rfc2509.txt

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RFC 2509             IP Header Compression over PPP        February 1999


   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 [IPHC] 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 [CRTP] 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 [CRTP] Section
         3.3.1.  This is the same as the FULL_HEADER specified in [IPHC]
         Section 5.3.
            Value: 0061 (hex)

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

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




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      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
         [IPHC].
            Value: 0065 (hex)

      COMPRESSED_RTP_8
         The frame contains a datagram with a compressed header with the
         format as specified in [CRTP] 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 [CRTP] 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 [CRTP] Section 3.3.3, 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 [CRTP] Section 3.3.3, 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 [CRTP] Section 3.3.5.
            Value: 2065 (hex)

5. References

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

   [IPHC]     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.



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RFC 2509             IP Header Compression over PPP        February 1999


   [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.

   [MCML]     Bormann, C., "The Multi-Class Extension to Multi-Link
              PPP", Work in Progress.

6. 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 [IPHC].  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.
























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7. Authors' Addresses

   Mathias Engan
   Effnet
   Aurorum 2
   SE-977 75 Lulea, Sweden

   Phone: [phone]
   Mobile: [phone]
   Fax: [phone]
   EMail: [e-mail]


   Stephen L. Casner
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   United States

   EMail: [e-mail]


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

   Phone: +49.421.218-7024
   Fax: +49.421.218-7000
   EMail: [e-mail]





















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RFC 2509             IP Header Compression over PPP        February 1999


8.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  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.
























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