How Does RTP Header Compression Work?
RTP has two parts: a data portion and a header portion.The header can be much
larger than the data portion and therefore can add quite a lot of overhead to
media applications that use RTP. RTP is based on UDP, as opposed to TCP, since
acknowledgements are not needed for real-time data streams. If a real-time data
packet is lost, it does not usually make sense to resend it, since the time when it
was needed would have already passed.
Since RTP encapsulates UDP and IP headers, the total amount of header
information (RTP/UDP/IP) adds up to 40 bytes (see Figure 8.7). Considering
the small packet size that usually comprises multimedia streams, this is a lot of
overhead. Since most of the header information does not change very much from
packet to packet, this lends to the idea of compressing it. RTP header compression
can reduce this 40-byte header to about 5 bytes on a link-by-link basis.
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