GSM & GPRS ARCHITECTURE
- 1. SAMUEL NDERITU BI/036/16 MOBILE COMPUTING ASSIGNMENT 1. ARCHITECTURE IN GSM GSM is the short form of Global System for Mobile Communications. It is called 2G or Second Generation technology. The GSM architecture consists of three major interconnected subsystems that interact with themselves and with users through certain network interface. The subsystems are Mobile Station (MS) Base Station Subsystem (BSS), Network Switching Subsystem (NSS) and Operational Support Subsystem (OSS). MOBILE STATION This Mobile station is GSM mobile phone equipment which houses DSP, RF chip and SIM (subscriber Identity Module). This SIM is enough to carry to avail the service of GSM network. SIM contains subscriber related all the information, network with which subscriber is subscribed with and encryption related information. Base station Subsystem Base station subsystem houses Base Transceiver station-BTS and Base station controller-BSC. This subsystem take care of radio control related functions and provides GSM air interface for GSM mobile phones to connect with GSM network. To provide GSM service, region/city on earth is divided into various cells. The cell size is usually about 100m to about 35 km. BTS coverage is limited to this cell. Like this many BTSs cover entire region Network Switch Subsystem (NSS) This subsystem provides interface between cellular system and circuit switched telephone network i.e. PSTN. It performs switching and operation & maintenance related functions. NSS takes care of call processing functions such as call setup, switching, tear down and also hand over between BSCs. NSS takes care of security and authentication related functions. GSM network areas In a GSM network, the following areas are defined:
- 2. Cell: Cell is the basic service area; one BTS covers one cell. Each cell is given a Cell Global Identity (CGI), a number that uniquely identifies the cell. Location Area: A group of cells form a Location Area (LA). This is the area that is paged when a subscriber gets an incoming call. Each LA is assigned a Location Area Identity (LAI). Each LA is served by one or more BSCs. MSC/VLR Service Area: The area covered by one MSC is called the MSC/VLR service area. PLMN: The area covered by one network operator is called the Public Land Mobile Network (PLMN). A PLMN can contain one or more MSCs. GSM ARCHITECTURE DIAGRAM VLR AuC HLR EIR MSC NSS BSC BTC MS OSS PSDN ISDN PSTN PLMN A interface
- 3. 2. ARCHITECTURE OF GPRS General packet Radio Service (GPRS) is an enhancement of GPS, which is packet oriented mobile data service on the 2G and 3G cellular communication system. It provide connection to the external packet data network through the GSM infrastructure with short access time to the network for independent short packets. It uses exactly uses the same physical radio channel as GSM and only new logical GPRS Radio Channel are defined. GPRS Network Architecture: GPRS is usually attempts to reuse the existing GSM network elements as much as possible. There are new entities called GPRS that supports nodes (GSN) which are responsible for delivery and routing of data packets between mobile stations and external packets networks. There are two types of GSNs, Serving GPRS Support Node (SGNS) Gateway GPRS Support Node (GGNS) Subsystems of GPRS Architecture Mobile Station: GPRS Services required New Mobile Station as the existing GSM phones are not capable of handling the enhanced air interface or the packet data. A wide variety of Mobile stations exist which includes a high-speed version of current phones to support high-speed data access like PC cards for laptop computers. These mobile stations are in backward compatibility mode in order to make voice calls which are used GSM. Base Station Subsystem: Each BSC requires the installation of Packet Control Units in addition to software upgrade. They provide physical and logical data interface to BSS to estimate packet data traffic. BTS too require a software upgrade but typically does not involve hardware enhancements. GRPS Support Nodes: SSGN: The Serving GPRS Support Node is responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information for charging for the use of the air interface. GGSN: The Gateway GPRS Support Nodeacts as an interface and a router to external networks. The GGSN contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct Serving GPRS Support Node.
- 4. Internal Back Network: The internal backbone is an IP based network which is used to carry the new packets between different GSN. The process of Tunneling is used in-between SGSNs and GGSNs, this is done to safe exchange of domain information’s outside the GPRS Network without informing internal backbone. Mobility Support: In a manner similar to GSM and CDPD, there are mechanism in GPRS to support mobility. There are two types of Mobility Support in GPRS Network- Attachment Procedure Location and Handoff Management Short Messaging Services in GSM: For the proliferation of GSM enable the introduction of SMS, which is similar to peer-to-peer instant messaging on the Internet. Users of SMS can exchange alphanumeric message of up to 160 char. within seconds of submission of the message.