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Versions: (RFC 2509) 00 01 02 RFC 3544

PPPEXT Working Group                                            M. Engan
Internet Draft                                                 Microsoft
June 21, 2002                                                  S. Casner
Expires January 2003                                       Packet Design
draft-koren-pppext-rfc2509bis-02.txt                          C. Bormann
Updates: RFC 2509                                Universitaet Bremen TZI
                                                                T. Koren
                                                           Cisco Systems


                     IP Header Compression over PPP

Status of this Memo

This document is an Internet Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. 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.

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Internet Drafts may be updated, replaced, or obsolete by other
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Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

   This document describes an option for negotiating the use of header
   compression on IP datagrams transmitted over the Point-to-Point
   Protocol [RFC1661]. It defines extensions to the PPP Control
   Protocols for IPv4 and IPv6 [RFC1332, RFC2023]. Header compression
   may be applied to IPv4 and IPv6 datagrams in combination with TCP,
   UDP and RTP transport protocols as specified in [RFC2507],
   [RFC2508] and [RFCYYYY].

1. Introduction

   The IP Header Compression (IPHC) defined in [RFC2507] may be used for
   compression of both IPv4 and IPv6 datagrams or packets encapsulated
   with multiple IP headers. IPHC is also capable of compressing both
   TCP and UDP transport protocol headers.  The IP/UDP/RTP header
   compression defined in [RFC2508] and [RFCYYYY] fits within the
   framework defined by IPHC so that it may also be applied to both IPv4
   and IPv6 packets.

   In order to establish compression of IP datagrams sent over a PPP
   link each end of the link must agree on a set of configuration
   parameters for the compression. The process of negotiating link
   parameters for network layer protocols is handled in PPP by a family
   of network control protocols (NCPs).  Since there are separate NCPs
   for IPv4 and IPv6, this document defines configuration options to be
   used in both NCPs to negotiate parameters for the compression scheme.

   This document obsoletes RFC 2509, adding two new suboptions to the IP
   header compression configuration option. One suboption negotiates
   usage of Enhanced RTP-Compression (specified in [RFCYYYY]), and the
   other suboption negotiates header compression for only TCP or only
   non-TCP packets.

   IPHC relies on the link layer's ability to indicate the types of
   datagrams carried in the link layer frames. In this document nine new
   types for the PPP Data Link Layer Protocol Field are defined along
   with their meaning.

   In general, header compression schemes that use delta encoding of
   compressed packets require that the lower layer does not reorder
   packets between compressor and decompressor. IPHC uses delta encoding
   of compressed packets for TCP and RTP.  The IPHC specification
   [RFC2507] includes methods that allow link layers that may reorder
   packets to be used with IPHC.  Since PPP does not reorder packets
   these mechanisms are disabled by default.  When using reordering
   mechanisms such as multiclass multilink PPP [RFC2686], care must be
   taken so that packets that share the same compression context are not
   reordered.

2. Configuration Option

   This document specifies a new compression protocol value for the IPCP
   IP-Compression-Protocol option as specified in [RFC1332].  The new
   value and the associated option format are described in section 2.1.

   The option format is structured to allow future extensions to the
   IPHC scheme.

      NOTE: The specification of link and network layer parameter
      negotiation for PPP [RFC1661], [RFC1331], [RFC1332] does not
      prohibit multiple instances of one configuration option but states
      that the specification of a configuration option must explicitly
      allow multiple instances. [RFC3241] updates RFC 1332 by
      explicitly allowing the sending of multiple instances of the
      IP-Compression-Protocol configuration option, each with a
      different value for IP-Compression-Protocol. Each type of
      compression protocol may independently establish its own
      parameters.

      NOTE: [RFC1332] is not explicit about whether the option
      negotiates the capabilities of the receiver or of the sender.  In
      keeping with current practice, we assume that the option describes
      the capabilities of the decompressor (receiving side) of the peer
      that sends the Config-Req.

2.1. Configuration Option Format

   Both the network control protocol for IPv4, IPCP [RFC1332] and the
   IPv6 NCP, IPV6CP [RFC2023] may be used to negotiate IP Header
   Compression parameters for their respective protocols.  The format of
   the configuration option is the same for both IPCP and IPV6CP.

   Description

      This NCP configuration option is used to negotiate parameters for
      IP Header Compression. Successful negotiation of parameters
      enables the use of Protocol Identifiers FULL_HEADER,
      COMPRESSED_TCP, COMPRESSED_TCP_NODELTA, COMPRESSED_NON_TCP and
      CONTEXT_STATE as specified in [RFC2507]. The option format is
      summarized below. The fields are transmitted from left to right.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Type      |    Length     |    IP-Compression-Protocol    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           TCP_SPACE           |         NON_TCP_SPACE         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         F_MAX_PERIOD          |          F_MAX_TIME           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           MAX_HEADER          |          suboptions...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type
      2

   Length
      >= 14

      The length may be increased if the presence of additional
      parameters is indicated by additional suboptions.

   IP-Compression-Protocol
      0061 (hex)

   TCP_SPACE
      The TCP_SPACE field is two octets and indicates the maximum value
      of a context identifier in the space of context identifiers
      allocated for TCP.

         Suggested value: 15

      TCP_SPACE must be at least 0 and at most 255 (the value 0 implies
      having one context).

   NON_TCP_SPACE
      The NON_TCP_SPACE field is two octets and indicates the maximum
      value of a context identifier in the space of context identifiers
      allocated for non-TCP. These context identifiers are carried in
      COMPRESSED_NON_TCP, COMPRESSED_UDP and COMPRESSED_RTP packet
      headers.

         Suggested value: 15

      NON_TCP_SPACE must be at least 0 and at most 65535 (the value 0
      implies having one context).

   F_MAX_PERIOD
      Maximum interval between full headers.  No more than F_MAX_PERIOD
      COMPRESSED_NON_TCP headers may be sent between FULL_HEADER
      headers.

         Suggested value: 256

      A value of zero implies infinity, i.e. there is no limit to the
      number of consecutive COMPRESSED_NON_TCP headers.

   F_MAX_TIME
      Maximum time interval between full headers.  COMPRESSED_NON_TCP
      headers may not be sent more than F_MAX_TIME seconds after sending
      the last FULL_HEADER header.

         Suggested value: 5 seconds

      A value of zero implies infinity.

   MAX_HEADER
      The largest header size in octets that may be compressed.

         Suggested value: 168 octets

      The value of MAX_HEADER should be large enough so that at least
      the outer network layer header can be compressed.  To increase
      compression efficiency MAX_HEADER should be set to a value large
      enough to cover common combinations of network and transport layer
      headers.

   suboptions
      The suboptions field consists of zero or more suboptions.  Each
      suboption consists of a type field, a length field and zero or
      more parameter octets, as defined by the suboption type.  The
      value of the length field indicates the length of the suboption in
      its entirety, including the lengths of the type and length fields.

             0                   1                   2
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |     Type      |    Length     |  Parameters...
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.2 RTP-Compression Suboption

   The RTP-Compression suboption is included in the NCP
   IP-Compression-Protocol option for IPHC if IP/UDP/RTP compression is
   to be enabled.

   Inclusion of the RTP-Compression suboption enables use of
   additional Protocol Identifiers COMPRESSED_RTP and
   COMPRESSED_UDP along with additional forms of CONTEXT_STATE as
   specified in [RFC2508].

   Description

      Enable use of Protocol Identifiers COMPRESSED_RTP, COMPRESSED_UDP
      and CONTEXT_STATE as specified in [RFC2508].


             0                   1
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            |     Type      |    Length     |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Type
            1

         Length
            2

2.3 Enhanced RTP-Compression Suboption

    To use the enhanced RTP header compression defined in [RFCYYYY],
    a new sub-option 2 is added. Sub-option 2 is negotiated instead of,
    not in addition to, sub-option 1.

    Description

       Enable use of Protocol Identifiers COMPRESSED_RTP and
       CONTEXT_STATE as specified in [RFC2508]. In addition, enable
       use of [RFCYYYY] compliant compression including the use of
       Protocol Identifier COMPRESSED_UDP with additional flags and
       use of the C flag with the FULL_HEADER Protocol Identifier
       to indicate use of HDRCKSUM with COMPRESSED_RTP and
       COMPRESSED_UDP packets.

                 0                   1
                 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                |     Type      |    Length     |
                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Type
                2

             Length
                2


2.4 Negotiating header compression for only TCP or only non-TCP packets

    In RFC 2509 it was not possible to negotiate only TCP header
    compression or only non-TCP header compression because a value of 0
    in the TCP_SPACE or the NON_TCP_SPACE fields actually means that 1
    context is negotiated.

    A new suboption 3 is added to allow specifying that the number of
    contexts for TCP_SPACE or NON_TCP_SPACE is zero, disabling use of
    the corresponding compression.

       Description

       Enable header compression for only TCP or only non-TCP packets.

              0                   1                   2
              0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             |     Type      |    Length     |   Parameter   |
             +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Type
                3

             Length
                3

             Parameter

             The parameter is 1 byte with one of the following values:

             1 = the number of contexts for TCP_SPACE is 0
             2 = the number of contexts for NON_TCP_SPACE is 0

       This suboption overrides the values that were previously assigned
       to TCP_SPACE and NON_TCP_SPACE in the IP Header Compression
       option.

       If suboption 3 is included multiple times with parameter 1 and 2,
       compression is disabled for all packets.

3. Multiple Network Control Protocols

   The IPHC protocol is able to compress both IPv6 and IPv4 datagrams.
   Both IPCP and IPV6CP are able to negotiate option parameter values
   for IPHC.  These values apply to the compression of packets where the
   outer header is an IPv4 header and an IPv6 header, respectively.

3.1. Sharing Context Identifier Space

   For the compression and decompression of IPv4 and IPv6 datagram
   headers the context identifier space is shared.  While the parameter
   values are independently negotiated, sharing the context identifier
   spaces becomes more complex when the parameter values differ.  Since
   the compressed packets share context identifier space, the
   compression engine must allocate context identifiers out of a common
   pool; for compressed packets, the decompressor has to examine the
   context state to determine what parameters to use for decompression.

   Context identifier spaces are not shared between TCP and non-
   TCP/UDP/RTP.  Doing so would require additional mechanisms to ensure
   that no error can occur when switching from using a context
   identifier for TCP to non-TCP.

4. Demultiplexing of Datagrams

   The IPHC specification [RFC2507] defines four header formats for
   different types of compressed headers.  They are compressed TCP,
   compressed TCP with no delta encoding, compressed non-TCP with 8 bit
   CID and compressed non-TCP with 16 bit CID. The two non-TCP formats
   may be distinguished by their contents so both may use the same
   link-level identifier.  A fifth header format, the full header is
   distinct from a regular header in that it carries additional
   information to establish shared context between the compressor and
   decompressor.

   The specification of IP/UDP/RTP Header Compression [RFC2508] defines
   four additional formats of compressed headers.  They are for
   compressed UDP and compressed RTP (on top of UDP), both with either
   8- or 16-bit CIDs.  In addition, there is an explicit error message
   from the decompressor to the compressor.

   The link layer must be able to indicate these header formats with
   distinct values.  Nine PPP Data Link Layer Protocol Field values are
   specified below.

      FULL_HEADER
         The frame contains a full header as specified in [RFC2508]
         Section 3.3.1.  This is the same as the FULL_HEADER specified in
         [RFC2507] Section 5.3.
            Value: 0061 (hex)

      COMPRESSED_TCP
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2507] Section 6a.
            Value: 0063 (hex)

      COMPRESSED_TCP_NODELTA
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2507] Section 6b.
            Value: 2063 (hex)

      COMPRESSED_NON_TCP
         The frame contains a datagram with a compressed header with the
         format as specified in either Section 6c or Section 6d of
         [RFC2507].
            Value: 0065 (hex)

      COMPRESSED_RTP_8
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2508] Section 3.3.2, using 8-bit
         CIDs.
            Value: 0069 (hex)

      COMPRESSED_RTP_16
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2508] Section 3.3.2, using 16-bit
         CIDs.
            Value: 2069 (hex)

      COMPRESSED_UDP_8
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2508] Section 3.3.3 or as specified
         in [RFCYYYY] Section 2.1, using 8-bit CIDs.
            Value: 0067 (hex)

      COMPRESSED_UDP_16
         The frame contains a datagram with a compressed header with the
         format as specified in [RFC2508] Section 3.3.3 or as specified
         in [RFCYYYY] Section 2.1, using 16-bit CIDs.
            Value: 2067 (hex)

      CONTEXT_STATE
         The frame is a link-level message sent from the decompressor to
         the compressor as specified in [RFC2508] Section 3.3.5.
            Value: 2065 (hex)

5. Changes from RFC 2509

   Two new suboptions are specified.  See Sections 2.3 and 2.4.

6. References

   [RFC2508]  Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
              Headers for Low-Speed Serial Links", RFC 2508, February
              1999.

   [RFC2507]  Degermark, M., Nordgren, B. and S. Pink, "Header
              Compression for IP", RFC 2507, February 1999.

   [RFC2023]  Haskin, E. and E. Allan, "IP Version 6 over PPP", RFC
              2023, October 1996.

   [RFC1144]  Jacobson, V., "Compressing TCP/IP Headers for Low- Speed
              Serial Links", RFC 1144, February 1990.

   [RFC1332]  McGregor, G., "The PPP Internet Protocol Control Protocol
              (IPCP)", RFC 1332, May 1992.

   [RFC1889]  Schulzrinne, H., Casner, S., Frederick, R. and V.
              Jacobson, "RTP: A Transport Protocol for real-time
              applications", RFC 1889, January 1996.

   [RFC1661]  Simpson, W., Ed., "The Point-To-Point Protocol (PPP)", STD
              51, RFC 1661, July 1994.

   [RFC2686]  Bormann, C., "The Multi-Class Extension to Multi-Link
              PPP", RFC 2686, September 1999.

   [RFC3241]  Bormann, C., "Robust Header Compression (ROHC) over PPP",
              RFC3241, April 2002.

   [RFC2434]  Narten, T., Alvestrand, H., "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC2434,
              October 1998.

   [RFCYYYY]  Koren, T., S. Casner, J. Geevarghese, B. Thompson, P.
              Ruddy, "Compressing IP/UDP/RTP headers on links with high
              delay, packet loss and reordering",
              draft-ietf-avt-crtp-enhance-04.txt, Work in Progress.

7. IANA Considerations

   This document does not require any additional allocations from
   existing namespaces in the IANA Point-to-Point Protocol Field
   Assignments registry.  However, there are three namespaces that
   were defined by RFC 1332, RFC 2023 and RFC 2509 but not created in
   the registry.  Those three namespaces, described below, need to be
   added to the PPP registry.  This document specifies two additional
   allocations in the third one.

   Section 3.2 of RFC 1332 specifies an IP-Compression-Protocol
   Configuration Option for the PPP IP Control Protocol and defines
   one value for the IP-Compression-Protocol type field in that
   option.  An IANA registry is needed to allocate additional values
   for that type field.  As stated in RFC 1332, the values for the
   IP-Compression-Protocol type field are always the same as the
   (primary) PPP DLL Protocol Number assigned to packets of the
   particular compression protocol. Assignment of additional
   IP-Compression-Protocol type values is through the IETF consensus
   procedure as specified in [RFC2434].

   Section 4.2 of RFC 2023 specifies an IPv6-Compression-Protocol
   Configuration Option for the PPP IPv6 Control Protocol and defines
   one value for the IPv6-Compression-Protocol type field in that
   option.  An IANA registry is needed to allocate additional values
   for that type field.  The IPv6-Compression-Protocol Configuration
   Option has the same structure as the IP-Compression-Protocol
   Configuration Option defined in RFC 1332, but the set of values
   defined for the type field may be different.  As stated in RFC
   2023, the values for the IPv6-Compression-Protocol type field are
   always the same as the (primary) PPP DLL Protocol Number assigned
   to packets of the particular compression protocol. Assignment of
   additional IPv6-Compression-Protocol type values is through the
   IETF consensus procedure as specified in [RFC2434].

   Section 2.1 of RFC 2509 specifies an additional type value to be
   registered for both the IP-Compression-Protocol Configuration
   Option and the IPv6-Compression-Protocol Configuration Option to
   indicate use of the "IP Header Compression" protocol.  The
   specification of that type value is repeated in Section 2.1 of this
   document which obsoletes RFC 2509.  In conjunction with the
   additional type value, the format for the variable-length option is
   specified.  The format includes a suboption field that may contain
   one or more suboptions.  Each suboption begins with a suboption
   type value.  An IANA registry is needed for the suboption type
   values; it may be titled "IP Header Compression Configuration
   Option Suboption Types".

   Section 2.2 of RFC 2509 (and this document) defines one suboption
   type.  Sections 2.3 and 2.4 of this document define two additional
   suboption types.  It is expected that the number of additional
   suboptions that will need to be defined is small.  Therefore,
   anyone wishing to define new suboptions is required to produce a
   revision of this document to be vetted through the normal Internet
   Standards process, as specified in [RFC2434].

   RFC 2509 also defines nine PPP Data Link Layer Protocol Field
   values which are already listed in the IANA registry of
   Point-to-Point Protocol Field Assignments.  Section 4 of this
   document repeats the specification of those values without change.


8. Security Considerations

   Negotiation of the option defined here imposes no additional security
   considerations beyond those that otherwise apply to PPP [RFC1661].

   The use of header compression can, in rare cases, cause the
   misdelivery of packets. If necessary, confidentiality of packet
   contents should be assured by encryption.

   Encryption applied at the IP layer (e.g., using IPSEC mechanisms)
   precludes header compression of the encrypted headers, though
   compression of the outer IP header and authentication/security
   headers is still possible as described in [RFC2507].  For RTP packets,
   full header compression is possible if the RTP payload is encrypted
   by itself without encrypting the UDP or RTP headers, as described in
   [RFC1889].  This method is appropriate when the UDP and RTP header
   information need not be kept confidential.

9. Authors' Addresses

   Mathias Engan
   Microsoft Mobile Internet
   Box 27151
   SE-102 52 Stockholm
   Sweden

   Phone: +46 8 56306000
   EMail: mengan@microsoft.com


   Stephen L. Casner
   Packet Design
   2465 Latham Street, Third Floor
   Mountain View, CA 94040
   United States

   EMail: casner@packetdesign.com


   Carsten Bormann
   Universitaet Bremen FB3 TZI
   Postfach 330440
   D-28334 Bremen, GERMANY

   Phone: +49.421.218-7024
   Fax: +49.421.218-7000
   EMail: cabo@tzi.org


   Tmima Koren
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   United States

   EMail: tmima@cisco.com


10.  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























Engan, et. al.              Standards Track                    [Page 10]


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