06-12-2012, 05:04 PM
MIGRATION FROM GSM NETWORK TO GPRS
MIGRATION FROM GSM.doc (Size: 104.5 KB / Downloads: 26)
INTRODUCTION
The General Packet Radio System (GPRS) is a new service that provides actual packet radio access for mobile Global System for Mobile Communications (GSM) and Time-Division Multiple Access (TDMA) users. The main benefits of GPRS are that it reserves radio resources only when there is data to send and it reduces reliance on traditional circuit-switched network elements. The increased functionality of GPRS will decrease the incremental cost to provide data services, an occurrence that will, in turn, increase the penetration of data services among consumer and business users. In addition, GPRS will allow improved quality of data services as measured in terms of reliability, response time, and features supported. The unique applications that will be developed with GPRS will appeal to a broad base of mobile subscribers and allow operators to differentiate their services. These new services will increase capacity requirements on the radio and base-station subsystem resources. One method GPRS uses to alleviate the capacity impacts is sharing the same radio resource among all mobile stations in a cell, providing effective use of the scarce resources. In addition, new core network elements will be deployed to support the high burst ness of data services more efficiently.
The General Packet Radio Service (GPRS) is a new non voice value added service that allows information to be sent and received across a mobile telephone network. It supplements today's Circuit Switched Data and Short Message Service. GPRS is NOT related to GPS (the Global Positioning System), a similar acronym that is often used in mobile contexts.
GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM)
Global system for mobile(GSM) is a second generation cellular system standard that was developed to solve the fragmentation problems of the first cellular systems in Europe’s is the world’s first cellular system to specify the digital modulation and network level architecture and services. Before GSM, European countries used different cellular standards throughout the continent, and it was not possible for customer to use a single subscriber unit throughout Europe. GSM’s success has exceeded the expectations of virtually everyone, and it is now the world’s most popular standard for new cellular radio and personal communication equipment throughout the world.
A variety of data service is offered by GSM. GSM users can send and receive data, at rates up to 9600 bps. A unique feature of GSM is short message services (SMS). SMS is bidirectional service for alphanumeric (up to 160 bytes) messages. The access method chosen by GSM is combination of time and frequency division multiple access (TDMA/FDMA).The FDMA part involves the division by frequency of the (maximum) 25 MHz bandwidth of 124 carrier frequencies spaced 200KHz apart. One or more carrier assigned to each base station .each of this frequency is then divided in time, using a TDMA scheme. Eight burst periods are grouped into TDMA frames, which form the basic unit for definition of logical channels. The type of switching used in GSM network is circuit switching.
FEATURES OF GPRS
Key user features of GPRS
GPRS has several unique features which can be summarized as:
Speed
Theoretical maximum speeds of up to 171.2 kilobits per second (kbps) are achievable with GPRS using all eight timeslots at the same time. This is about three times as fast as the data transmission speeds possible over today's fixed telecommunications networks and ten times as fast as current Circuit Switched Data services on GSM networks. By allowing information to be transmitted more quickly, immediately and efficiently across the mobile network, GPRS may well be a relatively less costly mobile data service compared to SMS and Circuit Switched Data.
Immediacy
GPRS facilitates instant connections whereby information can be sent or received immediately as the need arises, subject to radio coverage. No dial-up modem connection is necessary. This is why GPRS users are sometimes referred to be as being "always connected". Immediacy is one of the advantages of GPRS (and SMS) when compared to Circuit Switched Data. High immediacy is a very important feature for time critical applications such as remote credit card authorization where it would be unacceptable to keep the customer waiting for even thirty extra seconds.
New and better application
GPRS facilitates several new applications that have not previously been available over GSM networks due to the limitations in speed of Circuit Switched Data (9.6 kbps) and message length of the Short Message Service (160 characters). GPRS will fully enable the Internet applications you are used to on your desktop from web browsing to chat over the mobile network..
Key Network Features of GPRS
Packet switching
GPRS involves overlaying a packet based air interface on the existing circuit switched GSM network. This gives the user an option to use a packet-based data service. To supplement circuit switched network architecture with packet switching is quite a major upgrade. However, as we shall see later, the GPRS standard is delivered in a very elegant manner- with network operators needing only to add a couple of new infrastructure nodes and making a software upgrade to some existing network elements.
With GPRS, the information is split into separate but related "packets" before being transmitted and reassembled at the receiving end. Packet switching is similar to a jigsaw puzzle- the image that the puzzle represents is divided into pieces at the manufacturing factory and put into a plastic bag. During transportation of the now boxed jigsaw from the factory to the end user, the pieces get jumbled up. When the recipient empties the bag with all the pieces, they are reassembled to form the original image. All the pieces are all related and fit together, but the way they are transported and assembled varies. The Internet itself is another example of a packet data network, the most famous of many such network types.
GPRS TERMINALS
A complete understanding of the application availability and GPRS timeline requires understanding of terminal types and availability. The term "terminal equipment" is generally used to refer to the variety of mobile phones and mobile stations that can be used in a GPRS environment; the equipment is defined by terminal classes and types.
GPRS Terminal Classes
A GPRS terminal can be one of three classes: A, B, or C. A Class A terminal supports GPRS and other GSM services (such as SMS and voice) simultaneously. This support includes simultaneous attach, activation, monitor, and traffic. As such, a Class A terminal can make or receive calls on two services simultaneously. In the presence of circuit-switched services, GPRS virtual circuits will be held or placed on busy rather than being cleared.
A Class B terminal can monitor GSM and GPRS channels simultaneously, but can support only one of these services at a time. Therefore, a Class B terminal can support simultaneous attach, activation, and monitor, but not simultaneous traffic. As with Class A, the GPRS virtual circuits will not be closed down when circuit-switched traffic is present. Instead, they will be switched to busy or held mode. Thus, users can make or receive calls on either a packet or a switched call type sequentially, but not simultaneously.
GPRS ARCHITECTURE
From a high level, GPRS can be thought of as an overlay network onto a second-generation GSM network. This data overlay network provides packet data transport at rates from 9.6 to 171 kbps. Additionally, multiple users can share the same air-interface resources.
GPRS attempts to reuse the existing GSM network elements as much as possible, but in order to effectively build a packet-based mobile cellular network, some new network elements, interfaces, and protocols that handle packet traffic are required. Therefore, GPRS requires modifications to numerous network elements, as summarized in Table 1 and illustrated in Figure 5.1.