Existing general purpose protocols, such as TCP or UDP, have proved very successful at meeting the demands of classical applications like electronic mail or file transfer. However, these protocols turned out to be unsuitable for distributed multimedia applications with real-time requirements.
TCP for example is not capable of multicasting; in addition, the retransmission of one lost packet stops an application from processing other packets until the lost one finally arrives. But by the time a late or retransmitted packet arrives, it might be useless for a real-time sensitive application.
UDP, on the other hand, incurs considerable less overhead than TCP and does not delay an application in cases of packet loss, but offers no support for the detection of packet loss or miss-ordered packets. Both UDP and TCP do not guarantee minimum transmission rates or upper bounds on the end-to-end delay.
A list of features desirable for multimedia real-time transmission protocols includes:
In the remainder of Section 
, I will first present the Real-Time Transport Protocol
(Section ), which fulfills the listed requirements and offers some additional features.