1. Overview of ROHC framework

2. 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

3. 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

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 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

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. 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

8. 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

9. 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

10. ROHC packet types and header formatIR
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-directional Reliable (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/IP Header 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/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

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 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