To make more efficient the use of your bandwidth on slow-speed links, we can use 2 types of compression.
- Payload compression : Reduces the payload size, using approaches such as STAC, predictor or MPPC
- Header compression : Reduces the size of the TCP and RTP headers
The goal of compressions technologies is to increase the throughput over a WAN link while we are reducing the delay.
However , especially with payload compression approaches , the time that is required by lower-end routers to run the compression algorithm can increase the overall delay so in order to avoid this , you still can equip your router with a compression module like the CAIM.
With header compression , a header typically is reduced from approximately 40 bytes to 3 up to 5 bytes for TCP header compression or 2 up to 4 bytes for RTP header compression.
However, the routers technically are not doing real compression. Rather, these routers cache information that does not change during a conversation, such as source and destination IP address and TCP/UDP port numbers. The compressed header then carries such information as UDP checksums and a session context ID (CID) which identifies which flow the packet is a part of.