Definition

The advent of Voice over IP (VoIP) has given a new dimension to Internet and opened a host of new possibilities and opportunities for both corporate and public network planners. More and more companies are seeing the value of
transporting voice over IP networks to reduce telephone and facsimile costs.

Adding voice to packet networks requires an understanding of how to deal with system level challenges such as interoperability, packet loss, delay,density, scalability, and reliability. This is because of the real time constraints that come into picture. But then the basic protocols being used at the network and transport layer have remained unchanged. This calls for the definition of new protocols, which can be used in addition with the existing protocols.

Such a protocol should provide the application using them with enough information to conform to the real-time constraints. This paper discusses the significance of Real-time Transport Protocol (RTP) in VoIP applications. A brief introduction to VoIP and then a description of the RTP header are given in sections 1-5.

The actual realisation of the RTP header, packetisation and processing of an RTP packet is discussed section six. Section 7, called 'Realising RTP functionalities', discusses a few problems that occur in a real time environment and how RTP provides information to counter the same. Finally, sample codes that we wrote for realising RTP packetisation, processing and RTP functionalities, written in 'C', for a Linux platform are presented.

Please note that RTP is incomplete without the companion RTP Control Protocol (RTCP), but a detailed description of RTCP is beyond the scope of this paper.