Cellular Connectivity and Beyond
Wireless wide area networks (WANs) are cellular networks that provide data access either as a layer on top of the standard voice service or as a separate data service. The most important difference between these two approaches is that in the first method, a connection is explicitly established by a device (much like dialing up an ISP), and users are typically charged by the cellular provider based on connection airtime. The second approach is more like a traditional office network, in which the device is always connected. In this case, the cellular provider usually charges based on volume of data transferred. This approach has the added advantage that it can replace traditional pagers, allowing alerts to be received by the device as soon as they are sent. Access speeds using today's prevalent cellular networks are in the 10kbps to 20kbps range.
Some of the choices for cellular network access include the following:
Digital cell phone and cable or infrared
Wireless cellular modem card, expansion module, or sled
Wireless digital assistant
Data-enabled cell phone
The first option uses a data-enabled digital cell phone and a special connection cable, or in some cases, an infrared port to link the phone to a device such as a laptop. GSM, CDMA, and TDMA phones can provide connectivity, and it is usually charged by the minute of connection time. When considering hardware only, this is the least-expensive option. However, for heavy use, by-the-minute connection charges can go through the roof, so it is perhaps most suitable for occasional use.
Wireless cellular modems are available as PC cards, add-on modules, and sleds. These modems usually work with packet-switched networks and require a contract with a network provider. Usage is charged by the amount of data transferred in addition to a base fee. For frequent use, an unlimited access plan may be the best choice.
The RIM Blackberry is probably the best-known WDA, but Palm and HP have both created competitors that combine the capabilities of a PDA with a wireless modem. Some of these devices even add cellular voice services. Like a wireless modem, users are charged for the amount of data transferred. The main advantage of this approach is integration and having to carry only one device. Disadvantages include fairly steep device costs and being limited in choices of cellular networks.
The data-enabled cell phone is another all-in-one device, and the distinction between the WDA and cell phone is becoming blurred as cell phones gain larger screens and more powerful applications. Data access is typically charged separately from voice services.
In some situations, it is not enough to have enterprise access when in metropolitan areas. Satellite networks extend access around the globe, and are most frequently used by transportation companies (fleet management) and by people whose jobs are inherently very remote (such as those involved in oil exploration or geology). The cost of cellular access is a barrier, and some solutions make use of cellular connections wherever feasible, falling back onto satellite coverage when outside cellular network coverage.