While wireless technology is not yet sufficiently mature to reliably connect remote library facilities to a central site, it may be worth investigating for bookmobiles. The use of wireless makes it possible to offer online circulation and patron access catalog in the bookmobile. If the connection fails--something that happens four to eight percent of the time--circulation can be continued in back-up mode.
The type of wireless service available is an important factor in deciding whether to use the technology for connecting a bookmobile to a central site. Analog cellular telephone service--generally called Advanced Mobile Phone Service (AMPS)--is the most widely available. However, its signal strength often varies too much for reliable data transmission. The factors which affect the signal include distance, terrain, large buildings, dense trees, and vehicles moving nearby. However, there are special modem protocols for overcoming problems of signal degradation when the conditions are not severe. They are MNP1OEC, TX-CEL, and ETC. If the modems at both ends of the transmission support the same special protocol, it is often possible to achieve reliable data transmission at 9.6 to 14.4 Kbps. However, most modems do not support these special protocols. Before purchasing specialized modems, a library should seek to test them on its bookmobile route(s).
Digital cellular is much to be preferred over analog because signal strength fluctuates less and there is much less interference. When used for data transmission, a serial port of the computer on the bookmobile is connected directly to a data connection on the digital cellular phone, rather than being connected through a modem. While data transmission has generally been at 14.4 [(bps, techniques have recently been developed to boost the transmission rate to 64 bps.
Since the battery life of cellular telephones tends to be very limited, it is a good idea to connect the cellular telephone directly to the bookmobile's electrical system.
Maintaining a connection using a cellular telephone service can be expensive, up to $.30 per minute. Unless a flat rate charge can be negotiated with the service provider, it may be necessary to limit the connections to periodic data exchanges involving relatively short connection times, For example, inquiries of the patron access catalog might be made by a staff member at a specified time during each stop, and circulation might be handled offline, but with hourly updates.
Libraries that have established wireless connections between bookmobiles and the central site using cellular telephone service report that the service is not as good as regular telephone connections, but far superior to the alternative of operating bookmobiles entirely offline. A third technology is becoming available in major metropolitan areas CDPD (cellular digital packet data). It packetizes data and sends the packets over unused AMPS voice channels. Packet switching does not require a dedicated channel for the duration of its network connection; therefore, the service provider charges by the amount of data transmitted or received, rather than by the time connected to the network. Costs can be as little as $.10 per Rb. Degradation also is less of a problem than with AMPS because the channel is not dedicated. CDPD is an Internet Protocol. As the base station, the CDPD channels are connected to the Internet, allowing mobile users to communicate with any entity connected to the Web.
There is yet a fourth option, Richocet, a commercial packet radio network. It is reliable and very inexpensive (a $30 per month flat rate for 28.8 Kbps). Unfortunately, Richocet is available only in the San Francisco, Seattle, and Washington, D.C. areas. Expansion to other major cities is planned over the next two years.
A library should carefully research all of the options before committing itself, because the anecdotal evidence suggests that more than half of all libraries that have studied wireless connectivity between bookmobiles and a central site have found that it is not feasible or cost-effective.
