This is a valuable book for anyone considering moving their telephone system to VoIP, so long as you don't mind its US bias.

This book aims to fill the gap. It explains the convergence of voice and data, the basics of the older Public-Switched Telephone Network (PSTN) versus new IP telephony, and, of course, goes into the technical details of how VoIP works. You can get into long but silly arguments over whether it should be 'IP telephony' or 'VoIP'; Wallingford has chosen 'VoIP' as the umbrella term to cover all all types of telephone-like IP connections, and 'IP telephony' to mean specifically voice connections. You may think that's backwards -- I do -- but at least he's consistent about it.

All that material is useful and generally applicable to anyone. So is the material on how to structure a multi-site network with multiple PBXs, all of which need to support traditional telephone connections as well as VoIP. More suitable for the hands-on technologist is a lengthy section on Asterisk, an open-source VoIP server. Wallingford spends the equivalent of several chapters talking about how to install and configure it, and how to set it up for various applications. That's not as limiting as it sounds, since understanding what Asterisk can do helps give some detail about what VoIP in general can do, and he does include some information about proprietary products from companies such as Cisco.

Wallingford also uses Asterisk and other open-source software in his hands-on examples of how to accomplish tasks like securing SIP passwords or building an inbound fax-to-email gateway. Where the book really falls down for a British audience is that it is -- as so many of these books are -- thoroughly American. The discussions of costs, suppliers and public infrastructure all assume that you're based in the US.

That carp aside, most of this book really is valuable for anyone considering shifting their telephone systems to VoIP. Wallingford does a good job explaining the factors that affect call quality, how to manage bandwidth and security. This last topic has its own chapter, and Wallingford makes the interesting point that despite popular belief to the contrary, VoIP can actually be more secure than its older, PSTN counterpart, which largely relies on the assumption that few can gain unauthorised access to the physical lines that carry the voice signal. With VoIP, however, the security issues surrounding protecting call traffic and service availability are generally the same as those surrounding protecting the network itself -- at least so far, although there's no reason to assume that crackers won't come up with VoIP-specific attacks as these systems spread and become better known.

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