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	Issue TOC Print full article Print this page Download as PDF E-Mail this URL Flame the author     In this article Introduction IP Packet Architecture Throughput Versus Latency But Is It Secure? Executive Summary GPRS: Problem-Free Connections Verizon Wireless' 1XRTT: Safe At Almost Any Speed

As part of the research FOR this article, we obtained a GPRS-capable handset and GSM/GPRS service from AT&T Wireless, and conducted tests in Portland, Ore., and Bellevue, Wash. Our overall experience was positive.

AT&T Wireless supplied us with an Ericsson T68, an extremely popular new model globally, featuring data capabilities, color display, WAP browser and Bluetooth connectivity. We created a model based on a user who uses the phone primarily for voice, but occasionally connects it to a notebook computer to transmit data. In this configuration, Microsoft Windows sees the phone as a modem, through which it can establish a dial-up networking session. The first choice was whether to connect using Bluetooth or a cable. We took the easy route and used the cable, but after connecting and disconnecting the cable dozens of times, we decided Bluetooth would be much more convenient, especially if it were integrated into the notebook as it is on some new notebook models. The cable comes in a connectivity package that also includes software.

If you are technically inclined, you can use the modem information file for the phone and create a dial-up networking icon in Windows with the appropriate parameters. However, this would defeat most users. Fortunately, AT&T Wireless provides a connection utility that installs all the right drivers and configures the computer appropriately for immediate access. The utility then provides a small window in which you can connect, disconnect, and monitor your connection status. When you press the connect button, the network authenticates the device and assigns it an IP address. At that point you can send and receive data. Being connected does not result in any usage charges; you are charged only when you communicate data. This may not be obvious to the average user. The utility does not keep track of how much data you send and receive, but if you click on the Windows dial-up-networking icon in the system tray, you can monitor data usage.

In actual usage, we learned that we needed a certain level of signal strength--at least two bars, and preferably three (out of five)--for reliable operation. Although GPRS employs extensive error correction, a poor signal throttles throughput due to retransmissions that cause TCP and application time-outs. You can obtain a numerical indication of signal strength from the connection utility, but only when you are in a disconnected state. With PC Card modems, you can view signal strength while online, which is much more convenient.

For actual data transmissions, we were very pleased. Throughput tests measured between 31 Kbps and 36 Kbps. We did not notice any differences in throughput based on time of day, but this is probably because the network is not yet heavily loaded. Using ping, we consistently measured round-trip time latency of about 750 ms. Web browsing, file transfers and e-mail applications worked perfectly, and were put solidly to the test during a business trip where we used GPRS for all business communications, both in a hotel room and in a conference room where access to e-mail during the day proved extremely convenient. For Web browsing, we experienced a significant boost in speed when we enabled Web compression, an option in the connection manager. --Peter Rysavy