专业术语-GPRS

 

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 dedicated¹ to those users who are actually sending at any given moment, providing higher utilisation where users only send or receive data intermittently³. Web browsing⁴, receiving e-mails as they arrive and instant messaging are examples of uses that require intermittent² 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 wireless⁵ 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 allocating⁶ 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 capability⁷. Generally, the connection speed drops logarithmically with distance from the base station. This is not an issue in heavily populated areas with high cell density⁸, but may become an issue in sparsely⁹ 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 lesser¹⁰ 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

Minimal¹¹ GPRS implementation¹²

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 robust¹³ (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 coverage¹⁴ 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 relatively¹⁵ 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 allocated¹⁶. 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 throttling¹⁷ in transmission speed.

GPRS Services

GPRS upgrades GSM data services providing:
Point-to-point (PTP) service: internetworking with the Internet (IP protocols¹⁸) 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.
Anonymous¹⁹ 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 tariffs²⁰ on data transferred, usually rounded off per 100 kilobyte.

Typical rates vary wildly, ranging from EUR

1 dedicated   

adj.一心一意的；献身的；热诚的

参考例句：

• He dedicated his life to the cause of education.他献身于教育事业。
• His whole energies are dedicated to improve the design.他的全部精力都放在改进这项设计上了。

2 intermittent   

adj.间歇的，断断续续的

参考例句：

• Did you hear the intermittent sound outside?你听见外面时断时续的声音了吗？
• In the daytime intermittent rains freshened all the earth.白天里，时断时续地下着雨，使整个大地都生气勃勃了。

3 intermittently   

adv.间歇地；断断续续

参考例句：

• Winston could not intermittently remember why the pain was happening. 温斯顿只能断断续续地记得为什么这么痛。 来自英汉文学
• The resin moves intermittently down and out of the bed. 树脂周期地向下移动和移出床层。 来自辞典例句

4 browsing   

v.吃草( browse的现在分词 )；随意翻阅；（在商店里）随便看看；（在计算机上）浏览信息

参考例句：

• He sits browsing over[through] a book. 他坐着翻阅书籍。 来自《简明英汉词典》
• Cattle is browsing in the field. 牛正在田里吃草。 来自《简明英汉词典》

5 wireless   

adj.无线的；n.无线电

参考例句：

• There are a lot of wireless links in a radio.收音机里有许多无线电线路。
• Wireless messages tell us that the ship was sinking.无线电报告知我们那艘船正在下沉。

6 allocating   

分配，分派( allocate的现在分词 )； 把…拨给

参考例句：

• Administrative practice generally follows the judicial model in allocating burdens of proof. 在分配举证责任方面，行政实践通常遵循司法模式。
• A cyclical multiplexing technique, allocating resources in fixed-time slices. 以固定的时间片分配资源的循环复用技术。

7 capability   

n.能力；才能；(pl)可发展的能力或特性等

参考例句：

• She has the capability to become a very fine actress.她有潜力成为杰出演员。
• Organizing a whole department is beyond his capability.组织整个部门是他能力以外的事。

8 density   

n.密集，密度，浓度

参考例句：

• The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
• The region has a very high population density.该地区的人口密度很高。

9 sparsely   

adv.稀疏地；稀少地；不足地；贫乏地

参考例句：

• Relative to the size, the city is sparsely populated. 与其面积相比，这个城市的人口是稀少的。 来自《简明英汉词典》
• The ground was sparsely covered with grass. 地面上稀疏地覆盖草丛。 来自《简明英汉词典》

10 lesser   

adj.次要的，较小的；adv.较小地，较少地

参考例句：

• Kept some of the lesser players out.不让那些次要的球员参加联赛。
• She has also been affected,but to a lesser degree.她也受到波及，但程度较轻。

11 minimal   

adj.尽可能少的，最小的

参考例句：

• They referred to this kind of art as minimal art.他们把这种艺术叫微型艺术。
• I stayed with friends, so my expenses were minimal.我住在朋友家，所以我的花费很小。

12 implementation   

n.实施，贯彻

参考例句：

• Implementation of the program is now well underway.这一项目的实施现在行情看好。

13 robust   

adj.强壮的，强健的，粗野的，需要体力的，浓的

参考例句：

• She is too tall and robust.她个子太高，身体太壮。
• China wants to keep growth robust to reduce poverty and avoid job losses,AP commented.美联社评论道，中国希望保持经济强势增长，以减少贫困和失业状况。

14 coverage   

n.报导，保险范围，保险额，范围，覆盖

参考例句：

• There's little coverage of foreign news in the newspaper.报纸上几乎没有国外新闻报道。
• This is an insurance policy with extensive coverage.这是一项承保范围广泛的保险。

15 relatively   

adv.比较...地，相对地

参考例句：

• The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
• The operation was relatively painless.手术相对来说不痛。

16 allocated   

adj. 分配的 动词allocate的过去式和过去分词

参考例句：

• The Ford Foundation allocated millions of dollars for cancer research. 福特基金会拨款数百万美元用于癌症研究。
• More funds will now be allocated to charitable organizations. 现在会拨更多的资金给慈善组织。

17 throttling   

v.扼杀( throttle的现在分词 )；勒死；使窒息；压制

参考例句：

• This fight scarf is throttling me. 这条束得紧紧的围巾快要把我窒息死了。 来自《简明英汉词典》
• The latter may be used with bypass or throttling valves in the tower water pipework circuit. 近来，可采用在冷却塔的水管系统中设置旁通阀或节流阀。 来自辞典例句

18 protocols   

n.礼仪( protocol的名词复数 )；（外交条约的）草案；（数据传递的）协议；科学实验报告（或计划）

参考例句：

• There are also protocols on the testing of nuclear weapons. 也有关于核武器试验的协议。 来自辞典例句
• Hardware components and software design of network transport protocols are separately introduced. 介绍系统硬件组成及网络传输协议的软件设计。 来自互联网

19 anonymous   

adj.无名的；匿名的；无特色的

参考例句：

• Sending anonymous letters is a cowardly act.寄匿名信是懦夫的行为。
• The author wishes to remain anonymous.作者希望姓名不公开。

20 tariffs   

关税制度； 关税( tariff的名词复数 )； 关税表； （旅馆或饭店等的）收费表； 量刑标准

参考例句：

• British industry was sheltered from foreign competition by protective tariffs. 保护性关税使英国工业免受国际竞争影响。
• The new tariffs have put a stranglehold on trade. 新的关税制对开展贸易极为不利。