GPRS (general packet radio service)

INTRODUCTION       

     Wireless telecommunication infrastructure is evolving fast to accommodate high-speed data traffic while simultaneously handling voice traffic. New approaches in wireless communication are intended to achieve voice-to-data crossover as also voice-and-data integration through realization of third generation (3G) system.  3G stands for third generation, technologies aimed at increasing efficiency and improving the performance of mobile wireless networks.3G wireless services offer enhancements to current   applications, including greater data speeds, increased capacity for voice and data and the advent of packet data networks versus today’s switched networks.
To narrow the gap between 2G and 3G communication system, general packet radio service (GPRS), or the so-called 2.5G, has been introduced as an intermediary. GPRS allows high speed-data transfer over conventional GSM and TDMA network .It is the outcome of continued effort to push high-speed data over exiting mobile network is used to obtain GPRS user profile data from location register data-base. GPRS utilizes 1 to 8 radio time slots for multiple users to share. The user data is put into packets and transported over public land and mobile network (PLMN) using the internet protocol (IP) backbone. GPRS offers high speeds of 14400 bps to 115000 bps for wireless internet access and interfaces to the public data network (PDNs). It allows short burst of traffic, such as e-mail, but can also handle large volume of data.
     GPRS is based on modulation technique called Gaussian minimum shift keying (GMSK) and has fast connectivity, without the need to dial through a network. Services providers are now offering selective services to their subscribers.

The architecture

                 To avail the GPRS facility, subscribers need to have a GPRS-enabled mobile phone or terminal. A subscriber should know how to send and receive GPRS-enabled mobile phone or terminal. A subscriber should know how to send and receive GPRS information. Data transfer cannot be achieved without a destination to send or receive information. While some service providers guarantee automatic access to GPRS, others treat it as opt-in-to-use services.
     In order to integrate GPRS into the existing GSM infrastructure and ensure soothing interworking of PLMN, PDN, and wireless networks, some additional components need to be incorporated into the system. These components, so-called GPRS support nodes (GSNs), are responsible for delivery and routing of packets between mobile stations and external packet data networks.The serving GPRS support node (SGSN) server to deliver data packets to mobile station within the service area. It performs mobility management, logical link control, packet routing and transfer, authentication and charging. SGSn refers to a location register that stores subscriber’s profile and location information. The gateways GPRS support node (GGSN) converts GPRS packets coming from SGSN into packet data protocal for transmission through packet data networks. It acts as an interface for the GPRS backbone to the packet data network. The packet data protocol (PDP) address of incoming data packets are then converted into GSM addresses of the proper destination.
GGSN stores the current SGSN addresses and subscriber profile in its location register and directs the readdressed packet to the responsible SGSN. GGSN also performs charging and authentication. It acts as an interface to external packet data networks for several SGSNs. SGSN may route its packets over different packet data networks. Connecting GSNs of different PLMNs through gateways requires agreements between GPRS network providers.
Signaling and user data are transmitted between GSNs through Gn and Gp interfaces. If SGSN and GGSN are located in the same PLMN, the Gn interface is used. if the PLMNs, are different, a Gp interface is used. Gn and Gp interface permit GSNs to exchange user profile when a mobile station moves from one SGSN locality to station moves from one SGSN locality to another.  SGNs encapsulate PDN packets and tunnel them using GPRS tunneling protocol (GTP), which operates on top of TCP/IP. All GSNs are connected through        IP-based GPRS backbone.Connection between SGSN and base station controller (BSC) is achieved through the Gb interface. Gi interfaces connect PLMN with PDNs. Home location register (HLR) stores user profile, current SGSN address, and PDP address of each subscriber and communicates with SGSN through Gr interface. GGSN connects HLR through Gc interface. In order to update its location register, GGSN queries HLR of the user location and profile through Gc interface. To permit coordination between GPRS and the existing GSM service, GSM network must be functionally upgraded to suit the requirements.
      Fig.1 shows the system architecture of a GSM public land mobile network (PLMN) with essential components. A GSM mobile station is denoted as MS. A cell is formed by the radio area coverage of a base transceiver station (BTS). Several BTSs together are controlled by one base station controller (BSC). The BTS and BSC together form the base station subsystem (BSS). The combined traffic of the mobile stations in their respective cells is routed through a switch, the mobile switching center (MSC). Connections originating from or terminating in the fixed network (e.g., ISDN) are handled by a dedicated gateway mobile switching center (GMSC). GSM networks are structured hierarchically.          They consist of at least one administrative region, which is assigned to a MSC. Each administrative region is made up of at least one location area (LA). A location area consists of several cell groups. Each cell group is assigned to a BSC. Several data bases are available for call control and network management: the home location register (HLR), the visited location register (VLR), the authentication center (AUC), and the equipment identity register (EIR).

For all users registered with a network operator, permanent data (such as the user's profile) as well as temporary data (such as the user's current location) are stored in the HLR. In case of a call to a user, the HLR is always first queried, to determine the user's current location. A VLR is responsible for a group of location areas and stores the data of those users who are currently in its area of responsibility. This includes parts of the permanent user data that have been transmitted from the HLR to the VLR for faster access. VLR also stores the data for temporary identification. The AUC generates and stores security-related data such as keys used for authentication, whereas the EIR registers equipment data rather than subscriber data. In order to integrate GPRS into the existing GSM architecture, a new class of network nodes, called GPRS support nodes (GSN), has been introduced. GSNs are responsible for the delivery and routing of data packets between the mobile stations and the external packet data networks (PDN). Fig. 2 illustrates the system architecture. A serving GPRS support node (SGSN) is responsible for the delivery of data packets from and to the mobile stations within its service area. Its tasks include packet routing and transfer, mobility management (attach/detach and location management), logical link management, and authentication and charging functions. The location register of the SGSN stores location information (e.g., current cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the packet data network) of all GPRS users registered with this SGSN. A gateway GPRS support node (GGSN) acts as an interface between the GPRS backbone network and the external packet data networks. It converts the GPRS packets coming from the SGSN into the appropriate packet data protocol (PDP) format (e.g., IP or X.25) and sends them out on the corresponding packet data network. In the other direction, PDP addresses of incoming data packets are converted to the GSM address of the destination user.

The readdressed packets are sent to the responsible SGSN. For this purpose, the GGSN stores the current SGSN address of the user and his or her profile in its location register. The GGSN also performs authentication and charging functions. In general, there is a many-to-many relationship between the SGSNs and the GGSNs: A GGSN is the interface to external packet data networks for several SGSNs; an SGSN may route its packets over different GGSNs to reach different packet data networks. Fig. 2 also shows the interfaces between the new network nodes and the GSM network as defined by ETSI. The Gb interface connects the BSC with the SGSN. Via the Gn and the Gp interfaces, user data and signaling data are transmitted between the GSNs. The Gn interface will be used if SGSN and GGSN are located in the same PLMN, whereas the Gp interface will be used if they are in different PLMNs. All GSNs are connected via an IP-based GPRS backbone network. Within this backbone, the GSNs encapsulate the PDN packets and transmit (tunnel) them using the GPRS Tunneling Protocol GTP. There are two kinds of GPRS backbones:

• Intra-PLMN backbone networks connect GSNs of the same PLMN and are therefore private IP-based networks of the GPRS network provider.
• Inter-PLMN backbone networks connect GSNs of different PLMNs. A roaming agreement between two GPRS network providers is necessary to install such a backbone.

Fig.3 shows two intra-PLMN backbone networks of different PLMNs connected with an inter-PLMN backbone. The gateways between the PLMNs and the external inter-PLMN backbone are called border gateways. Among other things, they perform security functions to protect the private intra-PLMN backbones against unauthorized users and attacks. The illustrated routing example will be explained later.

The Gn and Gp interfaces are also defined between two SGSNs. This allows the SGSNs to exchange user profiles when a mobile station moves from one SGSN area to another. Across the Gf interface, the SGSN may query the IMEI of a mobile station trying to register with the network.
 The Gi interface connects the PLMN with external public or private PDNs, such as the Internet or corporate intranets. Interfaces to IP (IPv4 and IPv6) and X.25 networks are supported. The HLR stores the user profile, the current SGSN address, and the PDP address(es) for each GPRS user in the PLMN. The Gr interface is used to exchange this information between HLR and SGSN. For example, the SGSN informs the HLR about the current location of the MS. When the MS registers with a new SGSN, the HLR will send the user profile to the new SGSN. The signaling path between GGSN and HLR (Gc interface) may be used by the GGSN to query a user's location and profile in order to update its location register.
 In addition, the MSC/VLR may be extended with functions and register entries that allow efficient coordination between packet switched (GPRS) and circuit switched (conventional GSM) services. Examples of this are combined GPRS and non-GPRS location updates and combined attachment procedures. Moreover, paging requests of circuit switched GSM calls can be performed via the SGSN. For this purpose, the Gs interface connects the data bases of SGSN and MSC/VLR. To exchange messages of the short message service (SMS) via GPRS, the Gd interface is defined. It interconnects the SMS gateway MSC (SMS-GMSC) with the SGSN.

Features

    Gprs applies a packet radio principle to transfer user data packets in an efficientway between mobile stations and external packet data networks.
          GPRS is essentially a value-added service tailored to carry non-voice information across the mobile telephone networks. The key features of GPRS include high speed, immediacy, wider services access, and adaptability to a variety of applications. Technical features like high spectrum efficiency, packet switching internetworking, and GSM/TDMA support add to its utility.Transmission speeds of up to ten times higher than data transmission speed over circuit-switched data services on GSM networks can be achieved when all the eight times slot are used simultaneously. Theoretically, a speed of up to 1711.2 kb/s is possible. This is about three times the data transmission speed above fixed networks.
GPRS cost less than SMS and circuits-switched data. This always on service facilitates instant access to information without the need for a dial up modem. Immediacy is critical for such applications as remote credit card authorization. GPRS can be though of as a sub-net-work of the internet that adds mobility to the internet. Each GPRS terminal can own a unique IP address and hence can be viewed as a mobile host. Existing services over the internet such as chat, browsing, file transfer, e-mail, and telnet can be accessed on the move. GPRS overlays a packet-based air-interface over GSM networks.The information is split into fixed packets before transmission through the network. At the receiving end, these packets, which follow more than one route, are reassembled. GPRS users potentially share the same bandwidth. The bandwidth is utilized only when users potentially share the same bandwidth. The bandwidth is utilized only when users transfer data. There is no dedicated radio channel, as in circuit switching, between end users. Due to efficient utilization of available resources, there is no need to build in idle capacity and the changes of congestion are less.
GPRS (General Packet Radio Service) is a step between GSM i.e. 2G and 3G cellular networks. GPRS offers faster data transmission via a GSM network within a range 9.6Kbits to 115Kbits. This new technology makes it possible for users to make telephone calls and transmit data at the same time. (For example, if you have a mobile phone using GPRS, you will be able to simultaneously make calls and receive e-mail massages.) 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. With GPRS, an IP data transmission protocol, which is characteristic of computer networks, is being introduced to GSM. IP is a data transmission protocol which is used in Internet, the largest computer network in the world today.Before introduction of GPRS, the radio capacity was used for data transmission the entire channel was occupied and was thus insufficiently used. With the GPRS technology, the channel is used more efficiently owing to the possibility of more than one user sharing the same channel. GPRS telephones user several channels for data transfer thus facilitating greater transfer speeds The GPRS support a data transmission speed of up to 13.4Kbits per channel.

GPRS Telephones:--

PPPThe GPRS mobile phones can be classified into the following three classes in terms of the possibility of simultaneous calls (via GSM) and data transmission (via GPRS)...

1. Class A – Simultaneous calls (via GSM) and data transmission (via GPRS) .
2. Class B – Automatic switching between the GSM and the GPRS mode is possible according to telephone settings.
3. Class C – Hand operated switching between the GSM and the GPRS mode.

The Network

In the core network, the existing MSCs are based upon circuit-switched technology, and they cannot handle the GPRS style packet traffic. Thus two new components, called GPRS Support Nodes, are added:
Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN)
The SGSN can be viewed as a "packet-switched MSC;" it delivers packets to mobile stations (MSs) within its service area. SGSNs send queries to home location registers (HLRs) to obtain profile data of GPRS subscribers. SGSNs detect new GPRS MSs in a given service area, process registration of new mobile subscribers, and keep a record of their location inside a given area. Therefore, the SGSN performs mobility management functions such as mobile subscriber attach/detach and location management. GGSNs are used as interfaces to external IP networks such as the public Internet, other mobile service providers' GPRS services, or enterprise intranets. GGSNs maintain routing information.

Limitation

                    As both voice and GPRS calls use the same network resources, limited radio resources can be deployed for different uses. In other words GPRS offer limited cell capability for all users, the extent of which depends upon the no of time slot reserved for GPRS. A network operator is unlikely to allocate the entire time slot for a single user, and will allow two or three time slot at the maximum. The bandwidth per GPRS user is thus severely affected and the maximum speed cannot be achieved by individual users.
GPRS packets are not always sent in the same direction. They may take on multiple paths to reach the destination. One or more of these packets may get corrupted or lost during transmission. To maintain data integrity, error control approach and retransmission method have to be deployed, which, in turn, lead to latency hiccups between end users.
Unlike SMS, GPRS doesn’t incorporate stores-and-forward mechanism. This puts the users in disadvantages. There is probability of unsolicited and unwanted information reaching the user. This is absolutely undesirable, as the user will have to pay for junk reception.

Applications

GPRS finds a wide range of customers as well as corporate applications. Customer application includes home automation, where remote security can be combined with remote control. You can control the oven or program a video in your home from a remote location. Sizeable data of any form can be downloaded through the mobile network. The source of information could be another file or the internet. E-mail could be linked with alert mechanism to notify you of the arrival of new e-mails. Corporate e-mail applications allow employees to keep in touch with the office while away from their desks.
One major drawback of SMS is its inability to convey messages exceeding 160 characters. This calls for extensive use of abbreviations while messaging. GPRS has the potential to carry long messages through a channel.
           Users can download visual and textual information to their terminals, and stay informed about recent happenings. Maps and important graphs can be made available at hand. Images from digital cameras connected to GPRS devices can be uploaded to the internet. Movie previews and video messages can be downloaded to the mobile equipment. Video conferencing is also possible.

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