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It is often described as " 2.5G", that is, a technology between the second ( 2G) and third ( 3G) generations of digital mobile technology. It provides moderate speed data transfer, by using unused TDMA channels GSM network. Originally there was some thought to extend GPRS to cover other standards, but instead those networks are being converted to use the GSM standard, so that is the only kind of network where GPRS is in use. GPRS is integrated into GSM standards releases starting with
Release 97 and onwards, first it was standardised by ETSI but now that effort has been handed onto the 3GPP.GPRS is different from the older Circuit Switched Data (or CSD) connection included in GSM standards releases before Release 97 (from 1997, the year the standard was feature frozen ) using a GSM phone, in that in the older system, 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 multiple users share the same transmission channel, only transmitting when they have data to send. This means that the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher utilisation where users only send or receive data intermittently. Web browsing, receiving e-mails as they arrive 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 while circuit switched 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 originally supported (in theory) IP, PPP and X.25 connections. The latter has been typically used for applications like wireless payment terminals although it has been removed as a requirement from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a router to do encapsulation or intelligence built into the end terminal.
Packet switched data under GPRS is achieved by allocating unused cell bandwidth to transmit data. As dedicated voice (or data) channels are setup by phones, the bandwidth available for packet switched data shrinks. A consequence of this is that packet switched data has a poor bit rate in busy cells. The theoretical limit for packet switched data is approx. 170 kbit/s. A realistic bit rate is 30-70 kbit/s. A change to the radio part of GPRS called EDGE allows higher bit rates of between 20 and 200 kbit/s. The maximum data rates are achieved only by allocation of more than one time slot in the TDMA frame. Also, the higher the data rate, the lower the error correction capability. Generally, the connection speed drops logarithmically with distance from the base station. This is not an issue in heavily populated areas with high cell density, but may become an issue in sparsely populated/rural areas.
GPRS class 8 is also known as 4+1. This means that 4 slots are allocated to downloading and 1 slot to uploading. This profile is appropriate for applications where data is mostly downloaded, such as web browsingA web browser is a software package that enables a user to display and interact with documents hosted by web servers. Popular browsers include Microsoft Internet Explorer and Mozilla Firefox. A browser is the most commonly used kind of user agent. The lar. If the user reads more e-mail than he or 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 4+2. This means that 4 slots are allocated to downloading and 2 slots to uploading, but no more than 5 slots may be used at the same time. This profile is appropriate for applications where data is sent back-and-forth in roughly equal amount, such as instant messaging.
Other classes exists, including GPRS class 6 (3+2) and GPRS class 4 (3+1) used in older devices. Some rare devices can do as much as 4+4 (up to 4 slots in both upload and upload, but maximum 5 total). Those are for industrial use only, through, as more than 2 upload slots are considered a health hazard for nearby user.
The transfer speed depends also on the channel encoding used. The best encoding scheme (CS-4) is available near the BTS while the worst encoding scheme (CS-1) is used when the MS is further away from the BTS.
Using the CS-4 it is possible to achieve a speed of 21,4 kbit/s per time slot. However by using this scheme the cell coverage is 25% from the normal. CS-1 can achieve a speed of 9.05 kbit/s per time slot and has 98% of the normal coverage.
Each slot can reach a maximum of 14.4 kilobitA Kilobit is a unit of information storage 1 Kilobit 103 bits 1000 bits bit 10bits 1024 bits See also Binary prefix Units of information. per second.
download upload 4r1t 57.6 kbit/s 14.4 kbit/s (class 8) 3r2t 43.2 kbit/s 28.8 kbit/s (class 10) CSD 9.6 kbit/s 9.6 kbit/s HSCSD 28.8 kbit/s 14.4 kbit/s (2+1) HSCSD 43.2 kbit/s 14.4 kbit/s (3+1)Note; Like CSD, HSCSD establishes a circuit and is usually billed per second. For an application such as downloading, HSCSD 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 packet switched data is packet based. When IP is used, each phone can have one (or more?) IP addressAn IP address is a unique number, akin to a telephone number, used by machines (usually computers) to refer to each other when sending information through the Internet using the Internet Protocol. This allows machines passing the information onwards on bees allocated. GPRS will store and forward the IP packets to the phone during cell handover (when you move from one cell to another). TCPTransmission Control Protocol (TCP is a connection-oriented, reliable delivery byte-stream transport layer communication protocol, currently documented in IETF RFC 793. It does the task of the transport layer in the simplified OSI model of computer networ's inability to differ between radio noise induced pauses and network congestion makes the protocol unsuitable for GPRS (or any radio based IP traffic). A radio noise induced pause will make TCP (unnecessarily) throttle back its transmission speed.
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