Overview

In the last chapter we described the overall operation of an IP routing network, and the TCP/IP protocols that are used to carry real-time voice and video traffic. In that discussion we introduced the major performance attributes of traditional and QoS-capable IP networks and how protocols like RTP can reestablish the packet sequencing and timing recovery that are essential for good quality voice.

In this chapter we will look at these issues from the standpoint of voice quality. We will describe the major quality issues that have been identified for packet voice, and the impact these various parameters will have on the user experience. Issues like delay, jitter, and packet loss are inherent in any packet voice system, and we will look at the additional challenge the will be introduced with the use of a wireless LAN as part of the transmissions path.

It is important to recognize that the wireless LAN is only part of the overall transmission path the voice packets will travel between the source and destination. The quality the user will experience is based on the overall performance of all of the elements within the path. Whether we are discussing packet loss or the delay factors, the performance of all of the elements in the path is additive. Whether the receive buffer, the local network, or the wide area network drops the packet, the result is the same: that packet does not arrive at the destination. Similarly, the delay introduced by the WLAN is...