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However, Black's long-winded explanations often make it tough to digest the information he presents. For example, he approaches voice coders like so: "The principle function of a voice coder is to encode pulse code modulation or PCM user speech samples into a small number of bits in such a manner that the speech is robust in the presence of link errors, jittery networks, and bursty transmissions." And though there is an appendix that lists all the acronyms used in the text and what they stand for, this book would have benefited mightily from a full-blown glossary.

On the positive side, Voice Over IP is chock-full of terrific tables and charts that illustrate network topologies and the different elements of protocols involved in transmitting voice traffic over an IP network. In addition, an extremely useful chapter titled "Performance Considerations" provides the results of three voice over IP studies conducted in various networking environments as well as comparative product information on such market leaders as Cisco and Lucent. So if you're not put off by high-voltage technology and its murky vocabulary, this book is a good selection. However, it may be a little much for those who are unfamiliar or only vaguely acquainted with IP telephony. --Sarah L. Roberts-Witt