JNTU B.Tech III DATA COMMUNICATIONS AND NETWORKS Previous Question Paper (September - 2021 - R18)

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers, allowing diverse systems to communicate. The layers are as follows:

1. Physical Layer: Transmits raw bit streams over a physical medium. It defines mechanical, electrical, and procedural interfaces.
2. Data Link Layer: Provides node-to-node data transfer, error detection, and correction. It handles framing and physical addressing (MAC).
3. Network Layer: Manages packet forwarding, including routing through intermediate routers and logical addressing (IP).
4. Transport Layer: Ensures transparent transfer of data between end systems, providing flow control, segmentation, and error recovery.
5. Session Layer: Establishes, manages, and terminates connections between applications.
6. Presentation Layer: Handles data formatting, encryption, and compression to ensure the application layer receives readable data.
7. Application Layer: Provides network services directly to user applications, such as HTTP, FTP, or SMTP.

The IEEE 802.11 architecture defines the components and services for wireless local area networks (WLANs). The fundamental building block is the Basic Service Set (BSS), which consists of a group of stations (STAs) communicating with each other. If the BSS uses an Access Point (AP) to connect to a wired network, it is an Infrastructure BSS.

Key architectural components include:

• Station (STA): Any device that has IEEE 802.11 compliant wireless connectivity.
• Access Point (AP): A bridge between the wireless network and the wired backbone.
• Distribution System (DS): The architectural component used to interconnect multiple BSSs. It allows the creation of an Extended Service Set (ESS), which appears as a single logical network to the Logical Link Control (LLC) layer.
• Portal: A device that integrates the 802.11 network with other non-802.11 wired networks.