CDPD in the Real World

In "Air War" (Special Report, August), Marty Jerome suggests that CDPD is a standardized and useable product. While CDPD is available and being employed by some wireless users, many of the nation's largest wireless users have shied away from it. On two occasions I have been involved in an evaluation of CDPD technology. In both tests it came up lacking.

There were two primary concerns with CDPD. First, the suggestion that CDPD works on channels that the voice system is not using. This is technically true, but in a metropolitan environment where cellular traffic is heaviest, most CDPD vendors have supplied dedicated channels to CDPD traffic, and the channel-hopp ing mode has proven qu ite difficult to use. Without the overhead of adding TCP to our IP packets, it was almost impossible to get any data through reliably.

Second, the system claims to have coverage that is not really available. Not all cell sites in a given metropolitan area are equipped with CDPD base stations, nor all repeaters. In fringe and rural areas, the coverage is even worse. For our circumstances, with thousands of mobile units using wireless every day, CDPD was not a viable solution.

Chris Chappell
iim1cjc@smtpgwy.roadnet.ups.com