GPRS was invented as part of the move to what is called 3G or third-generation cellular phone service. That's the idea that cell phones can also be computers, e-mail and Web browsers and even TV receivers. It's a tall order for a technology that was originally designed to simply make telephones mobile.
So, how does GPRS work? It uses the idle radio capacity in GSM telephone systems. All cell phone systems have capacity that isn't being used except when everybody is on the phone in a particular cell. Normally that idle capacity wouldn't be doing anything. It would simply be held in reserve for the next callers. What GPRS does is to use that extra capacity to create a data network. If the system gets really busy with telephone calls, then the data gets a lower priority and data rates slow down.
GSM is the most popular cellular technology in the world with over a billion subscribers in 85 countries. It's based on TDMA or Time Division Multiple Access. GSM channels are 200 KHz wide and divided into 8 time slots. Each slot can carry a digital telephone call coded at 13 Kbps or 14.4 Kbps of IP or Internet Protocol data. Busy cells may use multiple channels to support the call demand.
If you could use an entire GSM channel to carry data, you could have a bandwidth of over 100 Kbps. With compression, the maximum bandwidth for GPRS is 170 Kbps. Don't get your heart set on that rate. GPRS is set up on a class system, with class 8 being the default. Class 8 is known as 4+1. You get 4 time slots for download and 1 for upload. Another popular class is GPRS class 10, also known as 4+2. That's 4 time slots for download and 2 for upload.
Typical download rates might be on the order of 40 Kbps or so. That's not the blazing speed of broadband but is plenty for SMS messaging, e-mail, order entry and Web browsing. Laptop computers can also access the Internet through GPRS with an adaptor. T-Mobile offers the Sony Ericsson GC79 PC Cellular Card that has both GPRS and Wi-Fi capability. Within a Wi-Fi hot spot you get the speed of Wi-Fi. Elsewhere, within the coverage of the T-Mobile GSM cellular network, you use GPRS. This can be the perfect combination for mobile business people who need access to their Internet based tools while visiting clients.
At this writing, the Sony Ericsson GC79 PC Cellular Card is $49.99 after rebate and T-Mobile unlimited Internet service is $29.99 a month with an activation fee of $35. Find this service and a wide variety of cell phones and cellular service plans from Cognigen Cellular.
T1 Rex's Business Telecom Explainer offers easy to understand information about complex telecommunications and networking technology. T1 Rex explains how T1 lines work, VoIP telephone, PBX, virtual private networks, digital audio transport, Wi-Fi & WiMax, fiber optic carriers and other business telecom services.
John Shepler has been a published writer for over 30 years. With a background in electronics
engineering technology, he has worked in a variety of industries including radio broadcast,
aerospace and manufacturing. Involved in telecommunications since 1998, he combines his interests
in writing and technology with T1Rex.com and T1 Rex's Business Telecom Explainer.
Copyright 2003 - 2005 by John E. Shepler
Contact me at John (at) T1Rex.com
This was first published in May 2005