Voice Over Internet Protocol (VoIP)

VoIP Implementation Guide

Quality of Service

Quality of service is a prime concern. With the traditional phone system, users are accustomed to good quality calls - they may occasionally get 'echo on the line' but this is the exception.

If you're using a data network for voice calls, it means you are chopping up the phone conversation into packets that are reassembled at the other end of the line.

With voice calls, voice transmission has to happen in real-time, and it can be difficult to guarantee this if there is too much traffic on the network. If voice data takes too long to arrive, it can result in a stuttering effect, where words get cut in half and syllables get lost - and this will not be acceptable to users.

Congestion in the network is the most likely reason for loss of quality. You need to test your network performance at peak times and at its weakest point.

As a rough rule of thumb, at least 25% of bandwidth should be kept available for administrative tasks, ie routine automatic system management.

VoIP uses bandwidth efficiently. But you need to look at worstcase scenarios when deciding whether you will need to upgrade your network. Are there bottlenecks at times of high activity?

How does the network perform while very large files are being transferred? It is normally advisable to separate voice and data traffic on the same network to control the potential impact of one on the other. Additionally, you need to plan for the future. Will there be more use of video once VoIP is up and running, as staff start videoconferencing, and how will this affect network performance?

And while it's possible to control your internal network traffic to some extent, it's impossible to manage traffic on the internet, where you have no control over the hubs, routers and pipelines that make up the public network.