GPRS' Constant Connection

It's ironic that the European heavyweight is the underdog in the United States, but GSM/PCS-1900 may have the last laugh after all. Less than 2% of the GSM users worldwide are in North America. Yet GSM already has the best data story among the three major North American digital cellular/PCS standards, and it's about to get better with the introduction of general packet radio service (GPRS), its packet-switching technology.

GPRS defines the packet-switching standard for GSM technology. It supports both X.25 and TCP/IP bearer services with multiple quality-of-service levels. A GPRS radio can begin sending variable-length IP packets within 500ms to 1,000ms at a rate of 115kb/s. The terminals can have either static or dynamic IP addresses assigned to them, and domain name services (DNS) are supported in both directions. This allows wireless terminals to receive a domain name and be found by the Internet at large.

SETTING PRIORITIESMore than one IP address can be activated at one time, although such a scenario would be rare. The IP addresses stay with the mobile, and routing is handled by the mobile IP standard. GPRS also supports priority of service, something that has plagued other wireless data networks for many years. Certain IP addresses can be given higher priority over others, assigned and managed by the carrier. These high-priority IP addresses presumably would be sold as a premium service.

To maximize efficiency, the service bypasses the voice-switching network and deploys new nodes. These are called the servicing GPRS support node (SGSN) and the gateway GPRS support node (GGSN). These two network elements focus on the highly efficient transport of IP datagrams. The SGSN concentrates on servicing and tracking the mobile, while the GGSN establishes connectivity to and from the outside world.

Because the new fixed elements are based on IP routing equipment, there is no longer a limit of 64kb/s. The basic GPRS data transmission rate is about the same as circuit-switched GSM, but under good conditions this can be increased to 21.4kb/s per time slot. With the concatenation of eight time slots, the GSM carrier theoretically could offer rates as high as 170kb/s -- beyond the commonly stated 115kb/s figure.

GPRS also is friendly to the carrier. Airlink resources only are allocated when data actually is being sent or received. The forward and reverse channels are assigned separately, unlike circuit switching, which locks resources in both directions regardless of primary data flow. GPRS also is used to send short message service (SMS) datagrams.

MASS APPEAL?What makes GPRS so appealing to the user community is that an Internet connection can be initiated and held up all day without a penalty. Telephone calls still come through, as do SMS datagrams. Presumably, the carriers will not charge for the length of time their subscribers are on the connection, because those subscribers are not taking up airlink resources.

Compare this to a dial-up Internet service provider that charges by the hour (like AOL or CompuServe) to a dedicated packet-switched provider in an office setting that charges for bandwidth and/or total data traffic. Circuit-switched data (either analog or digital) is the equivalent of using a dial-up ISP; the incentive is to work quickly and log off. In an office setting or with a home cable modem, however, the subscriber can stay logged into the Internet all day and night; it's always there. GPRS runs on the same principle by giving continuous access.

GPRS terminals come in several flavors. The specification defines a GPRS-only device as well as a combination voice/data device. A GPRS-only product could be used for monitoring and telemetry applications or be embedded within certain personal digital assistants (PDAs). Combination GPRS/voice phones will be used as the basis for WAP-enabled browser phones. GPRS provides the snappy performance characteristics that make moving menu options one screen at a time palatable to users.

BLUETOOTH CONNECTIONA GPRS-enabled phone with a Bluetooth connection would be a killer product for PDA-carrying professionals. Bluetooth enables devices that are near one another to establish a personal area network (PAN). The GSM phone in a subscriber's pocket or belt holster would create a PAN connection to the PDA or laptop on his desk. GPRS would allow that connection to the Internet to remain alive all day.

From the subscriber's point of view, the laptop always is connected to the Internet; e-mail never stops; Web access is a click away; and on-line trading is done just as it is from a desktop computer. The Internet connection is faster than the 28.8 modem at home, and if a call comes in, no problem. Just keeping the GSM phone nearby is all it would take to keep the laptop/PDA activated. No cables. No extra weight. No reduced battery life. No custom "integrated" phone/PDA product to buy. So when your subscribers are off to the bar to watch the game with their friends, the GSM phone fits nicely into their pockets just as it always did, and the geeky computer stays home. The scenario paints a powerful picture.

It also sounded pretty good to the UWCC, which announced that it will use GPRS as its packet-switching standard for future versions of IS-136 technology.

GPRS seems to be a viable option for carriers, as long as it delivers on the high promises that surround it. Every year the industry gets closer to creating a wireless data service easy enough to break through to the mass market. GPRS may be the technology finally to do that.