Router Requirements with VoIP

By Gene Teglovic
Updated: February 14, 2011

Adding Voice over Internet Protocol (VoIP) to a network requires careful planning. Since voice packets will be now integrated with data packets, adjustments may be needed. Network features such as data bandwidth, voice quality, capacity planning, and router selection/configuration should be carefully examined, and corresponding changes need to be scheduled and implemented. While many network components are likely to be affected, this article focuses on VoIP routers, with emphasis on Quality of Service (QoS).

Traditional routers can handle VoIP calls if VoIP phones are used in the network. A VoIP router performs the same functions as a regular router, with the additional feature of a built-in Analog Telephone Adapter (ATA), which allows analog phones to plug into the network. The ATA is also available as a separate device, which can be placed between the analog phones and traditional routers.

The most important requirement of a VoIP router (as well as the network as a whole) when adding VoIP services is QoS, which is a blanket term that describes measuring and improving VoIP conversations. QoS deals with guaranteeing that packet traffic for VoIP calls is not slowed or dropped by other interfering traffic. Slowing and dropping of packets results in latency, jitter, packet loss and bursting, which all degrade the quality of voice conversations. Call degradation results in delays, echoing, dropped calls, static, and other unpleasant conversational experiences.

Most VoIP service providers negotiate a Service Level Agreement (SLA) with customers to address QoS specifics end to end, such as less than one percent packet loss or 150 milliseconds maximum latency. Most VoIP phones have buffers built in to compensate for network jitter, and VoIP routers can be somewhat configured to control specific settings related to QoS.

Here are a couple quick tips for configuring a VoIP router to ensure it is doing all it can to contribute to the best possible QoS:

Priority Queuing

Configure the VoIP router(s) for priority queuing (a.k.a. “low latency” queuing) for the voice packets, so they go out ahead of the data packets. This goes for any other routers in the network, such as WAN and POP routers. If this functionality is not available in the routers, set the QoS priority for each device using its MAC address.

Port Forwarding

If the router does not support QoS settings as mentioned above, port forwarding can send packets traveling through specified ports to a specific device (e.g., a VoIP phone). This helps lowers the lag from the router, so that the destination device handles more of the processing. Specify the port numbers, protocol, and MAC addresses.

Note that configuration of the VoIP router is one of many steps needed to successfully configure VoIP into a network. Select the best VoIP router and configure it to optimize QoS as noted above, and this will complete one of the critical steps to optimal VoIP performance.
 

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