Troubleshooting and analyzing VoIP networks


Best Practices

A few cornerstones contribute to quick problem analysis when troubleshooting VoIP networks. Targeted data acquisition is a must-have. To correctly assess a network and the applications used on it, the corresponding basic data must be available. You will want to collect the VoIP-specific data before the installation, including, for example, the number of simultaneous VoIP connections, the current LAN and wireless bandwidths, and the current and planned network loads. With this basic information, the specific boundary parameters for the VoIP network can be calculated quickly.

Furthermore, the quality and performance of the networks and applications are determined by the link components (routers, switches) on the data paths. For this reason, it is important for you to know the performance characteristics and limits of individual components. RFC 2544 defines the general test and throughput criteria that allow a subjective comparison of the products. The prioritization mechanisms used must be available throughout the components.

Because the best type of troubleshooting is prevention, you should always measure networks up front. The expected telephone volume is simulated in a realistic way, letting you discover the points on the network where improvements are still required. You will need to pay special attention to delay times, jitter, and available bandwidths. Peak loads on many corporate networks ensure that the situation can get tight repeatedly, and depending on the workload and overload, data loss can be considerable. Incorrect prioritization of real-time traffic results in delays, packet loss, and poor service quality.

In the long term, IT departments simply have to provide resources to monitor VoIP parameters actively, which means that after each extension or improvement of the network, you have to repeat the tests until the overall system meets the expectations for the required quality. Monitoring of the entire network is also indispensable. Even if a VoIP component fails, the damage can be kept to a minimum, because you can react quickly. All the parameters described in this article should be monitored on a long-term and permanent basis (Figure 3).

Figure 3: Wireshark is also VoIP-capable: For example, it supports long-term monitoring of voice quality by playing VoIP streams.


Research and troubleshooting of VoIP problems on networks are highly complex issues; casual attempts without qualified measuring tools are pointless. Today, a VoIP analysis device is an indispensable tool for troubleshooting convergent voice and data networks. However, even purchasing the best device does not mean you can sit back and relax. If you do not have an understanding of the special issues of voice transmission over the Internet, as discussed here, even technically impeccable troubleshooting will be in vain.

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