JNTU B.Tech IV WIRELESS NETWORKS AND MOBILE COMPUTING Previous Question Paper (September - 2021 - R15)

HIPERLAN (High Performance Radio Local Area Network) is a European standard for high-speed wireless networks. Its architecture is divided into the Physical (PHY) layer and the Medium Access Control (MAC) layer.

The Physical Layer is responsible for data transmission over the radio medium. It utilizes GMSK (Gaussian Minimum Shift Keying) modulation to achieve high data rates, typically up to 23.5 Mbps. It handles frequency selection, signal modulation and demodulation, and synchronization. It also manages power control to minimize interference and optimize battery life in mobile devices.

The MAC Layer is designed to support both asynchronous and synchronous traffic. It employs a mechanism called Elimination-Yield Non-preemptive Priority Multiple Access (EY-NPMA). This protocol operates in three phases: the prioritization phase (where nodes contend based on priority levels), the contention phase (where nodes eliminate others to gain access), and the transmission phase. This ensures that time-sensitive data receives higher priority, making it suitable for multimedia applications.

GSM (Global System for Mobile Communications) provides a comprehensive suite of services categorized into three main types:

1. Bearer Services: These provide the capacity for data transfer between access points, including circuit-switched and packet-switched data services.
2. Teleservices: These include standard voice telephony, Short Message Service (SMS), and Fax services.
3. Supplementary Services: These enhance basic services, such as Call Forwarding, Call Waiting, Caller ID, and Multiparty conferencing.

Regarding Security Issues, GSM addresses vulnerabilities through several mechanisms:

1. Authentication: Uses a challenge-response mechanism involving the SIM card and the Authentication Center (AuC) to verify the subscriber's identity.
2. Encryption: Employs algorithms like A5/1 and A5/3 to encrypt the air interface (the link between the mobile station and the Base Transceiver Station), protecting data from eavesdropping.
3. Anonymity: Uses a Temporary Mobile Subscriber Identity (TMSI) instead of the permanent International Mobile Subscriber Identity (IMSI) during transmissions to prevent tracking of user location.

Despite these, security challenges persist, such as the vulnerability of older encryption algorithms to brute-force attacks and the risk of rogue base stations (IMSI catchers) performing man-in-the-middle attacks.