Header Compression addresses the reduction of protocol header data. Today’s Internet communication is based on the Internet Protocol (IP and IPv6). In opposite to high bandwidth connections with fixed lines, wireless communication and low bandwidth systems faces scarc network resources, high error probabilities, high delays, and simply limited capacity compared to the fixed line communication.
Thus, by employing header compression to this kind of low bandwidth links the amount of resources available to network users is increased, bandwidth can be saved, and QoS will be improved.
acticoms RFC2507 compliant IPHC (IP Header Compression) implements the less complex (in comparison to RoHC or RoHCv2) IP header compression – available as software protocol stack from acticom for the use in devices or environments that actually need RFC 2507 compliant header compression.
Benefits described in RFC 2507
To get low end-to-end delay small packets are preferred. Without header compression, the smallest possible IPv6/UDP headers (48 octets) consume 19.2 kbit/s with a packet rate of 50 packets/s. 50 packets/s is equivalent to having 20 ms worth of voice samples in each packet. IPv4/UDP headers consumes 11.2 kbit/s at 50 packets/s. Tunneling or routing headers, for example to support mobility, will increase the bandwidth consumed by headers by 10-20 kbit/s. This should be compared with the bandwidth required for the actual sound samples, for example 13 kbit/s with GSM encoding. Header compression can reduce the bandwidth needed for headers significantly, in the example to about 1.7 kbit/s. This enables higher quality voice transmission over 14.4 and 28.8 kbit/s modems.
Decrease header overhead.
A common size of TCP segments for bulk transfers over medium-speed links is 512 octets today. When TCP segments are tunneled, for example because Mobile IP is used, the IPv6/IPv6/TCP header is 100 octets. Header compression will decrease the header overhead for IPv6/TCP from 19.5 per cent to less than 1 per cent, and for tunneled IPv4/TCP from 11.7 to less than 1 per cent. This is a significant gain for line-speeds as high as a few Mbit/s.
The IPv6 specification prescribes path MTU discovery, so with IPv6 bulk TCP transfers should use segments larger than 512 octets when possible. Still, with 1400 octet segments (RFC 894 Ethernet encapsulation allows 1500 octet payloads, of which 100 octets are used for IP headers), header compression reduces IPv6 header overhead from 7.1% to 0.4%.
Reduce packet loss rate over lossy links.
Because fewer bits are sent per packet, the packet loss rate will be lower for a given bit-error rate. This results in higher throughput for TCP as the sending window can open up more between losses, and in fewer lost packets for UDP.