Personal Area Networks

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These are the networks that span our body and several meters beyond. About the only option today is infrared communications based on the Infrared Data Association (IRDA) standards. Many laptops and some handhelds and smart phones have IRDA ports built it. Data rates are 115 Kbps or 4 Mbps. You need to aim the device and distance is limited to a meter. But expect significant progress in this area over the next year with a new radio-frequency technology called Bluetooth that will be built into many mobile devices (see Figure 5). Bluetooth will use specialized communications protocols at the physical and medium-access control layers. At higher layers, it will either emulate serial port connections or enable the use of networking protocols such as TCP/IP. With a cost goal of $5 per device, Bluetooth could truly become ubiquitous.

Local Area Networks
Plugging a mobile computer into a wired network such as Ethernet will depend mostly on whether the computer has a PC Card slot. More likely, you will be interested in using a wireless LAN. These are becoming quite popular because of a recently completed interoperability standard (IEEE 802.11), rapidly decreasing prices (below $200 in some instances), convenient form factors such as PC Cards, and increasing throughput rates, now as high as 11 Mbps. Wireless LANs operate in unlicensed bands which simplifies deployment. Realize that coverage will be restricted to where you place access points. These cost between $1000 to $1500, provide a bridge to the wired network and offer coverage areas between 30 and 100 meters depending on the particular product, the technology used and the physical environment.

You can plug in a wireless LAN card if the computer has a PC Card slot, which many handheld do. And some vendors are integrating wireless LAN technology directly into handheld computers. Watch also for developments in the home market with the HomeRF standard designed for low-cost wireless LANs and cordless phones.

Wireless LANs employ specialized physical layer and medium-access-control protocols, but are designed so that standard networking protocols (TCP/IP, SPX/IPX and NetBEUI, for example) can be used.

For more details on local-area wireless, see the Network Design Manual chapter at: http://www.networkcomputing.com/netdesign/wireless1.html

Wide Area Networks
What we really want is connectivity from anywhere. You can do this with most mobile computers with a conventional modem. But, because we are mobile, we are likely not to have a convenient place to jack in. Again, wireless offers the greatest potential. Today, wireless networks provide data rates that are in the 10-to-14-Kbps range. This is slow by some standards, but more than sufficient for e-mail, driving directions, traffic updates, stock quotes, calendar synchronization, airline schedules, and thousands of other applications just waiting for the market to ripen.

BellSouth Wireless Data (http://www.bellsouthips.com) and ARDIS (http://www.ammobile.com) are two providers with broadly available service. Both networks use specialized communications protocols, making the number of applications you can run limited. A variety of devices (RIM Inter@ctive Pager, Palm VII) come with wireless modems built in for these networks. Service is relatively expensive at about 25 cents per KB. Cellular Digital Packet Data (CDPD) is an overlay to the cellular network, and because it is based on IP, allows any IP application to operate; though throughput is a consideration. CDPD service is available on a flat-rate basis for about $55 per month or on a usage basis at about 5 cents per kilobyte. Using modems over the analog-cellular network is also possible, though tricky.

Many are waiting for when data service is broadly available over digital cellular and PCS networks. Such service is already widely available in Europe and Asia and in some areas of the United States where GSM networks offer circuit-switched data service. Circuit-switched data service for CDMA should be available by the end of 1999. See Figure 6. Higher speed (50 to 384 Kbps) packet data for digital cellular will start to roll out in 2000 and will be broadly available by 2002.

Metricom is another service provider. Its Ricochet service (http://www.ricochet.net) offers approximately 30-Kbps service at a flat rate of $30 per month. Service is limited at this time to a small number of cities that include the San Francisco Bay area, Seattle and Washington.

For more details on wide-area wireless, see the Network Design Manual chapter at: http://www.networkcomputing.com/netdesign/wireless1.html