Dear Dennis...
EN-Genius Network's Dennis Feucht answers your design
queries in his new Circuit Design Clinic!
July, 2008
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EN-Genius Network presents a new, interactive
analog design service to readers! Send us your design questions (with
relevant data; schematics in JPEG or GIF, please) for some free
engineering advice from EN-Genius Network's circuit
consultant, Dennis Feucht, on how you might solve a design problem or
improve circuit performance. Submissions may be edited for clarity or
brevity, and submitters and their email addresses will remain anonymous
(unless otherwise indicated). Please send your questions to Dennis here.
Voice Over WLANs: The Complete Guide
by Dennis L Feucht
by Michael F Finneran, Published by Newnes
ISBN 13: 978-0-7506-8299-2, paperback, 400 pp, $59.95, November 2007
This book is part of the Newnes Communications Engineering series. I become skeptical when I read complete -in-book titles, but this one comes reasonably close to covering everything I can imagine that an introduction to VoWLAN should cover. The topic is (from Preface) about:
“Two of the major developments reshaping the telecommunications landscape are mobile wireless connectivity and the migration of voice telephone services to IP [Internet Protocol] technology. Those two ideas come together in networks that carry voice services over a wireless LAN (VoWLAN).
The book is intended to provide the technical background to “deploy” these networks.”
Voice communications over the Internet was proposed in the 1970s, though the network was incapable of supporting it then. WLAN voice is local VoIP delivered over a wireless LAN, sometimes called “wireless VoIP,” an IP-based alternative to PBXs. What challenges the development of VoWLAN is the merger of two new technologies, both of which are often poorly understood.
“… there are three critical areas to address in a WLAN voice deployment: voice, data, and radio. This book is not targeted specifically at any of those three areas, but rather looks to provide an overall description of the interaction among them. In essence, the goal is to inform voice people about data networking, data people about voice networking, and both groups about VoIP and WLAN technologies.”
The book, in short, is suited for network designers.
The author has organized the book into four parts. The first is an overview of WLAN and VoIP markets, applications, and the general technical challenges. The second and third parts cover, in turn, WLAN and VoIP technologies and, in the last part, they are brought together.
The opening explanation of radio transmission fundamentals starts delivering some electronics, with basic concepts of bandwidth and Shannon’s law of channel capacity. The 802.11 protocol is explained beginning with the Ethernet CSMA/CD, based on collision detection on the network medium by nodes competing to use it. Wireless media cannot both receive and transmit at the same time and must instead use CSMA/CA - collision avoidance. The 802.11 frame format is given in detail, and version a, b, and g differences are explained. A full chapter is devoted to 802.11 radio link specifications.
Succeeding chapters cover privacy and security issues in WLANs, then the IP protocol and IP routing for voice. How the Internet works is explained, followed by packet telephony using IP, then by telephone traffic engineering. For this coverage alone, the book has a wider appeal than its title suggests.
The last part of the book expounds upon various VoWLAN considerations, including such practical matters as air conditioning requirements (p 335) and security monitoring. Various possible vulnerabilities of the network to hacker attack are enumerated. The appendix gives the IEEE 802.11 and Wi-Fi standards, and also those for Bluetooth (802.15) and WiMAX (802.16). An extensive glossary preceded by a glossary of acronyms (which are many) finishes the book.
VoWLAN is in its infancy and at one point in the book the author even raises the question of the desirability of integrating it into the larger Internet network. For those wanting to know from an implementer what it is or to know more about Wi-Fi, the Internet, or the telephone system as it relates to voice and Internet communications, this book is a good place to begin.
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