ROHC for GTP-U

draft-lei-tsvwg-gtpu-compression-00

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 SpotFixed,

NomadicTwo hops Coverage and Throughput

Dead spot Fixed Two hops or Multi-hops Coverage

Indoor Hot SpotFixed,

NomadicTwo 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 sta

cks 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 IETF.

IP

UDP

GTP

PDCPRLCMACPHY

IP

UDP

RN DeNB S-GWS1-U

GTP

S1-U

UDP

GTP

UDP

GTP

PDCPRLCMACPHY

IP

L1

L2

L1

L2

IP

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 need a reserved identifier which is to be carried in ROHC IR and CO packet.

• Existing compression profiles are historically referenced by 3GPP PDCP layer spec (36.323 and 25.323). The referenced RFCs are shown in the table.

Profile Identifier Usage: Reference

0x0000 No compression RFC 4995

0x0001 RTP/UDP/IP RFC 3095, RFC 4815

0x0002 UDP/IP RFC 3095, RFC 4815

0x0003 ESP/IP RFC 3095, RFC 4815

0x0004 IP RFC 3843, RFC 4815

0x0006 TCP/IP RFC 4996

0x0101 RTP/UDP/IP RFC 5225

0x0102 UDP/IP RFC 5225

0x0103 ESP/IP RFC 5225

0x0104 IP RFC 5225

Ox010n IP/IDP/GTP-U

n/a

Conclusions

• 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.