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					ROHC for GTP-U

    IETF 79th meeting
        Nov 2010
         Lei Zhu
     Scenarios to compress GTP-U header
 •    LTE-A (to addressing IMT-Advanced requirements) developed
      Relay architectures by 3GPP RAN1/2/3 in Release 10.
 •    Relay architecture is to address the needs to optimize coverage and
      cell-edge user throughput

Scenario                          Mobility         Hops                     Purposes
Urban Hot Spot                    Fixed, Nomadic   Two hops                 Coverage and Throughput

Dead spot                         Fixed            Two hops or Multi-hops   Coverage

Indoor Hot Spot                   Fixed, Nomadic   Two hops                 Throughput

Rural Area                        Fixed            Two hops                 Coverage and Throughput

Emergency or Temporary Coverage   Nomadic          Two hops or Multi-hops   Coverage and Throughput

Wireless Backhaul Only            Fixed            Two hops or Multi-hops   Coverage or Throughput
    Needs to compress GTP-U header
•   The layer 3 Relay architecture was selected together with protocol
    stacks through L1/2 and L3 protocols. Shown below.

•   For some reasons, protocol stack of the added interface (Un
    interface) cross IP/UDP/GTP-U at user plane and IP/SCTP at
    control plane.
•   The traffic model at Un interface is not 100% sure, but VoIP
    applications are assumed by service providers when specify it.
•   The mechanisms of basic ROHC profile are very good to be reused.
    But the alternative proposals are also possible to create since the
    signaling to exchange status and information are not owned by
 Classification of GTP-U header fields
• STATIC-DEF: Version, Protocol type, Extension Header
  Flag, Sequence Number Flag, N-PDU Number Flag,
  Message Type and TEID.
• PATTERN: Sequence number
• Result:
   – IANA reserves a new compression profile identifier for
     IP/UDP/GTP-U header chain.
   – The compression profile for GTP-U headers would be developed
     with minor changes to existing compression profile for
     IP/UDP/RTP. GTP-U header compression profile should take
     care the reuse the different sequence number(s) of GTP-U
     header, ROHC header and further RTP header and perform
     same behavior as profiles before, even it seems SN of GTP-U
     could not exist in real traffic.
     Changes to ROHC IR packet
•     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 type octet
•   +---+---+---+---+---+---+---+---+
•   :                                       :
•   / 0-2 octets of CID                    / 1-2 octets if for large CIDs
•   :                                     :
•   +---+---+---+---+---+---+---+---+
•   | Profile = 0xXXXX                    | 1 octet
•   +---+---+---+---+---+---+---+---+
•   | CRC                                   | 1 octet
•   +---+---+---+---+---+---+---+---+
•   |                                       |
•   / Static chain                          / variable length
•   |                                       |
•   +-------------------------------------+
•   |                                       |
•   + Dynamic chain                       + variable length
•   |                                       |
•   +-------------------------------------+
•   |                                       |
•   / Payload                             / variable length
•   |                                       |
    Extension to profile identifiers
•   The proposed compression            Profile Identifier         Usage:            Reference

    profile need a reserved             0x0000               No compression   RFC 4995

    identifier which is to be carried
                                        0x0001               RTP/UDP/IP       RFC 3095, RFC 4815
    in ROHC IR and CO packet.
                                        0x0002               UDP/IP           RFC 3095, RFC 4815
•   Existing compression profiles
    are historically referenced by      0x0003               ESP/IP           RFC 3095, RFC 4815

    3GPP PDCP layer spec                0x0004               IP               RFC 3843, RFC 4815

    (36.323 and 25.323). The            0x0006               TCP/IP           RFC 4996
    referenced RFCs are shown in
    the table.                          0x0101               RTP/UDP/IP       RFC 5225

                                        0x0102               UDP/IP           RFC 5225

                                        0x0103               ESP/IP           RFC 5225

                                        0x0104               IP               RFC 5225

                                        Ox010n               IP/IDP/GTP-      n/a
• The compression profile for GTP-U header
  is highly possible to IETF turn to develop a
  new profile in somewhere of tsv area.
• A new work item is expected to be
  approved ASAP.
• A working group draft addressing the
  needs to a compression profile for GTP-U
  are done before the end of next year and
  acts as fundamental reference.

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