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The principal specification for ROHC is RFC 3095. The ROHC family
of header compression protocols is intended for wireless links which have
moderate to high error rates and/or packet loss rates. The prime application of
ROHC will probably be to 3G wireless mobile telephony to facilitate the
efficient integration of voice (and other real-time traffic) with data.
ROHC compresses only packet headers, not packet payloads. For example, the RTP compression protocol compresses the IP/UDP/RTP headers of voice and video RTP traffic typically from 40 bytes down to 4 bytes. The ROHC family also includes IP/UDP, IP/TCP and IP-only header compression. (The RoHC literature writes protocol layers in reverse order to the Internet community. This is because they write layers according to the order of packet headers. E.g. IP/UDP instead of UDP/IP.)
The word robustmeans that ROHC compression is not less robust than the corresponding uncompressed traffic. The word robustin ROHC does not mean that ROHC traffic is more robust than uncompressed traffic. The word robustdistinguishes ROHC from other header compression protocols which are not robust for links with moderate to high error rates. It should be noted, however, that smaller packets offer a smaller target for bit errors. So the packet loss rate for any compression method should be lower than for uncompressed packets. So if RoHC has only a very small probability of loss of sync between compressor/decompressor state machines, there should be a small reduction in overall packet loss rate between applications. This is a minor effect. The main purpose of RoHC is just to not increase the packet loss rate between applications. |
