JNTU MCA 2021 COMPUTER NETWORKS Previous Question Paper (February - 2021 - R17)

The OSI (Open Systems Interconnection) reference model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. This layered approach promotes interoperability by allowing different systems to communicate through standardized protocols.

1. Physical Layer: Responsible for the transmission and reception of raw bit streams over a physical medium. It defines mechanical, electrical, and procedural interfaces, such as voltage levels, timing, and physical connectors.
2. Data Link Layer: Provides node-to-node data transfer and handles physical addressing (MAC addresses). It ensures reliable transmission by performing error detection and flow control, typically organized into frames.
3. Network Layer: Manages logical addressing (IP addresses) and routing of packets across interconnected networks. It determines the best path for data to travel from source to destination using routers.
4. Transport Layer: Ensures end-to-end communication and data integrity. It handles segmentation, flow control, and error correction (e.g., TCP for reliable delivery or UDP for speed), providing transparent data transfer between end systems.
5. Session Layer: Establishes, manages, and terminates connections (sessions) between applications. It provides mechanisms for session synchronization and checkpointing to resume interrupted communications.
6. Presentation Layer: Acts as the data translator for the application layer. It handles data formatting, encryption, decryption, and compression to ensure that data sent from the application layer of one system is readable by the application layer of another.
7. Application Layer: The topmost layer that interacts directly with software applications. It provides network services to end-user programs, such as file transfer (FTP), email (SMTP), and web browsing (HTTP).

The significance of this architecture lies in its modularity; each layer provides services to the layer above it while hiding the implementation details of the layers below. This abstraction simplifies troubleshooting, encourages vendor independence, and allows for independent updates to protocols at any specific layer without requiring changes to the entire stack.

Transmission media are the physical paths between transmitters and receivers in a data communication system. They are broadly classified into two categories: Guided (Wired) and Unguided (Wireless) media.

1. Guided Transmission Media
In guided media, signals are directed along a physical path. The characteristics are defined by the physical material used.

• Twisted Pair Cable: Consists of two insulated copper wires twisted together to reduce electromagnetic interference (crosstalk). It is cost-effective and easy to install but has limited bandwidth and is susceptible to external noise.
• Coaxial Cable: Composed of a central conductor, an insulating layer, a metallic shield, and an outer jacket. It provides higher bandwidth and better noise immunity than twisted pair, making it suitable for cable television and broadband networks.
• Fiber Optic Cable: Uses light pulses to transmit data through a glass or plastic core. It offers extremely high bandwidth, immunity to electromagnetic interference, and low signal attenuation over long distances, though it is expensive and requires specialized installation.

2. Unguided Transmission Media
Unguided media transmit electromagnetic waves through free space without a physical conductor. The characteristics depend on the frequency spectrum used.

• Radio Waves: Omnidirectional waves that propagate easily through walls and obstacles. They are widely used for AM/FM radio, television, and mobile communications.
• Microwaves: Unidirectional waves that require line-of-sight propagation. They are used for long-distance point-to-point communication, satellite links, and radar systems.
• Infrared: High-frequency waves used for short-range communication, such as remote controls and local wireless data transfer. They cannot penetrate walls, providing a level of inherent security.

The choice of transmission medium depends on factors such as data rate, distance, cost, installation environment, and susceptibility to interference.