Overview of ROHC framework

Various header size reduction mechanisms R - Received packet L - Packet over link F - Forwarded packet Header Removal (IP is terminated before the cellular link) No extra header overhead No service flexibility or access independence NO IP!!! R L F Header Compression Completely transparent Provides IP service flexibility and access independence Application assumptions not allowed Real Wireless Internet access!!! About one extra header octet is added R L F Header Stripping Less extra overhead than HC Requires more functionality from lower layers Non-transparent header compression No service flexibility or access independence No Wireless Internet access (Only fake headers)!!! R L F

Definitions and general principles … the art of transparently minimizing the necessary bit rate for information carried in packet headers on a per-hop basis. “IP all the way” internet Cellular access Header compression HC HD

ROHC (RFC3095) - a protocol specification of 155 pages? The ROHC RFC is not only a simple protocol specification for one single header compression scheme but a document defining: The ROHC header compression framework (30 pages) IP/UDP/RTP profile (25 pages) IP/UDP profile (4 pages) IP/ESP profile (2 pages) A profile for uncompressed traffic (3 pages) In addition, there is lots of extra information General encoding methods to use with header compression (10 pages) An encoding scheme for extension headers, lists etc (20 pages) A background of the header compression issues and history (11 pages) An appendix motivating the way header fields are compressed (14 pages) Implementation guidelines (6 pages)

ROHC framework and HC profiles Uncompressed, RFC 3095 Framework Negotiation requirements Link layer requirements General principles Compression states Encoding methods Three modes of operation Feedback mechanisms Common packet formats Profile concept Context identifiers Packet identifiers UDP RTP Profile, RFC 3095 UDP only Profile, RFC 3095 ESP/IP Profile, RFC 3095 TCP Profile, 2001 0-byte profile, 2001 ? Signaling compr. profile, 2001 ? Other Profiles

Channels and packet streams in ROHC One ROHC instance is set up for each logical link layer channel. This means that if multiple channels are used, e.g. with different channel properties, one ROHC instance must be set up for each logical channel ROHC A ROHC B ROHC C ROHC D ROHC E ROHC F Channel A Channel B Channel C Channel D Channel E Channel F Physical Link

Channels and packet streams in ROHC Stream A-0 Stream A-1 Stream A-N A ROHC instance can handle multiple packet streams, each compressed according to any, but exactly one, profile from the supported profile set ROHC A Packet streams compressed by one ROHC instance and sent over the corresponding channel are separated by ROHC internally, using context identifiers (CID’s) CID 0 CID 1 CID N Channel A

Channels and packet streams in ROHC Stream A-0 Stream A-1 Stream A-N A ROHC instance can handle multiple packet streams, each compressed according to any, but exactly one, profile from the supported profile set ROHC A Packet streams compressed by one ROHC instance and sent over the corresponding channel are separated by ROHC internally, using context identifiers (CID’s) CID 0 CID 1 CID N Bearer A1 Bearer A2

Context identification, CID handling A ROHC instance can be initiated with two kinds of CID capabilities Large CID, which means that one CID octet is added to all compressed packets allowing 256 different packet streams to be separated CID Compressed header for stream 0-255 Small CID means that one CID octet is added to the compressed packets for all streams except for one (CID=0), which has no CID overhead. Only 16 packet streams can be compressed by a ROHC instance initiated with small CID Compressed header for stream 0 CID Compressed header for stream 1-15

ROHC packet types and header format IR Initialization Complete update IR-DYN / EXT. COMPR. Dynamic update Compressed packets with non-trivial extensions COMPR. 1 CRC + Sequence number + Timestamp COMPR. 0 CRC + Sequence number About 40/60 octets 3-… octets 2 octets 1 octet

ROHC overview - Three modes CRC-based ACK-based Starting point Unidirectional (U) mode No usage of feedback Bi-directional Optimistic (O) mode Bi-directional Reliable (R) mode Limited usage of feedback Periodic usage of feedback

ROHC in the WCDMA protocol stack (Release 3) Speech Codec Video Codec Session Signal WWW RTP RTCP HTTP UDP TCP IP Traffic Classification, Channel Setup Header Compression RFC 2507 TCP,UDP/IP Header Compression Link Layer Non-transparent PDCP MAC Layer Data Channel Physical Layer

ROHC in the WCDMA protocol stack (Release 4) Speech Codec Video Codec Session Signal WWW RTP RTCP HTTP UDP TCP IP Traffic Classification, Channel Setup Header Compression ROHC RTP/UDP/IP Header Compression ROHC RTP/UDP/IP Header Compression ROHC (RTP)/UDP/IP Header Compression RFC 2507 TCP/IP Header Compression Link Layer Transparent PDCP Non-transparent PDCP MAC Layer Speech Channel Video Channel Un-reliable Data Channel Reliable Data Channel Physical Layer

ROHC in the WCDMA protocol stack (Expectations for release 5) Speech Codec Video Codec Session Signal WWW RTP RTCP HTTP UDP TCP IP Traffic Classification, Channel Setup Header Compression ROHC RTP/UDP/IP Header Compression ROHC RTP/UDP/IP Header Compression ROHC (RTP)/UDP/IP Header Compression with Signaling Compression ROHC TCP/IP Header Compression with Signaling Compression Link Layer Transparent PDCP MAC Layer Speech Channel Video Channel Un-reliable Data Channel Reliable Data Channel Physical Layer