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General Packet Radio Service (GPRS) is aÂ packet orientedÂ mobile data serviceÂ on theÂ 2GÂ andÂ 3GÂ communication systems in GSM and it is a new bearer service that greatly improves and simplifies wireless access to packet data networks . The specification of the GPRS is framed by European Telecommunications Standard Institute (ETSI), the European counter part of American Standard Institute (ANSI) . GPRS applies packet radio principal to transfer user data packets in an efficient way between Mobile station & external packet data network. GPRS is basically a Best effort service where a certain Quality of Service (QOS) is guaranteed . GPRS is the important migration step towards the Third Generation networks and it allows the network operators to develop and expand the 3G network by creating a certain platform in which it supports many Integrated Voice and Data applications. The current version of the GPRS supports the Internet Protocol and X.25 networks. The Mobile phone which has GPRS in it can access the internet by means of Wireless Application Protocol (WAP) .
FEATURES OF GPRS
The GPRS removes the Dial up process and it makes the applications to be accessed easily,
Network operators do not have to replace their Equipment instead GPRS is added on the top of the existing network , the Billing is based on the Volume of the data transferred, GPRS utilises the existing features like GSM authentication and privacy procedures  and the GPRS is the core network for the future 3G systems and existing systems like EDGE and WCDMA.
BENEFITS OF GPRS
GPRS provides new Voice and Data services and the Data Rate of GPRS varies from 14.4 Kbps to 115 Kbps . Another advantage is that the GPRS use Statistical Multiplexing Technique so that the Bandwidth is used efficiently . GPRS ensures guaranteed connectivity and the Circuit Switching & Packet Switching can be used in Parallel.
The GPRS offers end to end packet data transfer without any interruption and it provides different services such as
Quality of service
The Bearer services include the Point To Point (PTP) Connectionless Network Service (CLNS) and Point To Multipoint (PTM) Connection Oriented Network Service (CONS). The PTM offers two types of services and they are PTM-M (Multicast service) and PTM-G (Group call service) . The Supplementary Services includes the Short Messaging Service (SMS) which is used massively by everyone and the other service is Call Forwarding. The Call forwarding is of two types. One is Conditional and other is Unconditional. The conditional call forwarding is done when the mobile subscriber is not reachable . The Quality of Service ensures the reliability of the connection without any delays and it aims to achieve the maximum throughput.
The devices that have the GPRS already installed are divided into 3 different classes and they are classified as 1. Class-A devices can be connected to both GPRS and GSM services. It can be used simultaneously, 2. Class-B devices can be connected to GPRS as well as GSM services but only one can be used at a particular point of time. 3. Class-C devices can be connected either with the GPRS service or the GSM service and the switching between these two is done manually.
The GPRS architecture is similar to GSM architecture but there are few nodes added to the structure which performs the specific tasks. In the GSM architecture there are three important nodes and they are Base Station Sub-system (BSS), Network and Switching Sub-system (NSS) and Operation Support Sub-system (OSS). 
Figure-1 GSM Architecture 
The BSS provides the radio transmission path between the MSC (Mobile Service Centre). Each BSS contains BTS (Base Transceiver Station) and BSC (Base Station Controller). The BSS which has many BSC's which connects the MS to the NSS via MSC's. The NSS manages and controls the Network and switching operation which helps the MSC to communicate with the other networks like PSTN (Public Switched Telephone Networks). The OSS helps in operation and maintenance of the entire GSM network and it allows the system engineers to monitor and troubleshoot the problems if necessary. The NSS is the major part in the communication system as it is responsible for switching the calls between the external networks and the BSC's and more over it is responsible for managing and granting access to several customers database. The NSS has three main parts and they are Home Location Register (HLR), Visitor Location Register (VLR) and the Authentication Centre (AUC) which has Equipment Identity Register (EIR)  & . The HLR is a database which stores the subscriber's information and the location of each user who is in the range of the MSC.
For each subscriber there will be an International Mobile Subscriber Identity (IMSI) and it has the information of the home location along with the user details. The VLR is a database which stores the temporary IMSI for roaming customers in the coverage area. The VLR is connected to many MSC's so as to achieve a greater coverage area possible and more over whenever a roaming mobile comes under VLR the MSC sends the information to the subscriber's HLR so that the routing of calls can be done in a efficient manner . The Authentication centre has strong encryption standards and every single user has the separate key in the HLR and VLR . The AUC has Equipment Identity Register (EIR) which is unique and it helps to find out stolen or altered phones. When the stolen device transmits a signal there will be certain encryption standards and if the key doesn't match with each other it sends information to the HLR about that VLR.
Figure-2 GPRS Networks 
The GPRS is an enhancement over the GSM architecture and it has some additional nodes to perform the packet switched services. The additional nodes are known as GPRS Support Nodes (GSN) and they are responsible for the routing and delivery of the data packets to their respective destination. There are 2 additional nodes called Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). The GPRS terminals alone can access GPRS servers because the GSM don't handle the enhanced air interface and cannot packetize the data. The multiple users can share the same interface as this data overlay network provides the packet data rates from 9.6 to 171Kbps .
The GPRS architecture just needs some upgrade and a certain modifications. The modifications to GSM Networks are listed below  & .
A software upgrade is required for both the BTS as well as the BSC but in the case of BSC a small piece of hardware is included and it is known as Packet Control Unit (PCU).
The PCU provides the logical and physical data interface which handles the packet data transfer.
The Mobile Stations (MS) has the GPRS terminal which will be compatible with GSM voice calls.
GPRS SUPPORT NODES (GSN)
There are two core elements in the network which handles the network traffic and they are Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN).
SGSN performs Packet Routing, Authentication, User profile maintenance, Transfer and Mobility management.
GGSN function is to convert the GPRS packets to PDP format and this PDP address is modified into GSM address of the destination and the current SGSN address and profile is stored.
GPRS DATABASE & INTERFACES
The Database such as HLR & VLR requires a software update in order to handle the new call models and the functions which are compatible with the GPRS architecture.
The interfaces used in the network architecture is Gb which connects PCUSN and SGSN, Gr which connects SGSN and HLR extension of MAP, Gn which connects the SGSN and GGSN using GTP, Gi which connects GGSN and PSPDN (X.25 and IP), Gs which connects SGSN and MSC/VLR for simultaneous operations, Gd which connects SGSN and SMC which delivers SMS, Gc which connects GGSN and HLR.
Figure - 3 GPRS Interfaces 
GPRS DATA ROUTING
GPRS data routing is the integral part of the design process and its major function is to route the data packets to and from a mobile users. This is divided into two areas and they are
Data Packet Routing