Introduction

Part 1 of this series covered VoIP basics and introduced the topic of Quality of Service. This time, I'll look at Traffic Shaping and Power Considerations.

My experience has been that the QoS mechanisms covered previously don't provide a complete solution to the need for assured bandwidth when using VOIP over DSL. When the connection to the ISP becomes saturated for any reason VOIP traffic can be delayed, which is always a problem. When managed QoS was combined with "traffic shaping" our VOIP phone service became much more reliable. This has proven to be true even on a very busy connection to my ISP.

Like the QoS mechanisms covered previously, traffic shaping is an edge process that occurs in your router. Traffic shaping is actually a process of reserving bandwidth specifically for selected applications. That bandwidth will not be used for other forms of internet access. As before, this tends to be most critical with outbound traffic where available bandwidth is most limited. It's also true with inbound traffic, but this tends to be less of an issue.

By the time I was ready to put my Asterisk server into production I had shifted to using m0n0wall [reviewed] as my router. m0n0wall is simply outstanding. It's a router based upon FreeBSD and using a PHP-based GUI that's accessed as a web site.

It's available for a variety of hardware platforms including:

• Generic PC
• Soekris Net 4501 single board embedded computer
• Soekris Net 4801 single board embedded computer
• PC Engines Wrap series of single board embedded computers [review]
• PC Engines Alix series of single board embedded computers

Soekris Net 4801 embedded platform

I decided to use a Soekris Net4801 as the host platform for my m0n0wall. This is a small system based upon a National Semiconductor Geode 266 MHz CPU. It boots from a CF card and stores the router configuration on a USB key.

The Net4801 has three on-board Ethernet ports. These are typically used as; WAN, LAN and DMZ.

By default, the traffic shaping feature on m0n0wall is disabled. Before going about its setup, you need to know for certain what your actual upload and download speeds will be. To measure your internet access speeds, use a reliable series of speed test tools such as those found at Broadband Reports. It's also a good idea to take measurements at various times of day to see if there is any significant variability.

The online documentation for the traffic shaper is a little thin but can be found here.

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Tags: Asterisk, m0n0wall, PoE, VoIP,

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