Chapter 11. Header Compression

• Introductory Concepts

• Compressed RTP

• Robust Header Compression

• Considerations for RTP Applications

One area where RTP is often criticized is the size of its headers. Some argue that 12 octets of RTP header plus 28 octets of UDP/IPv4 header is excessive for, say, a 14-octet audio packet, and that a more efficient reduced header could be used instead. This is true to some extent, but the argument neglects the other uses of RTP in which the complete header is necessary, and it neglects the benefit to the community of having a single open standard for audio/video transport.

Header compression achieves a balance between these two worlds : When applied to a link layer, it can compress the entire 40-octet RTP/UDP/IP header into 2 octets, giving greater efficiency than a proprietary protocol over UDP/IP could achieve, with the benefits of a single standard. This chapter provides an introduction to the principles of header compression, and a closer look at two compression standards: Compressed RTP (CRTP) and Robust Header Compression (ROHC).