As increasingly powerful computers find their way into people's homes, there is growing interest in extending Internet connectivity to those computers. Unfortunately, this extension exposes some complex problems in link-level framing, address assignment, routing, authentication and performance. As of this writing there is active work in all these areas. This memo describes a method that has been used to improve TCP/IP performance over low speed (300 to 19,200 bps) serial links.
The compression proposed here is similar in spirit to the Thinwire-II protocol described in . However, this protocol compresses more effectively (the average compressed header is 3 bytes compared to 13 in Thinwire-II) and is both efficient and simple to implement (the Unix implementation is 250 lines of C and requires, on the average, 90us (170 instructions) for a 20MHz MC68020 to compress or decompress a packet).
This compression is specific to TCP/IP datagrams./2/ The author investigated compressing UDP/IP datagrams but found that they were too infrequent to be worth the bother and either there was insufficient datagram-to-datagram coherence for good compression (e.g., name server queries) or the higher level protocol headers overwhelmed the cost of the UDP/IP header (e.g., Sun's RPC/NFS). Separately compressing the IP and the TCP portions of the datagram was also investigated but rejected since it increased the average compressed header size by 50% and doubled the compression and decompression code size.