JNTU B.Tech III MOBILE COMPUTING Previous Question Paper (January/February - 2021 - R16)

The GSM (Global System for Mobile Communications) architecture is divided into three primary subsystems: the Mobile Station (MS), the Base Station Subsystem (BSS), and the Network and Switching Subsystem (NSS), supported by the Operation and Support Subsystem (OSS).

The Mobile Station (MS) consists of the Mobile Equipment (ME) and the Subscriber Identity Module (SIM), which stores user-specific data and authentication keys.

The Base Station Subsystem (BSS) handles radio communication. It comprises the Base Transceiver Station (BTS), which manages radio links with the MS, and the Base Station Controller (BSC), which manages radio resources for multiple BTSs, including handover decisions and frequency hopping.

The Network and Switching Subsystem (NSS) performs call control and mobility management. Key components include:

• Mobile Switching Center (MSC): The central node that routes calls and manages connections.
• Home Location Register (HLR): A database containing permanent subscriber data and current location information.
• Visitor Location Register (VLR): A temporary database that stores data for subscribers currently roaming in the MSC's area.
• Authentication Center (AuC): Provides security parameters for user authentication and encryption.
• Equipment Identity Register (EIR): A database used to track handset validity via the International Mobile Equipment Identity (IMEI).

The Operation and Support Subsystem (OSS) provides centralized monitoring and maintenance of the network, including fault management and billing.

Diagram description: The MS communicates over the Um interface (air interface) to the BTS. The BTS connects to the BSC via the Abis interface. The BSC connects to the MSC via the A interface. The HLR, VLR, AuC, and EIR are interconnected with the MSC to facilitate mobility and security management.

The GPRS architecture extends the existing GSM network to support packet-switched data services. It introduces two primary nodes: the Serving GPRS Support Node (SGSN) and the Gateway GPRS Support Node (GGSN).

The architecture components and their functions are as follows:

• Mobile Station (MS): The user device that communicates via the Base Station Subsystem (BSS).
• Base Station Subsystem (BSS): Comprising the Base Transceiver Station (BTS) and Base Station Controller (BSC), it handles the radio interface and packet scheduling.
• SGSN: Acts as the main packet-switching node. It handles packet routing, transfer, mobility management, authentication, and logical link management for all MSs in its service area.
• GGSN: Serves as the gateway to external packet-switched networks (e.g., the Internet or corporate intranets). It performs IP address allocation and acts as the anchor point for the MS.
• GPRS Backbone: An IP-based network that connects the SGSN and GGSN using the GPRS Tunneling Protocol (GTP).
• HLR/VLR: Databases that store subscriber profiles and location information, integrated with the GPRS nodes for authentication and routing.

The architecture is conceptually divided into the radio access network (MS and BSS) and the GPRS core network (SGSN, GGSN, and backbone). Data packets are encapsulated and tunneled between the SGSN and GGSN, allowing the mobile station to maintain a continuous connection to external data networks while moving between different SGSN service areas.