GPRS General Packet Radio Service Tutorial Includes:
GPRS basics Network architecture Mobile / multislot classes Radio interface Coding Channels: physical, logical, control GPRS protocol stack Operational states
GPRS - General Packet Radio Service was the evolution of 2G GSM to provide packet switched data at rates up to a maximum of 172 kbps.
GPRS was something of a revolution because all previous mobile phone systems had used circuit switched channels. Also previous cell phone systems including GSM had focussed in voice communications, but the need for mobile data was starting to come about and GPRS was one of the first to address this in a real way.
Although 2G GSM could provide some data capability it was far too slow to be used for any real applications. As a result, GPRS was developed to enable data to be handled and it also provided a stepping stone on the path to 3G.
What is GPRS? - benefits
GPRS technology brings a number of benefits for users and network operators alike over the basic GSM system. It was widely deployed to provide a realistic data capability via cellular telecommunications technology.
GPRS technology offered some significant benefits when it was launched:
- Speed: One of the headline benefits of GPRS technology is that it offers a much higher data rate than was possible with GSM. Rates up to 172 kbps are possible, although the maximum data rates realistically achievable under most conditions will be in the range 15 - 40 kbps.
- Packet switched operation: Unlike GSM which was used circuit switched techniques, GPRS technology uses packet switching in line with the Internet. This makes far more efficient use of the available capacity, and it allows greater commonality with Internet techniques.
- Always on connectivity: A further advantage of GPRS is that it offers an "Always On" capability. When using circuit switched techniques, charges are based on the time a circuit is used, i.e. how long the call is. For packet switched technology charges are for the amount of data carried as this is what uses the services provider's capacity. Accordingly, always on connectivity is possible.
- More applications: The packet switched technology including the always on connectivity combined with the higher data rates opens up many more possibilities for new applications. One of the chief growth areas that arose from GPRS was the Blackberry form of mobile or PDA. This provided for remote email applications along with web browsing, etc.
- CAPEX and OPEX: The Capital expenditure (CAPEX) and operational expenditure (OPEX) are two major concerns for operators. As GPRS was an upgrade to existing GSM networks (often implemented as a software upgrade achieved remotely), the capital expenditure for introducing GPRS technology was not as high as deploying a complete new network. Additionally OPEX was not greatly affected as the basic base-station infrastructure remained basically the same. It was mainly new core network elements that were required.
The GSM and GPRS elements of the system operated separately. The GSM technology still carried the voice calls, while GPRS technology was used for the data. As a result voice and data can be sent and received simultaneously. Some people refer to the system as GSM GPRS.
In order to further develop the capability of GPRS, further advances were made and another system known as EDGE or Enhanced GPRS, EGPRS was developed.
What is GPRS? - packet switching
The key element of GPRS technology was that it uses packet switched data rather than circuit switched data, and this technique made much more efficient use of the available capacity. This is because most data transfer occurs in what is often termed a "bursty" fashion. The transfer occurs in short peaks, followed by breaks when there is little or no activity.
Using a traditional approach a circuit was switched permanently to a particular user. This is known as a circuit switched mode. In view of the "bursty" nature of data transfer it means that there are periods when it will not be carrying data.
To improve the situation the overall capacity can be shared between several users. To achieve this, the data is split into packets and tags inserted into the packet to provide the destination address. Packets from several sources can then be transmitted over the link. As it is unlikely that the data burst for different users will occur all at the same time, by sharing the overall resource in this fashion, the channel, or combined channels can be used far more efficiently. This approach is known as packet switching, and it is at the core of many cellular data systems, and in this case GPRS.
|Packet Switching vs Circuit Switching
|Circuit Switched Mode||Packet Switched Mode|
|IMSI attach||GPRS attach|
|Call setup|| TBF establishment
PDP context activation
|Call state (bi-directional)||Block transfer (uni-directional)|
|Exclusive use of channel||Channel shared between users|
|Calls cleared on completion||Always on|
GPRS and GSM are able to operate alongside one another on the same network, and using the same base stations. However upgrades are needed. The network upgrades reflect many of those needed for 3G, and in this way the investment in converting a network for GPRS prepares the core infrastructure for later evolution to a 3G W-CDMA / UMTS.
The upgraded network, as described in later pages of this tutorial, has both the elements used for GSM as well as new entities that are used for the GPRS packet data service.
The upgrades that were required for GPRS also formed the basis of the network required for the 3G deployments (UMTS Rel 99). In this way the investment required for GPRS would not be a one off investment used only on GPRS, it also formed the basis of the network for further developments. In this way GPRS became a stepping stone used for the migration from 2G to 3G.
Not only does the network need to be upgraded for GPRS, but new GPRS mobiles were also required. It is not possible to upgrade an existing GSM mobile for use as a GPRS mobile, although GSM mobiles can be used for GSM speech on a network that also carries GPRS. To utilise GPRS new modes are required to enable it to transmit the data in the required format.
With the incorporation of packet data into the network, this allowed far greater levels of functionality to be accessed by mobiles. As a result a new breed of mobiles started to appear. These PDAs were able to provide email and Internet browsing, and they were widely used especially by businesses as they allowed their key people to remain in touch with the office at all times.
What is GPRS? key parameters
The key parameters for the GPRS, General Packet Radio System, are tabulated below:
|What is GPRS? - the key parameters
|Channel Bandwidth||200 kHz|
|Data handling||Packet data|
|Max data rate||172 kbps|
GPRS provided the first real evolution of GSM and the first in this series to provide a real data capability. It enabled emails and some simple web browsing to be undertaken, although speeds were still very slow by comparison with what is standard today.
With the advent of GPRS, and later GSM EDGE mobile handsets started to incorporate data capabilities and the first smartphones like the Blackberry from RIM set the tone for the future. GPRS enabled businessmen to keep in touch with the office whilst they were away and this trend increased as time progressed and data capabilities improved. With 2G GPRS data usage started to increase and the trend to move towards data rather than voice being the primary requirement for cellphone handsets was set in motion, although it would be some years before data revenues outstripped voice revenues.
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