Predeployment Tips

Getting networks ready for Voice over IP

Voice over IP is very sensitive to IP network problems, hence it is highly desirable to create a clean network environment prior to deployment. This can in general be achieved by well understood network design practice however it is important to realize that network problems that may not cause problems for data applications may be very problematic for VoIP.

At a minimum you should:

1. Use Switched 100BaseT LAN with a dedicated segment to each desktop
2. Consider using Gigabit Ethernet for Switch to Switch/ Router/ Server connection
3. Select good quality IP phones, with integrated switch ports that prioritize voice over data packets
4. Discuss your plans with your WAN service provider to ensure that you have adequate bandwidth, and that the service provider supports the prioritization of RTP traffic.
5. Ensure that routers support prioritization of RTP traffic and firewalls are configured to allow Voice over IP related traffic to pass through.
6. Design a good monitoring and management infrastructure to help to detect and resolve problems quickly.
7. Do pre-deployment testing!!!!!

Pre-Deployment Testing

Pre-deployment testing is the systematic testing of the ability of your network to support Voice over IP traffic. This generally involves sampling of the network performance and is hence not a substitute for planning, however can help to provide a level of confidence and to identify potential problems.

You may consider three forms of pre-deployment testing:

1. Inter-site testing. As problems are often related to congestion in access link and WAN, it is essential to run tests between sites over an extended period of say one month. This can be done with simple tools however should be performed using simulated RTP traffic as routers may handle this differently to ICMP.
2. Pilot trial. A limited trial of the IP telephony system you plan to deploy can help to highlight problems that may occur with a full deployment
3. Desktop testing. Ethernet segments can suffer from a variety of problems - develop a simple pre-installation check to verify each segment. This can involve simple checks for high collision counts or bad frames (generally available stats from managed switches) and the use of a VoIP analyzer to check packet loss and jitter levels during installation.

Useful App Note on Network Readiness Assessment

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