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General Packet Radio Service
General Packet Radio Service (GPRS) is a digital mobile phone technology. It is considered as 2.5G, between the second and third generation. It provides high-speed data transfer, and is only compatible with GSM networks.
GPRS is basically an addition to enable packet based communications in the TDMA-based GSM system.
GPRS is different from a data connection using a GSM phone (Cellular Switched Data or CSD), in that a data connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection. GPRS is packet-switched which means that the data connection is not used if no data is being transmitted or received. This means that the total available bandwidth can be shared among many users if they only send or receive data intermittedly. Webbrowsing, receiving e-mails, and instant messaging are examples of uses that require intermittent data transfers, which benefit from sharing the available bandwidth.
Usually, GPRS data is billed per kilobytes of information transceived, and regular data connections are billed per second. The latter is to reflect the fact that even during times when no data is being transferred, the bandwidth is unavailable to other potential users.
GPRS speeds and profiles
GPRS class 8 is also known as 4r1t. This means that 4 slots are allocated to downloading and 1 slot to uploading. This profile is approriate for applications where data is mostly downloaded, such as web browsing. If the user reads more e-mail than she sends, this is also an appropriate profile. Class 8 is usually selected by default on mobile devices that support GPRS.
GPRS class 10 is also known as 3r2t. This means that 3 slots are allocated to downloading and 2 slots to uploading. This profile is appropriate for applications where data is sent back-and-forth in roughly equal amount, such as instant messaging.
Each slot can reach a maximum of 14.4 kilobit per second.
download upload 4r1t 57.6 kbps 14.4 kbps (class 8) 3r2t 43.2 kbps 28.8 kbps (class 10) CSD 9.6 kbps 9.6 kbps HSCDS 28.8 kbps 14.4 kbps (2+1) HSCDS 43.2 kbps 14.4 kbps (3+1)
Note; Like CSD, HSCDS establishes a circuit and is usually billed per second. For an application such as downloading, HSCDS may be preferred, since circuit-switched data is usually given priority over packet-switched data on a mobile network, and there are few seconds when no data is being transferred.
GPRS in Practice
Telephone operators have priced GPRS relatively cheaply (compared to older GSM data transfer, CSD and HSCSD) in many areas, such as Finland. Most telco operators donīt offer flat rate access to the Internet, instead basing their tariffs on data transferred, usually rounded of per 100 kilobyte. Typical rates vary wildly, ranging from EUR 1 per megabyte to EUR 10 per megabyte.
The maximum speed of a GPRS connection (as offered in 2003) is the same as modem connection in an analog wire telephone network, about 5 kB/s (kilobytes per second). Latency is very bad, ping being about 1 second round trip time. GPRS is typically prioritised lower than speech, and thus the quality of connection varies greatly. Most of the limitations are not technical, as GPRS could be made to work a lot faster.
Last update: April 03, 2005
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