Cellular Data Communications Made Easy By Peter Rysavy   Huge numbers of people are hitting the road with their cellular telephones and notebook computers, many of which have PC Card modems installed. Thanks to recent advances in modem technology and cellular services, users can easily connect those modems to their cellular phones. And they can reliably dial up connections over cellular links at rates of 9,600 bps-sometimes higher-gaining mobile access to corporate e-mail and databases, online services and the Internet. But few are taking advantage o f cellular data. Why? One reason is that most people are not aware that cellular data communications is a viable option. Others are unsure of the costs they will incur. And finally, there are some significant hurdles for the user to overcome. Although these hurdles are relatively minor for IS managers and technical users, they can defeat the average user. In this article, we'll tell you what you need to know to make cellular data work for you. For our testing, we concentrated on the Advanced Mobile Phone Service (AMPS) network. This analog cellular network provides service throughout the United States and Canada, accounting for more than 90 percent of cellular phone use in North America today. AMPS technology is used in other countries as well. Digital and Analog Technologies Cellular and Personal Communications Services (PCS) companies are rapidly deploying new networks based on digital technology. However, though data services for some of these digital networks are available today, th ey will not be broadly available until 1998 or later. For more details, see "Update on Data Over Digital Cellular and PCS," which can be found on Network Computing Online at techweb.cmp.com/nc/812/ws2.html. Additionally, see "Digital Cellular Networks: On the Road to PCS," at techweb.cmp.com/nc/702/702f2.html. Just to confuse things, Cellular Digital Packet Data (CDPD) networks also operate over the analog cellular network (see "Wireless Data Made to Order," at techweb.cmp.com/nc/704/704f2.html). For CDPD, you need a special modem or a new-generation smart cellular phone (such as AT&T PocketNet phone) that incorporates a CDPD modem. CDPD is a packet data technology best-suited for transmission of short messages. RAM Mobile Data and ARDIS are two other packet data networks available in the United States. With packet data, the modem occupies the radio channel only for the time it takes to transmit that packet. Typically, users are billed for the amount of data they send. In contrast, when you use you r PC Card modem to communicate over a cellular connection, you are making a circuit connection and paying for the duration of the call just as when you make a voice call. The per-minute charges are usually the same. How does cellular circuit data work? Instead of plugging your modem into a telephone jack, you plug it into your cellular ph one with what is called a "direct connect" cable. Easy so far. But cellular connections are noisier because of interference and they are more prone to errors. Additionally, the radio channel's spectral characteristics differ from those of a landline copper wire connection. The result is that conventional modem modulation and error control do not work well. Therefore, modem vendors have developed new protocols and other techniques specifically for cellular connections. All the Right Moves The key to success is to take advantage of these new cellular protocols. We assume your PC Card modem is already installed in your computer along with all the appropriate P C Card drivers, and that you can readily make landline connections. · Use the right application Because cellular calls can cost more than landline calls, use cellular connections judiciously and with programs that give you control over how much data you download. For example, Microsoft Exchange lets you view headers before you transfer mail items. QUALCOMM's Eudora Pro lets you specify a maximum message size. Most Web browsers let you operate in a text mode (eliminating data-hogging graphics).

Which Duplication Method Is Right for You? by Jonathan Feldman Updated June 27, 1997