An Introduction to VoIP: End-to-End Elements and QoS Parameters

Abstract

In this chapter, two of the existing communication networks are studied: voice and data networks. Each network was created with the simple goal of transporting a specific type of information. For instance, the Public Switched Telephone Network (PSTN) was designed to carry voice and the IP network was designed to carry data. In the PSTN, the main terminal device is a simple telephone set, while in the network, it is more complex, and it is provided with most of the intelligence necessary for providing various types for voice services. On the other hand, in the IP network the most of intelligence was placed in the terminal device, which is typically a host computer and the network only offers the best effort service (Park, 2005). In mid 1990’s, the two separate networks started to merge. A buzz word around this time is voice and data convergence. The idea is to create a single network to carry both voice and data. However, with this convergence, a new technical challenge has emerged. In the converged network, the best effort services that are offered by the IP network is no longer good enough to meet requirements of real-time applications, such as Voice over Internet Protocol (VoIP). VoIP refers to the transmission of voice using IP technologies over packet switched networks. It consists of a set of end-to-end elements, recommendations and protocols for managing the transmission of voice packets using IP. A basic VoIP system consists of three main elements: the sender, the IP network and the receiver. VoIP is one of the most attractive and important service nowadays in communication networks and it demands strict QoS levels and real-time voice packet delivery. The QoS level of VoIP applications depends on many parameters, such as: bandwidth, One Way Delay (OWD), jitter, Packet Loss Rate (PLR), codec type, voice data length, and de-jitter buffer size. In particular, OWD, jitter, and PLR have an important impact. This chapter presents an introduction to the main concepts and mathematical background relating to communications networks, VoIP networks and QoS parameters.