Robust Header Compression

Robust Header Compression ( ROHC ) is a method for compression of IP, TCP, UDP, and RTP headers, described in RFC 3095 of the IETF from 2001.

Its uses are mainly radio links which are characterized by high bit error rate of up to 10-2 and round-trip times of up to 100-200 ms RFC 3095th During the compression of the payload in multimedia and VoIP streaming through the application layer does is, the header of each packet use a lot of bandwidth. Without compression, the overhead of IP ( 20 bytes or 40 bytes ), UDP (8 bytes) and RTP summed ( 12 bytes ) to 40 bytes per packet together for IPv4 and 60 bytes for IPv6 for typical VoiceOverIP applications, with each be transported on the used codec only 15 to 20 bytes of user data per packet. This imbalance is for mobile use, but when the bandwidth is expensive and scarce, not tolerable.

ROHC compresses these 40 bytes or 60, typically in a few bytes (depending on the description of the technology is achievable size between 2 and 5 bytes ) by a compressor to be used in front of the transmission channel with limited bandwidth, and a decompressor beyond. For the compression similarities between the header data of multiple packets in the same connection and the predictability of the header data of the different protocols are used with each other. A large part of the header data can be considered as static or quasi- static.

ROHC compression can be understood extensible framework than by packet stream profiles for new combinations of protocols and is located in the ISO / OSI model between the IP-based network layer and the link layer.