General Packet Radio Service
General packet radio rvice (GPRS) is a packet oriented mobile data rvice available to urs of the 2G cellular communication systems global system for mobile communications (GSM), as well as in the 3G systems. In 2G systems, GPRS provides data rates of 56-114 kbit/s.
GPRS data transfer is typically charged per megabyte of traffic transferred, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the ur actually is using the capacity or is in an idle state. GPRS is a best-effort packet switched rvice, as oppod to circuit switching, where a certain quality of rvice (QoS) is guaranteed during the connection for non-mobile urs.
2G cellular systems combined with GPRS are often described as 2.5G, that is, a technology between the cond (2G) and third (3G) generations of mobile telephony. It provides moderate speed data transfer, by using unud time division multiple access (TDMA) channels in, for example, the GSM system. Originally there was some thought to extend GPRS to cover other standards, but instead tho networks are being converted to u the GSM standard, so that GSM is the only kind of network where GPRS is in u. GPRS is integrated into GSM Relea 97 and newer releas. It was originally standa
rdized by European Telecommunications Standards Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP) .
GPRS was developed as a GSM respon to the earlier CDPD and i-mode packet switched cellular technologies.
Technical overview
Services offered
GPRS extends the GSM circuit switched data capabilities and makes the following rvices possible:
"Always on" internet access
Multimedia messaging rvice (MMS)
Push to talk over cellular (PoC/PTT)
Instant messaging and prence—wireless village
Internet applications for smart devices through wireless application protocol (WAP)
Point-to-point (P2P) rvice: inter-networking with the Internet (IP)
If SMS over GPRS is ud, an SMS transmission speed of about 30 SMS messages per minute may be achieved. This is much faster than using the ordinary SMS over GSM, who SMS transmission speed is about 6 to 10 SMS messages per minute.
Protocols supported
GPRS supports the following protocols:
internet protocol (IP). In practice, mobile built-in browrs u IPv4 since IPv6 is not yet popular.
point-to-point protocol (PPP). In this mode PPP is often not supported by the mobile phone operator but if the mobile is ud as a modem to the connected computer, PPP is ud to tunnel IP to the phone. This allows an IP address to be assigned dynamically to the mobile equipment.
X.25 connections. This is typically ud for applications like wireless payment terminals, although it has been removed from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a network bad router to perform encapsulation or intelligence built in to the end-device/terminal; e.g., ur equipment (UE).
When TCP/IP is ud, each phone can have one or more IP address allocated. GPRS will store and forward the IP packets to the phone during cell handover (when you move from one cell to another). TCP handles any packet loss (e.g. due to a radio noi induced pau) resulting in a temporary throttling in transmission speed.
Hardware
Devices supporting GPRS are divided into three class:
Class A :
Can be connected to GPRS rvice and GSM rvice (voice, SMS), using both at the same time. Such devices are known to be available today.
Class B :
Can be connected to GPRS rvice and GSM rvice (voice, SMS), but using only one or the other at a given time. During GSM rvice (voice call or SMS), GPRS rvice is suspended, and then resumed automatically after the GSM rvice (voice call or SMS) has concluded. Most GPRS mobile devices are Class B.
Class C :
Are connected to either GPRS rvice or GSM rvice (voice, SMS). Must be switched manually between one or the other rvice.
A true Class A device may be required to transmit on two different frequencies at the same time, and thus will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual transfer mode (DTM) feature. A DTM-capable mobile may u simultaneous voice and packet data, with the network coordinating to ensure that it is not required to transmit on two different frequencies at the same time. Such mobiles are considered pudo-Class A, sometimes referred to as "simple class A". Some networks are expected to support DTM in 2007.
USB GPRS modems u a terminal-like interface USB 2.0 and later, data formats V .42bis, and RFC 1144 and external antennas. Modems can be added as cards (for laptops) or external USB devices which are similar in shape and size to a computer mou.
Coding schemes and speeds
qq邮箱登陆登录The upload and download speeds that can be achieved in GPRS depend on a number of factors such as:
the number of BTS TDMA time slots assigned by the operator
the maximum capability of the mobile device expresd as a GPRS multislot class the channel encoding ud summarid in the following table.
The least robust, but fastest, coding scheme (CS-4) is available near a ba transceiver station
(BTS), while the most robust coding scheme (CS-1)
is ud when the mobile station (MS) is further away from a BTS.
Using the CS-4 it is possible to achieve a ur 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 ur 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.
In addition to GPRS, there are two other GSM technologies which deliver data rvices: circuit-switc
hed data (CSD) and high-speed circuit-switched data (HSCSD). In contrast to the shared nature of GPRS, the instead establish a dedicated circuit (usually billed per minute). Some applications such as video calling may prefer HSCSD, especially when there is a continuous flow of data between the endpoints.
The following table summaris some possible configurations of GPRS and circuit switched data rvices.
Coding scheme Speed (kbit/s) CS-1 8.0 CS-2 12.0 CS-3 14.4 CS-4 20.0
双三角形的折法Technology Download
(kbit/s)
Upload (kbit/s)
TDMA
Timeslots
allocated
CSD 9.6 9.6 1+1 HSCSD 28.8 14.4 2+1 HSCSD 43.2 14.4 3+1
GPRS 80.0 20.0 (Class 8 & 10 and
CS-4)
4+1
什么的呼唤GPRS 60.0 40.0 (Class 10 and CS-4) 3+2
EGPRS (EDGE) 236.8
59.2 (Class 8, 10 and
MCS-9)
4+1
EGPRS (EDGE) 177.6
118.4 (Class 10 and
MCS-9)
3+2
Multiple access schemes
The multiple access methods ud in GSM with GPRS are bad on frequency division duplex (FDD) and TDMA. During a ssion, a ur is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain statistical multiplexing; i.e., packet mode communication, which makes it possible for veral urs to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. The down-link us first-come first-rved packet scheduling, while the up-link us a scheme very similar to rervation ALOHA (R-ALOHA). This means that slotted ALOHA (S-ALOHA) is ud for rervation inquiries during a contention pha, and then the actual data is transferred using dynamic TDMA with first-come first-rved scheduling.
Addressing
啫喱粉A GPRS connection is established by reference to its access point name (APN). The APN defines th
e rvices such as wireless application protocol (WAP) access, short message rvice (SMS), multimedia messaging rvice (MMS), and for Internet communication rvices such as email and World Wide Web access.
In order to t up a GPRS connection for a wireless modem, a ur must specify an APN, optionally a ur name and password, and very rarely an IP address, all provided by the network operator.
Usability
The maximum speed of a GPRS connection offered in 2003 was similar to a modem connection in an analog wire telephone network, about 32-40 kbit/s, depending on the phone ud. Latency is very high; round-trip time (RTT) is typically about 600-700 ms and often reaches 1 s. GPRS is typically prioritized lower than speech, and thus the quality of connection varies greatly.
Devices with latency/RTT improvements (via, for example, the extended UL TBF mode feature) are generally available. Also, network upgrades of features are available with certain operators. With the enhancements the active round-trip time can be reduced, resulting in significant increa in application-level throughput speeds.
通用分组无线服务技术
通用分组无线服务（GPRS）是一种面向服务的移动分组数据，它提供给2G的蜂窝通信系统的使用者全球移动通信系统（GSM），以及在3G系统。在2G系统中GPRS能提供56-114千比特/秒的数据传输速率。
我会变身GPRS数据传输通常是收取每兆字节的传输流量，而数据通信是通过传统的电路交换每分钟的连接时间计费的，不管用户实际是处于使用状态还是处于空闲状态都是独立的。GPRS是一种非常有效的分组交换服务，而不是电路交换，能够为非移动用户的连接保证一定的服务质量。
与GPRS结合的2G蜂窝系统通常被描述为2.5G，就是一种在2G和3G之间的移动电话技术。它提供了中等速度的数据传输，利用闲置时分多址（TDMA）的渠道，例如，GSM系统。本来有一些想法扩展到包括其他的GPRS标准，而是那些网络正在转换为使用的GSM标准，这样的GSM网络是唯一一种在正在使用的GPRS。GPRS是在97年发布的基于GSM的整合和新版本。它最初是由欧洲电信标准协会（ETSI）的标准，但现在由第三代合作伙伴项目（3GPP）替代。
作为一个GSM ，GPRS较早的回答了CDPD和i - mode分组交换蜂窝技术的发展。
技术概览
提供的服务漫漶
GPRS的扩展了GSM电路交换数据的能力，并有可能提出以下服务：
―永远在线‖的互联网接入
多媒体短信服务（MMS）
手机一键通(PoC/PTT)
即时消息和出现无线村
通过无线应用协议的互联网应用智能设备(WAP)
点对点（P2P）的服务：内部局域网（IP）
如果通过GPRS使用短信，可能会实现传输每分钟约30封短信邮件。GSM传输速度大约是每封邮件6至10分钟，GPRS短信的传输速度更快。
支持的协议
GPRS支持以下协议：
互联网协议（IP）。在实践中，手机内置的浏览器使用的IPv4，因为IPv6尚未普及。
点对点协议（PPP）。移动电话运营商往往不支持PPP这种模式，但如果是作为移动连接的电脑调制解调器使用，PPP是用来连接IP和手机的。它允许动态分配一个IP地址到移动设备。
X.25连接。这通常是用于诸如无线支付终端的应用，虽然它已经从标准中删除。X.25仍然是可以的PPP，甚至超过IP，但这样做要求是要么基于路由器来执行封装或在建的end-device/terminal情报网，例如，用户设备（UE）。
当TCP / IP使用，每个电话可以有一个或多个IP地址分配。GPRS将存储和转发的IP数据包到手机，在小区切换（当你从一个细胞转移到另一个），能够处理在一个临时节流造成的传输任何的TCP数据包丢失的问题（例如，由于无线电噪声引起的停顿）。
硬件
设备支持的GPRS可分为三类：
A类：
可以连接到GPRS服务和GSM服务（语音，短信），在同一时间使用两种。这种设备到现在还是有效的。
图片头像动漫B类：
可以连接到GPRS 服务和GSM 服务（语音，短信），在一特定时间只使用一个或其他。当GSM 业务（语音通话或短信），GPRS 服务暂停时，然后恢复的GSM 服务（语音通话或短信）将自动结束。大多数GPRS 移动设备属于B 类。
C 类：
无论是连接到GPRS 服务或GSM 服务（语音，短信）。必须手动切换之间的一种或其他服务。
一个真正的A 类设备可能需要在同一时间两个不同的频率间传输，因此将需要两个收音机。为了解决这个昂贵的规定，一个GPRS 手机可以实现双传输模式（DTM ）的特征。一个有DTM 功能的手机可能会建立语音和分组数据，使之协调以确保它不需要在同一时间两个不同的频率时传送。这种手机被认为是伪类，有时也被称为―简单的A 类‖的。有些网络预计DTM 将在2007年获得支持。
GPRS 的调制解调器使用的USB 终端型接口的USB 2.0和更高版本，数据格式V .42bis 和RFC 1144和外部天线。调制解调器可以增加一条，作为卡（笔记本电脑）或外部USB 设备是在形状和大小，类似电脑鼠标。
编码方案和速度
可以在GPRS 实现的上传和下载速度取决于很多因素，如以下：
输血服务中心的TDMA 的运营商分配的时间槽数
作为一个GPRS 多时隙级表示最高性能的移动设备
通道编码使用总结如下表：
(CS-4)是最不强劲，但速度最快，编码方案，由一个基站收发信台（BTS ）提供，而最强大的编码方案是（CS - 1型），它使用移动台（MS ）来进一步脱离输血服务中心。
使用CS – 4编码方案有可能达到20.0千比特用
户速度/时间s 每插槽。但是，使用此计划的细胞正常范围为25％。 CS - 1型可实现用户只有8.0千比
特的速度/时间s 每插槽，但有98％的正常范围。较新的网络设备能够自动适应不同的传输速度的移动位置。
除了GPRS 的，还有两个其他的GSM 技术，提供数据服务：电路交换数据（CSD ）和高速电路交换数据（HSCSD ）。相较于GPRS 的共享性质，这些不是建立一个专用电路（通常是每分钟计费）。如视频电话的某些应用程序可能更喜欢HSCSD ，尤其是当有一个端点之间的数据源源不断。
下表总结了一些可能的配置的GPRS 和电路交换数据服务： 编码方案 速度 (kbit/s) CS-1 8.0 CS-2 12.0 CS-3 14.4 CS-4 20.0
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