TABLE OF CONTENTS While TCP and IP were originally developed to support the requirements of data applications, there are now protocols to support real-time voice and video services in an IP network. As we noted earlier, there are actually two sets of protocols that come into play: voice transport and signaling. First let s look at the protocols for transporting voice through an IP network.
To support voice over an IP network, two protocols are required:
Real-Time Transport Protocol (RTP): RTP transports real-time voice and video packets.
Real-Time Control Protocol (RTCP): RTCP reports on the quality of the network service and generates feedback messages that can be used to measure the performance of the network service.
Voice calls have traditionally been carried over circuit switched facilities that provide consistent delay. The term we use to identify a service that maintains timing continuity is isochronous (the term is derived from the Greek words iso for same and chronos for time ). As they do not allocate capacity dynamically, circuit switched networks inherently provide isochronous transmission capability.
The dynamic allocation mechanisms used in packet networks result in jitter, or a variation in transit delay from packet to packet. Voice is typically carried in packets that contain 20 to 40 msec of human speech; each speech burst can be several seconds in length and so it will be carried in dozens...
