RTP and RTCP—(Real-Time Transport Protocol and RTP Control Protocol) Protocols used to sequence the audio and video packets. The RTP header contains a time stamp and sequence number, allowing the receiving device to buffer as much as necessary to remove jitter and latency by synchronizing the packets to play back a continuous stream of sound. RTCP is used to control RTP. It gathers reliability information and periodically passes this information onto session participants.
Ref:http://www.cisco.com/en/US/docs/ios/12_1/voip/gktmp/reference/guide/h323intr.html
elhallak 
Nice but quite short article…
You can find more details in this page:
http://ozekiphone.com/what-is-rtcp-real-time-transport-control-protocol-322.html
Keep on searching with the Ozeki Phone System XE. These pages contain more info and tutorial videos as well.