VOIP Acceleration

VOIP is an integral part of many corporate data network. It should reduce their call charges irrespective of the locations of their office globally.


Some particular VoIP packet characteristics that have to be considered:


* Usually VoIP travels on RTP protocol over UDP.
* VoIP packets are very small. Payload is 20 to 150 bytes with a RTP/UDP/IP header of 40 bytes (IP=20 bytes; UDP=12 bytes; RTP=8 bytes). Then due to the high relation between header size and payload size the transmission of VoIP packets is not an efficient process.
* Being VoIP a protocol to service a playback application (voice playback) its maximum end to end delay should be less that 150-200ms; 150ms is better. This, to guarantee the good quality of the sound to be transmitted.









Kind of problems VoIP packets experience when traveling throughout lines, switches and routers:


* The efficient of transmission is low. For transmitting 20-150 bytes you need a header of 40 bytes. A relation of 200%-26.67%.
* Packets are small. When they travel throughout lines transmitting bulk traffic, with big packets (1000-1500 bytes, and even bigger), they have to make queues that looks like this:

********** * * ********** ********** * ********** * * **********

Here ********** is a big 1200 byte packet; * is a small VoIP packet. This kind of queue is formed on routers. Then VoIP packet have to wait its turn on the routers to be forwarded behind, perhaps several, big packets. This problem conspire against the restriction of having a low forwarding delay.


* They are UDP packets. Some routers are designed to control unresponsive flows, like UDP is. See below. Then, perhaps, they have a higher probability to be dropped on these kind of routers.