Network Working Group                                      Tat-Chee. Wan
Internet-Draft                                           Way-Chuang. Ang
Intended status: Standards Track                          Chee Hong. Teh
Expires: August, 2008                          Universiti Sains Malaysia
                                                          19 March, 2008


Robust Header Compression over Unidirectional Lightweight Encapsulation
              (ULE) and MPEG2 Transport Stream (TS) frames
                        draft-wan-ipdvb-rohc-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on August 25, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2008).












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Abstract

   This paper introduces approach to carry ROHC packets over ULE and
   MPEG2-TS frames.  For completeness, ROHC Channel Parameters
   Negotiation Protocol (RCPNP) is also presented.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminologies  . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Packet Format of ROHC Packet . . . . . . . . . . . . . . . . .  7
     3.1.  ROHC over ULE  . . . . . . . . . . . . . . . . . . . . . .  7
       3.1.1.  Dedicated EtherType Fields for ROHC Compressed
               Packet . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.1.2.  ROHC Compressed Packet as Payload of Ethernet
               Packet . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2.  ROHC over MPEG2-TS . . . . . . . . . . . . . . . . . . . .  8
   4.  Establishing ROHC Channel  . . . . . . . . . . . . . . . . . . 10
     4.1.  ROHC Channel Parameters Negotiation Protocol (RCPNP) . . . 10
       4.1.1.  Compressor Advertisement . . . . . . . . . . . . . . . 12
       4.1.2.  Compressor Solicitation  . . . . . . . . . . . . . . . 12
       4.1.3.  Request  . . . . . . . . . . . . . . . . . . . . . . . 13
       4.1.4.  Reply  . . . . . . . . . . . . . . . . . . . . . . . . 15
         4.1.4.1.  Medium Information . . . . . . . . . . . . . . . . 16
           4.1.4.1.1.  MPEG-2 TS Medium . . . . . . . . . . . . . . . 16
           4.1.4.1.2.  ULE Medium . . . . . . . . . . . . . . . . . . 17
       4.1.5.  Acknowledgement/Negative Acknowledgement . . . . . . . 18
       4.1.6.  Compressor Shutdown  . . . . . . . . . . . . . . . . . 18
       4.1.7.  Decompressor Shutdown  . . . . . . . . . . . . . . . . 18
     4.2.  Interaction of RCPNP . . . . . . . . . . . . . . . . . . . 19
   5.  Bidirectional ROHC Channels  . . . . . . . . . . . . . . . . . 20
   6.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 21
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 24
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
   Intellectual Property and Copyright Statements . . . . . . . . . . 26













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1.  Introduction

   This paper introduces approach to carry ROHC packets over ULE and
   MPEG2-TS frames.  For completeness, ROHC Channel Parameters
   Negotiation Protocol (RCPNP) is also presented.














































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2.  Terminologies

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   DVB

      Digital Video Broadcast.  A framework and set of associated
      standards published by the European Telecommunications Standards
      Institute (ETSI) for the transmission of video, audio, and data
      using the ISO MPEG-2 Standard [ISO-MPEG2].

   MAC

      Medium Access Control [IEEE-802.3].  A link-layer protocol defined
      by the IEEE 802.3 standard (or by Ethernet v2 [DIX]).

   MPEG-2

      A set of standards specified by the Motion Picture Experts Group
      (MPEG) and standardized by the International Standards
      Organisation (ISO/IEC 13818-1) [ISO-MPEG2], and ITU-T (in H.222
      [ITU-H222]).

   PDU

      Protocol Data Unit.  Examples of a PDU include Ethernet frames,
      IPv4 or IPv6 datagrams, and other network packets.

   Receiver

      Equipment that processes the signal from a TS Multiplex and
      performs filtering and forwarding of encapsulated PDUs to the
      network-layer service (or bridging module when operating at the
      link layer).

   Transmitter

      Router or host that sends data.

   SNDU

      SubNetwork Data Unit.  An encapsulated PDU sent as an MPEG-2
      Payload Unit.






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   TS

      Transport stream (TS) is a format specified in MPEG-2 Part 1,
      Systems (ISO/IEC standard 13818-1).  Its design goal is to allow
      multiplexing of digital video and audio and to synchronize the
      output.  Transport stream offers features for error correction for
      transportation over unreliable media, and is used in broadcast
      applications such as DVB and ATSC.

   ULE stream

      An MPEG-2 TS Logical Channel that carries only ULE encapsulated
      PDUs.  ULE Streams may be identified by definition of a
      stream_type in SI/PSI [ISO-MPEG2].

   ROHC

      Robust Header Compression.  A framework of compression headers of
      IP packet as defined in [RFC3095].

   ROHC channel

      A logical unidirectional point-to-point channel carrying ROHC
      packets from one compressor to one decompressor, optionally
      carrying ROHC feedback information on the behalf of another
      compressor-decompressor pair operating on a separate ROHC channel
      in the opposite direction.

   ROHC profile

      A logical unidirectional point-to-point channel carrying ROHC
      packets from one compressor to one decompressor, optionally
      carrying ROHC feedback information on the behalf of another
      compressor-decompressor pair operating on a separate ROHC channel
      in the opposite direction.

   MRRU

      Maximum Reconstructed Reception Unit as defined in [RFC3095].

   Context Identifier

      [RFC3095] provides a definition for context identifiers.

   MSB






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      Most significant bit.

   LSB

      Least significant bit.

   ACK

      Acknowledgement.

   NACk

      Negative acknowledgement.

   CID

      Contect Identifier.


































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3.  Packet Format of ROHC Packet

   This section briefly describes the notation used in all diagrams. ":"
   in a diagram indicates that the part is optional.  Likewise, "~" in a
   diagram indicates the number of octets by the part is not presented
   in a precise manner.  This situation appears when a field or part
   spans multiple or variable number of bytes.

3.1.  ROHC over ULE

   The packet format for ROHC packet encapsulated can be in one the
   following two formats:

3.1.1.  Dedicated EtherType Fields for ROHC Compressed Packet

           MSB                                           LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |  D  |                                         |
           +-----+              Length                     +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                   Type=ROHC                   +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           :                                               :
           ~              Dest Address* (6 octets)         ~
           :                                               :
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~    ROHC compressed packet (variable length)   ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~               CRC-32 (4 octets)               ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

       Figure 1: ROHC compressed packet encapsulated using dedicated
                                 EtherType

   The semantics of D-bit, Length, Type, Destination Address and CRC-32
   fields are defined in section 4 of [RFC 4326].  However, the Type
   fields requires a new IANA assigned EtherType value to indicate the
   presence of ROHC compressed packet in PDU.

   In the absence of multiple receivers, a transmitter can send an SNDU



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   without Destination Address Field (D bit marked).  However, when
   multiple receivers are listening to the same transmitter, destination
   address must be included in SNDU.

3.1.2.  ROHC Compressed Packet as Payload of Ethernet Packet

           MSB                                           LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           | D=1 |                                         |
           +-----+              Length                     +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                   Type=Ether                  +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~                Dest MAC (6 octets)            ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~              Source MAC (6 octets)            ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +              EtherType=ROHC                   +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~    ROHC compressed packet (varible length)    ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~               CRC-32 (4 octets)               ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

    Figure 2: ROHC compressed packet encapsulated in SNDU bridged frame

   This packet format should be used when there are multiple
   transmitters and receivers over a DVB link.  The value of EtherType
   field is similar to Type Field in section 3.1.1.

3.2.   ROHC over MPEG2-TS

   This encapsulation format is the smallest packet format in terms of
   packet size.  The format of SNDU is the following format:



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           +------+------------------------+--------+
           |Length| ROHC compressed packet | CRC-32 |
           +------+------------------------+--------+

      Figure 3: ROHC compressed packet compressed encapsulated direct
                      within MPEG2-TS frames' payload

   The meaning of each fields is specified below:

   Length

      This field indicates the ROHC compressed packet field only.  This
      field can be either 1 or 2 octets depending on the the most
      significant bit.  If the most significant bit is cleared, the
      length of this field is 1 octet and may represents values from 0
      until 127.  Otherwise, the length of this field is 2 octets and
      may represents values from 128 until 61566.

   ROHC Compressed Packet

      ROHC compressed packet as defined in section 5.2 of [RFC3095].

   CRC-32

      The 32-bit CRC is calculated over Length filed and ROHC compressed
      packet.  The polynomial used to calculate the CRC is 0x104C11DB7.

      Like ULE, ROHC over MPEG2-TS also supports packing and padding
      mode.  The mechanism of encapsulating this SNDU is similar to
      encapsulation of ULE packet within MPEG2-TS.  This approach
      requires that separate PID dedicated to a ROHC channel.




















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4.  Establishing ROHC Channel

   This standard presents two approaches to setup a ROHC channel over a
   DVB link.  The first approach is to setup ROHC channel manually.
   This requires that the operators at the every transmitters and
   receivers to manually configure the ROHC channel parameters.  When
   the size of network is small, this approach is favourable.

   But the former approach becomes nonviable if the network is dynamic
   and is not scalable as the size of the network grows.  Henceforth, we
   presents a negotiation protocol to create ROHC channel in the next
   section.

4.1.  ROHC Channel Parameters Negotiation Protocol (RCPNP)

   The approach presented in this section can only work if compressor
   site and decompressor site are connected through two dedicated
   unidirectional DVB links, with a unidirectional link originating from
   each of the sites, configured to form a bidirectional network link
   between the two sites.  This protocol works through ULE packets only.
   It is possible to extend this protocol to work over Generic Stream
   Encapsulation [GSE] in the future.  While it is possible to extend
   this protocol to work over asymmetrical link, this draft doesn't try
   to address this issue.  Since new EtherType is allocated, this
   protocol can be extended to asymmetrical link via Link-Layer
   Tunneling Mechanism [RFC3077] with little modifications.

   The basic format of ULE SNDU packet is as such:

           +---+--------+------------+----------+--------+
           |D=1| Length |Type=ROHCNeg|   Body   | CRC-32 |
           +---+--------+------------+----------+--------+

                 Figure 4: Minimal format of RCPNP message

















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           MSB                                           LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           | D=1 |                                         |
           +-----+              Length                     +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                   Type=Ether                  +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~                Dest MAC (6 octets)            ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~              Source MAC (6 octets)            ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +              EtherType=ROHCNeg                +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~              Body (varible length)            ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~               CRC-32 (4 octets)               ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

           Figure 5: RCPNP message encapsulated in bridged frame

   Type field requires a new separate IANA assigned EtherType number for
   ROHC Channel Negotiation Protocol.  The types of message in this
   protocol is defined in the Body field.  The following subsections
   will explain the type of messages for this protocol.  Compressor
   Advertisement and Compressor Solicitation uses packet format depicted
   in Figure 4.  While other forms of messages uses packet format
   depicted in Figure 5.

   The basic format for these messages is depicted is as such:








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           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version        |    Operation    |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+

                Figure 6: Basic format of RCPNP Body field

   Currently, version number is 0.  Operation field defines the type of
   message contained in the Body field.  The content of X-bit depends on
   operation type.

4.1.1.  Compressor Advertisement

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=0   |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~              Address (6 octets)               ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

           Figure 7: Format of Compressor Advertisement message

   This message is used by the compressor site to advertise the
   availability of ROHC Compressor.  Out of concern for bandwidth and
   energy consumption, compressor site should limit the broadcast of
   this message for a few times when it first join the network.  This
   message should also be broadcasted when a Compressor Solicitation
   message is received.  The decompressor site will use the value
   specified in the Address field when addressing compressor site.
   X-bit is unused and should be ignored.

4.1.2.  Compressor Solicitation

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=1   |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+

            Figure 8: Format of Compressor Solicitation message

   This message is broadcasted by decompressor to solicit for
   compressor.  X-bit is unused and should be ignored.  Decompressor
   site should rate-limit the frequency of solicitation if it is doesn't



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   receive any Compressor Advertisement to avoid flooding DVB link.

4.1.3.  Request

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=2   |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                  Maximum CID                  +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~                  MRRU (4 octets)              ~
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           | Number of Media |                             |
           ~-----+-----+-----+   Medium Types              ~
           :                                               :
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +             Num of profiles                   +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                Profile ID 1                   +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           :                                               :
           +                Profile ID 2                   +
           :                                               :
           +-----+-----+-----+-----+-----+-----+-----+-----+
           :                                               :
           +                Profile ID N                   +
           :|                                              :
           +-----+-----+-----+-----+-----+-----+-----+-----+

                    Figure 9: Format of Request message

   This message is sent by decompressor site to compressor site when it
   wishes to establish a ROHC channel.  The meaning of each fields in
   the message are described below:

   Maximum CID






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      Maximum Context Identifier tolerated by decompressor.

   MRRU

      Maximum Reconstructed Reception Unit tolerated by decompressor.
      Value of 0 indicates the negotiated channel doesn't allow for
      segmentation of ROHC compressed packet.

   Number of Media

      The number of medium types carried in Medium Types field.

   Medium Types

      This field consists of all supported medium types by the
      decompressor.  Each medium type consists of 3 bits and corresponds
      to Medium field described in Medium Information (Section 4.1.4.1)
      section.  The number of bits used by Medium Types and Number of
      Media fields must be expanded to multiple of 8 if actual number of
      required bits is not multiple of 8.  The unused bits for such case
      should be ignored by Compressor site.

   Number of profiles

      Number of profiles supported by decompressor.

   Profile IDs

      ROHC Profile IDs supported by decompressor.  Each profile ID
      occupy 2 octets.

      X-bit is unused and should be ignored.



















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4.1.4.  Reply

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=3   |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                  Maximum CID                  +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           ~                  MRRU (4 octets)              ~
           |                                               |
           +===============================================+
           |             Num of profiles                   |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |                                               |
           +                Profile ID 1                   +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+
           :                                               :
           +                Profile ID 2                   +
           :                                               :
           +-----+-----+-----+-----+-----+-----+-----+-----+
           :                                               :
           +                Profile ID N                   +
           :                                               :
           +-----+-----+-----+-----+-----+-----+-----+-----+

                    Figure 10: Format of Reply message

   This message is sent by compressor site to decompressor site in
   response to request message sent by decompressor site.  The meaning
   of each fields in the message are described below:

   Maximum CID

      Maximum CID tolerated by compressor.  This value of this field
      should be less than or equal to its counterpart in request
      message.  Decompressor site should send a NACK if it receives
      Maximum CID that is higher than the initial negotiated value.

   MRRU







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      Maximum Reconstructed Reception Unit tolerated by compressor.
      Likewise, decompressor site should send a NACK if it is receives
      higher MRRU than what it requested.

   Number of profile IDs

      Note that this field is 1 octet instead of 2 because there can be
      only 256 active profiles at any given ROHC channel.  Decompressor
      site should send a NACK if it receives more profile IDs than it
      can support.

   Profile IDs

      Profile Identifiers of the ROHC profiles that will be used for the
      negotiated ROHC channel.  Decompressor site should send a NACK if
      it receives any profile ID that it doesn't support.

      X-bit is unused and should be ignored.

4.1.4.1.  Medium Information

   The following notation depicted in the previous figure 10 indicates
   the presence of medium information.

           +===============================================+

   Medium information conveys how compressor is to send ROHC compressed
   packets to decompressor.  Currently only 2 media are supported,
   namely MPEG2-TS and ULE.  The details of packet format for ROHC over
   MPEG2-TS/ULE is described in section 3.  Medium type is conveyed by
   Medium field.  Other media may be supported in the future and the
   support for these media will specified in other documents.
   Decompressor receiving unsupported medium type should send a NACK.
   When an unrecognized medium type is received, decompressor site
   should send an NACK message to compressor.

4.1.4.1.1.  MPEG-2 TS Medium

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |    Medium=0     |                             |
           +-----+-----+-----+      PID                    +
           |                                               |
           +-----+-----+-----+-----+-----+-----+-----+-----+

           Figure 12: Medium information for ROHC over MPEG2-TS




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   PID

      Packet Identifier of MPEG2-TS frames that will carry ROHC
      compressed packet.

4.1.4.1.2.  ULE Medium

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |    Medium=1     |  ULE Type |    Reserved     |
           +-----+-----+-----+-----+-----+-----+-----+-----+

              Figure 13: Medium information for ROHC over ULE

   ULE Type:

   0

      No MAC address will be sent in ULE packets.  This option should
      only be used if the compressor site is certain that there is only
      one receiver and one transmitter over DVB link.

   1

      Only destination MAC address will be sent in ULE packets that
      carry ROHC compressed packet.  This means that Destination Absent
      bit in ULE header will be cleared.  This option is used only if
      there is one transmitter and many receivers listening to that
      transmitter via DVB link.

   2

      ROHC packets will be encapsulated in Ethernet bridged frame.  This
      option is used when there multiple transmitters and receivers over
      a DVB link.

   3

      Not used.  Receiver should treat it as corrupted packet, silently
      discard the message and wait for a valid Reply message or until a
      timeout occur at which the decompressor site will start the
      negotiation afresh by sending a Request message.

   Reserved field is not used and should be ignored.






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4.1.5.  Acknowledgement/Negative Acknowledgement

           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=4   | Ack |
           +-----+-----+-----+-----+-----+-----+-----+-----+

               Figure 14: Format of Acknowledgement message

   Decompressor site should send either an acknowledgement or negative
   acknowledgement if it receives a valid Reply message.  If Ack bit is
   set, then the message is an acknowledgement.  Otherwise, it is a
   negative acknowledgement.  If compressor site doesn't receive ACK nor
   NACK within a reasonable interval, it should discard any information
   of negotiated ROHC channel parameters.  An acknowledgement must be
   sent to decompressor site when compressor site receives Decompressor
   Shutdown message.

4.1.6.  Compressor Shutdown

             MSB                                          LSB
               0     1     2     3     4     5     6     7
            +-----+-----+-----+-----+-----+-----+-----+-----+
            |        Version=0      |   Operation=5   |  X  |
            +-----+-----+-----+-----+-----+-----+-----+-----+

             Figure 15: Format of Compressor Shutdown message

   This message is sent by the compressor site to notify the
   decompressor site that it is about to stop compressing IP packets.
   Upon receiving this message, decompressor should release all
   resources that are being held.

   Compressor must wait for an acknowledgement from decompressor site
   before freeing its resource.  If it doesn't an acknowledgement within
   a reasonable interval, it should keep sending a shutdown message for
   a number of times before freeing its resource.

   X-bit is unused and should be ignored.

4.1.7.  Decompressor Shutdown









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           MSB                                          LSB
              0     1     2     3     4     5     6     7
           +-----+-----+-----+-----+-----+-----+-----+-----+
           |        Version=0      |   Operation=6   |  X  |
           +-----+-----+-----+-----+-----+-----+-----+-----+

            Figure 16: Format of Decompressor Shutdown message

   This message is sent by the decompressor site to notify the
   compressor that it is about to stop decompressing IP packets.  Upon
   receiving this message, compressor should release all resources that
   are being held and stop sending compressed IP packets.

   Decompressor must wait for an acknowledgement from compressor site
   before freeing its resource.  If it doesn't an acknowledgement within
   a reasonable interval, it should keep sending a shutdown message for
   a number of times before freeing its resource.

   X-bit is unused and should be ignored.

4.2.  Interaction of RCPNP

   The following diagram depicts a possible interaction between
   compressor site and decompressor site in negotiating ROHC channel
   parameters.

       Compressor Site                                 Decompressor Site
             |<---------------- Solicit ---------------|
             |                                         |
             |-------------- Advertise --------------->|
             |                                         |
             |<-------------- Request -----------------|
             |                                         |
             |---------------- Reply ----------------->|
             |                                         | Create instance
             |                                         | of decompressor
 Create      |<---------------- ACK -------------------|
 compressor  |                                         |
             |                                         |
             |= (Compression can begin at this point) =|
             |                                         |
             |                                         |
 Destroy     |<------- Decompressor Shutdown ----------|
 compressor  |                                         |
             |----------------- ACK --- -------------->| Destroy
             |                                         | decompressor

                     Figure 17: Packets flow of RCPNP



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5.  Bidirectional ROHC Channels

   While establishing bidirectional ROHC channels allows for the use of
   ROHC bidirectional optimistic mode and bidirectional reliable mode,
   RCPNP doesn't concern itself with the establishment of bidirectional
   ROHC channels.  Therefore, it is up to implementers of this protocol
   to support bidirectional ROHC channels.  The implementation should be
   as straightforward as mapping correct pair of ROHC channels.











































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6.  IANA Consideration

   Two EtherTypes should be assigned.  One of it is for RCPNP and the
   other is to indicate the presence of ROHC compressed packet.















































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7.  Acknowledgements

   We would like to thank Rod Walsh (Nokia) for his valuable input and
   feedback.

   We also want to extend our gratitude to Dr. Gorry Fairhurst for his
   guidance.












































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8.  Security Considerations

   - None -
















































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9.  Normative References

   [DIX]      Digital Equipment Corp, Intel Corp, Xerox Corp, "Ethernet
              Local Area Network Specification Version 2.0",
              November 1982.

   [GSE]      Digital Video Broadcasting, ""Generic Stream Encapsulation
              (GSE) Protocol", DVB Document A116, 2007.

   [IEEE-802.3]
              IEEE 802.3, "Local and metropolitan area networks-Specific
              requirements Part 3: Carrier sense multiple access with
              collision detection (CSMA/CD) access method and physical
              layer specifications", IEEE Computer Society, (also ISO/
              IEC 8802-3), 2000.

   [ISO-MPEG2]
              ISO 13818-1, "Information technology -- Generic coding of
              moving pictures and associated audio information -- Part
              1: Systems", International Standards Organisation (ISO),
              2000.

   [ITU-H222]
              H.222.0, "Information technology - Generic coding of
              moving pictures and associated audio information: Systems,
              International Telecommunication Union, (ITU-T)", 1995.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3077]  Duros, E., "A Link-Layer Tunneling Mechanism for
              Unidirectional Links", RFC 3077, 2001.

   [RFC3095]  Borman, C., "RObust Header Compression (ROHC): Framework
              and four profiles: RTP, UDP, ESP, and uncompressed",
              RFC 3095, 2001.















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Authors' Addresses

   Tat-Chee Wan
   Universiti Sains Malaysia
   School of Computer Science
   Universiti Sains Malaysia
   Penang
   Malaysia

   Phone: +6 04 653 4633
   Email: tcwan@nav6.org
   URI:   http://nrg.cs.usm.my/~tcwan


   Way-Chuang Ang
   Universiti Sains Malaysia
   School of Computer Science
   Universiti Sains Malaysia
   Penang
   Malaysia

   Email: wcang@nav6.org


   Chee-Hong Teh
   Universiti Sains Malaysia
   School of Computer Science
   Universiti Sains Malaysia
   Penang
   Malaysia

   Email: chteh@nav6.org



















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