Network Working Group Ghyslain Pelletier, Ericsson INTERNET-DRAFT Expires: December 2003 June 19, 2003 RObust Header Compression (ROHC): Context Replication for ROHC Profiles 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 defines context replication, a complement to the context initialization procedure found in ROHC (Robust Header Compression) [RFC-3095]. Profiles defining support for context replication may use the mechanism described herein to establish a new context based on another already existing context. Context replication is introduced to reduce the overhead of the context establishment procedure, and may be especially useful for the compression of multiple short-lived flows that may be occurring simultaneously or near-simultaneously, such as for example short- lived TCP flows. Pelletier [Page 1] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Table of contents 1. Introduction....................................................3 2. Terminology.....................................................4 3. Context replication for ROHC profiles...........................4 3.1. Robustness considerations.................................4 3.2. Compressor logic..........................................5 3.2.1. Selection of the Base Context...........................5 3.2.2. Feedback logic..........................................6 3.2.2.1. Negative Acknowledgements (NACKs).....................6 3.2.2.2. Optional Acknowledgements (ACKs)......................7 3.3. Decompressor logic........................................7 3.3.1. Replication and context initialization..................7 3.3.2. Actions upon failure....................................7 3.4. Packet Formats............................................8 3.4.1. Checksums in the IR-REPLICATE packet....................8 3.4.1.1. 7-bit CRC.............................................9 3.4.1.2. 8-bit CRC.............................................9 3.4.2. General Format of the IR-REPLICATE packet...............9 4. Security considerations........................................11 5. Acknowledgements...............................................11 6. References.....................................................11 6.1. Normative References.....................................11 6.2. Informative References...................................12 7. Author's address...............................................12 Appendix A. General Format of the IR-REPLICATE packet.............13 A.1. General structure........................................12 A.2. Profile specific information.............................12 Appendix B. Replication Chains....................................15 B.1. Replication of the IPv6 Header [RFC-2460]................15 B.2. Replication of the IPv4 Header [RFC-791].................16 B.3. Replication of the TCP Header [RFC-793]..................18 B.4. Replication of the UDP Header [RFC-768]..................19 B.5. Replication of the UDP-Lite Header [UDP-Lite]............20 Pelletier [Page 2] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 1. Introduction There is often some redundancy between header fields of different flows passing through the same compressor-decompressor pair. This means that some of the information needed to initialize the context for compressing the headers of a new flow may already be present at the decompressor. It may be desirable to reuse this information and remove some of the overhead normally required for the initialization of a new header compression context. Reducing the overhead of the context establishment procedure is particularly useful when multiple short-lived connections (or flows) occurs simultaneously, or near-simultaneously, between the same compressor-decompressor pair. Such flows may lead to lower header compression gains, as each new packet stream requires most of the header information to be sent initially and smaller compressed headers may only be sent thereafter. Context replication allows some header fields, such as the IP source and/or destination addresses (16 octets each for IPv6), to be omitted within the IR packet specially defined for replication. It also allows other fields, such as source and/or destination ports, to be either omitted or sent in a compressed form from the very first packet of the header compressed flow. In addition, this mechanism allows contexts from different profiles to be used with context replication, where for obvious reasons only header fields common to both profiles can possibly be replicated. Context replication is herein defined as a general ROHC mechanism; its support may be defined for any ROHC profile. However, although the benefits of context replication are not limited to any particular protocol, it is best motivated for TCP compression. Specifically, many TCP transfers are short-lived; a behavior analysis of TCP/IP header fields among multiple short-lived connections may be found in [TCP-BEH]. In addition, [TCP-REQ] introduces considerations and requirements for the ROHC-TCP profile [ROHC-TCP] to efficiently compress such short-lived TCP transfers. For profiles supporting this mechanism, context replication is performed by the compressor first initializing a new context for the new flow. This context is then populated using parts of an existing context, i.e. a base context, to create the replicated context. The compressor then sends to the decompressor a packet that contains a reference to the selected base context, along with some data for the fields that need to be updated when creating the replicated context. Finally, the decompressor creates the replicated context based on the reference to the base context along with the uncompressed and compressed data from the received packet. This document specifies the context replication procedure for ROHC profiles. It defines the general compressor and decompressor logic Pelletier [Page 3] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 used during context replication, as well as the general format of the special IR packet required for this procedure. Profiles defining support for context replication must further specify the specific format of this packet. The fundamentals of the ROHC framework may be found in [RFC-3095]. These are assumed to be understood throughout this document. 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 A base context is a context that has been validated by both the compressor and the decompressor. A base context can be used by the compressor 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 initializes a new context based on another already existing context (a base context). 3. Context Replication for ROHC profiles For profiles defining its support, context replication may be used as an alternative to the context initialization procedure found in [RFC- 3095]. This section describes the compressor and decompressor logic as well as the general format of the IR packetused with context replication. 3.1. Robustness considerations Context replication deviates from the initialization procedure defined in [RFC-3095] by its capacity to achieve a certain level of compression already from the first packet used to initialize the Pelletier [Page 4] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 context for a new flow. It is therefore of particular importance that the context replication procedure be reliable. This requires that a base context suitable for replication be used, that the integrity of the initialization packet be guaranteed and finally that the outcome of the replication process be verified. The primary mechanisms used to achieve robustness of the context replication procedure are the selection of the base context based on prior feedback from the decompressor and the use of checksums. Specifically, the compressor must obtain enough confidence that a base context corresponding to the one selected for replication is available at the decompressor before initiating the replication procedure. The most reliable way to select the base context is thus to choose a context that has previously been acknowledged by the decompressor. In addition, the presence of a CRC covering the information used to initialize the context ensures the integrity of the IR header used for replication. Finally, an additional CRC calculated over the original uncompressed header allows the decompressor to validate the reconstructed header and the outcome of the replication process. 3.2. Compressor logic For profiles defining support for context replication, the compressor may replace any IR/IR-DYN packets during the context establishment procedure (i.e. in IR state) with the IR-REPLICATE packet, if an already existing context can be selected as a base context for replication. 3.2.1. Selection of a Base Context When initiating context replication, the compressor MUST select a context that has previously been acknowledged by the decompressor as the base context, and this base context must be valid at replication time. This also implies that a compressor is not allowed to use the context replication mechanism if a feedback channel is not present. Note however that this cannot provide the guarantee that the selected base context has not been corrupted after it has been acknowledged or that it is still part of the state managed by the decompressor when the IR-REPLICATE will be received. More specifically, [RFC-3095] defines the context identifier (CID) as a reference to the state information (i.e. the context) used for compression and decompression. Multiple packet streams with different contexts may thus share a channel, and the CID space along with its representation within packet formats may be negotiated as part of the channel state. However, because [RFC-3095] does not explicitly define context state management between compressor and decompressor, and in Pelletier [Page 5] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 particular for connection-oriented flows (e.g. TCP), only a high degree of confidence can be achieved when selecting a base context. The criteria whether an existing context is a suitable base context for replication for a new flow are left to implementations. For simplicity, contexts with the same Source-IP and/or Destination-IP may be considered as replicable contexts, and the most recent one should be selected as the candidate to be replicated. Finally, the Base CID within the packet format of the IR-REPLICATE may be assigned a different value than the context identifier associated to the new flow (i.e. Base CID != CID); otherwise the base context is overwritten with the new context by the replication process. 3.2.2. Feedback logic Context replication is designed to operate over links where a feedback channel is available. This is necessary to ensure that the information used to create a new context is synchronized between the compressor and the decompressor. In addition, context replication may also make use of feedback from decompressor to compressor for transition back to the IR state and for OPTIONAL improved forward transition towards a state with a higher compression ratio. [RFC-3095, section 5.2.2.] specifies the required format for the feedback field within the general ROHC packet format to be used by all profiles; the feedback information is structured using two possible formats: FEEDBACK-1 and FEEDBACK-2. In particular, FEEDBACK- 2 can carry one of three possible types of feedback information: ACK, NACK or STATIC-NACK. 3.2.2.1. Negative Acknowledgements (NACKs) A STATIC-NACK sent by the decompressor may indicate that a valid context could not be initialized by the decompressor during context replication, and the corresponding context has been invalidated. Upon reception of a STATIC-NACK, the compressor MUST transit back to its initial no context state and SHOULD refrain from sending IR- REPLICATE packets using the same base context. The compressor SHOULD re-initialize the decompressor context using an IR packet. A NACK sent by the decompressor may indicate that a valid context has been successfully initialized but that the decompression of one or more subsequent packets has failed. Upon reception of a NACK, the compressor may assume that the static part of the decompressor context is valid but that the dynamic part is invalid, and take actions accordingly. Pelletier [Page 6] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 3.2.2.2. Optional Acknowledgements (ACKs) An ACK may be sent by the decompressor to indicate that a context has been successfully initialized during context replication. Upon reception of an ACK, the compressor may assume that the context replication procedure was successful and transit from its initial state (e.g. IR state) to a higher compression state. 3.3. Decompressor logic 3.3.1. Replication and context initialization Upon reception of an IR-REPLICATE packet, the decompressor first determines its content (RFC-3095, section 5.2.6). The profile indicated in the IR-REPLICATE packet determines how it is to be processed. If the CRC (8-bit CRC) fails to verify the packet, the packet MUST be discarded. If the profile as indicated in the IR-REPLICATE packet defines the use of the Base CID and if its corresponding field is present within the packet format, this field is used to identify the base context; otherwise the CID is used. The decompressor then creates a new context using the information present in the IR-REPLICATE packet together with the identified base context, and decompresses the original header. The decompressor validates the resulting header using the CRC calculated over the original uncompressed header; if the decompessor fails to validate the header, the actions specified in section 3.3.2 must be taken. 3.3.2. Actions upon failure For profiles supporting context replication, the feedback logic of a decompressor is similar to the logic used for context initialization, as described in [RFC-3095]. Specifically, when the decompressor fails to validate the context following the decompression of one or more initial IR-REPLICATE packets, it MUST invalidate the context and remain in its initial state. In addition, the decompressor SHOULD send a STATIC-NACK. If the context has been successfully validated from the decompression of one or more initial IR-REPLICATE packets, the decompressor SHOULD send a NACK when it fails to verify the context following the decompression of one or more subsequent IR-REPLICATE packets. The decompressor SHOULD send an ACK when it succeeds to validate the context as a result of the decompression of one or more IR-REPLICATE packets. Pelletier [Page 7] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 3.4. Packet Formats The format of the IR-REPLICATE packet has been designed under the following constraints: a) it must be possible to either overwrite a CID during context replication, or to use a CID different than the Base CID for the replicated context; b) it must be possible to replicate from a base context using a profile different than the one associated with the replicated context, for fields specifically common to both profiles; c) it must be possible to selectively include or exclude from the packet format some fields that may be replicable; d) it must be possible for some fields that may be replicable to be represented within the packet format using either a compressed or an uncompressed form; e) it must be possible for the decompressor to verify the success of the replication procedure; f) it is anticipated that profiles other than [ROHC-TCP] will also define support for context replication, therefore it is desirable that the packet format be as profile independent as possible. 3.4.1. CRCs in the IR-REPLICATE packet The IR packet, as defined in [RFC-3095], is used to communicate static and/or dynamic parts of a context, and typically initialize the context. For example, the static and dynamic chains of IR packets may contain an uncompressed representation of the original header. The IR packet format includes an 8-bit CRC, calculated over the initial part of the IR packet. This CRC is meant to protect any information that initialize the context. In particular, its coverage always includes any CID information as well as the profile used to interpret the remainder of the IR packet. The purpose of the 8-bit CRC is to ensure the integrity of the IR header itself. Profiles may extend the coverage of this CRC to include the entire IR header, thus allowing the verification of the integrity of the entire uncompressed header. However because the format of the IR packet is common to all ROHC profiles and verified as part of the initial processing of a ROHC decompressor (see [RFC- 3095, section 5.2.6.]), profiles may not redefine this CRC beyond the extent of its coverage. [RFC-3095] also defines a 3-bit CRC and a 7-bit CRC for compressed headers, used to verify proper decompression and validate the context. This type of CRC is calculated over the original uncompressed header, as it is not sufficient to only protect the compressed data being exchanged between compressor and decompressor to ensure a robust reconstruction of the original header. Pelletier [Page 8] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 There is thus a clear distinction in purposes between the 8-bit CRC found in the IR packet and the 3-bit or 7-bit CRC found in compressed headers. With context replication, where the IR-REPLICATE packet may contain both compressed as well as uncompressed information and omit entirely replicable fields, this distinction in no longer present. Profiles supporting context replication MUST define a CRC over the original uncompressed header as part of the profile specific information in the IR-REPLICATE packet. This is necessary to allow a decompressor to verify that the replication process has succeeded. 3.4.1.1. 7-bit CRC The 7-bit CRC in the IR-REPLICATE packet is calculated over all octets of the entire original header, before replication, in the same manner as described in [RFC-3095, section 5.9.2]. The initial content of the CRC register is to be preset to all 1's. The CRC polynomial used for the 7-bit CRC in the IR-REPLICATE is: C(x) = 1 + x + x^2 + x^3 + x^6 + x^7 3.4.1.2. 8-bit CRC The coverage of the 8-bit CRC in the IR-REPLICATE packet is profile- dependent, but it MUST cover at least the initial part of the packet ending with the Profile field and if present, the Base CID field. For profiles that define the usage of the Base CID within the packet format of the IR-REPLICATE as optional, the CRC MUST also cover the information used to indicate the presence of this field within the packet. Any other information which initializes the context of the decompressor should also be protected by the CRC. The initial content of the CRC register is to be preset to all 1's. The CRC polynomial used for the 8-bit CRC in the IR-REPLICATE is: C(x) = 1 + x + x^2 + x^8 3.4.2. General Format of the IR-REPLICATE packet The context replication mechanism requires a dedicated IR packet format that uniquely identifies the IR-REPLICATE packet. This packet communicates the static and the dynamic parts of the replicated context. It may also communicate a reference to a base context. With consideration to the extensibility of the IR packet type defined in [RFC-3095], support for replication can be added using the profile specific part of the IR packet. Note that there is one bit, (x), left in the IR header for "Profile specific information". The definition Pelletier [Page 9] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 of this bit is profile-specific. Thus, profiles supporting context replication may use this bit as a flag indicating whether the packet is an IR packet or an IR-REPLICATE packet. Note also that profiles may define an alternative method to identify the IR-REPLICATE packet within the profile specific information, instead of using this bit. The IR-REPLICATE header associates a CID with a profile, and initializes the context using the context replication mechanism. It is not recommended to use this packet to repair a damaged context. The IR-REPLICATE has the following general 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 x | IR type octet +---+---+---+---+---+---+---+---+ : : / 0-2 octets of CID / 1-2 octets if for large CIDs : : +---+---+---+---+---+---+---+---+ | Profile | 1 octet +---+---+---+---+---+---+---+---+ | CRC | 1 octet +---+---+---+---+---+---+---+---+ | | / profile specific information / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - x: Profile specific information. Interpreted according to the profile indicated in the Profile field. Profile: The profile to be associated with the CID. In the IR- REPLICATE packet, the profile identifier is abbreviated to the 8 least significant bits. It selects the highest-number profile in the channel state parameter PROFILES that matches the 8 LSBs given (see also [RFC-3095]). CRC: 8-bit CRC computed using the polynomial of section 3.4.1.2. Profile specific information: The contents of this part of the IR- REPLICATE packet are defined by the individual profiles. This information is interpreted according to the profile indicated in the Profile field. It MUST include a 7-bit CRC over the original uncompressed header using the polynomial of section Pelletier [Page 10] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 3.4.1.1. It also includes the static and dynamic subheader information used for replication. Payload: The payload of the corresponding original packet, if any. 4. Security considerations This document does not bring any new additional security considerations than those already listed in [ROHC-TCP]. 5. Acknowledgements The author would like to thank Lars-Erik Jonsson, Richard Price, Mark West and HongBin Liao for valuable input to this document. 6. References 6.1. Normative References [RFC-768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC-791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC-793] Postel, J., "Transmission Control Protocol," RFC 793 (STD7), September 1981. [RFC-2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [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. [UDP-Lite] Larzon, L., Degermark, M., Pink, S., Jonsson, L., Fairhurst, G., "The UDP-Lite Protocol", Internet draft (work in progress), December 2002, Pelletier [Page 11] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 6.2. Informative References [ROHC-TCP] Pelletier, G., Zhang, Q., Jonsson, L-E., Liao, H., West, M., "RObust Header Compression (ROHC): TCP/IP Profile (ROHC-TCP)", Internet Draft (work in progress), , May 2003. [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 Draft (work in progress), , March 2003. [RFC-2026] Bradner, S., "The Internet Standards Process", RFC 2026, October 1996. [ROHC-FN] "Formal Notation for Robust Header Compression (ROHC-FN)", R. Price et al., (work in progress), March 2003 7. Author's address Ghyslain Pelletier Box 920 Ericsson AB SE-971 28 Lulea, Sweden Phone: +46 920 20 24 32 Fax: +46 920 20 20 99 Email: ghyslain.pelletier@epl.ericsson.se Pelletier [Page 12] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 <# Author's These sections are meant to exemplify one possible #> <# note : way of structuring the IR-REPLICATE packet with a #> <# structure similar to the general IR packet format #> <# of [RFC-3095]. Other alternative exists, such as a #> <# packet format generated using the formal notation #> <# [ROHC-FN]. This remains an open question. The packet #> <# format can be reworked when this question is #> <# answered. This applies for Appendix A and B. #> Appendix A. General Format of the IR-REPLICATE packet (Informative) Appendix A.1. General structure (Informative) This section provides an example of the format of the profile specific information within the general format of the IR-REPLICATE based on the use of static and dynamic replication. Examples of chains for IPv6, IPv4, UDP, UDP-Lite and TCP are found in Appendix B. 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | | / profile specific information / variable length | | +---+---+---+---+---+---+---+---+ | | | Static replication chain / variable length | | +---+---+---+---+---+---+---+---+ | | / Dynamic replication chain / variable length | | - - - - - - - - - - - - - - - - Profile specific information: The contents of this part of the IR- REPLICATE packet are defined by the individual profiles. This information is interpreted according to the profile indicated in the Profile field. It MUST include a 7-bit CRC over the original uncompressed header using the polynomial of section 3.4.1.1. See Appendix A.2 for a more detailed example. Static replication chain: A chain of static subheader information used for replication. Dynamic replication chain: A chain of dynamic subheader information used for replication. What dynamic information is present is inferred from the static replication chain. Pelletier [Page 13] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Appendix A.2. Profile specific information (Informative) This section provides a more detailed example of the possible format of the profile specific information described in Appendix A.1: +---+---+---+---+---+---+---+---+ | B | CRC* | 1 octet +---+---+---+---+---+---+---+---+ | | present if B = 1, / Base CID / 1 octet if for small CIDs, or | | 1-2 octets if for large CIDs +---+---+---+---+---+---+---+---+ B: B = 1 indicates that the Base CID field is present. CRC*: The CRC over the original, uncompressed, header. This 7-bit CRC is computed according to section 3.4.1.1. Base CID: The CID identifying the base context used for replication. Pelletier [Page 14] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Appendix B. Replication Chains (Informative) This section provides examples of static and dynamic replication chains for IPv6, IPv4, UDP, UDP-Lite and TCP. <# Author's note: An open question: Is it possible to extend #> <# the context replication mechanism to handle #> <# the complete list of extension headers for #> <# the IP header? #> B.1. Replication of the IPv6 Header [RFC-2460] (Informative) <# Author's note: The Traffic Class field and the Hop Limit #> <# field could also be replicated. #> Static part: +---+---+---+---+---+---+---+---+ | F | N | S | D |Flow Label(msb)| +---+---+---+---+---+---+---+---+ / Flow Label (lsb) / 2 octets, if F = 1 +---+---+---+---+---+---+---+---+ | Next Header | 1 octet, if N = 1 +---+---+---+---+---+---+---+---+ / Source Address / 16 octets, if S = 1 +---+---+---+---+---+---+---+---+ / Destination Address / 16 octets, if D = 1 +---+---+---+---+---+---+---+---+ Dynamic part: +---+---+---+---+---+---+---+---+ | Traffic Class | 1 octet +---+---+---+---+---+---+---+---+ | Hop Limit | 1 octet +---+---+---+---+---+---+---+---+ / Generic extension header list / variable length +---+---+---+---+---+---+---+---+ Eliminated: Payload Length Version Replicable: Flow Label (Flow Label must be all '0's) Flow Label must not be used, i.e. this field must be all '0's. Note that the Flow Label(msb) field is valid only if F = 1. Pelletier [Page 15] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Next Header The type of the following header in the static replication chain must be the same type as the one found in the static chain of the base context. Source Address Destination Address Extras: F, N, S and D: replication flags. Generic extension header list: see [RFC-3095, section 5.7.7.3]. CRC-DYNAMIC: Payload Length field (octets 5-6). CRC-STATIC: All other fields (octets 1-4, 7-40). CRC coverage for extension headers is defined in [RFC-3095, section 5.8.7]. Note: The Next Header field indicates the type of the following header in the static chain, rather than being a copy of the Next Header field of the original IPv6 header. See also [RFC-30905, section 5.7.7.8]. Note: When using context replication from a base context where the static part contains multiple IP levels for a flow with a different number of IP levels, only the outer IP header can be replicated. B.2. Replication of the IPv4 Header [RFC-791] (Informative) <# Author's note: The Type of Service field, the TTL field and #> <# the IP-ID field could also be replicated. #> <# #> Static part: +---+---+---+---+---+---+---+---+ | P | S | D | DF|RND|NBO| 0 | +---+---+---+---+---+---+---+---+ | Protocol | 1 octets, if P = 1 +---+---+---+---+---+---+---+---+ / Source Address / 4 octets, if S = 1 +---+---+---+---+---+---+---+---+ / Destination Address / 4 octets, if D = 1 +---+---+---+---+---+---+---+---+ Pelletier [Page 16] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Dynamic part: +---+---+---+---+---+---+---+---+ | Type of Service | +---+---+---+---+---+---+---+---+ | Time to Live | +---+---+---+---+---+---+---+---+ / Identification / 2 octets +---+---+---+---+---+---+---+---+ / Generic extension header list / variable length +---+---+---+---+---+---+---+---+ Eliminated: IHL, Total Length, MF flag, Fragment Offset, Header Checksum, Options, Padding and Version. See also [RFC-3095, section 5.7.7.4]. Replicable: Protocol The type of the following header in the static replication chain must be the same type as the one found in the static chain of the base context. Source Address Destination Address Extras: P, S and D: replication flags. RND, NBO. See [RFC-3095, section 5.7]. CRC-DYNAMIC: Total Length, Identification, Header Checksum (octets 3-4, 5-6, 11-12). CRC-STATIC: All other fields (octets 1-2, 7-10, 13-20) CRC coverage for extension headers is defined in [ROHC, section 5.8.7]. Note: The Protocol field indicates the type of the following header in the static chain, rather than being a copy of the Protocol field of the original IPv4 header. See also [RFC-3095, section 5.7.7.8]. Note: When using context replication from a base context where the static part contains multiple IP levels for a flow with a different number of IP levels, only the outer IP header can be replicated. Pelletier [Page 17] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 B.3. Replication of the TCP Header [RFC-793] (Informative) Static part: +---+---+---+---+---+---+---+---+ | S | SC| D | DC| W | U | M | 0 | +---+---+---+---+---+---+---+---+ : : Present, if S = 1 and / Source Port / 1 octet, if SC = 1 : : 2 octets, if SC = 0 +---+---+---+---+---+---+---+---+ : : Present, if D = 1 and / Destination Port / 1 octet, if DC = 1 : : 2 octets, if DC = 0 +---+---+---+---+---+---+---+---+ Dynamic part: +---+---+---+---+---+---+---+---+ / Master Sequence Number / 2 octets, if M = 1 +---+---+---+---+---+---+---+---+ / Sequence Number / 4 octets +---+---+---+---+---+---+---+---+ / Acknowledgement Number / 4 octets +---+---+---+---+---+---+---+---+ | Data Offset | Reserved | 1 octet +---+---+---+---+---+---+---+---+ |CWR|ECE|URG|ACK|PSH|RST|SYN|FIN| 1 octet +---+---+---+---+---+---+---+---+ / Window / 2 octets, present if W = 1 +---+---+---+---+---+---+---+---+ / Checksum / 2 octets +---+---+---+---+---+---+---+---+ / Urgent Pointer / 2 octets, present if U = 1 +---+---+---+---+---+---+---+---+ / Options / variable length +---+---+---+---+---+---+---+---+ Eliminated: Nothing. Extras: S, SC, D, DC, W, U, M: replication flags. Replicable: Source Port Destination Port Master Sequence Number Pelletier [Page 18] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Window Urgent Pointer CRC-DYNAMIC: Length field, Checksum (octets 5-8). CRC-STATIC: All other fields (octets 1-4). Note: This chain is always the last chain in the IR-Replicate packet. B.4. Replication of the UDP Header [RFC-768] (Informative) <# Author's How much can we really save by replicating the UDP #> <# note : part of a context? Is it worth it? If not, for UDP #> <# the static and dynamic chains found in [RFC-3095] #> <# could be used. #> Static part: +---+---+---+---+---+---+---+---+ | S | SC| D | DC| C | 0 | +---+---+---+---+---+---+---+---+ : : Present if S = 1 and / Source Port / 1 octet if SC = 1 : : 2 octets if SC = 0 +---+---+---+---+---+---+---+---+ : : Present if D = 1 and / Destination Port / 1 octet if DC = 1 : : 2 octets if DC = 0 +---+---+---+---+---+---+---+---+ Dynamic part: +---+---+---+---+---+---+---+---+ / Checksum / 2 octets, present if C = 1 +---+---+---+---+---+---+---+---+ Eliminated: Length The Length field of the UDP header MUST match the Length field(s) of the preceding subheaders, i.e., there must not be any padding after the UDP payload that is covered by the IP Length. Replicable: Source Port Destination Port Checksum Pelletier [Page 19] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 Extras: S, SC, D, DC, C: replication flags. CRC-DYNAMIC: Length field, Checksum (octets 5-8). CRC-STATIC: All other fields (octets 1-4). B.5. Replication of the UDP-Lite Header [UDP-Lite] (Informative) <# Author's How much can we really save by replicating the #> <# note : UDP-Lite part of a context? Is it worth it? If not, #> <# for UDP-Lite the static and dynamic chains defined #> <# in the UDP-Lite profile could be used. #> Static part: +---+---+---+---+---+---+---+---+ | S | SC| D | DC| C | CC| 0 | +---+---+---+---+---+---+---+---+ : : Present if S = 1 and / Source Port / 1 octet if SC = 1 : : 2 octets if SC = 0 +---+---+---+---+---+---+---+---+ : : Present if D = 1 and / Destination Port / 1 octet if DC = 1 : : 2 octets if DC = 0 +---+---+---+---+---+---+---+---+ Dynamic part: +---+---+---+---+---+---+---+---+ : : Present if C = 1 and / Checksum Coverage / 1 octet if CC = 1 : : 2 octets if CC = 0 +---+---+---+---+---+---+---+---+ / Checksum / 2 octets +---+---+---+---+---+---+---+---+ Replicable: Source Port Destination Port Checksum Coverage Checksum Extras: Pelletier [Page 20] INTERNET-DRAFT Context Replication for ROHC profiles June 19, 2003 S, SC, D, DC, C, CC: replication flags. CRC-DYNAMIC: Checksum Coverage field, Checksum field (octets 5-8). CRC-STATIC: All other fields (octets 1-4). 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 December 19, 2003. Pelletier [Page 21]