General Packet Radio Service (GPRS) is a mobile data service available to users of GSM mobile phones. It is often described as "2.5G", that is, a technology between the second (2G) and third (3G) generations of mobile telephony. It provides moderate speed data transfer, by using unused TDMA channels in the 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 basics
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). In CSD, 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 are 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 are 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.
GPRS speeds and profile
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. 160.0 kbit/s (using 8 time slots and CS-4). A realistic bit rate is 30–80 kbit/s, because it is possible to use max 4 time slots for downlink. A change to the radio part of GPRS called EDGE allows higher bit rates of between 160 and 236.8 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.
The GPRS Capability Classes
Class A
Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time. No such devices are known to be available today.
Class B
Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.
Class C
Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually between one or the other service.
GPRS Multislot Classes
GPRS speed is a direct function of the number of TDMA time slots assigned, which is the lesser of (a) what the particular cell supports and (b) the maximum capability of the mobile device expressed as a GPRS Multislot Class.
The most common GPRS Multislot Classes are:
Class 2
Minimal GPRS implementation
Class 4
Modest GPRS implementation, 50% faster download than Class 2
Class 6
Modest implementation, but with better uploading than Class 4
Class 8
Better implementation, 33% faster download than Classes 4 & 6
Class 10
Better implementation, and with better uploading than Class 8, seen in better cell phones and PC Cards
Class 12
Best implementation, with maximum upload performance, typically seen only in high-end PC Cards
GPRS Coding
Transfer speed depends also on the channel encoding used. The least robust (but fastest) encoding scheme (CS-4) is available near the Base Transceiver Station (BTS) while the most robust encoding scheme (CS-1) is used when the Mobile Station (MS) is further away from the BTS.
Using the CS-4 it is possible to achieve a user speed of 20.0 kbit/s per time slot. However, using this scheme the cell coverage is 25% of normal. CS-1 can achieve a user speed of only 8.0 kbit/s per time slot, but has 98% of normal coverage. Newer network equipment can adapt the transfer speed automatically depending on the mobile location.
Speed (kbit/s)
CS-1 8.0
CS-2 12.0
CS-3 14.4
CS-4 20.0
Download (kbit/s) Upload (kbit/s)
CSD 9.6 9.6
HSCSD 28.8 14.4 (2+1)
HSCSD 43.2 14.4 (3+1)
GPRS 4+1 80.0 20.0 (Class 8 & 10 and CS-4)
GPRS 3+2 60.0 40.0 (Class 10 and CS-4)
Note: Like CSD, HSCSD establishes a circuit and is usually billed per minute. For an application such as downloading, HSCSD may be preferred, since circuit-switched data are usually given priority over packet-switched data on a mobile network, and there are relatively few seconds when no data are being transferred.
GPRS is packet based. When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store and forward the IP packets to the phone during cell handover (when you move from one cell to another). A radio noise induced pause can be interpreted by TCP as packet loss, and cause a temporary throttling in transmission speed.
GPRS Services
GPRS upgrades GSM data services providing:
Point-to-point (PTP) service: internetworking with the Internet (IP protocols) and X.25 networks.
Point-to-multipoint (PT2MP) service: point-to-multipoint multicast and point-to-multipoint group calls.
Short Message Service (SMS): bearer for SMS.
Anonymous service: anonymous access to predefined services.
Future enhancements: flexible to add new functions, such as more capacity, more users, new accesses, new protocols, new radio networks.
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 mobile phone operators don't offer flat rate access to the Internet (with the notable exceptions of T-Mobile and Cingular in the United States), instead basing their tariffs on data transferred, usually rounded off per 100 kilobyte.
Typical rates vary wildly, ranging from EUR €1 per megabyte to over €20 per megabyte. In the U.S., T-Mobile offers US$30 per month unlimited GPRS. In India, BPL Mobile (Bombay) offers unlimited GPRS for Rs.500 (USD 11) per month. AirTel offers nation-wide unlimited GPRS and EDGE for Rs. 600 (USD 13.5). Orange (UK) offers a 1 Gigabyte package for €128 a month, and a £1 per day unlimited use package for pre-paid users. In Poland, Era GSM offers a 2 Gigabyte package of GPRS and UMTS transmission under Blueconnect brand for €30 a month and Plus GSM offerts a 1 Gigabyte package for €15 a month.
GPRS Data on pre-paid packages is usually expensive, and limited to WAP and MMS. Full internet access, allowing Web browsing, access to POP/IMAP mail, FTP and other mainstream Web applications is usually restricted to contract packages, and are made available at lower cost.
The maximum speed of a GPRS connection (as offered in 2003) is the same as modem connection in an analog wire telephone network, about 4–5 kB/s (depending on the phone used). Latency is very high; a round-trip ping being typically about 600–700 ms and often reaching one second round trip time. GPRS is typically prioritised lower than speech, and thus the quality of connection varies greatly.
In order to set up a GPRS connection, a user needs to specify Access Point Name (APN), user name and password, and very often an IP address, all provided by the network operator.
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General Packet Radio Service (GPRS)通用分組無線服務(wù) 是GSM移動電話用戶可用的一種移動數(shù)據(jù)業(yè)務(wù)。 它經(jīng)常被描述成 "2.5G",也就是說這項(xiàng)技術(shù)位于第二代 (2G)和第三代(3G)移動通訊技術(shù)之間。它通過利用GSM網(wǎng)絡(luò)中未使用的TDMA信道，提供中速的數(shù)據(jù)傳遞。最初有人想通過擴(kuò)展GPRS來覆蓋其他標(biāo)準(zhǔn)，只是這些網(wǎng)絡(luò)都正在轉(zhuǎn)而使用GSM標(biāo)準(zhǔn)，這樣GSM就成了GPRS能夠使用的網(wǎng)絡(luò)。GPRS在Release 97之后被集成進(jìn)GSM標(biāo)準(zhǔn),起先它是由ETSI標(biāo)準(zhǔn)化的，但是當(dāng)前已經(jīng)移交3GPP負(fù)責(zé)。
GPRS原理
GPRS 區(qū)別于舊的 電路交換 (or CSD) 連接，連接在Release 97之前（GSM電話功能還沒怎么開發(fā)）就已經(jīng)包含進(jìn)GSM標(biāo)準(zhǔn)中。在舊有系統(tǒng)中一個數(shù)據(jù)連接要創(chuàng)建并保持一個電路連接，在整個連接過程中這條電路被獨(dú)占直到連接被拆除。 GPRS 基于報文交換，也就是說多個用戶可以共享一個相同的傳輸通道，每個用戶只有在傳輸數(shù)據(jù)的時候才會占用信道。這就意味著所有的可用帶寬可以立即分配給當(dāng)前發(fā)送數(shù)據(jù)的用戶，這樣更多的間隙發(fā)送或者接受數(shù)據(jù)的用戶可以共享帶寬。 WEB瀏覽，收發(fā)電子郵件和即時消息都是共享帶寬的間歇傳輸數(shù)據(jù)的服務(wù)。
通常GPRS數(shù)據(jù)的計費(fèi)是不是按照電路交換方式的秒，而是千字節(jié)KB。電路交換方式下，即使網(wǎng)絡(luò)上沒有數(shù)據(jù)傳輸，其他用戶也不能使用空閑的信道。
GPRS最初支持(理論上)互聯(lián)網(wǎng)協(xié)議IP,點(diǎn)到點(diǎn)協(xié)議PPP和X.25連接。后者典型的應(yīng)用是無線付費(fèi)終端，盡管它已經(jīng)作為標(biāo)準(zhǔn)需求被去除。X.25依然可以通過PPP甚至是IP得到支持, 但是這樣做既不需要重新封裝也不用集成什么到終端里。
GPRS速度和屬性
基于GPRS的報文數(shù)據(jù)交換使用未使用的蜂窩網(wǎng)絡(luò)帶寬傳輸數(shù)據(jù)。 而作為專門為電話系統(tǒng)設(shè)計的語音信道（或者數(shù)據(jù)信道）一旦被報文數(shù)據(jù)交換使用，將降低可用帶寬，其結(jié)果是如果在一個忙碌的電話域內(nèi)，報文傳輸速度極慢。理論上報文數(shù)據(jù)交換速度是大約170千比特/秒，而實(shí)際速度是30-70千比特/秒。在GPRS的射頻部分的改進(jìn)，取名為EDGE技術(shù)，將支持從20至200千比特/秒的更高速度傳輸。數(shù)據(jù)速率取決于同時分配到的TDMA幀的時隙。因此，數(shù)據(jù)速率越高，糾錯可靠性就越低。一般來說，連接速度隨著與距離的增加迅速下降。在人口密集的高網(wǎng)絡(luò)密度城區(qū)這倒不是什么大問題，但是在人口比較少的郊區(qū)這就真是問題了。
GPRS class 8 也就是平常所說的4+1。這表示4個時隙用于下行流量，1個時隙用于上行流量。 This profile is appropriate for 這樣做是為了優(yōu)化象WEB瀏覽器這樣的大部分是下載流量的應(yīng)用。如果用戶閱讀郵件量大于他發(fā)送的量，這個也適用。一般來說GPRS手機(jī)默認(rèn)使用 Class 8 來傳輸。
GPRS class 10也就是4+2。4個時隙下行，2個時隙上行。不過同時使用的時隙不能超過5個。 這個方案適用于雙向數(shù)據(jù)差不多相等的情況下，例如即時消息.
其他存在的級別，包括GPRS class 6 (3+2) 和GPRS class 4 (3+1)，只有老設(shè)備才使用。有些個別設(shè)備能夠做到 4+4 (四個時隙用于上行和下行，最多5個同時工作).這只是工業(yè)應(yīng)用，超過2個上行時隙電磁輻射就會對人體產(chǎn)生一定的影響。.
傳輸速率還依賴于信道編碼。編碼方案（CD-4）適用于在基站附近的時候，最差編碼方案（CD-1）用于離基站比較遠(yuǎn)的地方。.
使用CS-4 有可能達(dá)到21,4 kbps每時隙的速度。但是如果使用這個方案先有網(wǎng)絡(luò)只能覆蓋一般情況的25%的區(qū)域。. CS-1能達(dá)到9.05 kbit/s 每時隙的速率而且可以覆蓋98%的正常區(qū)域。
每一個時間片可以達(dá)到14.4Kbps的速率。
下載 上傳
GPRS 4+1 57.6 Kbps 14.4Kbps(class 8 & 10)
GPRS 3+2 43.2 Kbps 28.8Kbps(class 10)
CSD 9.6 Kbps 9.6Kbps
HSCSD 28.8 Kbps 14.4Kbps (2+1)
HSCSD 43.2 Kbps 14.4Kbps (3+1)
注意！CSD及HSCSD這類服務(wù)通常都按使用時間來計費(fèi),就像通話時間般。假如要長時進(jìn)行下載檔案的動作,則會比GPRS優(yōu)勝，因?yàn)樵谝苿与娫捑W(wǎng)絡(luò)中CSD]及HSCSD的優(yōu)先次序都會比GPRS為高,較少有數(shù)據(jù)傳輸中斷的情況出現(xiàn)。
GPRS報文數(shù)據(jù)交換基于數(shù)據(jù)包。 當(dāng)使用TCP/IP協(xié)議時，每個電話分配到有一個或多個IP地址。 當(dāng)電話切換扇區(qū)或者基站時，GPRS要暫時存儲轉(zhuǎn)發(fā)數(shù)據(jù)包到電話里。當(dāng)因?yàn)闊o線電噪聲干擾導(dǎo)致傳輸暫停和丟包可以由TCP來處理，這將導(dǎo)致臨時的傳輸速率調(diào)整。
GPRS服務(wù)
GPRS提升GSM的數(shù)據(jù)服務(wù)性能:
點(diǎn)到點(diǎn) (P2P) 服務(wù): 連接 (IP protocols)IP網(wǎng)絡(luò) and X.25網(wǎng)絡(luò)。
多播 (P2MP)服務(wù) : 一點(diǎn)到多點(diǎn)的組播和多方通話。
短信服務(wù) (SMS): 發(fā)送SMS。
彩信服務(wù)MMS: 發(fā)送攜帶語音和圖像信息的短消息。
因特網(wǎng)服務(wù)提供商服務(wù): 提供互聯(lián)網(wǎng)內(nèi)容服務(wù)。
郵件服務(wù)通過POP3或者IMAP協(xié)議檢查閱讀發(fā)送電子郵件
匿名服務(wù): 匿名訪問預(yù)定服務(wù)
未來功能: 靈活加入新的功能，例如更大容量，更多用戶，新的資源和無線網(wǎng)絡(luò)。
現(xiàn)實(shí)中的GPRS
運(yùn)營商已經(jīng)給GPRS制定了相對便宜的價格(相對于舊的GSM數(shù)據(jù)通訊、蜂窩數(shù)據(jù)交換、高速電路交換數(shù)據(jù)）在很多地方例如芬蘭，多數(shù)運(yùn)營商不支持包價收費(fèi)訪問因特網(wǎng) (但是美國的T-Mobile是一個的例外), 取而代之的是按照數(shù)據(jù)流量，通常以100KB或者1KB（中國移動通信）作為計費(fèi)單位。
典型的費(fèi)率比較高昂，在美國T-Mobile提供每月20美元無限量GPRS使用的服務(wù)。 其他運(yùn)營商象AT&T Wireless也提供包月。Orange (英國)提供88英鎊每月1GB流量套餐。中國運(yùn)營商中國移動通信的費(fèi)率提供多種選擇方式，比如神州行用戶可以選擇15元人民幣包月GPRS上網(wǎng)（這相當(dāng)便宜）而動感地帶用戶可以選擇包月限定流量，或者不繳納月租費(fèi)而以每KB0.03元人民幣計費(fèi)。
GPRS預(yù)付費(fèi)數(shù)據(jù)服務(wù)一般比較貴, 局限在WAPMMS。
GPRS連接速度跟模擬電話網(wǎng)絡(luò)上的調(diào)制解調(diào)器一樣大約4-5 kB/s (依賴于電話)。 延遲比較高，在回路測試ping中，典型的要大約600-700毫秒，往返時間經(jīng)常達(dá)到 1 秒 。 GPRS的實(shí)際性能十分普遍的低于理論值，而且連接質(zhì)量很不穩(wěn)定，很易受到影響產(chǎn)生大幅波動。
GPRS的性能
GPRS分為三級性能， 第一個類別是A級性能，指可以同時連接使用GPRS和GSM的服務(wù)傳送語音和數(shù)據(jù)，移動電臺需具備雙工以支援上述功能。
第二個類別是B級實(shí)施，即同時支持GPRS附件和GSM附件，但是不同時支持以上兩種服務(wù)。移動電臺可以自動轉(zhuǎn)換使用GPRS服務(wù)或是GSM服務(wù)，但不能同時傳送voice與傳送data。所以當(dāng)移動電臺在傳送資料收到來電話的呼叫時，會暫停傳送資料，接聽電話后在繼續(xù)傳送火數(shù)據(jù)資料。
第三個類別是C級實(shí)施，功能是只能使用GPRS或是GSM的服務(wù)（語音、短信）。必須靠手動在兩種服務(wù)中進(jìn)行切換。
GPRS basics
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). In CSD, 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 are 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 are 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.
GPRS speeds and profile
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. 160.0 kbit/s (using 8 time slots and CS-4). A realistic bit rate is 30–80 kbit/s, because it is possible to use max 4 time slots for downlink. A change to the radio part of GPRS called EDGE allows higher bit rates of between 160 and 236.8 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.
The GPRS Capability Classes
Class A
Can be connected to GPRS service and GSM service (voice, SMS), using both at the same time. No such devices are known to be available today.
Class B
Can be connected to GPRS service and GSM service (voice, SMS), but using only one or the other at a given time. During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.
Class C
Are connected to either GPRS service or GSM service (voice, SMS). Must be switched manually between one or the other service.
GPRS Multislot Classes
GPRS speed is a direct function of the number of TDMA time slots assigned, which is the lesser of (a) what the particular cell supports and (b) the maximum capability of the mobile device expressed as a GPRS Multislot Class.
The most common GPRS Multislot Classes are:
Class 2
Minimal GPRS implementation
Class 4
Modest GPRS implementation, 50% faster download than Class 2
Class 6
Modest implementation, but with better uploading than Class 4
Class 8
Better implementation, 33% faster download than Classes 4 & 6
Class 10
Better implementation, and with better uploading than Class 8, seen in better cell phones and PC Cards
Class 12
Best implementation, with maximum upload performance, typically seen only in high-end PC Cards
GPRS Coding
Transfer speed depends also on the channel encoding used. The least robust (but fastest) encoding scheme (CS-4) is available near the Base Transceiver Station (BTS) while the most robust encoding scheme (CS-1) is used when the Mobile Station (MS) is further away from the BTS.
Using the CS-4 it is possible to achieve a user speed of 20.0 kbit/s per time slot. However, using this scheme the cell coverage is 25% of normal. CS-1 can achieve a user speed of only 8.0 kbit/s per time slot, but has 98% of normal coverage. Newer network equipment can adapt the transfer speed automatically depending on the mobile location.
Speed (kbit/s)
CS-1 8.0
CS-2 12.0
CS-3 14.4
CS-4 20.0
Download (kbit/s) Upload (kbit/s)
CSD 9.6 9.6
HSCSD 28.8 14.4 (2+1)
HSCSD 43.2 14.4 (3+1)
GPRS 4+1 80.0 20.0 (Class 8 & 10 and CS-4)
GPRS 3+2 60.0 40.0 (Class 10 and CS-4)
Note: Like CSD, HSCSD establishes a circuit and is usually billed per minute. For an application such as downloading, HSCSD may be preferred, since circuit-switched data are usually given priority over packet-switched data on a mobile network, and there are relatively few seconds when no data are being transferred.
GPRS is packet based. When TCP/IP is used, each phone can have one or more IP addresses allocated. GPRS will store and forward the IP packets to the phone during cell handover (when you move from one cell to another). A radio noise induced pause can be interpreted by TCP as packet loss, and cause a temporary throttling in transmission speed.
GPRS Services
GPRS upgrades GSM data services providing:
Point-to-point (PTP) service: internetworking with the Internet (IP protocols) and X.25 networks.
Point-to-multipoint (PT2MP) service: point-to-multipoint multicast and point-to-multipoint group calls.
Short Message Service (SMS): bearer for SMS.
Anonymous service: anonymous access to predefined services.
Future enhancements: flexible to add new functions, such as more capacity, more users, new accesses, new protocols, new radio networks.
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 mobile phone operators don't offer flat rate access to the Internet (with the notable exceptions of T-Mobile and Cingular in the United States), instead basing their tariffs on data transferred, usually rounded off per 100 kilobyte.
Typical rates vary wildly, ranging from EUR €1 per megabyte to over €20 per megabyte. In the U.S., T-Mobile offers US$30 per month unlimited GPRS. In India, BPL Mobile (Bombay) offers unlimited GPRS for Rs.500 (USD 11) per month. AirTel offers nation-wide unlimited GPRS and EDGE for Rs. 600 (USD 13.5). Orange (UK) offers a 1 Gigabyte package for €128 a month, and a £1 per day unlimited use package for pre-paid users. In Poland, Era GSM offers a 2 Gigabyte package of GPRS and UMTS transmission under Blueconnect brand for €30 a month and Plus GSM offerts a 1 Gigabyte package for €15 a month.
GPRS Data on pre-paid packages is usually expensive, and limited to WAP and MMS. Full internet access, allowing Web browsing, access to POP/IMAP mail, FTP and other mainstream Web applications is usually restricted to contract packages, and are made available at lower cost.
The maximum speed of a GPRS connection (as offered in 2003) is the same as modem connection in an analog wire telephone network, about 4–5 kB/s (depending on the phone used). Latency is very high; a round-trip ping being typically about 600–700 ms and often reaching one second round trip time. GPRS is typically prioritised lower than speech, and thus the quality of connection varies greatly.
In order to set up a GPRS connection, a user needs to specify Access Point Name (APN), user name and password, and very often an IP address, all provided by the network operator.
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General Packet Radio Service (GPRS)通用分組無線服務(wù) 是GSM移動電話用戶可用的一種移動數(shù)據(jù)業(yè)務(wù)。 它經(jīng)常被描述成 "2.5G",也就是說這項(xiàng)技術(shù)位于第二代 (2G)和第三代(3G)移動通訊技術(shù)之間。它通過利用GSM網(wǎng)絡(luò)中未使用的TDMA信道，提供中速的數(shù)據(jù)傳遞。最初有人想通過擴(kuò)展GPRS來覆蓋其他標(biāo)準(zhǔn)，只是這些網(wǎng)絡(luò)都正在轉(zhuǎn)而使用GSM標(biāo)準(zhǔn)，這樣GSM就成了GPRS能夠使用的網(wǎng)絡(luò)。GPRS在Release 97之后被集成進(jìn)GSM標(biāo)準(zhǔn),起先它是由ETSI標(biāo)準(zhǔn)化的，但是當(dāng)前已經(jīng)移交3GPP負(fù)責(zé)。
GPRS原理
GPRS 區(qū)別于舊的 電路交換 (or CSD) 連接，連接在Release 97之前（GSM電話功能還沒怎么開發(fā)）就已經(jīng)包含進(jìn)GSM標(biāo)準(zhǔn)中。在舊有系統(tǒng)中一個數(shù)據(jù)連接要創(chuàng)建并保持一個電路連接，在整個連接過程中這條電路被獨(dú)占直到連接被拆除。 GPRS 基于報文交換，也就是說多個用戶可以共享一個相同的傳輸通道，每個用戶只有在傳輸數(shù)據(jù)的時候才會占用信道。這就意味著所有的可用帶寬可以立即分配給當(dāng)前發(fā)送數(shù)據(jù)的用戶，這樣更多的間隙發(fā)送或者接受數(shù)據(jù)的用戶可以共享帶寬。 WEB瀏覽，收發(fā)電子郵件和即時消息都是共享帶寬的間歇傳輸數(shù)據(jù)的服務(wù)。
通常GPRS數(shù)據(jù)的計費(fèi)是不是按照電路交換方式的秒，而是千字節(jié)KB。電路交換方式下，即使網(wǎng)絡(luò)上沒有數(shù)據(jù)傳輸，其他用戶也不能使用空閑的信道。
GPRS最初支持(理論上)互聯(lián)網(wǎng)協(xié)議IP,點(diǎn)到點(diǎn)協(xié)議PPP和X.25連接。后者典型的應(yīng)用是無線付費(fèi)終端，盡管它已經(jīng)作為標(biāo)準(zhǔn)需求被去除。X.25依然可以通過PPP甚至是IP得到支持, 但是這樣做既不需要重新封裝也不用集成什么到終端里。
GPRS速度和屬性
基于GPRS的報文數(shù)據(jù)交換使用未使用的蜂窩網(wǎng)絡(luò)帶寬傳輸數(shù)據(jù)。 而作為專門為電話系統(tǒng)設(shè)計的語音信道（或者數(shù)據(jù)信道）一旦被報文數(shù)據(jù)交換使用，將降低可用帶寬，其結(jié)果是如果在一個忙碌的電話域內(nèi)，報文傳輸速度極慢。理論上報文數(shù)據(jù)交換速度是大約170千比特/秒，而實(shí)際速度是30-70千比特/秒。在GPRS的射頻部分的改進(jìn)，取名為EDGE技術(shù)，將支持從20至200千比特/秒的更高速度傳輸。數(shù)據(jù)速率取決于同時分配到的TDMA幀的時隙。因此，數(shù)據(jù)速率越高，糾錯可靠性就越低。一般來說，連接速度隨著與距離的增加迅速下降。在人口密集的高網(wǎng)絡(luò)密度城區(qū)這倒不是什么大問題，但是在人口比較少的郊區(qū)這就真是問題了。
GPRS class 8 也就是平常所說的4+1。這表示4個時隙用于下行流量，1個時隙用于上行流量。 This profile is appropriate for 這樣做是為了優(yōu)化象WEB瀏覽器這樣的大部分是下載流量的應(yīng)用。如果用戶閱讀郵件量大于他發(fā)送的量，這個也適用。一般來說GPRS手機(jī)默認(rèn)使用 Class 8 來傳輸。
GPRS class 10也就是4+2。4個時隙下行，2個時隙上行。不過同時使用的時隙不能超過5個。 這個方案適用于雙向數(shù)據(jù)差不多相等的情況下，例如即時消息.
其他存在的級別，包括GPRS class 6 (3+2) 和GPRS class 4 (3+1)，只有老設(shè)備才使用。有些個別設(shè)備能夠做到 4+4 (四個時隙用于上行和下行，最多5個同時工作).這只是工業(yè)應(yīng)用，超過2個上行時隙電磁輻射就會對人體產(chǎn)生一定的影響。.
傳輸速率還依賴于信道編碼。編碼方案（CD-4）適用于在基站附近的時候，最差編碼方案（CD-1）用于離基站比較遠(yuǎn)的地方。.
使用CS-4 有可能達(dá)到21,4 kbps每時隙的速度。但是如果使用這個方案先有網(wǎng)絡(luò)只能覆蓋一般情況的25%的區(qū)域。. CS-1能達(dá)到9.05 kbit/s 每時隙的速率而且可以覆蓋98%的正常區(qū)域。
每一個時間片可以達(dá)到14.4Kbps的速率。
下載 上傳
GPRS 4+1 57.6 Kbps 14.4Kbps(class 8 & 10)
GPRS 3+2 43.2 Kbps 28.8Kbps(class 10)
CSD 9.6 Kbps 9.6Kbps
HSCSD 28.8 Kbps 14.4Kbps (2+1)
HSCSD 43.2 Kbps 14.4Kbps (3+1)
注意！CSD及HSCSD這類服務(wù)通常都按使用時間來計費(fèi),就像通話時間般。假如要長時進(jìn)行下載檔案的動作,則會比GPRS優(yōu)勝，因?yàn)樵谝苿与娫捑W(wǎng)絡(luò)中CSD]及HSCSD的優(yōu)先次序都會比GPRS為高,較少有數(shù)據(jù)傳輸中斷的情況出現(xiàn)。
GPRS報文數(shù)據(jù)交換基于數(shù)據(jù)包。 當(dāng)使用TCP/IP協(xié)議時，每個電話分配到有一個或多個IP地址。 當(dāng)電話切換扇區(qū)或者基站時，GPRS要暫時存儲轉(zhuǎn)發(fā)數(shù)據(jù)包到電話里。當(dāng)因?yàn)闊o線電噪聲干擾導(dǎo)致傳輸暫停和丟包可以由TCP來處理，這將導(dǎo)致臨時的傳輸速率調(diào)整。
GPRS服務(wù)
GPRS提升GSM的數(shù)據(jù)服務(wù)性能:
點(diǎn)到點(diǎn) (P2P) 服務(wù): 連接 (IP protocols)IP網(wǎng)絡(luò) and X.25網(wǎng)絡(luò)。
多播 (P2MP)服務(wù) : 一點(diǎn)到多點(diǎn)的組播和多方通話。
短信服務(wù) (SMS): 發(fā)送SMS。
彩信服務(wù)MMS: 發(fā)送攜帶語音和圖像信息的短消息。
因特網(wǎng)服務(wù)提供商服務(wù): 提供互聯(lián)網(wǎng)內(nèi)容服務(wù)。
郵件服務(wù)通過POP3或者IMAP協(xié)議檢查閱讀發(fā)送電子郵件
匿名服務(wù): 匿名訪問預(yù)定服務(wù)
未來功能: 靈活加入新的功能，例如更大容量，更多用戶，新的資源和無線網(wǎng)絡(luò)。
現(xiàn)實(shí)中的GPRS
運(yùn)營商已經(jīng)給GPRS制定了相對便宜的價格(相對于舊的GSM數(shù)據(jù)通訊、蜂窩數(shù)據(jù)交換、高速電路交換數(shù)據(jù)）在很多地方例如芬蘭，多數(shù)運(yùn)營商不支持包價收費(fèi)訪問因特網(wǎng) (但是美國的T-Mobile是一個的例外), 取而代之的是按照數(shù)據(jù)流量，通常以100KB或者1KB（中國移動通信）作為計費(fèi)單位。
典型的費(fèi)率比較高昂，在美國T-Mobile提供每月20美元無限量GPRS使用的服務(wù)。 其他運(yùn)營商象AT&T Wireless也提供包月。Orange (英國)提供88英鎊每月1GB流量套餐。中國運(yùn)營商中國移動通信的費(fèi)率提供多種選擇方式，比如神州行用戶可以選擇15元人民幣包月GPRS上網(wǎng)（這相當(dāng)便宜）而動感地帶用戶可以選擇包月限定流量，或者不繳納月租費(fèi)而以每KB0.03元人民幣計費(fèi)。
GPRS預(yù)付費(fèi)數(shù)據(jù)服務(wù)一般比較貴, 局限在WAPMMS。
GPRS連接速度跟模擬電話網(wǎng)絡(luò)上的調(diào)制解調(diào)器一樣大約4-5 kB/s (依賴于電話)。 延遲比較高，在回路測試ping中，典型的要大約600-700毫秒，往返時間經(jīng)常達(dá)到 1 秒 。 GPRS的實(shí)際性能十分普遍的低于理論值，而且連接質(zhì)量很不穩(wěn)定，很易受到影響產(chǎn)生大幅波動。
GPRS的性能
GPRS分為三級性能， 第一個類別是A級性能，指可以同時連接使用GPRS和GSM的服務(wù)傳送語音和數(shù)據(jù)，移動電臺需具備雙工以支援上述功能。
第二個類別是B級實(shí)施，即同時支持GPRS附件和GSM附件，但是不同時支持以上兩種服務(wù)。移動電臺可以自動轉(zhuǎn)換使用GPRS服務(wù)或是GSM服務(wù)，但不能同時傳送voice與傳送data。所以當(dāng)移動電臺在傳送資料收到來電話的呼叫時，會暫停傳送資料，接聽電話后在繼續(xù)傳送火數(shù)據(jù)資料。
第三個類別是C級實(shí)施，功能是只能使用GPRS或是GSM的服務(wù)（語音、短信）。必須靠手動在兩種服務(wù)中進(jìn)行切換。