rfc3242.txt

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      NHP packets can be delivered to the lower layer only if the
      payload size is part of the preferred packet size set.
      Furthermore, if RESTRICTED_TYPE is set to one of NHP_ONLY or
      RHP_ONLY for any of the preferred packet sizes, that size is
      allowed only for packets of the specified type.

      By default, no preferred packet sizes are specified.  When sizes
      are specified, the default value for RESTRICTED_TYPE is
      NO_RESTRICTION.



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   LARGE_PACKETS_ALLOWED -- value: boolean

      This parameter may be set by an external entity to specify how to
      handle packets that do not fit any of the preferred packet sizes
      specified.  If it is set to TRUE, the compressor MUST deliver the
      larger packet as-is and MUST NOT use segmentation.  If it is set
      to FALSE, the ROHC segmentation scheme MUST be used to split the
      packet into two or more segments, and each segment MUST further be
      padded to fit one of the preferred packet sizes.

      By default, this parameter is set to TRUE, which means that
      segmentation is disabled.

   VERIFICATION_PERIOD -- value: integer

      This parameter may be set by an external entity to specify to the
      compressor the minimum frequency with which a packet validating
      the context must be sent.  This tells the compressor that a packet
      containing a CRC field MUST be sent at least once every N packets,
      where N=VERIFICATION_PERIOD (see section 4.6).

      By default, this parameter is set to 0, which indicates that
      periodical verifications are disabled.

5.1.2.  Implementation Parameters at the Decompressor

   NHP_PACKET -- value: boolean

      This parameter informs the decompressor that the packet being
      delivered is an NHP packet.  The decompressor MUST accept this
      packet type indicator from the lower layer.  An assisting layer
      MUST set this indicator to true for every NHP packet delivered,
      and to false for any other packet.

   PHYSICAL_PACKET_LOSS -- signal

      This signal indicates to the decompressor that a packet has been
      lost on the link between the compressing and the decompressing
      sides, due to a physical link error.  The signal is given once for
      each packet that was lost, and a decompressor must increase the
      sequence number accordingly when this signal is received.

   PRE_LINK_PACKET_LOSS -- signal

      This signal tells the decompressor to increase the sequence number
      due to a gap in the sequencing, not related to a physical link
      error.  A receiving assisting layer may for example use this




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      signal to indicate to the decompressor that a packet was lost
      before the compressor, or that a packet was discarded by the
      transmitting assisting layer.

5.2.  Implementation over Various Link Technologies

   This document provides the semantics and requirements of the
   interface needed from the ROHC compressor and decompressor towards
   the assisting layer to perform link-layer assisted header
   compression.

   However, this document does not provide any link layer specific
   operational information, except for some implementation suggestions.
   Further details about how this profile is to be implemented over
   various link technologies must be described in other documents, where
   specific characteristics of each link layer can be taken into account
   to provide optimal usage of this profile.

   These specifications MAY use a packet type bit pattern unused by this
   profile to implement signaling on the lower layer.  The pattern
   available to lower layer implementations is [11111001].

6.  IANA Considerations

   ROHC profile identifier 0x0005 has been reserved by the IANA for the
   IP/UDP/RTP profile defined in this document.

7.  Security Considerations

   The security considerations of ROHC RTP [ROHC section 7] apply also
   to this document with one addition: in the case of a denial-of-
   service attack scenario where an intruder injects bogus CCP packets
   onto the link using random CRC values, the CRC check will fail for
   incorrect reasons at the decompressor side.  This would obviously
   greatly reduce the advantages of ROHC and any extra efficiency
   provided by this profile due to unnecessary context invalidation,
   feedback messages and refresh packets.  However, the same remarks
   related to the presence of such an intruder apply.

8.  Acknowledgements

   The authors would like to thank Lila Madour, Ulises Olvera-Hernandez
   and Francis Lupien for input regarding the typical links in which LLA
   can be applied.  Thanks also to Mikael Degermark for fruitful
   discussions that led to improvements of this profile, and to Zhigang
   Liu for many valuable comments.





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9.  References

   [ROHC]      Bormann, C., Burmeister, C., Degermark, M., Fukushima,
               H., Hannu, H., Jonsson, L., 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.

   [IPv4]      Postel, J., "Internet Protocol", STD 5, RFC 791,
               September 1981.

   [IPv6]      Deering, S. and R. Hinden, "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, December 1998.

   [UDP]       Postel, J., "User Datagram Protocol", STD 6, RFC 768,
               August 1980.

   [RTP]       Schulzrinne, H., Casner S., Frederick, R. and V.
               Jacobson, "RTP: A Transport Protocol for Real-Time
               Applications", RFC 1889, January 1996.

   [TCP]       Postel, P., "Transmission Control Protocol", STD 7, RFC
               793, September 1981.

   [RTP-REQ]   Degermark, M., "Requirements for IP/UDP/RTP Header
               Compression", RFC 3096, July 2001.

   [0B-REQ]    Jonsson, L-E., "RObust Header Compression (ROHC):
               Requirements and Assumptions for 0-byte IP/UDP/RTP
               Compression", RFC 3243, April 2002.

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

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

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

   [CRTPC]     Degermark, M., Hannu, H., Jonsson, L-E. and K. Svanbro,
               "Evaluation of CRTP Performance over Cellular Radio
               Networks", IEEE Personal Communications Magazine, Volume
               7, number 4, pp. 20-25, August 2000.





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   [VTC2000]   Svanbro, K., Hannu, H., Jonsson, L-E. and M. Degermark,
               "Wireless real time IP-services enabled by header
               compression", proceedings of IEEE VTC2000, May 2000.

   [MOMUC01]   Liu, G., et al., "Experimental field trials results of
               Voice-over IP over WCDMA links", MoMuC'01 - The
               International Workshop on Mobile Multimedia
               Communications, Conference proceedings, February 2001.

10.  Authors' Addresses

   Lars-Erik Jonsson
   Ericsson AB
   Box 920
   SE-971 28 Lulea
   Sweden

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


   Ghyslain Pelletier
   Ericsson AB
   Box 920
   SE-971 28 Lulea
   Sweden

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




















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11.  Full Copyright Statement

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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