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Overview of ROHC framework

Overview of ROHC framework. Various header size reduction mechanisms. Header Removal (IP is terminated before the cellular link) No extra header overhead No service flexibility or access independence NO IP!!!. R L F. R L F. R L F. Header Compression Completely transparent

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Overview of ROHC framework

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  1. Overview of ROHC framework

  2. Various header size reduction mechanisms • Header Removal (IP is terminated before the cellular link) • No extra header overhead • No service flexibility or access independence • NO IP!!! R L F R L F 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 • 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 - Received packet L - Packet over link F - Forwarded packet

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

  4. 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)

  5. ROHC framework and HC profiles Uncompressed, RFC 3095 Framework Negotiation requirementsLink layer requirementsGeneral principlesCompression states Encoding methods Three modes of operation Feedback mechanismsCommon packet formatsProfile conceptContext 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

  6. 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

  7. Stream A-0 Stream A-1 Stream A-N CID 0 CID 1 CID N Channels and packet streams in ROHC • 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) Channel A

  8. Stream A-0 Stream A-1 Stream A-N Channels and packet streams in ROHC • 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

  9. Compressed header for stream 0-255 CID Compressed header for stream 0 Compressed header for stream 1-15 CID 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 • 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

  10. 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

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

  12. 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/IPHeader Compression Link Layer Non-transparent PDCP MAC Layer Data Channel Physical Layer

  13. 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/IPHeader Compression Link Layer Non-transparent PDCP Transparent PDCP MAC Layer Un-reliable Data Channel Speech Channel Video Channel Reliable Data Channel Physical Layer

  14. 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 withSignaling Compression ROHC TCP/IPHeader Compression withSignaling Compression Link Layer Transparent PDCP MAC Layer Un-reliable Data Channel Speech Channel Video Channel Reliable Data Channel Physical Layer

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