number, % 2 bits tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 3 bits tcp_seq_number_residue, % 0 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits Pelletier, et al. [Page 46] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 { discriminator ::= '101', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(3, 3) } }, co_format_17 ::= discriminator, % 6 bits msn, % 2 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit tcp_ack_number, % 2 bits header_crc, % 3 bits tcp_seq_number_scaled, % 10 bits tcp_seq_number_residue, % 0 bit tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '110101', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(10, 255) } }, Pelletier, et al. [Page 47] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 co_format_18 ::= discriminator, % 2 bits msn, % 1 bit tcp_flags_psh, % 1 bit tcp_seq_number, % 12 bits tcp_checksum, % 16 bits tcp_ack_number, % 2 bits header_crc, % 3 bits tcp_flags_rsf, % 3 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '01', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_seq_number ::= lsb(12, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_checksum ::= irregular(16) }, co_format_19 ::= discriminator, % 6 bits msn, % 1 bit tcp_flags_psh, % 1 bit tcp_checksum, % 16 bits header_crc, % 3 bits tcp_seq_number, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '110100', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_seq_number ::= lsb(13, 1023), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_20 ::= discriminator, % 7 bits msn, % 1 bit Pelletier, et al. [Page 48] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 3 bits tcp_ack_number, % 12 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '1100010', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_ack_number ::= lsb(12, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_21 ::= discriminator, % 6 bits msn, % 1 bit tcp_flags_psh, % 1 bit tcp_checksum, % 16 bits header_crc, % 3 bits tcp_seq_number_scaled, % 7 bits tcp_seq_number_residue, % 0 bit tcp_ack_number, % 14 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '110111', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(3), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(7, 63) } }, Pelletier, et al. [Page 49] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 co_format_22 ::= discriminator, % 7 bits tcp_flags_psh, % 1 bit tcp_checksum, % 16 bits msn, % 2 bits tcp_ack_number, % 14 bits header_crc, % 3 bits tcp_seq_number, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '1101101', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(3), tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_23 ::= discriminator, % 7 bits tcp_flags_psh, % 1 bit ip_ttl, % 8 bits tcp_checksum, % 16 bits msn, % 2 bits tcp_ack_number, % 2 bits header_crc, % 7 bits tcp_seq_number, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '1100000', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_ttl ::= irregular(8), tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(2, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) Pelletier, et al. [Page 50] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 }, co_format_24 ::= discriminator, % 5 bits msn, % 1 bit tcp_flags_psh, % 1 bit header_crc, % 7 bits tcp_seq_number_scaled, % 7 bits tcp_seq_number_residue, % 0 bits tcp_window, % 13 bits tcp_ack_number, % 14 bits tcp_checksum, % 16 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '11001', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_window ::= lsb(13, 2047), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(7, 63) } }, co_format_25 ::= discriminator, % 9 bits msn, % 1 bit tcp_flags_psh, % 1 bit tcp_seq_number, % 2 bits header_crc, % 3 bits tcp_ack_number, % 32 bits tcp_checksum, % 16 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '110110001', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, Pelletier, et al. [Page 51] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 header_crc ::= crc(3), tcp_seq_number ::= lsb(2, 0), tcp_ack_number ::= irregular(32), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_checksum ::= irregular(16) }, co_format_26 ::= discriminator, % 2 bits msn, % 1 bit tcp_window, % 13 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 7 bits tcp_seq_number, % 12 bits tcp_ack_number, % 12 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '00', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), tcp_seq_number ::= lsb(12, 1023), tcp_ack_number ::= lsb(12, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_window ::= lsb(13, 2047), tcp_checksum ::= irregular(16) }, co_format_27 ::= discriminator, % 7 bits msn, % 1 bit tcp_window, % 16 bits tcp_checksum, % 16 bits tcp_flags_psh, % 1 bit header_crc, % 7 bits tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 7 bits tcp_seq_number_residue, % 0 bit tcp_ack_number, % 14 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '1100011', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), Pelletier, et al. [Page 52] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(7, 63) } }, co_format_28 ::= discriminator, % 7 bits tcp_flags_psh, % 1 bit ip_ttl, % 8 bits tcp_checksum, % 16 bits msn, % 2 bits tcp_ack_number, % 14 bits tcp_seq_number_scaled, % 4 bits tcp_seq_number_residue, % 0 bit header_crc, % 7 bits tcp_window, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '1100001', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_ttl ::= irregular(8), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= value(3, 0), tcp_window ::= lsb(13, 2047), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(4, 3) } }, Pelletier, et al. [Page 53] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 co_format_29 ::= discriminator, % 9 bits header_crc, % 7 bits ip_ttl, % 8 bits tcp_window, % 16 bits tcp_checksum, % 16 bits ip_dont_frag, % 1 bit tcp_flags_psh, % 1 bit ip_tos, % 6 bits msn, % 2 bits tcp_ack_number, % 14 bits tcp_flags_rsf, % 3 bits tcp_seq_number, % 13 bits tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '110110000', discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(2, -1) }, header_crc ::= crc(7), ip_tos ::= irregular(6), ip_dont_frag ::= irregular(1), ip_ttl ::= irregular(8), tcp_seq_number ::= lsb(13, 1023), tcp_ack_number ::= lsb(14, 0), tcp_flags_ack ::= value(1, 1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16) }, co_format_30 ::= discriminator, % 8 bits ip_ttl, % 8 bits tcp_ack_number, % 32 bits tcp_window, % 16 bits tcp_checksum, % 16 bits msn, % 1 bit header_crc, % 7 bits tcp_flags_ack, % 1 bit tcp_flags_psh, % 1 bit tcp_flags_rsf, % 3 bits tcp_seq_number_scaled, % 3 bits tcp_seq_number_residue, % 0 bit tcp_ecn_and_reserved, % 0 or 8 bits ip_id, % 0 or 16 bits { discriminator ::= '11011001', Pelletier, et al. [Page 54] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 discriminator.format ::= same_as(random_ip_id), msn ::= control_field, { base_field ::= counter(16), compressed_method ::= lsb(1, -1) }, header_crc ::= crc(7), ip_ttl ::= irregular(8), tcp_ack_number ::= irregular(32), tcp_flags_ack ::= irregular(1), tcp_flags_psh ::= irregular(1), tcp_flags_rsf ::= index(3, [0, 1, 2, 4]), tcp_window ::= irregular(16), tcp_checksum ::= irregular(16), tcp_seq_number_scaled ::= control_field, { base_field ::= expression(uncomp(tcp_ip.tcp_seq_number) // uncomp(tcp_ip.tcp_payload_size)), compressed_method ::= lsb(3, 3) } }, co_common ::= tcp_payload_size, % 0 bit tcp_options, % variable no. of bits { tcp_payload_size ::= expression(uncomp(tcp_ip.ip_length) - ((uncomp(tcp_ip.ip_header_length) + uncomp(tcp_ip.tcp_data_offset)) * 4)) }, 6.6. Feedback formats and options 6.6.1. Feedback formats This section describes the feedback format for ROHC-TCP. ROHC-TCP uses the ROHC feedback format described in [ROHC, section 5.2.2]. All feedback formats carry a field labeled SN. The SN field contains LSBs of the Master Sequence Number (MSN) described in section 4.1.3. The sequence number to use is the MSN corresponding to the header that caused the feedback information to be sent. If that MSN cannot be determined, for example when decompression fails, the MSN to use is that corresponding to the latest successfully decompressed header. Pelletier, et al. [Page 55] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 FEEDBACK-1 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | MSN | +---+---+---+---+---+---+---+---+ MSN: The lsb-encoded master sequence number. A FEEDBACK-1 is an ACK. In order to send a NACK or a STATIC-NACK, FEEDBACK-2 must be used. FEEDBACK-2 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ |Acktype| MSN | +---+---+---+---+---+---+---+---+ | MSN | +---+---+---+---+---+---+---+---+ / Feedback options / +---+---+---+---+---+---+---+---+ Acktype: 0 = ACK 1 = NACK 2 = STATIC-NACK 3 is reserved (MUST NOT be used for parseability) MSN: The lsb-encoded master sequence number. Feedback options: A variable number of feedback options, see section 5.5.4.2. Options may appear in any order. 6.6.2. Feedback options ROHC-TCP uses the same feedback options as the options defined in [RFC-3095, section 5.7.6], with the following exceptions: 1) The MSN replaces RTP SN in the feedback information. 2) The CLOCK option [RFC-3095, section 5.7.6.6] is not used. 3) The JITTER option [RFC-3095, section 5.7.6.7] is not used. Pelletier, et al. [Page 56] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 7. Security considerations Because encryption eliminates the redundancy that header compression schemes try to exploit, there is some inducement to forego encryption of headers in order to enable operation over low-bandwidth links. However, for those cases where encryption of data (and not headers) is sufficient, TCP does specify an alternative encryption method in which only the TCP payload is encrypted and the headers are left in the clear. That would still allow header compression to be applied. A malfunctioning or malicious header compressor could cause the header decompressor to reconstitute packets that do not match the original packets but still have valid IP, and TCP headers and possibly also valid TCP checksums. Such corruption may be detected with end-to-end authentication and integrity mechanisms which will not be affected by the compression. Moreover, this header compression scheme uses an internal checksum for verification of reconstructed headers. This reduces the probability of producing decompressed headers not matching the original ones without this being noticed. Denial-of-service attacks are possible if an intruder can introduce (for example) bogus IR, CO or FEEDBACK packets onto the link and thereby cause compression efficiency to be reduced. However, an intruder having the ability to inject arbitrary packets at the link layer in this manner raises additional security issues that dwarf those related to the use of header compression. 8. IANA Considerations ROHC profile identifier 0x00XX <# Editor's Note: To be replaced before publication #> has been reserved by the IANA for the profile defined in this document. <# Editor's Note: To be removed before publication #> A ROHC profile identifier must be reserved by the IANA for the profile defined in this document. Profiles 0x0000-0x0005 have previously been reserved, which means this profile could be 0x0006. As for previous ROHC profiles, profile numbers 0xnnXX must also be reserved for future updates of this profile. A suggested registration in the "RObust Header Compression (ROHC) Profile Identifiers" name space would then be: Profile Usage Document identifier 0x0006 ROHC TCP [RFCXXXX (this)] 0xnn06 Reserved Pelletier, et al. [Page 57] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 9. Acknowledgements Header compression schemes from [RFC-1144, RFC-2507, RFC-3095] have been important sources of ideas and knowledge. The authors would like to thank Carsten Bormann, Qian Zhang, HongBin Liao and Robert Finking for valuable input and reviews. 10. References 10.1. Normative References [RFC-3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H., Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le, K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K., Wiebke, T., Yoshimura, T. and H. Zheng, "RObust Header Compression (ROHC): Framework and four profiles: RTP, UDP, ESP, and uncompressed", RFC 3095, July 2001. [ROHC-CR] Pelletier, G., "Robust Header Compression (ROHC): Context replication for ROHC profiles", Internet Draft (work in progress), , October 2003. [ROHC-FN] R. Price et al., "Formal Notation for Robust Header Compression (ROHC-FN)", Internet Draft (work in progress),, October 2003. [RFC-791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC-793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. [RFC-2026] S. Bradner, "The Internet Standards Process - Revision 3", RFC-2026, October 1996. [RFC-2119] S. Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC-2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. 10.2. Informative References [TCP-REQ] Jonsson, L-E., "Requirements on ROHC IP/TCP header compression", Internet Draft (work in progress),, October 2002. [TCP-BEH] West, M. and S. McCann, "TCP/IP Field Behavior", Internet Pelletier, et al. [Page 58] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Draft (work in progress), , March 2003. [IP-ONLY] Jonsson, L. and G. Pelletier, "RObust Header Compression (ROHC): A compression profile for IP", Internet draft (work in progress), , June 2003. [RFC-1072] Jacobson, V., and R. Braden, "TCP Extensions for Long- Delay Paths", LBL, ISI, October 1988. [RFC-1144] Jacobson, V.,"Compressing TCP/IP Headers for Low-Speed Serial Links", RFC 1144, February 1990. [RFC-1323] Jacobson, V., Braden, R. and D. Borman, "TCP Extensions for High Performance", RFC 1323, May 1992. [RFC-1644] Braden, R. "T/TCP -- TCP Extensions for Transactions Functional Specification", ISI, July 1994. [RFC-1693] Connolly, T., et al, "An Extension to TCP : Partial Order Service", University of Delaware, November 1994. [RFC-1889] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", RFC 1889, January 1996. [RFC-2001] Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery Algorithms", NOAO, January 1997. [RFC-2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP Selective Acknowledgment Options", RFC 2018, October 1996. [RFC-2507] Degermark, M., Nordgren, B. and S. Pink, "IP Header Compression", RFC 2507, February 1999. [RFC-2883] Floyd, S., Mahdavi, J., Mathis, M. and M. Podolsky, "An Extension to the Selective Acknowledgement (SACK) Option for TCP", RFC 2883, July 2000. [E2E] Jacobson, V., "Fast Retransmit", Message to the end2end- interest mailing list, April 1990. [Mobi96] Degermark, M., Engan, M., Nordgren, B. and S. Pink, "Low- loss TCP/IP header compression for wireless networks", In the Proceedings of MobiCom, 1996. Pelletier, et al. [Page 59] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 11. Authors' addresses Ghyslain Pelletier Ericsson AB Box 920 SE-971 28 Lulea, Sweden Phone: +46 920 20 24 32 Fax: +46 920 20 20 99 Email: ghyslain.pelletier@ericsson.com Lars-Erik Jonsson Ericsson AB Box 920 SE-971 28 Lulea, Sweden Phone: +46 920 20 21 07 Fax: +46 920 20 20 99 Email: lars-erik.jonsson@ericsson.com Mark A West Roke Manor Research Ltd Romsey, Hants, SO51 0ZN United Kingdom Phone: +44 1794 833311 Email: mark.a.west@roke.co.uk Richard Price Roke Manor Research Ltd Romsey, Hants, SO51 0ZN United Kingdom Phone: +44 1794 833681 Email: Richard.price@roke.co.uk Pelletier, et al. [Page 60] INTERNET-DRAFT ROHC Profile for TCP/IP October 27, 2003 Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. This Internet-Draft expires April 27, 2004. Pelletier, et al. [Page 61]