Robust Header Compression G. Pelletier Internet-Draft K. Sandlund Intended status: Standards Track Ericsson Expires: March 10, 2007 September 6, 2006 RObust Header Compression Version 2 (RoHCv2): Profiles for RTP, UDP, IP, ESP and UDP Lite draft-ietf-rohc-rfc3095bis-rohcv2-profiles-00.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 10, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document specifies ROHC (Robust Header Compression) profiles that efficiently compress RTP/UDP/IP (Real-Time Transport Protocol, User Datagram Protocol, Internet Protocol), RTP/UDP-Lite/IP (User Datagram Protocol Lite), UDP/IP, UDP-Lite/IP, IP and ESP/IP (Encapsulating Security Payload) headers. This specification update the profiles defined in RFC 3095, RFC 3843 Pelletier & Sandlund Expires March 10, 2007 [Page 1] Internet-Draft ROHCv2 Profiles September 2006 and RFC 4019 to their second version (RoHCv2 profiles). The profiles herein thus supersede their earlier definition, but they do not obsolete them. The RoHCv2 specification introduce a number of simplifications to the rules and algorithms that govern the behavior of the compression endpoints. It also defines robustness mechanisms that may be used by a compressor implementation to increase the probability of decompression success when packets can be lost and/or reordered on the ROHC channel. Finally, the RoHCv2 profiles define its own specific set of packet formats, using the ROHC formal notation. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Background . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Classification of header fields . . . . . . . . . . . . . 8 4.2. Operational Characteristics of RoHCv2 Profiles . . . . . 9 5. Overview of the RoHCv2 Profiles . . . . . . . . . . . . . . . 9 5.1. General Concepts . . . . . . . . . . . . . . . . . . . . 10 5.1.1. Control Fields and Context Updates . . . . . . . . . 10 5.2. Compressor Concepts . . . . . . . . . . . . . . . . . . . 10 5.2.1. Optimistic Approach . . . . . . . . . . . . . . . . . 10 5.2.2. Tradeoff between robustness to losses and to reordering . . . . . . . . . . . . . . . . . . . . . 11 5.2.3. Interactions with the Decompressor Context . . . . . 12 5.3. Decompressor Concepts . . . . . . . . . . . . . . . . . . 13 5.3.1. Decompressor State Machine . . . . . . . . . . . . . 14 5.3.2. Decompressor Context Management . . . . . . . . . . . 16 5.3.3. Feedback logic . . . . . . . . . . . . . . . . . . . 17 6. RoHCv2 Profiles (Normative) . . . . . . . . . . . . . . . . . 18 6.1. Profile Operation, per-context . . . . . . . . . . . . . 18 6.2. Control Fields . . . . . . . . . . . . . . . . . . . . . 19 6.2.1. Master Sequence Number (MSN) . . . . . . . . . . . . 19 6.2.2. IP-ID behavior . . . . . . . . . . . . . . . . . . . 20 6.3. Reconstruction and Verification . . . . . . . . . . . . . 20 6.4. Compressed Header Chains . . . . . . . . . . . . . . . . 21 6.5. Packet Formats and Encoding Methods . . . . . . . . . . . 22 6.5.1. baseheader_extension_headers . . . . . . . . . . . . 22 6.5.2. baseheader_outer_headers . . . . . . . . . . . . . . 22 6.5.3. inferred_udp_length . . . . . . . . . . . . . . . . . 23 6.5.4. inferred_ip_v4_header_checksum . . . . . . . . . . . 23 6.5.5. inferred_mine_header_checksum . . . . . . . . . . . . 23 6.5.6. inferred_ip_v4_length . . . . . . . . . . . . . . . . 24 6.5.7. inferred_ip_v6_length . . . . . . . . . . . . . . . . 24 Pelletier & Sandlund Expires March 10, 2007 [Page 2] Internet-Draft ROHCv2 Profiles September 2006 6.5.8. Scaled RTP Timestamp Encoding . . . . . . . . . . . . 25 6.5.9. inferred_scaled_field . . . . . . . . . . . . . . . . 26 6.5.10. control_crc3 . . . . . . . . . . . . . . . . . . . . 26 6.5.11. inferred_sequential_ip_id . . . . . . . . . . . . . . 27 6.5.12. list_csrc(cc_value) . . . . . . . . . . . . . . . . . 27 6.6. Packet Formats . . . . . . . . . . . . . . . . . . . . . 31 6.6.1. Initialization and Refresh Packet (IR) . . . . . . . 31 6.6.2. IR Packet Payload Discard (IR-PD) . . . . . . . . . 32 6.6.3. IR Dynamic Packet (IR-DYN) . . . . . . . . . . . . . 33 6.6.4. Compressed Packet Formats (CO) . . . . . . . . . . . 34 6.7. Feedback Formats and Options . . . . . . . . . . . . . . 85 6.7.1. Feedback Formats . . . . . . . . . . . . . . . . . . 85 6.7.2. Feedback Options . . . . . . . . . . . . . . . . . . 87 7. Security Considerations . . . . . . . . . . . . . . . . . . . 89 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 89 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 90 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 90 10.1. Normative References . . . . . . . . . . . . . . . . . . 90 10.2. Informative References . . . . . . . . . . . . . . . . . 92 Appendix A. Detailed classification of header fields . . . . 92 Appendix A.1. General classification . . . . . . . . . . . . . 93 Appendix A.1.1. IPv4 header fields . . . . . . . . . . . . . . . 93 Appendix A.1.2. IPv6 header fields . . . . . . . . . . . . . . . 95 Appendix A.1.3. UDP header fields . . . . . . . . . . . . . . . 96 Appendix A.1.4. UDP-Lite header fields . . . . . . . . . . . . . 96 Appendix A.1.5. RTP header fields . . . . . . . . . . . . . . . 97 Appendix A.2. Analysis of change patterns of header fields . . 98 Appendix A.2.1. IPv4 Identification . . . . . . . . . . . . . . 100 Appendix A.2.2. IP Traffic Class / Type-Of-Service . . . . . . . 101 Appendix A.2.3. IP Hop-limit / Time-To-Live . . . . . . . . . . 101 Appendix A.2.4. IPv4 Don't Fragment . . . . . . . . . . . . . . 102 Appendix A.2.5. UDP Checksum . . . . . . . . . . . . . . . . . . 102 Appendix A.2.6. UDP-Lite Checksum Coverage . . . . . . . . . . . 102 Appendix A.2.7. UDP-Lite Checksum . . . . . . . . . . . . . . . 102 Appendix A.2.8. RTP CSRC Counter . . . . . . . . . . . . . . . . 102 Appendix A.2.9. RTP Marker . . . . . . . . . . . . . . . . . . . 102 Appendix A.2.10. RTP Padding . . . . . . . . . . . . . . . . . . 103 Appendix A.2.11. RTP Extension . . . . . . . . . . . . . . . . . 103 Appendix A.2.12. RTP Payload Type . . . . . . . . . . . . . . . . 103 Appendix A.2.13. RTP Sequence Number . . . . . . . . . . . . . . 103 Appendix A.2.14. RTP Timestamp . . . . . . . . . . . . . . . . . 103 Appendix A.2.15. RTP Contributing Sources (CSRC) . . . . . . . . 104 Appendix A.3. Header compression strategies . . . . . . . . . 104 Appendix A.3.1. Do not send at all . . . . . . . . . . . . . . . 104 Appendix A.3.2. Transmit only initially . . . . . . . . . . . . 104 Appendix A.3.3. Transmit initially, be prepared to update . . . 105 Appendix A.3.4. Be prepared to update, or send as-is frequently . . . . . . . . . . . . . . . . . . . 105 Pelletier & Sandlund Expires March 10, 2007 [Page 3] Internet-Draft ROHCv2 Profiles September 2006 Appendix A.3.5. Guarantee continuous robustness . . . . . . . . 105 Appendix A.3.6. Transmit as-is in all packets . . . . . . . . . 105 Appendix A.3.7. Establish and be prepared to update delta . . . 106 Appendix B. Differences between RoHCv2 and RFC3095 profiles . . . . . . . . . . . . . . . . . . . . 106 Appendix C. Sample CRC algorithm . . . . . . . . . . . . . . 106 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 108 Intellectual Property and Copyright Statements . . . . . . . . . 110 Pelletier & Sandlund Expires March 10, 2007 [Page 4] Internet-Draft ROHCv2 Profiles September 2006 1. Introduction The ROHC WG has developed a header compression framework on top of which various profiles can be defined for different protocol sets or compression requirements. The ROHC framework was first documented in [RFC3095], together with profiles for compression of RTP/UDP/IP (Real-Time Transport Protocol, User Datagram Protocol, Internet Protocol), UDP/IP, IP and ESP/IP (Encapsulating Security Payload) headers. Additional profiles for compression of IP headers [RFC3843] and UDP-Lite (User Datagram Protocol Lite) headers [RFC4019] were later specified to complete the initial set of ROHC profiles. This document defines an updated version for each of the above mentionned profiles, and its definition is based on the specification of the RoHC framework as found in [I-D.ietf-rohc-rfc3095bis-framework]. Specifically, this document defines header compression schemes for: o RTP/UDP/IP : profile 0x0101 (updates profile 0x0001 [RFC3095]) o UDP/IP : profile 0x0102 (updates profile 0x0002 [RFC3095]) o ESP/IP : profile 0x0103 (updates profile 0x0003 [RFC3095]) o IP : profile 0x0104 (updates profile 0x0004 [RFC3843]) o RTP/UDP-Lite/IP : profile 0x0107 (updates profile 0x0007 [RFC4019]) o UDP-Lite/IP : profile 0x0108 (updates profile 0x0008 [RFC4019]) ROHCv2 compresses the following type of extension headers: o AH [RFC4302] o GRE [RFC2784][RFC2890] o MINE [RFC2004] o NULL-encrupted ESP [RFC4303] o IPv6 Destination Options header[RFC2460] o IPv6 Hop-by-hop Options header[RFC2460] o IPv6 Routing header [RFC2460]. 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 RFC 2119 [RFC2119]. This document is consistent with the terminology found in the ROHC framework [I-D.ietf-rohc-rfc3095bis-framework] and in the formal notation for ROHC [I-D.ietf-rohc-formal-notation]. In addition, this document uses or defines the following terms: Pelletier & Sandlund Expires March 10, 2007 [Page 5] Internet-Draft ROHCv2 Profiles September 2006 Chaining of Items A chain groups fields based on similar characteristics. ROHCv2 defines chain items for static, dynamic and irregular fields. Chaining is done by appending an item for e.g. each header to the chain in their order of appearance in the uncompressed packet. Chaining is useful to construct compressed headers from an arbitrary number of any of the protocol headers for which a ROHCv2 profile defines a compressed format. CRC-8 validation The CRC-8 validation refers to the validation of the integrity against bit error(s) of the received IR and in the IR-DYN header, using the 8-bit CRC that is included in the header. CRC verification The CRC verification refers to the verification of the result of a decompression attempt, using the 3-bit CRC or 7-bit CRC included in the header of a compressed packet format (CO). Delta The delta refers to the difference in terms of the absolute value of a field between two consecutive packets and processed by the same compression endpoint. Reordering Depth The number of packets by which a packet made late in its sequence. See definition of sequentially late packet below. ROHCv2 packet types ROHCv2 profiles use two different packet types: the Initialization and Refresh (IR) packet type, and the Compressed packet type (CO). Sequentially early packet A packet that reaches the decompressor before one or several packets that were delayed over the channel, whereas all of the said packets belong to the same header-compressed flow and are associated to the same compression context (CID). At the time of the arrival of a sequentially early packet, the packet(s) delayed on the link cannot be differentiated from lost packet(s). Sequentially late packet Pelletier & Sandlund Expires March 10, 2007 [Page 6] Internet-Draft ROHCv2 Profiles September 2006 A packet is late within its sequence if it reaches the decompressor after one or several other packets belonging to the same CID have been received, although the sequentially late packet was sent from the compressor before the other packet(s). Timestamp stride (ts_stride) The timestamp stride (TS_STRIDE) is the expected increase in the timestamp value between two RTP packets with consecutive sequence numbers. 3. Acronyms This section lists most acronyms used for reference, in addition to those defined in [I-D.ietf-rohc-rfc3095bis-framework]. AH Authentication Header. ESP Encapsulating Security Payload. GRE Generic Routing Encapsulation. RFC 2784, RFC 2890. IC Initial Context state (decompressor) FC Full Context state (decompressor) IP Internet Protocol. LSB Least Significant Bits. MINE Minimal Encapsulation in IP MSB Most Significant Bits. MSN Master Sequence Number. NC No Context state (decompressor). OA Optimistic Approach. ROHCv2 Set of header compression profiles defined in this document RTP Real-time Transport Protocol. SSRC Synchronization source. Field in RTP header. CSRC Contributing source. Optional list of CSRCs in RTP header. TC Traffic Class. Octet in IPv6 header. See also TOS. TOS Type Of Service. Octet in IPv4 header. See also TC. TS RTP Timestamp. UDP User Datagram Protocol. UDP-Lite User Datagram Protocol Lite. 4. Background This section provides background information on the compression profiles defined in this document. The fundamentals of general header compression and of the ROHC framework may be found in section 3 and 4 of [I-D.ietf-rohc-rfc3095bis-framework], respectively. The fundamentals of the formal notation for ROHC are defined in [I-D.ietf-rohc-formal-notation]. [RFC4224] describes the impacts of Pelletier & Sandlund Expires March 10, 2007 [Page 7] Internet-Draft ROHCv2 Profiles September 2006 out-of-order delivery on profiles based on [RFC3095]. 4.1. Classification of header fields Section 3.1 of [I-D.ietf-rohc-rfc3095bis-framework] explains that header compression is possible due to the fact that there is much redundancy between field values within the headers of a packet, but especially between the headers of consecutive packets. Appendix A lists and classifies in detail all the header fields relevant to this document. The appendix concludes with recommendations on how the various fields should be handled by header compression algorithms. The main conclusion is that most of the header fields can easily be compressed away since they never or seldom change. A small number of fields however need more sophisticated mechanisms. These fields are: - IPv4 Identification (16 bits) - IP-ID - ESP Sequence Number (32 bits) - ESP SN - UDP Checksum (16 bits) - Checksum - UDP-Lite Checksum (16 bits) - Checksum - UDP-Lite Checksum Coverage (16 bits) - CC - RTP Marker ( 1 bit ) - M-bit - RTP Sequence Number (16 bits) - RTP SN - RTP Timestamp (32 bits) - TS In particular, for RTP, the analysis in Appendix A reveals that the values of the RTP Timestamp (TS) field usually have a strong correlation to the RTP Sequence Number (SN), which increments by one for each packet emitted by an RTP source. The RTP M-bit is expected to have the same value most of the time, but it needs to be communicated explicitly on occasion. For UDP, the Checksum field cannot be inferred or recalculated at the receiving end without violating its end-to-end properties, and is thus sent as-is when enabled (mandatory with IPv6). The same applies to the UDP-Lite Checksum (mandatory with both IPv4 and IPv6), while the UDP-Lite Checksum Coverage may in some cases be compressible. For IPv4, a similar correlation as the one of the RTP TS to the RTP SN is often observed between the Identifier field (IP-ID) and the master sequence number used for compression (e.g. the RTP SN when compressing RTP headers). Pelletier & Sandlund Expires March 10, 2007 [Page 8] Internet-Draft ROHCv2 Profiles September 2006 4.2. Operational Characteristics of RoHCv2 Profiles Robust header compression can be used over many type of link technologies. Section 4.4 of [I-D.ietf-rohc-rfc3095bis-framework] lists the operational characteristics of the ROHC channel. The RoHCv2 profiles address a wide range of applications, and this section summarizes some of the operational characteristics that are specific to these profiles. Packet length ROHCv2 profiles assume that the lower layer indicates the length of a compressed packet. ROHCv2 compressed headers do not contain length information for the payload. Out-of-order delivery between compression endpoints The definition of the RoHCv2 profiles places no strict requirement on the delivery sequence between the compression endpoints, i.e. packets may be received in a different order than the compressor sent them with a fair chance of successfully be decompressed. However, frequent out-of-order delivery and/or significant reordering depth will negatively impact the compression efficiency. More specifically, if the channel state includes parameters that provide a proper estimate of such significant out- of-order delivery, larger headers can be sent more often to increase the robustness against decompression failures due to reordering. Otherwise if the compressor cannot operate with sufficient knowledge for such reordering, the efficiency will be impaired from an increase in the frequency of decompression failures and recovery attempts. 5. Overview of the RoHCv2 Profiles This section provides an overview of important and useful concepts of ROHCv2 profiles. These concepts may be used as guidelines for implementations but they are not part of the normative definition of the profiles, as these concepts relates to the compression efficiency of the protocol without impacting the interoperability characteristics of an implementation. Pelletier & Sandlund Expires March 10, 2007 [Page 9] Internet-Draft ROHCv2 Profiles September 2006 5.1. General Concepts 5.1.1. Control Fields and Context Updates Control fields have the same attributes and properties as uncompressed fields [I-D.ietf-rohc-formal-notation]. These fields are used for compression and decompression of some of the uncompressed header fields. Updating the value of one or more control field(s) is thus no less important than updating context values for header fields. Control fields are defined in [I-D.ietf-rohc-formal-notation]. Packet types that initialize or update the value of one or more control field(s) thus include an additional 3-bit CRC, as defined by the packet formats in Section 6.6. The CRC is calculated using the UVALUE of the control field(s) that it covers. This CRC validates all the control fields that are updated. Failure to verify this CRC should be interpreted by the decompressor as a decompression failure, in the algorithm it implements to assess the validity of its context. 5.2. Compressor Concepts Header compression can be conceptually characterized as the interaction of a compressor with a decompressor state machine, one per context. The responsability of the compressor is to minimally send the information needed to successfully decompress a packet, based on a certain confidence regarding the state of the decompressor context. This confidence is obtained from the frequency and the type of information the compressor sends when updating the decompressor context, from the optimistic approach and optionally from feedback messages received from the decompressor. 5.2.1. Optimistic Approach A compressor always uses the optimistic approach when it performs context updates. The compressor normally repeats the same type of update until it is fairly confident that the decompressor has successfully received the information. If the decompressor successfully receives any of the headers containing this update, state will be available for the decompressor to process smaller compressed headers. If field X in the uncompressed header changes value, the compressor uses a packet type that contains an encoding of field X until it has Pelletier & Sandlund Expires March 10, 2007 [Page 10] Internet-Draft ROHCv2 Profiles September 2006 gained confidence that the decompressor has received at least one packet containing the new value for X. The compressor normally selects a compressed format with the smallest header that can convey the changes needed to achieve confidence. The number N of repetitions for the optimistic approach that is needed to obtain this confidence is normally related to the packet loss and to the out-of-order delivery characteristics of the link where header compression is used; it is thus not defined in this document and is left open to implementations. 5.2.2. Tradeoff between robustness to losses and to reordering The ability of a header compression algorithm to handle sequentially late packets is mainly limited by two factors: the interpretation interval offset of the sliding window used for LSB encoded fields [I-D.ietf-rohc-formal-notation], and the optimistic approach Section 5.2.1 for seldom changing fields. The interpretation interval offset specifies an upper limit for the maximum reordering depth, by which is it possible for decompressor to recover the original value of a dynamically changing field that is encoded using W-LSB. Its value is bound to the number of LSB compressed bits in the compressed header format, and grows with the number of bits transmitted. However, the offset and the LSB encoding only provide robustness for the field that it compresses, and (implicitly) for other sequentially changing fields that are derived from that field. This is shown in the figure below: <--- interpretation interval (size is 2^k) ----> |------------------+---------------------------| v_ref-p v_ref v_ref + (2^k-1) - p Lower Upper Bound Bound <--- reordering --> <--------- losses ---------> where delta(SN) = p is the maximum negative delta, corresponding to the maximum reordering depth for which the lsb encoding can recover the original value of the field; where delta(SN) = (2^k-1) - p is the maximum positive delta, corresponding to the maximum number of consecutive losses for which the lsb encoding can recover the original value of the field; Pelletier & Sandlund Expires March 10, 2007 [Page 11] Internet-Draft ROHCv2 Profiles September 2006 where v_ref is the reference value, as defined in the lsb encoding method in [I-D.ietf-rohc-formal-notation]. The optimistic approach Section 5.2.1 provides the upper limit for the maximum reordering depth for seldom changing fields. There is thus a tradeoff between the robustness against reordering and the robustness against packet losses, with respect to the number of MSN bits needed and the distribution of the interpretation interval between negative and positive deltas in the MSN. There is also a tradeoff between compression efficiency and robustness. When only information on the MSN needs to be conveyed to the decompressor, the tradeoff relates to the number of compressed MSN bits in the compressed header format. Otherwise, the tradeoff relates to the implementation of the optimistic approach. 5.2.3. Interactions with the Decompressor Context The compressor normally starts compression with the initial assumption that the decompressor has no useful information to process the new flow, and sends Initialization and Refresh (IR) packets. The compressor can then adjust the compression level based on its confidence that the decompressor has the necessary information to successfully process the compressed headers that it selects. In other words, the responsability of the compressor is to ensure that the decompressor operates with state information that is sufficient to allow decompression of the most efficient compressed header(s), and to allow the decompressor to successfully recover that state information as soon as possible otherwise. The compressor thus has the entire responsability to ensure that the decompressor has the proper information to decompress the type of compressed header that it sends. In other words, the choice of compressed header depends on the following factors: o the outcome of the encoding method applied to each field; o the optimistic approach, with respect to the characteristics of the channel; o the presence or not of an established feedback channel, and if present, feedback received from the decompressor (ACKs, NACKs, Static-NACK and options). Encoding methods normally use previous value(s) from a history of packets whose headers it has previously compressed. The optimistic approach is meant to ensure that at least one compressed header containing the information to update the state for a field is Pelletier & Sandlund Expires March 10, 2007 [Page 12] Internet-Draft ROHCv2 Profiles September 2006 received. Finally, feedback indicates what actions the decompressor has taken with respect its assumptions regarding the validity of its context Section 5.3.2; it indicates what type of compressed header the decompressor can or cannot decompress. The decompressor has the means to detect decompression failures for any type of compressed (CO) header, using the CRC verification. Depending on the frequency and/or on the type of the failure, it might send a negative acknowledgement (NACK) or an explicit request for a complete context update (Static-NACK). However, the decompressor does not have the means to identify the cause of the failure, and in particular decompression of what field(s) is responsible for the failure. The compressor is thus always reponsible to figure out what is the most suitable response to a negative acknowledgement, using the confidence it has in the state of the decompressor context, when selecting the type of compressed header it will use when compressing a header. 5.3. Decompressor Concepts Initially, when sending the first IR packet for a compressed flow, the compressor does not expect to receive feedback for that flow, until such feedback is first received. At this point, the compressor may then assume that the decompressor will continue to send feedback in order to repair its context when necessary. The former is referred to as unidirectional operation, while the latter is called bidirectional operation. The decompressor normally always uses the last received and successfully validated (IR or IR-DYN packets) or verified (CO packets) header as the reference for future decompression. If the received packet is older than the current reference packet based on the MSN in the compressed header, the decompressor may refrain from using this packet as the new reference packet, even if the correctness of its header was successfully verified. The decompressor's responsability is thus to minimally consistently verify the outcome of the decompression attempt, update its context when successful and finally to request context repairs by making coherent usage of feedback, once it starts using it. Specifically, the outcome of every decompression attempt is verified using the CRC present in the compressed header; the decompressor updates the context information when this outcome is successfully verified; finally if the decompressor uses feedback once for a compressed flow then it will continue to do so for as long as the corresponding context is associated with the same profile. Pelletier & Sandlund Expires March 10, 2007 [Page 13] Internet-Draft ROHCv2 Profiles September 2006 5.3.1. Decompressor State Machine The decompressor operation may be represented as a state machine defining three states: No Context (NC), Initial Context (IC) and Full Context (FC). The decompressor starts with no valid context, the NC state. Successful CRC-8 validation of an IR packet moves the decompressor to the IC state, where it stays until it successfully verifies a decompression attempt for compressed header with a 7-bit CRC. The decompressor state machine normally does not leave 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. CRC-8(IR) or CRC-8(IR-DYN) Validation CRC-8(IR) or CRC-7(CO) or CRC-8(IR) CRC-8(IR) CRC-8(IR-DYN) CRC-7(CO) CRC-3(CO) Failure Validation Validation Verification Verification +--->---+ +-->---->--+ +-->----->--+ +-->---->--+ +-->---->--+ | | | | | | | | | | | v | v | v | v | v +-----------------+ +----------------------+ +-------------------+ | No Context (NC) | | Initial Context (IC) | | Full Context (FC) | +-----------------+ +----------------------+ +-------------------+ ^ | ^ CRC-7(CO) | ^ | | Static Context | | Failure or | | Context Damage | | Damage Detected | | PT not allowed | | Detected | +--<-----<-----<--+ +----<------<----+ +--<-----<-----<--+ where: CRC-8(IR) and/or CRC-8(IR-DYN) validation: successful CRC-8 validation for the IR header and the IR-DYN header, respectively. CRC-7(CO) and/or CRC-3(CO) verification: successful CRC verification for the CO header, based on the number of CRC bits carried in the CO header. CRC-7(CO) failure: failure to CRC verify the decompression of a CO header carrying a 7-bit CRC. PT not allowed: the decompressor has received a packet type (PT) for which the decopressor's current context does not provide enough valid state information for that packet to be decompressed. Pelletier & Sandlund Expires March 10, 2007 [Page 14] Internet-Draft ROHCv2 Profiles September 2006 Static Context Damaged Detected: see definition in Section 5.3.2. Context Damage Detected: see definition in Section 5.3.2. 5.3.1.1. No Context (NC) State Initially, while working in the No Context (NC) state, the decompressor has not yet successfully validated an IR packet. Attempting decompression: In the NC state, only packets carrying sufficient information on the static fields (i.e. IR packets) can be decompressed. Upward transition: Upon receiving an IR packet, the decompressor validates the integrity of its header using the CRC-8 validation. If the IR packet is successfully validated, the decompressor updates the context and use this packet as the reference packet. Once an IR packet has initialized the context, the decompressor can transit to the IC state. Feedback logic: In the No Context 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-8 validation, subject to the feedback rate limitation as described in Section 5.3.3. 5.3.1.2. Initial Context (IC) State In the IC state, the decompressor has successfully validated a IR packet. Attempting decompression: In the Initial Context state, only packets carrying sufficient information on the dynamic fields covered by an 8-bit CRC (e.g. IR and IR-DYN) or CO packets carrying a 7-bit CRC can be decompressed. Upward transition: The decompressor can move to the Full Context (FC) state when the CRC verification succeeds for a CO header carrying a 7-bit CRC. Downward transition: Pelletier & Sandlund Expires March 10, 2007 [Page 15] Internet-Draft ROHCv2 Profiles September 2006 The decompressor moves back to the NC state if it assumes static context damage. Feedback logic: In the IC state, the decompressor should send a STATIC-NACK when CRC-8 validation of an IR/IR-DYN fails, or when a CO header carrying a 7-bit CRC fails and if static context damage is assumed, subject to the feedback rate limitation as described Section 5.3.3. If any other packet type is received, the decompressor should treat it as a CRC verification failure when deciding if a NACK is to be sent. 5.3.1.3. Full Context (FC) State In the FC state, the decompressor has successfully verified a CO header with a 7-bit CRC. Attempting decompression: In the Full Context state, decompression can be attempted regardless of the type of packet received. Downward transition: I. Feedback logic: In the Full Context state, the decompressor should send a NACK when CRC-8 validation or CRC verification of any packet type fails and if context damage is assumed, subject to the feedback rate limitation as described in Section 5.3.3. 5.3.2. Decompressor Context Management All header formats carry a CRC and are context updating. A packet for which the CRC succeeds updates the reference values of all header fields, either explicitly (from the information about a field carried within the compressed header) or implicitly (fields that are inferred from other fields). The decompressor may assume that some or the entire context is invalid, following one or more failures to validate or verify a header using the CRC. Because the decompressor cannot know the exact reason(s) of a CRC failure or what field caused it, the validity of the context hence does not refer to what exact context entry is deemed valid or not. Pelletier & Sandlund Expires March 10, 2007 [Page 16] Internet-Draft ROHCv2 Profiles September 2006 Validity of the context rather relates to the detection of a problem with the context. The decompressor first assume that the type of information that most likely caused the failure(s) is the state that normally changes for each packet, i.e. context damage of the dynamic part of the context. Upon repeated failures and unsuccessful repairs, the decompressor then assume that the entire context, including the static part, needs to be repaired, i.e. static context damage. Context Damage Detection The assumption of context damage means that the decompressor will not attemp decompression of a CO headers that carries a 3-bit CRC, and only attempt decompression of IR or IR-DYN headers, or CO headers protected by a CRC-7. Static Context Damage Detection The assumption of static context damage means that the decompressor refrains from attempting decompression of any type of header other than the IR header, as it cannot know what part of its context can be relied upon after first assuming context damage and failed to repair its context, and as a result of too many failures. How these assumptions are made, i.e. how context damage is detected, is open to implementations. It can be based on the residual error rate, where a low error rate makes the decompressor assume damage more often than on a high rate link. The decompressor implements these assumptions by selecting the type of compressed header for it may attempt decompression. In other words, validity of the context refers to the ability of a decompressor to attempt or not decompression of specific packet types. 5.3.3. Feedback logic RoHCv2 profiles may be used in environments with or without feedback capabilities from decompressor to compressor. RoHCv2 however assumes that if a ROHC feedback channel is available and if this channel is used at least once by the decompressor for a specific context, this channel will be used during the entire compression operation for that context. If the connection is broken and the feedback channel disappears, compression should be restarted. The RoHC framework defines 3 types of feedback messages: ACKs, NACKs and STATIC-NACKs. The semantics of each message if defined insection 5.2.3.1. [I-D.ietf-rohc-rfc3095bis-framework] What feedback to send Pelletier & Sandlund Expires March 10, 2007 [Page 17] Internet-Draft ROHCv2 Profiles September 2006 is coupled to the context management of the decompressor, i.e. to the implementation of the context damage detection algorithms as described in Section 5.3.2. The decompressor should send a NACK when it assumes context damage, and it should send a STATIC-NACK when it assumes static context damage. The decompressor is not strictly expected to send ACK feedback upon successful decompression, other than for the purpose of improving compression efficiency. The decompressor should limit the rate at which it sends feedback , for both ACKs and STATIC-NACK/NACKs, and should avoid sending unnecessary duplicates of the same type of feedback message that may be associated to the same event. 6. RoHCv2 Profiles (Normative) 6.1. Profile Operation, per-context RoHCv2 profiles operates differently, per context, depending on how the decompressor uses of a feedback channel. Once the decompressor uses the feedback channel for a context, it establishes the feedback channel for that CID. The compressor always start assuming that the decompressor will not send feedback when it initializes a new context (see also , section 5.1.1.) [I-D.ietf-rohc-rfc3095bis-framework], i.e. there is no established feedback channel for the new context. There will always be a possibility of decompression failure with the optimistic approach, because the decompressor may not have received sufficient information for correct decompression. Therefore, until the decompressor has established a feedback channel, the compressor SHOULD periodically send IR packets. The periodicity can be based on timeouts, on the number of compressed packets sent for the flow, or any other strategy the implementer chooses. The reception of either positive feedback (ACKs) or negative feedback (NACKs) establishes the feedback channel from the decompressor for the context (CID) for which the feedback was received. Once there is an established feedback channel for a specific context, the compressor can make use of this feedback to estimate the current state of the decompressor. 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, and instead it can rely entirely on the optimistic approach and feedback from the decompressor. Pelletier & Sandlund Expires March 10, 2007 [Page 18] Internet-Draft ROHCv2 Profiles September 2006 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) establishes this channel. The decompressor is REQUIRED to continue sending feedback once it has established a feedback channel for a CID, for the lifetime of the context, i.e. until the CID is associated with a different profile from the reception of an IR packet, to send error recovery requests and (optionally) acknowledgments of significant context updates. Due to the periodic refreshes and the lack of feedback for initiation of error recovery, compression without an established feedback channel will be less efficient and have a slightly higher probability of loss propagation compared to the decompressor making use of feedback. 6.2. Control Fields RoHCv2 defines a number of control fields that are used by the decompressor in its interpretation of the packet formats received from the compressor. A control field is a field that is transmitted from the compressor to the decompressor, but is not part of the uncompressed header. Values for control fields can be set up in the context of both the compressor and the decompressor. Once established at the decompressor, the values of these fields MUST be kept until updated by another packet. 6.2.1. Master Sequence Number (MSN) The Master Sequence Number (MSN) field is either taken from a field that already exists in each of the headers of the protocol that the profile compresses (e.g. RTP SN), or alternatively it is created at the compressor. The MSN field has the following two functions: o Differentiating between packets when sending feedback data. o Inferring the value of incrementing fields (e.g. IPv4 Identifier). The MSN field is present in every packet sent by the compressor. The MSN is sent in full in IR and IR-DYN packets, while it is sent LSB encoded within CO header formats. The decompressor always sends the MSN as part of the feedback information. The compressor can later use the MSN to infer which packet the decompressor is acknowledging. Pelletier & Sandlund Expires March 10, 2007 [Page 19] Internet-Draft ROHCv2 Profiles September 2006 When the MSN is initialized, it is initialized to a random value. The compressor should only initialize a new MSN for the initial IR packet sent for a new context, i.e. for a CID that corresponds to a context that is not already associated with the profile used in the IR header. In other words, if the compressor reuses the same CID with the same profile to compress many flows one after the other, the MSN is not reinitialized but rather continues to increment monotonically. For profiles for which the MSN is created by the compressor, the following rules applies: o The compressor should only initialize a new MSN for the initial IR sent for a CID that corresponds to a context that is not already associated with this profile; o When the MSN is initialized, it is initialized to a random value; o The value of the MSN is incremented by one for each packet that the compressor sends. 6.2.2. IP-ID behavior The IP-ID field of the IPv4 header can have different change patterns: sequential in network byte order, sequential byte-swapped, random and constant (a constant value of zero, although not conformant with [RFC0791], as been observed in practice).The control field for the IP-ID behavior determines which set of packet formats will be used. Note that these control fields are also used to determine the contents of the irregular chain item for each IP header. If more than one level of IP headers is present, RoHCv2 profiles can assign a sequential behavior (network byte order or byte-swapped) only to the IP-ID of innermost IP header. This is because only this IP-ID can possibly have a sufficiently close correlation with the MSN to compress it as a sequentially changing field. Therefore, a compressor MUST assign either the constant zero IP-ID or the random IP-ID behavior to tunneling headers. 6.3. Reconstruction and Verification 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 verification, these updates MUST NOT be performed. A packet for which the decompression attempt cannot be verified using the CRC MUST NOT be delivered to upper layers. Pelletier & Sandlund Expires March 10, 2007 [Page 20] Internet-Draft ROHCv2 Profiles September 2006 Note: Decompressor implementations may attempt corrective or repair measures prior to performing the above actions, and the result of any decompression attempt MUST be verified using the CRC. 6.4. Compressed Header Chains Some packet types use one or more chains containing sub-header information. The function of a chain is to group fields based on similar characteristics, such as static, dynamic or irregular fields. Chaining is done by appending an item for each header to the chain in their order of appearance in the uncompressed packet, starting from the fields in the outermost header. Static chain: The static chain consists of one item for each header of the chain of protocol headers to be compressed, starting from the outermost IP header. In the formal description of the packet formats, this static chain item for each header type is labelled _static. The static chain is only used in IR packets. Dynamic chain: The dynamic chain consists of one item for each header of the chain of protocol headers to be compressed, starting from the outermost IP header. In the formal description of the packet formats, the dynamic chain item for each header type is labelled _dynamic. The dynamic chain is used both in IR and IR-DYN packet Irregular chain: The structure of the irregular chain is analogous to the structure of the static chain. For each compressed packet, the irregular chain is appended at the specified location in the general format of the compressed packets as defined in Section 6.6. The irregular chain is used for all CO packets. The format of the irregular chain for the innermost IP header differs from the format of the one for the outer IP headers, since this header is part of the compressed base header. What irregular chain items to use is determined by the argument "is_innermost", which is passed as an argument to the corresponding encoding method (ipv4 or ipv6). The format of the irregular chain item for the outer IP headers is also determined using one flag for TTL/Hop Pelletier & Sandlund Expires March 10, 2007 [Page 21] Internet-Draft ROHCv2 Profiles September 2006 Limit and one for TOS/TC. These flags are defined in the format of some of the compressed base headers. RoHCv2 profiles compresses extension headers as other headers, and thus extension headers have a static chain, a dynamic chain and an irregular chain. Chains are defined for all headers compressed by RoHCv2 profiles, i.e. RTP [RFC3550], UDP [RFC0768], UDP Lite [RFC3828], IPv4 [RFC0791], IPv6 [RFC2460], AH [RFC4302], GRE [RFC2784][RFC2890], MINE [RFC2004], NULL-encrupted ESP [RFC4303], IPv6 Destination Options header[RFC2460], IPv6 Hop-by-hop Options header[RFC2460] and IPv6 Routing header [RFC2460]. 6.5. Packet Formats and Encoding Methods The packet formats used for are defined using the ROHC formal notation. Some of the encoding methods used in the packet formats are defined in [I-D.ietf-rohc-formal-notation], while other methods are defined in this section. 6.5.1. baseheader_extension_headers In CO packets (see Section 6.6.4), the innermost IP header can be combined with other header(s) (i.e. UDP, UDP Lite, RTP) to create the compressed base header. In such case, the IP header may have a number of extension headers between itself and the other headers. The base header defines some representation of these extension headers, to comply with the syntax of the formal notation; this encoding method provides this representation. The baseheader_extension_headers encoding method skips over all fields of the extension headers of the innermost IP header, without encoding any of the them. Fields in these extension headers are instead encoded in the irregular chain. 6.5.2. baseheader_outer_headers This encoding method, similarly to the baseheader_extension_headers encoding method above, is needed to keep the definition of the packet formats syntactically correct. It describe tunneling IP headers and their respective extension headers (i.e. all headers located before the innermost IP header) for CO headers (see Section 6.6.4). The baseheader_outer_headers encoding method skips over all the fields of the extension header(s) that do not belong to the innermost IP header, without encoding any of them. Changed fields in outer headers are instead handled by the irregular chain. Pelletier & Sandlund Expires March 10, 2007 [Page 22] Internet-Draft ROHCv2 Profiles September 2006 6.5.3. inferred_udp_length The UDP length field is inferred by the decompressor to be the size of the UDP payload. This also means that the compressor MUST make sure that the UDP length field is consistent with the length field(s) of preceeding subheaders, i.e., there must not be any padding after the UDP payload that is covered by the IP Length. 6.5.4. inferred_ip_v4_header_checksum This encoding method compresses the header checksum field of the IPv4 header. This checksum is defined in RFC 791 [RFC0791] as follows: Header Checksum: 16 bits A checksum on the header only. Since some header fields change (e.g., time to live), this is recomputed and verified at each point that the internet header is processed. The checksum algorithm is: The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero. As described above, the header checksum protects individual hops from processing a corrupted header. When almost all IP header information is compressed away, and when decompression is verified by a CRC computed over the original header for every compressed packet, there is no point in having this additional checksum; instead it can be recomputed at the decompressor side. The "inferred_ip_v4_header_checksum" encoding method thus compresses the IPv4 header checksum down to a size of zero bit, i.e. no bits are transmitted in compressed headers for this field. Using this encoding method, the decompressor infers the value of this field using the computation above. The compressor MAY use the header checksum to validate the correctness of the header before compressing it, to avoid compressing a corrupted header. 6.5.5. inferred_mine_header_checksum This encoding method compresses the minimal encapsulation header checksum. This checksum is defined in RFC 2004 [RFC2004] as follows: Pelletier & Sandlund Expires March 10, 2007 [Page 23] Internet-Draft ROHCv2 Profiles September 2006 Header Checksum The 16-bit one's complement of the one's complement sum of all 16-bit words in the minimal forwarding header. For purposes of computing the checksum, the value of the checksum field is 0. The IP header and IP payload (after the minimal forwarding header) are not included in this checksum computation. The "inferred_mine_header_checksum" encoding method compresses the minimal encapsulation header checksum down to a size of zero bit, i.e. no bits are transmitted in compressed headers for this field. Using this encoding method, the decompressor infers the value of this field using the above computation. The motivations for inferring this checksum are similar to the ones explained above in Section 6.5.4. The compressor MAY use the minimal encapsulation header checksum to validate the correctness of the header before compressing it, to avoid compressing a corrupted header. 6.5.6. inferred_ip_v4_length This encoding method compresses the total length field of the IPv4 header. The total length field of the IPv4 header is defined in RFC 791 [RFC0791] as follows: Total Length: 16 bits Total Length is the length of the datagram, measured in octets, including internet header and data. This field allows the length of a datagram to be up to 65,535 octets. The "inferred_ip_v4_length" encoding method compresses the IPv4 header checksum down to a size of zero bit, i.e. no bits are transmitted in compressed headers for this field. Using this encoding method, the decompressor infers the value of this field by counting in octets the length of the entire packet after decompression. 6.5.7. inferred_ip_v6_length This encoding method compresses the payload length field in the IPv6 header. This length field is defined in RFC 2460 [RFC2460] as follows: Pelletier & Sandlund Expires March 10, 2007 [Page 24] Internet-Draft ROHCv2 Profiles September 2006 Payload Length: 16-bit unsigned integer Length of the IPv6 payload, i.e., the rest of the packet following this IPv6 header, in octets. (Note that any extension headers present are considered part of the payload, i.e., included in the length count.) The "inferred_ip_v6_length" encoding method compresses the payload length field of the IPv6 header down to a size of zero bit, i.e. no bits are transmitted in compressed headers for this field. Using this encoding method, the decompressor infers the value of this field by counting in octets the length of the entire packet after decompression. 6.5.8. Scaled RTP Timestamp Encoding The RTP timestamp usually increases by a multiple of the RTP Sequence Number's increase and is therefore a suitable candidate for scaled encoding. The scaling factor is decided by the compressor by observing the increase in Timestamp compared to the RTP Sequence Number. This scaling factor is labeled ts_stride in the definition of the profile in ROHC-FNSection 6.6. For the compressor to use the scaled timestamps, it MUST first explicitly transmit the value of ts_stride to the decompressor, using one of the packet types that can carry this information. Once the value of the scaling factor is established, before using this scaled encoding the compressor must have enough confidence that the decompressor has successfully calculated the residue (ts_offset) of the scaling function for the timestamp. This is done by sending unscaled timestamp values to allow the compressor to establish the residue based on the ts_stride established. Once the compressor has gained enough confidence that both the value of the scaling factor and the value of the residue have been established in the decompressor, the compressor can start compressing packets using the scaled representation of the timestamp. The compressor MUST NOT use the scaled timestamp encoding with the value of the ts_stride is set to zero. If the compressor notices that the residue (ts_offset) value changes, the compressor cannot use scaled timestamp packet formats until it has re-established the residue as described above. When the value of the timestamp field wraps around, the value of the residue of the scaling function is likely to change. When this occurs, the compressor re-establishes the new residue value, e.g. using the unscaled representation of the field as described above. Pelletier & Sandlund Expires March 10, 2007 [Page 25] Internet-Draft ROHCv2 Profiles September 2006 The compressor MAY use the scaled timestamp encoding; what value it will use as the scaling factor is up to the compressor implementation, but to achive any gains from the scaling, the ts_stride should be set to the value of the expected incease in timestamp between consecutive sequence numbers. When scaled timestamp encoding is used for packet formats that do not transmit any LSB-encoded timestamp bits at all, the Section 6.5.9 is used for encoding the timestamp. 6.5.9. inferred_scaled_field The "inferred_scaled_field" encoding method is used to encode a field that is defined as changing in relation to the MSN but for each increase is scaled by an established scaling factor. This encoding method is to be used in the case when a packet format contains MSN bits, but does not contain any bits for the scaled field. In this case, the new value for the field being scaled is calculated according to the following formula: unscaled_value = delta_msn * stride + previous_unscaled_value Where "delta_msn" is the difference is MSN between the previous value of MSN in the context and the value of the MSN decompressed from this packet, "previous_unscaled_value" is the value of the field being scaled in the context, and "stride" is the scaling value for this field. For example, when this encoding method is applied to the RTP timestamp in the RTP profile, the calculation above becomes: timestamp = delta_msn * ts_stride + previous_timestamp 6.5.10. control_crc3 Some control fields that can be transmit by the co_common packet type of each profile might not be used when decompressing this packet, and therefore will not be covered by the included 7-bit CRC. If such a control field has been corrupted on the link between compressor and decompressor, the decompressor might send an ACK for this packet which would be interpreted by the compressor as if the control fields included in this packet were successfully decompressed. To avoid such a situation, an additional 3-bit CRC is included in the co_common packets. This 3-bit CRC uses the same polynomial as the crc3 encoding method defined in the formal notation, but has a different coverage. This CRC should be calculated over the following field, in the order that they are listed below: Pelletier & Sandlund Expires March 10, 2007 [Page 26] Internet-Draft ROHCv2 Profiles September 2006 o reorder_ratio, padded by 6 MSB of zeroes o ts_stride, 16 bits (if applicable for this profile) 6.5.11. inferred_sequential_ip_id This encoding method is used when a sequential IP-ID behavior is used (sequential or sequential byte-swapped) and no coded IP-ID bits are present in the compressed header. When these packet types are used, the IP-ID offset from the MSN will be constant, and therefore, the IP-ID will increase by the same amount as the MSN increases by (similar to the inferred_scaled_field encoding method). Therefore, the new value for the IP-ID is calculated according to the following formula: IP-ID = delta_msn + previous_IP_ID_value Where "delta_msn" is the difference is MSN between the previous value of MSN in the context and the value of the MSN decompressed from this packet, "previous_IP_ID_value" is the value of the IP-ID in the context. If the IP-ID behavior is random or zero, this encoding method does not update any fields. 6.5.12. list_csrc(cc_value) This encoding method describes how the list of CSRC identifiers can be compressed using list compression. This list compression operates by establishing content for the different CSRC identifiers (items) and list describing the order that they appear. The argument to this encoding method (cc_value) is the CC field from the RTP header which the compressor passes to this encoding method. The decompressor is reuired to bind the value of this argument to the number of items in the list, which will allow the decompressor to corectly reconstruct the CC field. 6.5.12.1. List Compression The CSRC identifiers in the uncompressed packet can be represented as an ordered list, whose order and presence are usually constant between packets. The generic structure of such a list is as follows: +--------+--------+--...--+--------+ list: | item 1 | item 2 | | item n | +--------+--------+--...--+--------+ When performing list compression on a CSRC list, each item is the uncompressed value of one CSRC identifier. Pelletier & Sandlund Expires March 10, 2007 [Page 27] Internet-Draft ROHCv2 Profiles September 2006 The basic principles of list-based compression are the following: 1) When a context is being initialized, a complete representation of the compressed list of options is transmitted. All items that have any content are present in the compressed list of items sent by the compressor. Then, once the context has been initialized: 2) When the structure of the list is unchanged no information about the list is sent in compressed headers. 3) When the structure of the list changes, a compressed list is sent in the compressed header, including a representation of its structure and order. Previously unknown items are sent uncompressed in the list, while previously known items are only represented by an index pointing to the context. 6.5.12.2. Table-based Item Compression The Table-based item compression compresses individual items sent in compressed lists. The compressor assigns a unique identifier, "Index", to each item "Item" of a list. Compressor Logic The compressor conceptually maintains an Item Table containing all items, indexed using "Index". The (Index, Item) pair is sent together in compressed lists until the compressor gains enough confidence that the decompressor has observed the mapping between items and their respective index. Confidence is obtained from the reception of an acknowledgment from the decompressor, or by sending (Index, Item) pairs using the optimistic approach. Once confidence is obtained, the index alone is sent in compressed lists to indicate the presence of the item corresponding to this index. The compressor may reassign an existing index to a new item, by re-establishing the mapping using the procedure described above. Decompressor Logic The decompressor conceptually maintains an Item Table that contains all (Index, Item) pairs received. The Item Table is updated whenever an (Index, Item) pair is received and decompression is successfully verified using the CRC. The decompressor retrieves the item from the table whenever an Index without an accompanying Item is received. Pelletier & Sandlund Expires March 10, 2007 [Page 28] Internet-Draft ROHCv2 Profiles September 2006 If an index without an accompanying item is received and the decompressor does not have any context for this index, the packet MUST NOT be delivered to upper layers. 6.5.12.3. Encoding of Compressed Lists Each item present in a compressed list is represented by: o an index into the table of items, and o a presence bit indicating if a compressed representation of the item is present in the list. o an item (if the presence bit is set) If the presence bit is not set, the item must already be known by the decompressor. A compressed list of items uses the following encoding: 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | Reserved |PS | m | +---+---+---+---+---+---+---+---+ | XI_1, ..., XI_m | m octets, or m * 4 bits / --- --- --- ---/ | : Padding : if PS = 0 and m is odd +---+---+---+---+---+---+---+---+ | | / item_1, ..., item_n / variable | | +---+---+---+---+---+---+---+---+ Reserved: Must be set to zero. PS: Indicates size of XI fields: PS = 0 indicates 4-bit XI fields; PS = 1 indicates 8-bit XI fields. m: Number of XI item(s) in the compressed list. Also the value of the cc_value argument. XI_1, ..., XI_m: m XI items. Each XI represents one item in the list of item of the uncompressed header, in the same order as they appear in the uncompressed header. Pelletier & Sandlund Expires March 10, 2007 [Page 29] Internet-Draft ROHCv2 Profiles September 2006 The format of an XI item is as follows: +---+---+---+---+ PS = 0: | X | Index | +---+---+---+---+ 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ PS = 1: | X | Reserved | Index | +---+---+---+---+---+---+---+---+ X: Indicates whether the item present in the list: X = 1 indicates that the item corresponding to the Index is sent in the item_1, ..., item_n list; X = 0 indicates that the item corresponding to the Index is not sent. Reserved: Set to zero when sending, ignored when received. Index: An index into the item table. See Section 6.5.12.4 When 4-bit XI items are used and, the XI items are placed in octets in the following manner: 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | XI_k | XI_k + 1 | +---+---+---+---+---+---+---+---+ Padding: A 4-bit padding field is present when PS = 0 and the number of XIs is odd. The Padding field is set to zero when sending and ignored when receiving. Item 1, ..., item n: Each item corresponds to an XI with X = 1 in XI 1, ..., XI m. Each entry in the item list is the uncompressed representation of one CSRC identifier. 6.5.12.4. Item Table Mappings The item table for list compression is limited to 16 different items, since the RTP header can only carry at most 15 simultaneous CSRC identifiers. The effect of having more than 16 items will only cause a slight overhead to the compressor when items are swappen in/out of the item table. Pelletier & Sandlund Expires March 10, 2007 [Page 30] Internet-Draft ROHCv2 Profiles September 2006 6.5.12.5. Compressed Lists in Dynamic Chain A compressed list that is part of the dynamic chain (e.g. in IR or IR-DYN packets) must have all its list items present, i.e. all X-bits in the XI list MUST be set. 6.6. Packet Formats ROHCv2 profiles use two different packet types: the Initialization and Refresh (IR) packet type, and the Compressed packet type (CO). Each packet type defines a number of packet formats: two packet formats are defined for the IR type, and two sets base header formats are defined for the CO type with one additional format that is common to both sets. When the number of bits available in compressed header fields exceeds the number of bits in the value, the most significant field is padded with zeroes in its most significant bits. Updating Properties: all packet types carry a CRC and are context updating. Packets update the entire context besides the fields for which they explicitly convey information for, since the context can be expressed as the collection of the reference value of each field together with the function established with respect to the MSN. 6.6.1. Initialization and Refresh Packet (IR) The IR packet format uses the structure of the ROHC IR packet as defined in [I-D.ietf-rohc-rfc3095bis-framework], section 5.2.2.1. Packet type: IR This packet type communicates the static part and the dynamic part of the context. Pelletier & Sandlund Expires March 10, 2007 [Page 31] Internet-Draft ROHCv2 Profiles September 2006 The ROHCv2 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 1 | IR type octet +---+---+---+---+---+---+---+---+ : : / 0-2 octets of CID / 1-2 octets if for large CIDs : : +---+---+---+---+---+---+---+---+ | Profile | 1 octet +---+---+---+---+---+---+---+---+ | CRC | 1 octet +---+---+---+---+---+---+---+---+ | | / Static chain / variable length | | - - - - - - - - - - - - - - - - | | / Dynamic chain / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - Static chain: See Section 6.4. Dynamic chain: See Section 6.4. Payload: The payload of the corresponding original packet, if any. The presence of a payload is inferred from the packet length. 6.6.2. IR Packet Payload Discard (IR-PD) The IR-PD packet format uses the structure of the ROHC IR packet as defined in [I-D.ietf-rohc-rfc3095bis-framework], section 5.2.2.1. Packet type: IR-PD Pelletier & Sandlund Expires March 10, 2007 [Page 32] Internet-Draft ROHCv2 Profiles September 2006 This packet type communicates the static part and the dynamic part of the context, but without the payload of the original packet for which it carries the header information. The ROHCv2 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 +---+---+---+---+---+---+---+---+ | | / Static chain / variable length | | - - - - - - - - - - - - - - - - | | / Dynamic chain / variable length | | - - - - - - - - - - - - - - - - Static chain: See Section 6.4. Dynamic chain: See Section 6.4. 6.6.3. IR Dynamic Packet (IR-DYN) The IR-DYN packet format uses the structure of the ROHC IR-DYN packet as defined in [I-D.ietf-rohc-rfc3095bis-framework], section 5.2.2.2. Packet type: IR-DYN This packet type communicates the dynamic chains of the header(s) that it compresses. Pelletier & Sandlund Expires March 10, 2007 [Page 33] Internet-Draft ROHCv2 Profiles September 2006 The RoHCv2 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 +---+---+---+---+---+---+---+---+ | | / Dynamic chain / variable length | | - - - - - - - - - - - - - - - - | | / Payload / variable length | | - - - - - - - - - - - - - - - - Dynamic chain: See Section 6.4. Payload: The payload of the corresponding original packet, if any. The presence of a payload is inferred from the packet length. 6.6.4. Compressed Packet Formats (CO) 6.6.4.1. Design rationale for compressed base headers The compressed packet formats are defined as two separate sets for each profile: one set for the packets where the innermost IP header contains a sequential IP-ID (either network byte order or byte swapped), and one set for the packets without sequential IP-ID (either random, zero, or no IP-ID). The design of the packet formats is derived from the field behavior analysis found in Appendix A. All of the compressed base headers transmit LSB-encoded MSN bits and a CRC. In addition, each base header in the sequential packet format set contains LSB encoded IP-ID bits. The following packet formats exist in both the sequential and random Pelletier & Sandlund Expires March 10, 2007 [Page 34] Internet-Draft ROHCv2 Profiles September 2006 packet format sets: o Format 1: This packet format transmits changes [Author's note: TBW] o Format 2: This packet format transmits changes [Author's note: TBW] o Common packet format: The common packet format can be used indenpendently of the type of IP-ID behavior. It should also be useful when some of the more rarely changing fields in the IP header changes. Since this packet format modify the value of the control fields that determine how the decompressor interprets different compressed header format, it carries a 7-bit CRC to reduce the probability of context corruption. This packet can change most of the dynamic fields in the IP header, and it uses a large set of flags to provide information about which fields are present in the packet format. 6.6.4.2. General CO Header Format The CO packets communicate irregularities in the packet header. All CO packets carry a CRC and can update the context. The general format for a compressed header is as follows: 0 1 2 3 4 5 6 7 --- --- --- --- --- --- --- --- : Add-CID octet : if for small CIDs and CID 1-15 +---+---+---+---+---+---+---+---+ | first octet of base header | (with type indication) +---+---+---+---+---+---+---+---+ : : / 0, 1, or 2 octets of CID / 1-2 octets if large CIDs : : +---+---+---+---+---+---+---+---+ / remainder of base header / variable number of octets +---+---+---+---+---+---+---+---+ : : / Irregular Chain / variable : : --- --- --- --- --- --- --- --- The base header in the figure above is the compressed representation of the innermost IP header and other header(s), if any, in the uncompressed packet. Upon receiving other types of packet, the decompressor will decompress it. The decompressor MUST verify the correctness of the Pelletier & Sandlund Expires March 10, 2007 [Page 35] Internet-Draft ROHCv2 Profiles September 2006 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 packet. The entire set of base headers are described in the remainder of this section. //////////////////////////////////////////// // Constants //////////////////////////////////////////// // IP-ID behavior constants IP_ID_BEHAVIOR_SEQUENTIAL = 0; IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED = 1; IP_ID_BEHAVIOR_RANDOM = 2; IP_ID_BEHAVIOR_ZERO = 3; // UDP-lite checksum coverage behavior constants UDP_LITE_COVERAGE_INFERRED = 0; UDP_LITE_COVERAGE_STATIC = 1; UDP_LITE_COVERAGE_IRREGULAR = 2; UDP_LITE_COVERAGE_RESERVED = 3; // Variable reordering offset REORDERING_NONE = 0; REORDERING_QUARTER = 1; REORDERING_HALF = 2; REORDERING_THREEQUARTERS = 3; // Profile names and versions PROFILE_RTP_0101 = 1; PROFILE_UDP_0102 = 2; PROFILE_ESP_0103 = 3; PROFILE_IP_0104 = 4; PROFILE_RTP_0107 = 7; // With UDP-LITE PROFILE_UDPLITE_0108 = 8; // Without RTP //////////////////////////////////////////// // Global control fields //////////////////////////////////////////// CONTROL { msn [ 16 ]; reorder_ratio [ 2 ]; } /////////////////////////////////////////////// Pelletier & Sandlund Expires March 10, 2007 [Page 36] Internet-Draft ROHCv2 Profiles September 2006 // Encoding methods not specified in FN syntax: /////////////////////////////////////////////// baseheader_extension_headers "defined in Section X.Y.Z"; baseheader_outer_headers "defined in Section X.Y.Z"; inferred_udp_length "defined in Section X.Y.Z"; inferred_ip_v4_header_checksum "defined in Section X.Y.Z"; inferred_mine_header_checksum "defined in Section X.Y.Z"; inferred_ip_v4_length "defined in Section X.Y.Z"; inferred_ip_v6_length "defined in Section X.Y.Z"; list_csrc(cc_value) "defined in Section X.Y.Z"; inferred_scaled_field "defined in Section X.Y.Z"; inferred_sequential_ip_id "defined in Section X.Y.Z"; control_crc3 "defined in Section X.Y.Z"; //////////////////////////////////////////// // General encoding methods //////////////////////////////////////////// reorder_ratio_choice { UNCOMPRESSED { ratio [ 2 ]; } DEFAULT { ratio =:= irregular(2); } COMPRESSED none { ratio [ 2 ]; ENFORCE(ratio.UVALUE == REORDERING_NONE); } COMPRESSED quarter { ratio [ 2 ]; ENFORCE(ratio.UVALUE == REORDERING_QUARTER); } COMPRESSED half { ratio [ 2 ]; ENFORCE(ratio.UVALUE == REORDERING_HALF); } COMPRESSED three_quarters { ratio [ 2 ]; ENFORCE(ratio.UVALUE == REORDERING_THREEQUARTERS); } Pelletier & Sandlund Expires March 10, 2007 [Page 37] Internet-Draft ROHCv2 Profiles September 2006 } static_or_irreg(flag, width) { UNCOMPRESSED { field [ width ]; } COMPRESSED irreg_enc { field =:= irregular(width) [ width ]; ENFORCE(flag == 1); } COMPRESSED static_enc { field =:= static [ 0 ]; ENFORCE(flag == 0); } } optional32(flag) { UNCOMPRESSED { item [ 0, 32 ]; } COMPRESSED present { item =:= irregular(32) [ 32 ]; ENFORCE(flag == 1); } COMPRESSED not_present { item =:= compressed_value(0, 0) [ 0 ]; ENFORCE(flag == 0); } } // Self-describing variable length encoding sdvl(field_width) { UNCOMPRESSED { field [ field_width ]; } COMPRESSED lsb7 { discriminator =:= '0' [ 1 ]; field =:= lsb(7, 63) [ 7 ]; } Pelletier & Sandlund Expires March 10, 2007 [Page 38] Internet-Draft ROHCv2 Profiles September 2006 COMPRESSED lsb14 { discriminator =:= '10' [ 2 ]; field =:= lsb(14, 16383) [ 14 ]; } COMPRESSED lsb21 { discriminator =:= '110' [ 3 ]; field =:= lsb(21, 65535) [ 21 ]; } COMPRESSED lsb29 { discriminator =:= '110' [ 3 ]; field =:= lsb(29, 65535) [ 29 ]; } } optional_stride(flag, value) { UNCOMPRESSED { field [ 32 ]; } COMPRESSED present { field =:= sdvl(32); ENFORCE(flag == 1); } COMPRESSED not_present { field =:= static; ENFORCE(flag == 0); } } optional_scaled_timestamp(tss_flag, tsc_flag) { UNCOMPRESSED { timestamp [ 32 ]; } COMPRESSED present { timestamp =:= sdvl(32); ENFORCE((tss_flag == 0) && (tsc_flag == 1)); } COMPRESSED not_present { ENFORCE(((tss_flag == 1) && (tsc_flag == 0)) || ((tss_flag == 0) && (tsc_flag == 0))); } Pelletier & Sandlund Expires March 10, 2007 [Page 39] Internet-Draft ROHCv2 Profiles September 2006 } optional_unscaled_timestamp(tss_flag, tsc_flag) { UNCOMPRESSED { timestamp [ 32 ]; } COMPRESSED present { timestamp =:= sdvl(32); ENFORCE(((tss_flag == 1) && (tsc_flag == 0)) || ((tss_flag == 0) && (tsc_flag == 0))); } COMPRESSED not_present { ENFORCE((tss_flag == 0) && (tsc_flag == 1)); } } lsb_7_or_31 { UNCOMPRESSED { item [ 32 ]; } COMPRESSED lsb_7 { discriminator =:= '0' [ 1 ]; item =:= lsb(7, 8) [ 7 ]; } COMPRESSED lsb_31 { discriminator =:= '1' [ 1 ]; item =:= lsb(31, 256) [ 31 ]; } } opt_lsb_7_or_31(flag) { UNCOMPRESSED { item [ 0, 32 ]; } COMPRESSED present { item =:= lsb_7_or_31 [ 8, 32 ]; ENFORCE(flag == 1); } COMPRESSED not_present { Pelletier & Sandlund Expires March 10, 2007 [Page 40] Internet-Draft ROHCv2 Profiles September 2006 item =:= compressed_value(0, 0) [ 0 ]; ENFORCE(flag == 0); } } crc3(data_value, data_length) { UNCOMPRESSED { } COMPRESSED { crc_value =:= crc(3, 0x06, 0x07, data_value, data_length) [ 3 ]; } } crc7(data_value, data_length) { UNCOMPRESSED { } COMPRESSED { crc_value =:= crc(7, 0x79, 0x7f, data_value, data_length) [ 7 ]; } } optional_pt(flag) { UNCOMPRESSED { payload_type [ 7 ]; } COMPRESSED not_present { payload_type =:= static [ 0 ]; ENFORCE(flag == 0); } COMPRESSED present { reserved =:= compressed_value(1, 0) [ 1 ]; payload_type =:= irregular(7) [ 7 ]; ENFORCE(flag == 1); } } csrc_list_presence(presence, cc_value) { UNCOMPRESSED { Pelletier & Sandlund Expires March 10, 2007 [Page 41] Internet-Draft ROHCv2 Profiles September 2006 csrc_list; } COMPRESSED no_list { csrc_list =:= static [ 0 ]; ENFORCE(presence == 0); } COMPRESSED list_present { csrc_list =:= list_csrc(cc_value) [ VARIABLE ]; ENFORCE(presence == 1); } } // Variable reordering offset used for MSN msn_lsb(k) { UNCOMPRESSED { master [ 16 ]; } COMPRESSED none { master =:= lsb(k, -1); ENFORCE(reorder_ratio.UVALUE == REORDERING_NONE); } COMPRESSED quarter { master =:= lsb(k, ((2^k) / 4) - 1); ENFORCE(reorder_ratio.UVALUE == REORDERING_QUARTER); } COMPRESSED half { master =:= lsb(k, ((2^k) / 2) - 1); ENFORCE(reorder_ratio.UVALUE == REORDERING_HALF); } COMPRESSED threequarters { master =:= lsb(k, (((2^k) * 3) / 4) - 1); ENFORCE(reorder_ratio.UVALUE == REORDERING_THREEQUARTERS); } } // Encoding method for updating a scaled field and its associated // control fields. Should be used both when the value is scaled // or unscaled in a compressed format. field_scaling(stride_value, scaled_value, unscaled_value) { UNCOMPRESSED { Pelletier & Sandlund Expires March 10, 2007 [Page 42] Internet-Draft ROHCv2 Profiles September 2006 residue_field [ 32 ]; } COMPRESSED no_scaling { ENFORCE(stride_value == 0); ENFORCE(residue_field.UVALUE == unscaled_value); ENFORCE(scaled_value == 0); } COMPRESSED scaling_used { ENFORCE(stride_value != 0); ENFORCE(residue_field.UVALUE == (unscaled_value % stride_value)); ENFORCE(unscaled_value == scaled_value * stride_value + residue_field.UVALUE); } } //////////////////////////////////////////// // IPv6 Destination options header //////////////////////////////////////////// ip_dest_opt { UNCOMPRESSED { next_header [ 8 ]; length [ 8 ]; value [ VARIABLE ]; } DEFAULT { length =:= static; next_header =:= static; value =:= static; } COMPRESSED dest_opt_static { next_header =:= irregular(8) [ 8 ]; length =:= irregular(8) [ 8 ]; } COMPRESSED dest_opt_dynamic { value =:= irregular(length.UVALUE * 64 + 48) [ VARIABLE ]; } } //////////////////////////////////////////// // IPv6 Hop-by-Hop options header //////////////////////////////////////////// Pelletier & Sandlund Expires March 10, 2007 [Page 43] Internet-Draft ROHCv2 Profiles September 2006 ip_hop_opt { UNCOMPRESSED { next_header [ 8 ]; length [ 8 ]; value [ VARIABLE ]; } DEFAULT { length =:= static; next_header =:= static; value =:= static; } COMPRESSED hop_opt_static { next_header =:= irregular(8) [ 8 ]; length =:= irregular(8) [ 8 ]; } COMPRESSED hop_opt_dynamic { value =:= irregular(length.UVALUE*64+48) [ VARIABLE ]; } } //////////////////////////////////////////// // IPv6 Routing header //////////////////////////////////////////// ip_rout_opt { UNCOMPRESSED { next_header [ 8 ]; length [ 8 ]; value [ VARIABLE ]; } DEFAULT { length =:= static; next_header =:= static; value =:= static; } COMPRESSED rout_opt_static { next_header =:= irregular(8) [ 8 ]; length =:= irregular(8) [ 8 ]; value =:= irregular(length.UVALUE*64+48) [ VARIABLE ]; } Pelletier & Sandlund Expires March 10, 2007 [Page 44] Internet-Draft ROHCv2 Profiles September 2006 COMPRESSED rout_opt_dynamic { } } //////////////////////////////////////////// // GRE Header //////////////////////////////////////////// optional_checksum(flag_value) { UNCOMPRESSED { value [ 0, 16 ]; reserved1 [ 0, 16 ]; } COMPRESSED cs_present { value =:= irregular(16) [ 16 ]; reserved1 =:= uncompressed_value(16, 0) [ 0 ]; ENFORCE(flag_value == 1); } COMPRESSED not_present { value =:= compressed_value(0, 0) [ 0 ]; reserved1 =:= compressed_value(0, 0) [ 0 ]; ENFORCE(flag_value == 0); } } gre_proto { UNCOMPRESSED { protocol [ 16 ]; } COMPRESSED ether_v4 { discriminator =:= compressed_value(1, 0) [ 1 ]; protocol =:= uncompressed_value(16, 0x0800); } COMPRESSED ether_v6 { discriminator =:= compressed_value(1, 1) [ 1 ]; protocol =:= uncompressed_value(16, 0x86DD); } } gre { UNCOMPRESSED { Pelletier & Sandlund Expires March 10, 2007 [Page 45] Internet-Draft ROHCv2 Profiles September 2006 c_flag [ 1 ]; r_flag =:= uncompressed_value(1, 0) [ 1 ]; k_flag [ 1 ]; s_flag [ 1 ]; reserved0 =:= uncompressed_value(9, 0) [ 9 ]; version =:= uncompressed_value(3, 0) [ 3 ]; protocol [ 16 ]; checksum_and_res [ 0, 32 ]; key [ 0, 32 ]; sequence_number [ 0, 32 ]; } DEFAULT { c_flag =:= static; k_flag =:= static; s_flag =:= static; protocol =:= static; key =:= static; sequence_number =:= static; } COMPRESSED gre_static { protocol =:= gre_proto [ 1 ]; c_flag =:= irregular(1) [ 1 ]; k_flag =:= irregular(1) [ 1 ]; s_flag =:= irregular(1) [ 1 ]; padding =:= compressed_value(4, 0) [ 4 ]; key =:= optional32(k_flag.UVALUE) [ 0, 32 ]; } COMPRESSED gre_dynamic { checksum_and_res =:= optional_checksum(c_flag.UVALUE) [ 0, 16 ]; sequence_number =:= optional32(s_flag.UVALUE) [ 0, 32 ]; } COMPRESSED gre_irregular { checksum_and_res =:= optional_checksum(c_flag.UVALUE) [ 0, 16 ]; sequence_number =:= opt_lsb_7_or_31(s_flag.UVALUE) [ 0, 8, 32 ]; } } ///////////////////////////////////////////// // MINE header ///////////////////////////////////////////// Pelletier & Sandlund Expires March 10, 2007 [Page 46] Internet-Draft ROHCv2 Profiles September 2006 mine { UNCOMPRESSED { next_header [ 8 ]; s_bit [ 1 ]; res_bits [ 7 ]; checksum [ 16 ]; orig_dest [ 32 ]; orig_src [ 0, 32 ]; } DEFAULT { next_header =:= static; s_bit =:= static; res_bits =:= static; checksum =:= inferred_mine_header_checksum; orig_dest =:= static; orig_src =:= static; } COMPRESSED mine_static { next_header =:= irregular(8) [ 8 ]; s_bit =:= irregular(1) [ 1 ]; // Reserved are included - no benefit in removing them res_bits =:= irregular(7) [ 7 ]; orig_dest =:= irregular(32) [ 32 ]; orig_src =:= optional32(s_bit.UVALUE) [ 0, 32 ]; } COMPRESSED mine_dynamic { } } ///////////////////////////////////////////// // Authentication Header (AH) ///////////////////////////////////////////// ah { UNCOMPRESSED { next_header [ 8 ]; length [ 8 ]; res_bits [ 16 ]; spi [ 32 ]; sequence_number [ 32 ]; auth_data [ VARIABLE ]; } Pelletier & Sandlund Expires March 10, 2007 [Page 47] Internet-Draft ROHCv2 Profiles September 2006 DEFAULT { next_header =:= static; length =:= static; res_bits =:= static; spi =:= static; sequence_number =:= static; } COMPRESSED ah_static { next_header =:= irregular(8) [ 8 ]; length =:= irregular(8) [ 8 ]; spi =:= irregular(32) [ 32 ]; } COMPRESSED ah_dynamic { res_bits =:= irregular(16) [ 16 ]; sequence_number =:= irregular(32) [ 32 ]; auth_data =:= irregular(length.UVALUE*32-32) [ VARIABLE ]; } COMPRESSED ah_irregular { sequence_number =:= lsb_7_or_31 [ 8, 32 ]; auth_data =:= irregular(length.UVALUE*32-32) [ VARIABLE ]; } } ///////////////////////////////////////////// // ESP header (NULL encrypted) ///////////////////////////////////////////// // Since the "next header" field is located in the packet trailer // and ROHC-FN requires all UNCOMPRESSED fields to be contiguous, // the values of the next header field is passed as a parameter. // To avoid forcing the decompression to access the trailer part of // the packet, the next header is istead handled with a control field esp_null(next_header_value) { UNCOMPRESSED { spi [ 32 ]; sequence_number [ 32 ]; } CONTROL { nh_field [ 8 ]; } Pelletier & Sandlund Expires March 10, 2007 [Page 48] Internet-Draft ROHCv2 Profiles September 2006 DEFAULT { spi =:= static; sequence_number =:= static; nh_field =:= static; } COMPRESSED esp_static { nh_field =:= compressed_value(8, next_header_value) [ 8 ]; spi =:= irregular(32) [ 32 ]; } COMPRESSED esp_dynamic { sequence_number =:= irregular(32) [ 32 ]; } COMPRESSED esp_irregular { sequence_number =:= lsb_7_or_31 [ 8, 32 ]; } } ///////////////////////////////////////////// // IPv6 Header ///////////////////////////////////////////// fl_enc { UNCOMPRESSED { flow_label [ 20 ]; } COMPRESSED fl_zero { discriminator =:= '0' [ 1 ]; flow_label =:= uncompressed_value(20, 0) [ 0 ]; reserved =:= '0000' [ 4 ]; } COMPRESSED fl_non_zero { discriminator =:= '1' [ 1 ]; flow_label =:= irregular(20) [ 20 ]; } } // The is_innermost flag should be true if this is the innermost // IP header to be compressed. // If extracting the irregular chain for an compressed packet, // the TTL&TOS arguments must have the same value as it had when // processing co_baseheader. If extracting any other chain // items, this argument is not used. Pelletier & Sandlund Expires March 10, 2007 [Page 49] Internet-Draft ROHCv2 Profiles September 2006 ipv6(profile, is_innermost, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED { version =:= uncompressed_value(4, 6) [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dst_addr [ 128 ]; } DEFAULT { tos_tc =:= static; flow_label =:= static; payload_length =:= inferred_ip_v6_length; next_header =:= static; ttl_hopl =:= static; src_addr =:= static; dst_addr =:= static; } COMPRESSED ipv6_static { version_flag =:= '1' [ 1 ]; reserved =:= '00' [ 2 ]; flow_label =:= fl_enc [ 5, 21 ]; next_header =:= irregular(8) [ 8 ]; src_addr =:= irregular(128) [ 128 ]; dst_addr =:= irregular(128) [ 128 ]; } COMPRESSED ipv6_endpoint_dynamic { tos_tc =:= irregular(8) [ 8 ]; ttl_hopl =:= irregular(8) [ 8 ]; reserved =:= compressed_value(6, 0) [ 6 ]; reorder_ratio =:= reorder_choice [ 2 ]; ENFORCE((is_innermost == true) && (profile == PROFILE_IP_0104)); } COMPRESSED ipv6_regular_dynamic { tos_tc =:= irregular(8) [ 8 ]; ttl_hopl =:= irregular(8) [ 8 ]; ENFORCE((is_innermost == false) || (profile != PROFILE_IP_0104)); } Pelletier & Sandlund Expires March 10, 2007 [Page 50] Internet-Draft ROHCv2 Profiles September 2006 COMPRESSED ipv6_outer_irregular { tos_tc =:= static_or_irreg(tos_irregular_chain_flag) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_irregular_chain_flag) [ 0, 8 ]; ENFORCE(is_innermost == false); } COMPRESSED ipv6_innermost_irregular { ENFORCE(is_innermost == true); } } ///////////////////////////////////////////// // IPv4 Header ///////////////////////////////////////////// ip_id_enc_dyn(behavior) { UNCOMPRESSED { ip_id [ 16 ]; } COMPRESSED ip_id_seq { ip_id =:= irregular(16) [ 16 ]; ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) || (behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED) || (behavior == IP_ID_BEHAVIOR_RANDOM)); } COMPRESSED ip_id_zero { ip_id =:= uncompressed_value(16, 0) [ 0 ]; ENFORCE(behavior == IP_ID_BEHAVIOR_ZERO); } } ip_id_enc_irreg(behavior) { UNCOMPRESSED { ip_id [ 16 ]; } COMPRESSED ip_id_seq { ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL); } COMPRESSED ip_id_seq_swapped { Pelletier & Sandlund Expires March 10, 2007 [Page 51] Internet-Draft ROHCv2 Profiles September 2006 ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED); } COMPRESSED ip_id_rand { ip_id =:= irregular(16) [ 16 ]; ENFORCE(behavior == IP_ID_BEHAVIOR_RANDOM); } COMPRESSED ip_id_zero { ip_id =:= uncompressed_value(16, 0) [ 0 ]; ENFORCE(behavior == IP_ID_BEHAVIOR_ZERO); } } ip_id_behavior_choice { UNCOMPRESSED { behavior [ 2 ]; } DEFAULT { behavior =:= irregular(2); } COMPRESSED sequential { behavior [ 2 ]; ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL); } COMPRESSED sequential_swapped { behavior [ 2 ]; ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED); } COMPRESSED random { behavior [ 2 ]; ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } COMPRESSED zero { behavior [ 2 ]; ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_ZERO); } } // The is_innermost flag should be true if this is the innermost // IP header to be compressed. Pelletier & Sandlund Expires March 10, 2007 [Page 52] Internet-Draft ROHCv2 Profiles September 2006 // If extracting the irregular chain for an compressed packet, // the TTL&TOS arguments must have the same value as it had when // processing co_baseheader. If extracting any other chain // items, this argument is not used. ipv4(profile, is_innermost, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED { version =:= uncompressed_value(4, 4) [ 4 ]; hdr_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; protocol [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dst_addr [ 32 ]; } CONTROL { ip_id_behavior [ 2 ]; } DEFAULT { tos_tc =:= static; length =:= inferred_ip_v4_length; df =:= static; ttl_hopl =:= static; protocol =:= static; checksum =:= inferred_ip_v4_header_checksum; src_addr =:= static; dst_addr =:= static; ip_id_behavior =:= static; } COMPRESSED ipv4_static { version_flag =:= '0' [ 1 ]; reserved =:= '0000000' [ 7 ]; protocol =:= irregular(8) [ 8 ]; src_addr =:= irregular(32) [ 32 ]; dst_addr =:= irregular(32) [ 32 ]; } Pelletier & Sandlund Expires March 10, 2007 [Page 53] Internet-Draft ROHCv2 Profiles September 2006 COMPRESSED ipv4_endpoint_dynamic { reserved =:= '000' [ 5 ]; reorder_ratio =:= reorder_choice [ 2 ]; df =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; tos_tc =:= irregular(8) [ 8 ]; ttl_hopl =:= irregular(8) [ 8 ]; ip_id =:= ip_id_enc_dyn(ip_id_behavior.UVALUE) [ 0, 16 ]; ENFORCE((is_innermost == true) && (profile == PROFILE_IP_0104)); } COMPRESSED ipv4_regular_dynamic { reserved =:= '00000' [ 5 ]; df =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; tos_tc =:= irregular(8) [ 8 ]; ttl_hopl =:= irregular(8) [ 8 ]; ip_id =:= ip_id_enc_dyn(ip_id_behavior.UVALUE) [ 0, 16 ]; ENFORCE((is_innermost == false) || (profile != PROFILE_IP_0104)); } COMPRESSED ipv4_outer_irregular { ip_id =:= ip_id_enc_irreg(ip_id_behavior.UVALUE) [ 0, 16 ]; tos_tc =:= static_or_irreg(tos_irregular_chain_flag) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_irregular_chain_flag) [ 0, 8 ]; ENFORCE(is_innermost == false); } COMPRESSED ipv4_innermost_irregular { ip_id =:= ip_id_enc_irreg(ip_id_behavior.UVALUE) [ 0, 16 ]; ENFORCE(is_innermost == true); } } ///////////////////////////////////////////// // UDP Header ///////////////////////////////////////////// udp(profile) { Pelletier & Sandlund Expires March 10, 2007 [Page 54] Internet-Draft ROHCv2 Profiles September 2006 UNCOMPRESSED { src_port [ 16 ]; dst_port [ 16 ]; udp_length [ 16 ]; checksum [ 16 ]; ENFORCE((profile == PROFILE_RTP_0101) || (profile == PROFILE_UDP_0102)); } DEFAULT { src_port =:= static; dst_port =:= static; udp_length =:= inferred_udp_length; checksum =:= irregular(16); } COMPRESSED udp_static { src_port =:= irregular(16) [ 16 ]; dst_port =:= irregular(16) [ 16 ]; } COMPRESSED udp_endpoint_dynamic { checksum [ 16 ]; msn =:= irregular(16) [ 16 ]; reserved =:= uncompressed_value(6, 0); reorder_ratio =:= reorder_choice [ 2 ]; ENFORCE(profile == PROFILE_UDP_0102); } COMPRESSED udp_regular_dynamic { checksum [ 16 ]; } COMPRESSED udp_zero_checksum_irregular { ENFORCE(checksum.UVALUE == 0); checksum =:= uncompressed_value(16, 0); } COMPRESSED udp_with_checksum_irregular { ENFORCE(checksum.UVALUE == 1); checksum [ 16 ]; } } ///////////////////////////////////////////// // RTP Header ///////////////////////////////////////////// Pelletier & Sandlund Expires March 10, 2007 [Page 55] Internet-Draft ROHCv2 Profiles September 2006 csrc_list_dynchain(presence, cc_value) { UNCOMPRESSED { csrc_list; } COMPRESSED no_list { csrc_list =:= uncompressed_value(0, 0) [ 0 ]; ENFORCE(cc_value == 0); ENFORCE(presence == 0); } COMPRESSED list_present { csrc_list =:= list_csrc(cc_value) [ VARIABLE ]; ENFORCE(presence == 1); } } rtp(profile, ts_stride_value) { UNCOMPRESSED { rtp_version =:= uncompressed_value(2, 0) [ 2 ]; pad_bit [ 1 ]; extension [ 1 ]; cc [ 4 ]; marker [ 1 ]; payload_type [ 7 ]; sequence_number [ 16 ]; timestamp [ 32 ]; ssrc [ 32 ]; csrc_list [ VARIABLE ]; ENFORCE((profile == PROFILE_RTP_0101) || (profile == PROFILE_RTP_0107)); } CONTROL { // The ts_stride has an initial UVALUE=1, which means that it // can be encoded with 'static' even if it has not been // previously established in the context. ts_stride [ 32 ]; ts_scaled [ 32 ]; ts_offset =:= field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE, timestamp.UVALUE) [ 32 ]; } DEFAULT { pad_bit =:= static; Pelletier & Sandlund Expires March 10, 2007 [Page 56] Internet-Draft ROHCv2 Profiles September 2006 extension =:= static; cc =:= static; marker =:= static; payload_type =:= static; sequence_number =:= static; timestamp =:= static; ssrc =:= static; csrc_list =:= static; } COMPRESSED rtp_static { ssrc =:= irregular(32) [ 32 ]; } COMPRESSED rtp_dynamic { reserved =:= compressed_value(1, 0) [ 1 ]; reorder_ratio =:= reorder_choice [ 2 ]; list_present =:= irregular(1) [ 1 ]; tss_indicator =:= irregular(1) [ 1 ]; pad_bit =:= irregular(1) [ 1 ]; extension =:= irregular(1) [ 1 ]; marker =:= irregular(1) [ 1 ]; payload_type =:= irregular(7) [ 7 ]; sequence_number =:= irregular(16) [ 16 ]; timestamp =:= irregular(32) [ 32 ]; ts_stride =:= optional_stride(tss_indicator, ts_stride_value) [ VARIABLE ]; csrc_list =:= csrc_list_dynchain(list_present, cc.UVALUE) [ VARIABLE ]; } COMPRESSED rtp_irregular { } } ///////////////////////////////////////////// // UDP-Lite Header ///////////////////////////////////////////// checksum_coverage_dynchain(behavior) { UNCOMPRESSED { checksum_coverage [ 16 ]; } COMPRESSED inferred_coverage { checksum_coverage =:= inferred_udp_length [ 0 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 57] Internet-Draft ROHCv2 Profiles September 2006 ENFORCE(behavior == UDP_LITE_COVERAGE_INFERRED); } COMPRESSED static_coverage { checksum_coverage =:= irregular(16) [ 16 ]; ENFORCE(behavior == UDP_LITE_COVERAGE_STATIC); } COMPRESSED irregular_coverage { checksum_coverage =:= irregular(16) [ 16 ]; ENFORCE(behavior == UDP_LITE_COVERAGE_IRREGULAR); } } checksum_coverage_irregular(behavior) { UNCOMPRESSED { checksum_coverage [ 16 ]; } COMPRESSED inferred_coverage { checksum_coverage =:= inferred_udp_length [ 0 ]; ENFORCE(behavior == UDP_LITE_COVERAGE_INFERRED); } COMPRESSED static_coverage { checksum_coverage =:= static [ 0 ]; ENFORCE(behavior == UDP_LITE_COVERAGE_STATIC); } COMPRESSED irregular_coverage { checksum_coverage =:= irregular(16) [ 16 ]; ENFORCE(behavior == UDP_LITE_COVERAGE_IRREGULAR); } } udp_lite(profile) { UNCOMPRESSED { src_port [ 16 ]; dst_port [ 16 ]; checksum_coverage [ 16 ]; checksum [ 16 ]; ENFORCE((profile == PROFILE_RTP_0107) || (profile == PROFILE_UDPLITE_0108)); } CONTROL { Pelletier & Sandlund Expires March 10, 2007 [Page 58] Internet-Draft ROHCv2 Profiles September 2006 coverage_behavior [ 2 ]; } DEFAULT { src_port =:= static; dst_port =:= static; checksum_coverage =:= irregular(16); checksum =:= irregular(16); } COMPRESSED udp_lite_static { src_port =:= irregular(16) [ 16 ]; dst_port =:= irregular(16) [ 16 ]; } COMPRESSED udp_lite_endpoint_dynamic { reserved =:= compressed_value(4, 0) [ 4 ]; coverage_behavior =:= irregular(2) [ 2 ]; reorder_ratio =:= reorder_choice [ 2 ]; checksum_coverage =:= checksum_coverage_dynchain(coverage_behavior.UVALUE) [ 16 ]; checksum [ 16 ]; msn =:= irregular(16) [ 16 ]; ENFORCE(profile == PROFILE_UDPLITE_0108); } COMPRESSED udp_lite_regular_dynamic { coverage_behavior =:= irregular(2) [ 2 ]; reserved =:= compressed_value(6, 0) [ 6 ]; checksum_coverage =:= checksum_coverage_dynchain(coverage_behavior.UVALUE) [ 16 ]; checksum [ 16 ]; } COMPRESSED udp_lite_irregular { checksum_coverage =:= checksum_coverage_dynchain(coverage_behavior.UVALUE) [ 0, 16 ]; checksum [ 16 ]; } } ///////////////////////////////////////////// // ESP Header (Non-NULL encrypted // i.e. only used for the ESP profile ///////////////////////////////////////////// esp(profile) { Pelletier & Sandlund Expires March 10, 2007 [Page 59] Internet-Draft ROHCv2 Profiles September 2006 UNCOMPRESSED { spi [ 32 ]; sequence_number [ 32 ]; ENFORCE(profile == PROFILE_ESP_0103); } DEFAULT { spi =:= static; sequence_number =:= static; } COMPRESSED esp_static { spi =:= irregular(32) [ 32 ]; } COMPRESSED esp_dynamic { sequence_number =:= irregular(32) [ 32 ]; msn =:= irregular(16) [ 16 ]; reserved =:= uncompressed_value(6, 0) [ 6 ]; reorder_ratio =:= reorder_choice [ 2 ]; } COMPRESSED esp_irregular { } } /////////////////////////////////////////////////// // Encoding methods used in the profiles' CO packets /////////////////////////////////////////////////// ip_id_lsb(behavior, k, p) { UNCOMPRESSED { ip_id [ 16 ]; } CONTROL { ip_id_offset [ 16 ]; ip_id_nbo [ 16 ]; } COMPRESSED nbo { ip_id_offset =:= lsb(k, p) [ VARIABLE ]; ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL); ENFORCE(ip_id_offset.UVALUE == ip_id.UVALUE - msn.UVALUE); } COMPRESSED non_nbo { Pelletier & Sandlund Expires March 10, 2007 [Page 60] Internet-Draft ROHCv2 Profiles September 2006 ip_id_offset =:= lsb(k, p) [ VARIABLE ]; ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED); ENFORCE(ip_id_nbo.UVALUE == (ip_id.UVALUE / 256) + (ip_id.UVALUE % 256) * 256); ENFORCE(ip_id_nbo.ULENGTH == 16); ENFORCE(ip_id_offset.UVALUE == ip_id_nbo.UVALUE - msn.UVALUE); } } optional_ip_id_lsb(behavior, indicator) { UNCOMPRESSED { ip_id [ 16 ]; } COMPRESSED short { ip_id =:= ip_id_lsb(behavior, 8, 3) [ 8 ]; ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) || (behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); ENFORCE(indicator == 0); } COMPRESSED long { ip_id =:= irregular(16) [ 16 ]; ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) || (behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); ENFORCE(indicator == 1); } COMPRESSED not_present { ENFORCE((behavior == IP_ID_BEHAVIOR_RANDOM) || (behavior == IP_ID_BEHAVIOR_ZERO)); } } dont_fragment(version) { UNCOMPRESSED { df [ 1 ]; } COMPRESSED v4 { df =:= irregular(1) [ 1 ]; ENFORCE(version == 4); } COMPRESSED v6 { df =:= compressed_value(1, 0) [ 1 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 61] Internet-Draft ROHCv2 Profiles September 2006 ENFORCE(version == 6); } } //////////////////////////////////////////// // RTP profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag rtp_baseheader(profile, ts_stride_value, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED v4 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; udp_length [ 16 ]; checksum [ 16 ]; rtp_version =:= uncompressed_value(2, 0) [ 2 ]; pad_bit [ 1 ]; extension [ 1 ]; cc [ 4 ]; marker [ 1 ]; payload_type [ 7 ]; sequence_number [ 16 ]; timestamp [ 32 ]; ssrc [ 32 ]; csrc_list [ VARIABLE ]; ENFORCE(msn.UVALUE == sequence_number.UVALUE); } Pelletier & Sandlund Expires March 10, 2007 [Page 62] Internet-Draft ROHCv2 Profiles September 2006 UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; udp_length [ 16 ]; checksum [ 16 ]; rtp_version =:= uncompressed_value(2, 0) [ 2 ]; pad_bit [ 1 ]; extension [ 1 ]; cc [ 4 ]; marker [ 1 ]; payload_type [ 7 ]; sequence_number [ 16 ]; timestamp [ 32 ]; ssrc [ 32 ]; csrc_list [ VARIABLE ]; ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); ENFORCE(msn.UVALUE == sequence_number.UVALUE); } CONTROL { // The ts_stride has an initial UVALUE=1, which means that it // can be encoded with 'static' even if it has not been // previously established in the context. ts_stride [ 32 ]; ts_scaled [ 32 ]; ts_offset =:= field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE, timestamp.UVALUE) [ 32 ]; ip_id_behavior [ 2 ]; ENFORCE(ts_stride.UVALUE == ts_stride_value); ENFORCE(profile == PROFILE_RTP_0101); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; Pelletier & Sandlund Expires March 10, 2007 [Page 63] Internet-Draft ROHCv2 Profiles September 2006 src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; checksum =:= inferred_ip_v4_header_checksum; length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; src_port =:= static; dst_port =:= static; udp_length =:= inferred_udp_length; checksum =:= irregular(16); pad_bit =:= static; extension =:= static; cc =:= static; // When marker not present in packets, it is assumed 0 marker =:= uncompressed_value(1, 0); payload_type =:= static; sequence_number =:= static; timestamp =:= static; ssrc =:= static; csrc_list =:= static; ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; reorder_ratio =:= reorder_choice [ 2 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; control_crc3 =:= control_crc3 [ 3 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; tos_tc_present =:= irregular(1) [ 1 ]; ts_indicator =:= irregular(1) [ 1 ]; tss_indicator =:= irregular(1) [ 1 ]; pt_present =:= irregular(1) [ 1 ]; list_present =:= irregular(1) [ 1 ]; pad_bit =:= irregular(1) [ 1 ]; extension =:= irregular(1) [ 1 ]; reserved =:= compressed_value(6, 0) [ 6 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 64] Internet-Draft ROHCv2 Profiles September 2006 ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; sequence_number =:= sdvl(sequence_number.ULENGTH) [ 8, 16 ]; // Either scaled or unscaled timestamp ts_scaled =:= optional_scaled_timestamp(tss_indicator, tsc_indicator) [ VARIABLE ]; ts_scaled =:= optional_scaled_timestamp(tss_indicator, tsc_indicator) [ VARIABLE ]; payload_type =:= optional_pt(pt_present) [ 0, 8 ]; ts_stride =:= optional_stride(tss_indicator, ts_stride_value) [ VARIABLE ]; csrc_list =:= list_csrc(cc.UVALUE) [ VARIABLE ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; timestamp =:= inferred_scaled_field [ 0 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; timestamp =:= inferred_scaled_field [ 0 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1 replacement COMPRESSED pt_1_rnd { discriminator =:= '101' [ 3 ]; msn =:= msn_lsb(5, 8) [ 5 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 65] Internet-Draft ROHCv2 Profiles September 2006 marker =:= irregular(1) [ 1 ]; ts_scaled =:= lsb(4, 3) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UO-1-ID replacement COMPRESSED pt_1_seq_id { discriminator =:= '1010' [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(5, 8) [ 5 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; timestamp =:= inferred_scaled_field [ 0 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UO-1-TS replacement COMPRESSED pt_1_seq_ts { discriminator =:= '1011' [ 4 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(4, 4) [ 4 ]; ts_scaled =:= lsb(4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ts_scaled =:= lsb(6, 15) [ 6 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 6, 3) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 66] Internet-Draft ROHCv2 Profiles September 2006 timestamp =:= inferred_scaled_field [ 0 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2-TS replacement COMPRESSED pt_2_seq_ts { discriminator =:= '1101' [ 4 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ts_scaled =:= lsb(5, 7) [ 5 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } } //////////////////////////////////////////// // UDP profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag udp_baseheader(profile, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED v4 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 67] Internet-Draft ROHCv2 Profiles September 2006 dst_port [ 16 ]; udp_length [ 16 ]; checksum [ 16 ]; } UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; version [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; udp_length [ 16 ]; checksum [ 16 ]; ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } CONTROL { ip_id_behavior [ 2 ]; ENFORCE(profile == PROFILE_UDP_0102); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; checksum =:= inferred_ip_v4_header_checksum; length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; src_port =:= static; dst_port =:= static; udp_length =:= inferred_udp_length; checksum =:= irregular(16); ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); Pelletier & Sandlund Expires March 10, 2007 [Page 68] Internet-Draft ROHCv2 Profiles September 2006 } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; reorder_ratio =:= reorder_choice [ 2 ]; msn =:= msn_lsb(6, 16) [ 6 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; control_crc3 =:= control_crc3 [ 3 ]; tos_tc_present =:= irregular(1) [ 1 ]; reserved =:= compressed_value(7, 0) [ 7 ]; ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1-ID replacement (PT-1 only used for sequential) COMPRESSED pt_1_seq_id { Pelletier & Sandlund Expires March 10, 2007 [Page 69] Internet-Draft ROHCv2 Profiles September 2006 discriminator =:= '101' [ 3 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5, 3) [ 5 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; msn =:= msn_lsb(8, 64) [ 8 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } } //////////////////////////////////////////// // ESP profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag esp_baseheader(profile, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED v4 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 70] Internet-Draft ROHCv2 Profiles September 2006 rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; spi [ 32 ]; sequence_number [ 32 ]; ENFORCE(msn.UVALUE == sequence_number.UVALUE); } UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; version [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; spi [ 32 ]; sequence_number [ 32 ]; ENFORCE(msn.UVALUE == (sequence_number.UVALUE % 65536)); ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } CONTROL { ip_id_behavior [ 2 ]; ENFORCE(profile == PROFILE_ESP_0103); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; checksum =:= inferred_ip_v4_header_checksum; Pelletier & Sandlund Expires March 10, 2007 [Page 71] Internet-Draft ROHCv2 Profiles September 2006 length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; spi =:= static; sequence_number =:= static; ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; tos_tc_present =:= irregular(1) [ 1 ]; reorder_ratio =:= reorder_choice [ 2 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; control_crc3 =:= control_crc3 [ 3 ]; reserved =:= compressed_value(5, 0) [ 5 ]; sequence_number =:= sdvl(sequence_number.ULENGTH) [ 8, 16, 24, 32 ]; ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 72] Internet-Draft ROHCv2 Profiles September 2006 msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1-ID replacement (PT-1 only used for sequential) COMPRESSED pt_1_seq_id { discriminator =:= '101' [ 3 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5, 3) [ 5 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; msn =:= msn_lsb(8, 64) [ 8 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } } //////////////////////////////////////////// // IP-only profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag iponly_baseheader(profile, ttl_irregular_chain_flag, tos_irregular_chain_flag) { Pelletier & Sandlund Expires March 10, 2007 [Page 73] Internet-Draft ROHCv2 Profiles September 2006 UNCOMPRESSED v4 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; } UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; version [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } CONTROL { ip_id_behavior [ 2 ]; ENFORCE(profile == PROFILE_IP_0104); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; Pelletier & Sandlund Expires March 10, 2007 [Page 74] Internet-Draft ROHCv2 Profiles September 2006 checksum =:= inferred_ip_v4_header_checksum; length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; reorder_ratio =:= reorder_choice [ 2 ]; msn =:= msn_lsb(6, 16) [ 6 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; control_crc3 =:= control_crc3 [ 3 ]; tos_tc_present =:= irregular(1) [ 1 ]; reserved =:= compressed_value(7, 0) [ 7 ]; ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 75] Internet-Draft ROHCv2 Profiles September 2006 header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1-ID replacement (PT-1 only used for sequential) COMPRESSED pt_1_seq_id { discriminator =:= '101' [ 3 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5, 3) [ 5 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; msn =:= msn_lsb(8, 64) [ 8 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } } //////////////////////////////////////////// // UDP-lite/RTP profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag udplite_rtp_baseheader(profile, ts_stride_value, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED v4 { Pelletier & Sandlund Expires March 10, 2007 [Page 76] Internet-Draft ROHCv2 Profiles September 2006 outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; checksum_coverage [ 16 ]; checksum [ 16 ]; version =:= uncompressed_value(2, 0) [ 2 ]; pad_bit [ 1 ]; extension [ 1 ]; cc [ 4 ]; marker [ 1 ]; payload_type [ 7 ]; sequence_number [ 16 ]; timestamp [ 32 ]; ssrc [ 32 ]; csrc_list [ VARIABLE ]; ENFORCE(msn.UVALUE == sequence_number.UVALUE); } UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; version [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; checksum_coverage [ 16 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 77] Internet-Draft ROHCv2 Profiles September 2006 checksum [ 16 ]; version =:= uncompressed_value(2, 0) [ 2 ]; pad_bit [ 1 ]; extension [ 1 ]; cc [ 4 ]; marker [ 1 ]; payload_type [ 7 ]; sequence_number [ 16 ]; timestamp [ 32 ]; ssrc [ 32 ]; csrc_list [ VARIABLE ]; ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } CONTROL { ip_id_behavior [ 2 ]; coverage_behavior [ 2 ]; ts_stride [ 32 ]; ts_scaled [ 32 ]; ts_offset =:= field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE, timestamp.UVALUE) [ 32 ]; ENFORCE(ts_stride.UVALUE == ts_stride_value); ENFORCE(profile == PROFILE_RTP_0107); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; checksum =:= inferred_ip_v4_header_checksum; length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; src_port =:= static; dst_port =:= static; checksum_coverage =:= irregular(16); checksum =:= irregular(16); pad_bit =:= static; extension =:= static; cc =:= static; // When marker not present in packets, it is assumed 0 marker =:= uncompressed_value(1, 0); Pelletier & Sandlund Expires March 10, 2007 [Page 78] Internet-Draft ROHCv2 Profiles September 2006 payload_type =:= static; sequence_number =:= static; timestamp =:= static; ssrc =:= static; csrc_list =:= static; ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; reorder_ratio =:= reorder_choice [ 2 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; control_crc3 =:= control_crc3 [ 3 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; tos_tc_present =:= irregular(1) [ 1 ]; ts_indicator =:= irregular(2) [ 2 ]; tss_indicator =:= irregular(2) [ 2 ]; pt_present =:= irregular(1) [ 1 ]; list_present =:= irregular(1) [ 1 ]; pad_bit =:= irregular(1) [ 1 ]; extension =:= irregular(1) [ 1 ]; coverage_behavior =:= irregular(2) [ 2 ]; reserved =:= compressed_value(4, 0) [ 4 ]; sequence_number =:= sdvl(sequence_number.ULENGTH) [ 8, 16 ]; ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; // Either scaled or unscaled timestamp ts_scaled =:= optional_scaled_timestamp(tss_indicator, tsc_indicator) [ VARIABLE ]; ts_scaled =:= optional_scaled_timestamp(tss_indicator, tsc_indicator) [ VARIABLE ]; payload_type =:= optional_pt(pt_present) [ 0, 8 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 79] Internet-Draft ROHCv2 Profiles September 2006 ts_stride =:= optional_stride(tss_indicator, ts_stride_value) [ VARIABLE ]; csrc_list =:= list_csrc(cc.UVALUE) [ VARIABLE ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; timestamp =:= inferred_scaled_field [ 0 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; timestamp =:= inferred_scaled_field [ 0 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1 replacement COMPRESSED pt_1_rnd { discriminator =:= '101' [ 3 ]; msn =:= msn_lsb(5, 8) [ 5 ]; marker =:= irregular(1) [ 1 ]; ts_scaled =:= lsb(4, 3) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UO-1-ID replacement COMPRESSED pt_1_seq_id { discriminator =:= '1010' [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(5, 8) [ 5 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; timestamp =:= inferred_scaled_field [ 0 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); Pelletier & Sandlund Expires March 10, 2007 [Page 80] Internet-Draft ROHCv2 Profiles September 2006 } // UO-1-TS replacement COMPRESSED pt_1_seq_ts { discriminator =:= '1011' [ 4 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(4, 4) [ 4 ]; ts_scaled =:= lsb(4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ts_scaled =:= lsb(6, 15) [ 6 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 6, 3) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; timestamp =:= inferred_scaled_field [ 0 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2-TS replacement COMPRESSED pt_2_seq_ts { discriminator =:= '1101' [ 4 ]; msn =:= msn_lsb(7, 32) [ 7 ]; ts_scaled =:= lsb(5, 7) [ 5 ]; marker =:= irregular(1) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } Pelletier & Sandlund Expires March 10, 2007 [Page 81] Internet-Draft ROHCv2 Profiles September 2006 } //////////////////////////////////////////// // UDP-lite profile //////////////////////////////////////////// // ttl_irregular_chain_flag is set by the user if the TTL/Hop Limit // of an outer header. The same value must be passed as an argument // to the ipv4/ipv6 encoding methods when extracting the irregular // chain items. The same applies to the tos_irregular_chain_flag udplite_baseheader(profile, ttl_irregular_chain_flag, tos_irregular_chain_flag) { UNCOMPRESSED v4 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 4) [ 4 ]; header_length =:= uncompressed_value(4, 5) [ 4 ]; tos_tc [ 8 ]; length [ 16 ]; ip_id [ 16 ]; rf =:= uncompressed_value(1, 0) [ 1 ]; df [ 1 ]; mf =:= uncompressed_value(1, 0) [ 1 ]; frag_offset =:= uncompressed_value(13, 0) [ 13 ]; ttl_hopl [ 8 ]; next_header [ 8 ]; checksum [ 16 ]; src_addr [ 32 ]; dest_addr [ 32 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; src_port [ 16 ]; dst_port [ 16 ]; checksum_coverage [ 16 ]; checksum [ 16 ]; } UNCOMPRESSED v6 { outer_headers =:= baseheader_outer_headers [ VARIABLE ]; version =:= uncompressed_value(4, 6) [ 4 ]; version [ 4 ]; tos_tc [ 8 ]; flow_label [ 20 ]; payload_length [ 16 ]; next_header [ 8 ]; ttl_hopl [ 8 ]; src_addr [ 128 ]; dest_addr [ 128 ]; extension_headers =:= baseheader_extension_headers [ VARIABLE ]; Pelletier & Sandlund Expires March 10, 2007 [Page 82] Internet-Draft ROHCv2 Profiles September 2006 src_port [ 16 ]; dst_port [ 16 ]; checksum_coverage [ 16 ]; checksum [ 16 ]; ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM); } CONTROL { ip_id_behavior [ 2 ]; coverage_behavior [ 2 ]; ENFORCE(profile == PROFILE_UDPLITE_0108); } DEFAULT { tos_tc =:= static; dest_addr =:= static; version =:= static; ttl_hopl =:= static; src_addr =:= static; df =:= static; ip_id_behavior =:= static; payload_length =:= inferred_ip_v6_length; checksum =:= inferred_ip_v4_header_checksum; length =:= inferred_ip_v4_length; flow_label =:= static; next_header =:= static; src_port =:= static; dst_port =:= static; checksum_coverage =:= irregular(16); checksum =:= irregular(16); ENFORCE(ttl_irregular_chain_flag == 0); ENFORCE(tos_irregular_chain_flag == 0); } // Replacement for UOR-2-ext3 COMPRESSED co_common { discriminator =:= '1111101' [ 7 ]; ip_id_indicator =:= irregular(1) [ 1 ]; reorder_ratio =:= reorder_choice [ 2 ]; msn =:= msn_lsb(6, 16) [ 6 ]; df =:= dont_fragment(version.UVALUE) [ 1 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ttl_hopl_outer_flag =:= irregular(1) [ 1 ]; ttl_hopl_present =:= irregular(1) [ 1 ]; tos_tc_outer_flag =:= irregular(1) [ 1 ]; ip_id_behavior =:= ip_id_behavior_choice [ 2 ]; control_crc3 =:= control_crc3 [ 3 ]; tos_tc_present =:= irregular(1) [ 1 ]; Pelletier & Sandlund Expires March 10, 2007 [Page 83] Internet-Draft ROHCv2 Profiles September 2006 coverage_behavior =:= irregular(2) [ 2 ]; reserved =:= compressed_value(5, 0) [ 5 ]; ip_id =:= optional_ip_id_lsb(ip_id_behavior.UVALUE, ip_id_indicator.CVALUE) [ 0, 8, 16 ]; tos_tc =:= tos_tc_enc(tos_tc_present.CVALUE) [ 0, 8 ]; ttl_hopl =:= static_or_irreg(ttl_hopl_present.CVALUE, ttl_hopl.ULENGTH) [ 0, 8 ]; ENFORCE(ttl_irregular_chain_flag == ttl_hopl_outer_flag.UVALUE); ENFORCE(tos_irregular_chain_flag == tos_tc_outer_flag.UVALUE); } // UO-0 COMPRESSED pt_0_crc3 { discriminator =:= '0' [ 1 ]; msn =:= msn_lsb(4, 4) [ 4 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // New format, Type 0 with strong CRC and more SN bits COMPRESSED pt_0_crc7 { discriminator =:= '100' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ip_id =:= inferred_sequential_ip_id [ 0 ]; } // UO-1-ID replacement (PT-1 only used for sequential) COMPRESSED pt_1_seq_id { discriminator =:= '101' [ 3 ]; header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4, 3) [ 4 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } // UOR-2 replacement COMPRESSED pt_2_rnd { discriminator =:= '110' [ 3 ]; msn =:= msn_lsb(6, 16) [ 6 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) || Pelletier & Sandlund Expires March 10, 2007 [Page 84] Internet-Draft ROHCv2 Profiles September 2006 (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO)); } // UOR-2-ID replacement COMPRESSED pt_2_seq_id { discriminator =:= '1100' [ 4 ]; ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5, 3) [ 5 ]; header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ]; msn =:= msn_lsb(8, 64) [ 8 ]; ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) || (ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED)); } } 6.7. Feedback Formats and Options 6.7.1. Feedback Formats This section describes the feedback format for ROHCv2 profiles, using the formats described in section 5.2.3 of [I-D.ietf-rohc-rfc3095bis-framework]. All feedback formats carry a field labelled MSN, which contain LSBs of the MSN described in Section 6.2.1. The sequence number to use is the MSN corresponding to the last header that was successfully CRC-8 validated or CRC verified. 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. Pelletier & Sandlund Expires March 10, 2007 [Page 85] Internet-Draft ROHCv2 Profiles September 2006 FEEDBACK-2 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ |Acktype| MSN | +---+---+---+---+---+---+---+---+ | MSN | +---+---+---+---+---+---+---+---+ | CRC | +---+---+---+---+---+---+---+---+ / Feedback options / +---+---+---+---+---+---+---+---+ Acktype: 0 = ACK 1 = NACK 2 = STATIC-NACK 3 is reserved (MUST NOT be used for parsability) MSN: The lsb-encoded master sequence number. CRC: 8-bit CRC computed over the entire feedback payload including any CID fields but excluding the packet type, the 'Size' field and the 'Code' octet, using the polynomial defined in [I-D.ietf-rohc-rfc3095bis-framework]. If the CID is given with an Add-CID octet, the Add-CID octet immediately precedes the FEEDBACK-1 or FEEDBACK-2 format. For purposes of computing the CRC, the CRC field is zero. Feedback options: A variable number of feedback options, see Section 6.7.2. Options may appear in any order. A FEEDBACK-2 of type NACK or STATIC-NACK is always implicitely an acknowlegement for a successfully decompressed packet, which packet corresponds to the MSN of the feedback element, unless the MSN-NOT- VALID option Section 6.7.2.2 appears in the feedback element. The FEEDBACK-2 format always carry a CRC and is thus more robust than the FEEDBACK-1 format. When receiving FEEDBACK-2, the compressor MUST verify the information by computing the CRC and comparing the result with the CRC carried in the feedback format. If the two are not identical, the feedback element MUST be discarded. Pelletier & Sandlund Expires March 10, 2007 [Page 86] Internet-Draft ROHCv2 Profiles September 2006 6.7.2. Feedback Options A feedback option has variable length and the following general format: 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | Opt Type | Opt Len | +---+---+---+---+---+---+---+---+ / option data / Opt Length (octets) +---+---+---+---+---+---+---+---+ The CRC option contains an 8-bit CRC computed over the entire feedback payload including any CID fields but excluding the packet type, the 'Size' field and the 'Code' octet, using the polynomial of [I-D.ietf-rohc-rfc3095bis-framework], section 5.3.1.1. 6.7.2.1. The REJECT option The REJECT option informs the compressor that the decompressor does not have sufficient resources to handle the flow. +---+---+---+---+---+---+---+---+ | Opt Type = 2 | Opt Len = 0 | +---+---+---+---+---+---+---+---+ When receiving a REJECT option, the compressor MUST stop compressing the packet flow, and SHOULD refrain from attempting to increase the number of compressed packet flows for some time. Any FEEDBACK packet carrying a REJECT option MUST also carry a CRC option. The REJECT option MUST NOT appear more than once in the FEEDBACK-2 format, otherwise the decompressor MUST discard the entire feedback element. 6.7.2.2. The MSN-NOT-VALID option The MSN-NOT-VALID option indicates that the MSN of the feedback is not valid. +---+---+---+---+---+---+---+---+ | Opt Type = 3 | Opt Len = 0 | +---+---+---+---+---+---+---+---+ A compressor MUST NOT use the MSN of the feedback to find the corresponding sent header when this option is present. Consequently, a NACK or a STATIC-NACK feedback type sent with the MSN-NOT-VALID option is equivalent to a STATIC-NACK with respect to the type of context repair requested by the decompressor. Pelletier & Sandlund Expires March 10, 2007 [Page 87] Internet-Draft ROHCv2 Profiles September 2006 The MSN-NOT-VALID option MUST NOT appear more than once in the FEEDBACK-2 format and MUST NOT appear in the same feedback element as the MSN option, otherwise the decompressor MUST discard the entire feedback element. 6.7.2.3. The MSN option The MSN option provides 8 additional bits of MSN. +---+---+---+---+---+---+---+---+ | Opt Type = 4 | Opt Len = 1 | +---+---+---+---+---+---+---+---+ | MSN | +---+---+---+---+---+---+---+---+ the bits in the MSN option are concatenated with the MSN bits in the FEEDBACK-2 format, with the bits in the FEEDBACK-2 format being the most significant bits. The MSN option MAY appear more than once in the FEEDBACK-2 format, in which case the MSN is given by concatenating the MSN fields of each occurance of the MSN option. The MSN option MUST NOT appear in the same feedback element as the MSN-NOT-VALID option, otherwise the decompressor MUST discard the entire feedback element. 6.7.2.4. The CONTEXT_MEMORY Feedback Option The CONTEXT_MEMORY option informs the compressor that the decompressor does not have sufficient memory resources to handle the context of the packet flow, as the flow is currently compressed. 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | Opt Type = 9 | Opt Len = 0 | +---+---+---+---+---+---+---+---+ When receiving a CONTEXT_MEMORY option, the compressor SHOULD take actions to compress the packet flow in a way that requires less decompressor memory resources, or stop compressing the packet flow. The CONTEXT_MEMORY option MUST NOT appear more than once in the FEEDBACK-2 format, otherwise the decompressor MUST discard the entire feedback element. 6.7.2.5. Unknown option types If an option type unknown to the compressor is encountered, it must continue parsing the rest of the FEEDBACK packet, which is possible since the length of the option is explicit, but MUST otherwise ignore Pelletier & Sandlund Expires March 10, 2007 [Page 88] Internet-Draft ROHCv2 Profiles September 2006 the unknown option. 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, RTP does specify an alternative encryption method in which only the RTP payload is encrypted and the headers are left in the clear. That would still allow header compression to be applied. ROHC compression is transparent with regard to the RTP Sequence Number and RTP Timestamp fields, so the values of those fields can be used as the basis of payload encryption schemes (e.g., for computation of an initialization vector). 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, UDP and RTP headers and possibly also valid UDP 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, IR-DYN, IR-PD 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 The ROHC profile identifiers 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 updated profiles defined in this document. Profiles 0x0000-0x0004 have previously been reserved, and since there is no changes to Pelletier & Sandlund Expires March 10, 2007 [Page 89] Internet-Draft ROHCv2 Profiles September 2006 profile 0x0000, this document should thus update profiles 0x0001- 0x0004. 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 Reference 0x0000 ROHC uncompressed RFC 3095 0x0001 ROHC RTP RFC 3095 0x0101 ROHCv2 RTP [RFCXXXX (this)] 0xn101 - 0xn2nn Reserved 0x0002 ROHC UDP RFC 3095 0x0102 ROHCv2 UDP [RFCXXXX (this)] 0xn102 - 0xn2nn Reserved 0x0003 ROHC ESP RFC 3095 0x0103 ROHCv2 ESP [RFCXXXX (this)] 0xn103 - 0xn2nn Reserved 0x0004 ROHC IP RFC 3843 0x0104 ROHCv2 IP [RFCXXXX (this)] 0xn104 - 0xn7nn Reserved 0x0005 ROHC LLA RFC 3242 0x0105 ROHC LLA with R-mode RFC 3408 0xn105 - 0xn7nn Reserved 0x0007 ROHC RTP/UDP-Lite RFC 4019 0x0107 ROHCv2 RTP/UDP-Lite [RFCXXXX (this)] 0xn107 - 0xn2nn Reserved 0x0008 ROHC UDP-Lite RFC 4019 0x0108 ROHCv2 UDP-Lite [RFCXXXX (this)] 0xn108 - 0xn2nn Reserved Author's note: The list above is incorrect and incomplete. It must be updated before sending to IANA. 9. Acknowledgements The authors would like to thank the many people who have contributed to the ROHC specifications. The sample Perl implementation of Appendix A was written by Carsten Bormann. 10. References 10.1. Normative References [I-D.ietf-rohc-formal-notation] Pelletier, G. and R. Finking, "Formal Notation for Robust Header Compression (ROHC-FN)", Pelletier & Sandlund Expires March 10, 2007 [Page 90] Internet-Draft ROHCv2 Profiles September 2006 draft-ietf-rohc-formal-notation-09 (work in progress), June 2005. [I-D.ietf-rohc-rfc3095bis-framework] Jonsson, L., Pelletier, G., and K. Sandlund, "The RObust Header Compression (ROHC) Framework", draft-ietf-rohc-rfc3095bis-framework-01 (work in progress), December 2005. [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981. [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, October 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", RFC 2890, September 2000. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and G. Fairhurst, "The Lightweight User Datagram Protocol (UDP-Lite)", RFC 3828, July 2004. [RFC4019] Pelletier, G., "RObust Header Compression (ROHC): Profiles for User Datagram Protocol (UDP) Lite", RFC 4019, April 2005. [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. Pelletier & Sandlund Expires March 10, 2007 [Page 91] Internet-Draft ROHCv2 Profiles September 2006 10.2. Informative References [I-D.ietf-rohc-rfc3095bis-improvements] Jonsson, L., "Improvements for the ROHC Profile Set Update", draft-ietf-rohc-rfc3095bis-improvements-02 (work in progress), March 2006. [I-D.ietf-rohc-rtp-impl-guide] Jonsson, L., Pelletier, G., and K. Sandlund, "RObust Header Compression (ROHC): Corrections and Clarifications to RFC 3095", May 2006. [I-D.ietf-rohc-tcp] Pelletier, G., Sandlund, K., and M. West, "RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP)", draft-ietf-rohc-tcp-11 (work in progress), January 2006. [RFC3095] 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. [RFC3843] Jonsson, L-E. and G. Pelletier, "RObust Header Compression (ROHC): A Compression Profile for IP", RFC 3843, June 2004. [RFC4224] Pelletier, G., Jonsson, L-E., and K. Sandlund, "RObust Header Compression (ROHC): ROHC over Channels That Can Reorder Packets", RFC 4224, January 2006. Appendix A. Detailed classification of header fields Header compression is possible thanks to the fact that most header fields do not vary randomly from packet to packet. Many of the fields exhibit static behavior or change in a more or less predictable way. When designing a header compression scheme, it is of fundamental importance to understand the behavior of the fields in detail. In this appendix, all IP, UDP, UDP-Lite and RTP header fields are classified and analyzed in two steps. First, we have a general classification in [REF] where the fields are classified on the basis of stable knowledge and assumptions. The general classification does not take into account the change characteristics of changing fields because those will vary more or less depending on the implementation Pelletier & Sandlund Expires March 10, 2007 [Page 92] Internet-Draft ROHCv2 Profiles September 2006 and on the application used. A less stable but more detailed analysis of the change characteristics is then done in [REF]. Finally, [REF] summarizes this appendix with conclusions about how the various header fields should be handled by the header compression scheme to optimize compression and functionality. Appendix A.1. General classification INFERRED These fields contain values that can be inferred from other values, for example the size of the frame carrying the packet, and thus do not have to be handled at all by the compression scheme. STATIC These fields are expected to be constant throughout the lifetime of the packet stream. Static information must in some way be communicated once. STATIC-DEF STATIC fields whose values define a packet stream. They are in general handled as STATIC. STATIC-KNOWN These STATIC fields are expected to have well-known values and therefore do not need to be communicated at all. CHANGING These fields are expected to vary in some way: randomly, within a limited value set or range, or in some other manner. In this section, each of the IP, UDP and RTP header fields is assigned to one of these classes. For all fields except those classified as CHANGING, the motives for the classification are also stated. In section A.2, CHANGING fields are further examined and classified on the basis of their expected change behavior. Appendix A.1.1. IPv4 header fields Pelletier & Sandlund Expires March 10, 2007 [Page 93] Internet-Draft ROHCv2 Profiles September 2006 +---------------------+-------------+----------------+ | Field | Size (bits) | Class | +---------------------+-------------+----------------+ | Version | 4 | STATIC-KNOWN | | Header Length | 4 | STATIC-KNOWN | | Type Of Service | 8 | CHANGING | | Packet Length | 16 | INFERRED | | Identification | 16 | CHANGING | | Reserved flag | 1 | STATIC-KNOWN | | Don't Fragment flag | 1 | CHANGING | | More Fragments flag | 1 | STATIC-KNOWN | | Fragment Offset | 13 | STATIC-KNOWN | | Time To Live | 8 | CHANGING | | Protocol | 8 | STATIC | | Header Checksum | 16 | INFERRED | | Source Address | 32 | STATIC-DEF | | Destination Address | 32 | STATIC-DEF | +---------------------+-------------+----------------+ Version The version field states which IP version is used. Packets with different values in this field must be handled by different IP stacks. All packets of a packet stream must therefore be of the same IP version. Accordingly, the field is classified as STATIC. Header Length As long no options are present in the IP header, the header length is constant and well known. If there are options, the fields would be STATIC, but it is assumed here that there are no options. The field is therefore classified as STATIC-KNOWN. Packet Length Information about packet length is expected to be provided by the link layer. The field is therefore classified as INFERRED. Flags The Reserved flag must be set to zero and is therefore classified as STATIC-KNOWN. The Don't Fragment (DF) flag will changes rarely and is therefore classified as CHANGING. Finally, the More Fragments (MF) flag is expected to be zero because fragmentation is NOT expected, due to the small packet size expected. The More Fragments flag is therefore classified as STATIC-KNOWN. Fragment Offset Pelletier & Sandlund Expires March 10, 2007 [Page 94] Internet-Draft ROHCv2 Profiles September 2006 Under the assumption that no fragmentation occurs, the fragment offset is always zero. The field is therefore classified as STATIC-KNOWN. Protocol This field will have the same value in all packets of a packet stream. It encodes the type of the subsequent header. Header Checksum The header checksum protects individual hops from processing a corrupted header. When almost all IP header information is compressed away, there is no point in having this additional checksum; instead it can be regenerated at the decompressor side. The field is therefore classified as INFERRED. Source and Destination addresses These fields are part of the definition of a stream and must thus be constant for all packets in the stream. The fields are therefore classified as STATIC-DEF. Appendix A.1.2. IPv6 header fields +---------------------+-------------+----------------+ | Field | Size (bits) | Class | +---------------------+-------------+----------------+ | Version | 4 | STATIC-KNOWN | | Traffic Class | 8 | CHANGING | | Flow Label | 20 | STATIC-DEF | | Payload Length | 16 | INFERRED | | Next Header | 8 | STATIC | | Hop Limit | 8 | CHANGING | | Source Address | 128 | STATIC-DEF | | Destination Address | 128 | STATIC-DEF | +---------------------+-------------+----------------+ Version The version field states which IP version is used. Packets with different values in this field must be handled by different IP stacks. All packets of a packet stream must therefore be of the same IP version. Accordingly, the field is classified as STATIC. Flow Label Pelletier & Sandlund Expires March 10, 2007 [Page 95] Internet-Draft ROHCv2 Profiles September 2006 This field may be used to identify packets belonging to a specific packet stream. If not used, the value should be set to zero. Otherwise, all packets belonging to the same stream must have the same value in this field, it being one of the fields that define the stream. The field is therefore classified as STATIC-DEF. Payload Length Information about packet length (and, consequently, payload length) is expected to be provided by the link layer. The field is therefore classified as INFERRED. Next Header This field will have the same value in all packets of a packet stream. It encodes the type of the subsequent header. Source and Destination addresses These fields are part of the definition of a stream and must thus be constant for all packets in the stream. The fields are therefore classified as STATIC-DEF. Appendix A.1.3. UDP header fields +------------------+-------------+-------------+ | Field | Size (bits) | Class | +------------------+-------------+-------------+ | Source Port | 16 | STATIC-DEF | | Destination Port | 16 | STATIC-DEF | | Length | 16 | INFERRED | | Checksum | 16 | CHANGING | +------------------+-------------+-------------+ Source and Destination ports These fields are part of the definition of a stream and must thus be constant for all packets in the stream. The fields are therefore classified as STATIC-DEF. Length This field is redundant and is therefore classified as INFERRED. Appendix A.1.4. UDP-Lite header fields Pelletier & Sandlund Expires March 10, 2007 [Page 96] Internet-Draft ROHCv2 Profiles September 2006 +-------------------+-------------+-------------+ | Field | Size (bits) | Class | +-------------------+-------------+-------------+ | Source Port | 16 | STATIC-DEF | | Destination Port | 16 | STATIC-DEF | | Checksum Coverage | 16 | INFERRED | | | | STATIC | | | | CHANGING | | Checksum | 16 | CHANGING | +-------------------+-------------+-------------+ Source and Destination Port Same as for UDP Appendix A.1.3. Source and Destination ports Same as for UDP Appendix A.1.3. Checksum Coverage This field specifies which part of the UDP-Lite datagram is covered by the checksum. It may have a value of zero or be equal to the datagram length if the checksum covers the entire datagram, or it may have any value between eight octets and the length of the datagram to specify the number of octets protected by the checksum, calculated from the first octet of the UDP-Lite header. The value of this field may vary for each packet, and this makes the value unpredictable from a header-compression perspective. Checksum The information used for the calculation of the UDP-Lite checksum is governed by the value of the checksum coverage and minimally includes the UDP-Lite header. The checksum is a changing field that must always be sent as-is. Appendix A.1.5. RTP header fields Pelletier & Sandlund Expires March 10, 2007 [Page 97] Internet-Draft ROHCv2 Profiles September 2006 +-----------------+-------------+----------------+ | Field | Size (bits) | Class | +-----------------+-------------+----------------+ | Version | 2 | STATIC-KNOWN | | Padding | 1 | CHANGING | | Extension | 1 | CHANGING | | CSRC Counter | 4 | CHANGING | | Marker | 1 | CHANGING | | Payload Type | 7 | CHANGING | | Sequence Number | 16 | CHANGING | | Timestamp | 32 | CHANGING | | SSRC | 32 | STATIC-DEF | | CSRC | 0(-480) | CHANGING | +-----------------+-------------+----------------+ Version Only one working RTP version exists, namely version 2. The field is therefore classified as STATIC-KNOWN. Padding The use of this field is application-dependent, but when payload padding is used it is likely to be present in most or all packets. The field is classified as CHANGING to allow for the rare case where this field is updated. Extension If RTP extensions are used by the application, these extensions are likely to be present in all packets (but the use of extensions is very uncommon). However, for safety's sake this field is classified as CHANGING to allow for the rare case where this field is changed during the flow. SSRC This field is part of the definition of a stream and must thus be constant for all packets in the stream. The field is therefore classified as STATIC-DEF. Appendix A.2. Analysis of change patterns of header fields To design suitable mechanisms for efficient compression of all header fields, their change patterns must be analyzed. For this reason, an extended classification is done based on the general classification in A.1, considering the fields which were labeled CHANGING in that classification. Different applications will use the fields in Pelletier & Sandlund Expires March 10, 2007 [Page 98] Internet-Draft ROHCv2 Profiles September 2006 different ways, which may affect their behavior. For the fields whose behavior is variable, typical behavior for conversational audio and video will be discussed. The CHANGING fields are separated into five different subclasses: STATIC These are fields that were classified as CHANGING on a general basis, but are classified as STATIC here due to certain additional assumptions. SEMISTATIC These fields are STATIC most of the time. However, occasionally the value changes but will revert to its original value. RARELY-CHANGING (RC) These are fields that change their values occasionally and then keep their new values. ALTERNATING These fields alternate between a small number of different values. IRREGULAR These, finally, are the fields for which no useful change pattern can be identified. When the classification is done, other details are also stated regarding possible additional knowledge about the field values and/or field deltas, according to the classification. For fields classified as STATIC or SEMISTATIC, the case could be that the value of the field is not only STATIC but also well KNOWN a priori (two states for SEMISTATIC fields). For fields with non-irregular change behavior, it could be known that changes usually are within a LIMITED range compared to the maximal change for the field. For other fields, the values are completely UNKNOWN. Table A.1 classifies all the CHANGING fields on the basis of their expected change patterns, especially for conversational audio and video. +------------------------+-------------+-------------+-------------+ | Field | Value/Delta | Class | Knowledge | +========================+=============+=============+=============+ | Sequential | Delta | RC | LIMITED | | -----------+-------------+-------------+-------------+ | IPv4 Id: Seq. swap | Delta | RC | LIMITED | | -----------+-------------+-------------+-------------+ | Random | Value | IRREGULAR | UNKNOWN | | -----------+-------------+-------------+-------------+ | Zero | Value | IRREGULAR | UNKNOWN | +------------------------+-------------+-------------+-------------+ | IP TOS / Tr. Class | Value | RC | UNKNOWN | +------------------------+-------------+-------------+-------------+ | IP TTL / Hop Limit | Value | ALTERNATING | LIMITED | +------------------------+-------------+-------------+-------------+ | IP Don't Fragment | Value | RC | KNOWN | Pelletier & Sandlund Expires March 10, 2007 [Page 99] Internet-Draft ROHCv2 Profiles September 2006 +------------------------+-------------+-------------+-------------+ | Disabled | Value | STATIC | KNOWN | | UDP Checksum: ---------+-------------+-------------+-------------+ | Enabled | Value | IRREGULAR | UNKNOWN | +------------------------+-------------+-------------+-------------+ | UDP-Lite Checksum | Value | IRREGULAR | UNKNOWN | +------------------------+-------------+-------------+-------------+ | Case #1 | Value | CHANGING | INFERRED | | UDP-Lite ----------+-------------+-------------+-------------+ | Checksum: Case #2 | Value | RC | UNKNOWN | | Coverage ----------+-------------+-------------+-------------+ | Case #3 | Value | IRREGULAR | UNKNOWN | +------------------------+-------------+-------------+-------------+ | No mix | Value | STATIC | KNOWN | | RTP CSRC Count: -------+-------------+-------------+-------------+ | Mixed | Value | RC | LIMITED | +------------------------+-------------+-------------+-------------+ | RTP Marker | Value | SEMISTATIC | KNOWN/KNOWN | +------------------------+-------------+-------------+-------------+ | RTP Payload Type | Value | RC | UNKNOWN | +------------------------+-------------+-------------+-------------+ | RTP Extension | Value | RC | UNKNOWN | +------------------------+-------------+-------------+-------------+ | RTP Padding | Value | RC | UNKNOWN | +------------------------+-------------+-------------+-------------+ | RTP Sequence Number | Delta | STATIC | KNOWN | +------------------------+-------------+-------------+-------------+ | RTP Timestamp | Delta | RC | LIMITED | +------------------------+-------------+-------------+-------------+ | No mix | - | - | - | | RTP CSRC List: -------+-------------+-------------+-------------+ | Mixed | Value | RC | UNKNOWN | +------------------------+-------------+-------------+-------------+ Table A.1 : Classification of CHANGING header fields The following subsections discuss the various header fields in detail. Note that table A.1 and the discussions below do not consider changes caused by loss or reordering before the compression point. Appendix A.2.1. IPv4 Identification The Identification field (IP ID) of the IPv4 header is there to identify which fragments constitute a datagram when reassembling fragmented datagrams. The IPv4 specification does not specify exactly how this field is to be assigned values, only that each packet should get an IP ID that is unique for the source-destination pair and protocol for the time the datagram (or any of its fragments) Pelletier & Sandlund Expires March 10, 2007 [Page 100] Internet-Draft ROHCv2 Profiles September 2006 could be alive in the network. This means that assignment of IP ID values can be done in various ways, which we have separated into three classes. Sequential In this behavior, the IP-ID is expected to increment by one for most packets, but may increment by a value larger than one, depending on the behavior of the transmitting IPv4 stack. Sequential Swapped When using this behavior, the IP-ID behaves as in the Sequential bahvior, but the two bytes of IP-ID are byte swapped. Therefore, the IP-ID can be swapped before compression to make it behave exactly as the Sequential behavior. Random Some IP stacks assign IP ID values using a pseudo-random number generator. There is thus no correlation between the ID values of subsequent datagrams, and therefore there is no way to predict the IP ID value for the next datagram. For header compression purposes, this means that the IP ID field needs to be sent uncompressed with each datagram, resulting in two extra octets of header. Zero This behavior, although not a legal implementation of IPv4 is sometimes seen in existing IPv4 stacks. When this behavior is used, all IP packets have the IP-ID value set to zero. Appendix A.2.2. IP Traffic Class / Type-Of-Service The Traffic-Class (IPv6) or Type-Of-Service (IPv4) field is expected to be constant during the lifetime of a packet stream or to change relatively seldom. Appendix A.2.3. IP Hop-limit / Time-To-Live The Hop-Limit (IPv6) or Time-To-Live (IPv4) field is expected to be constant during the lifetime of a packet stream or to alternate between a limited number of values due to route changes. Pelletier & Sandlund Expires March 10, 2007 [Page 101] Internet-Draft ROHCv2 Profiles September 2006 Appendix A.2.4. IPv4 Don't Fragment The Don't Fragment flag in IPv4 will seldom change, and is therefore classified as RC. Appendix A.2.5. UDP Checksum The UDP checksum is optional. If disabled, its value is constantly zero and could be compressed away. If enabled, its value depends on the payload, which for compression purposes is equivalent to it changing randomly with every packet. Appendix A.2.6. UDP-Lite Checksum Coverage The Checksum Coverage field may behave in different ways: it may have a value of zero, it may be equal to the datagram length, or it may have any value between eight octets and the length of the datagram. From a compression perspective, this field is expected to either be entirely predictable (for the cases where it follows the same behavior as the UDP Length field or where it takes on a constant value) or either to change randomly for each packet (making the value unpredictable from a header-compression perspective). For all cases, the behavior itself is not expected to change for this field during the lifetime of a packet flow, or to change relatively seldom. Appendix A.2.7. UDP-Lite Checksum As opposed to the UDP checksum, the UDP-Lite checksum is not optional and it cannot be disabled. Its value depends on the payload and on the checksum coverage field, which for compression purposes is equivalent to it changing randomly with every packet. Appendix A.2.8. RTP CSRC Counter This is a counter indicating the number of CSRC items present in the CSRC list. This number is expected to be almost constant on a packet-to-packet basis and change by small amounts. As long as no RTP mixer is used, the value of this field is zero. Appendix A.2.9. RTP Marker For audio the marker bit should be set only in the first packet of a talkspurt, while for video it should be set in the last packet of every picture. This means that in both cases the RTP marker is classified as SEMISTATIC with well-known values for both states. Pelletier & Sandlund Expires March 10, 2007 [Page 102] Internet-Draft ROHCv2 Profiles September 2006 Appendix A.2.10. RTP Padding If padding is used, it is expected to be present in most packets, but is classified as RC to allow efficient compression even when this field changes. Appendix A.2.11. RTP Extension If extensions are used, it is expected to be used in most packets, but is classified as RC to allow efficient compression even when this field changes. Appendix A.2.12. RTP Payload Type Changes of the RTP payload type within a packet stream are expected to be rare. Applications could adapt to congestion by changing payload type and/or frame sizes, but that is not expected to happen frequently. Appendix A.2.13. RTP Sequence Number The RTP Sequence Number will be incremented by one for each packet sent. Appendix A.2.14. RTP Timestamp In the audio case: As long as there are no pauses in the audio stream, the RTP Timestamp will be incremented by a constant delta, corresponding to the number of samples in the speech frame. It will thus mostly follow the RTP Sequence Number. When there has been a silent period and a new talkspurt begins, the timestamp will jump in proportion to the length of the silent period. However, the increment will probably be within a relatively limited range. In the video case: Between two consecutive packets, the timestamp will either be unchanged or increase by a multiple of a fixed value corresponding to the picture clock frequency. The timestamp can also decrease by a multiple of the fixed value for certain coding schemes. The delta interval, expressed as a multiple of the picture clock frequency, is in most cases very limited. Pelletier & Sandlund Expires March 10, 2007 [Page 103] Internet-Draft ROHCv2 Profiles September 2006 Appendix A.2.15. RTP Contributing Sources (CSRC) The participants in a session, which are identified by the CSRC fields, are expected to be almost the same on a packet-to-packet basis with relatively few additions and removals. As long as RTP mixers are not used, no CSRC fields are present at all. Appendix A.3. Header compression strategies This section elaborates on what has been done in previous sections. On the basis of the classifications, recommendations are given on how to handle the various fields in the header compression process. Seven different actions are possible; these are listed together with the fields to which each action applies. Appendix A.3.1. Do not send at all The fields that have well known values a priori do not have to be sent at all. These are: o IPv6 Payload Length o IPv4 Header Length o IPv4 Reserved Flag o IPv4 Last Fragment Flag o IPv4 Fragment Offset o UDP Checksum (if disabled) o RTP Version Appendix A.3.2. Transmit only initially The fields that are constant throughout the lifetime of the packet stream have to be transmitted and correctly delivered to the decompressor only once. These are: o IP Version o IPv6 Next Header o IPv4 Protocol o IP Source Address o IP Destination Address o IPv6 Flow Label o UDP Source Port o UDP Destination Port o UDP-Lite Source Port o UDP-Lite Destination Port o RTP SSRC Pelletier & Sandlund Expires March 10, 2007 [Page 104] Internet-Draft ROHCv2 Profiles September 2006 Appendix A.3.3. Transmit initially, be prepared to update The fields that are changing only occasionally must be transmitted initially but there must also be a way to update these fields with new values if they change. These fields are: o IPv6 Traffic Class o IPv4 Don't Fragment Flag o IPv6 Hop Limit o IPv4 Type Of Service (TOS) o IPv4 Time To Live (TTL) o UDP-Lite Checksum Coverage (if constant or assigned to datagram length) o RTP CSRC Counter o RTP Padding Flag o RTP Extension Flag o RTP Payload Type o RTP CSRC List Appendix A.3.4. Be prepared to update, or send as-is frequently For fields that normally either are constant or have values deducible from some other field, but that frequently diverge from that behavior, there must be an efficient way to update the field value or send it as-is in some packets. These fields are: o IPv4 Identification (if not sequentially assigned) o RTP Marker o RTP Timestamp Appendix A.3.5. Guarantee continuous robustness For fields that behave like a counter with a fixed delta for ALL packets, the only requirement on the transmission encoding is that packet losses between compressor and decompressor must be tolerable. If several such fields exist, all these can be communicated together. Such fields can also be used to interpret the values for fields listed in the previous section. Fields that have this counter behavior are: o IPv4 Identification (if sequentially assigned) o RTP Sequence Number Appendix A.3.6. Transmit as-is in all packets Fields that have completely random values for each packet must be included as-is in all compressed headers. Those fields are: o IPv4 Identification (if randomly assigned) o UDP Checksum (if enabled) Pelletier & Sandlund Expires March 10, 2007 [Page 105] Internet-Draft ROHCv2 Profiles September 2006 o UDP-Lite Checksum o UDP-Lite Checksum Coverage (if randomly assigned) Appendix A.3.7. Establish and be prepared to update delta Finally, there is a field that is usually increasing by a fixed delta and is correlated to another field. For this field it would make sense to make that delta part of the context state. The delta must then be initiated and updated in the same way as the fields listed in A.3.3. The field to which this applies is: o RTP Timestamp Appendix B. Differences between RoHCv2 and RFC3095 profiles To be Written Profiles defined in RFC3095 were designed with the assumption that the channel between compressor and decompressor maintains packet ordering, i.e., that the decompressor always receive packets in the same order as the compressor sent them. RoHCv2 profiles does not make this assumption, i.e. reordering before and after the compression point is handled as part of the compression algorithm itself. Appendix C. Sample CRC algorithm #!/usr/bin/perl -w use strict; #================================= # # ROHC CRC demo - Carsten Bormann cabo@tzi.org 2001-08-02 # # This little demo shows the three types of CRC in use in # RFC3095, the RoHC Framework and ROHC profiles that # specificy robust header compression. # Type your data in hexadecimal form and then # press Control+D. # #--------------------------------- # # utility # sub dump_bytes($) { my $x = shift; my $i; for ($i = 0; $i < length($x); ) { Pelletier & Sandlund Expires March 10, 2007 [Page 106] Internet-Draft ROHCv2 Profiles September 2006 printf("%02x ", ord(substr($x, $i, 1))); printf("\n") if (++$i % 16 == 0); } printf("\n") if ($i % 16 != 0); } #--------------------------------- # # The CRC calculation algorithm. # sub do_crc($$$) { my $nbits = shift; my $poly = shift; my $string = shift; my $crc = ($nbits == 32 ? 0xffffffff : (1 << $nbits) - 1); for (my $i = 0; $i < length($string); ++$i) { my $byte = ord(substr($string, $i, 1)); for( my $b = 0; $b < 8; $b++ ) { if (($crc & 1) ^ ($byte & 1)) { $crc >>= 1; $crc ^= $poly; } else { $crc >>= 1; } $byte >>= 1; } } printf "%2d bits, ", $nbits; printf "CRC: %02x\n", $crc; } #--------------------------------- # # Test harness # $/ = undef; $_ = <>; # read until EOF my $string = ""; # extract all that looks hex: s/([0-9a-fA-F][0-9a-fA-F])/$string .= chr(hex($1)), ""/eg; dump_bytes($string); #--------------------------------- # # 32-bit segmentation CRC # Note that the text implies this is complemented like for PPP # (this differs from 8, 7, and 3-bit CRC) # Pelletier & Sandlund Expires March 10, 2007 [Page 107] Internet-Draft ROHCv2 Profiles September 2006 # C(x) = x^0 + x^1 + x^2 + x^4 + x^5 + x^7 + x^8 + x^10 + # x^11 + x^12 + x^16 + x^22 + x^23 + x^26 + x^32 # do_crc(32, 0xedb88320, $string); #--------------------------------- # # 8-bit IR/IR-DYN CRC # # C(x) = x^0 + x^1 + x^2 + x^8 # do_crc(8, 0xe0, $string); #--------------------------------- # # 7-bit FO/SO CRC # # C(x) = x^0 + x^1 + x^2 + x^3 + x^6 + x^7 # do_crc(7, 0x79, $string); #--------------------------------- # # 3-bit FO/SO CRC # # C(x) = x^0 + x^1 + x^3 # do_crc(3, 0x6, $string); Authors' Addresses Ghyslain Pelletier Ericsson Box 920 Lulea SE-971 28 Sweden Phone: +46 (0) 8 404 29 43 Email: ghyslain.pelletier@ericsson.com Pelletier & Sandlund Expires March 10, 2007 [Page 108] Internet-Draft ROHCv2 Profiles September 2006 Kristofer Sandlund Ericsson Box 920 Lulea SE-971 28 Sweden Phone: +46 (0) 8 404 41 58 Email: kristofer.sandlund@ericsson.com Pelletier & Sandlund Expires March 10, 2007 [Page 109] Internet-Draft ROHCv2 Profiles September 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Pelletier & Sandlund Expires March 10, 2007 [Page 110]