JNTU B.Tech III DATA COMMUNICATION AND COMPUTER NETWORKS Previous Question Paper (September - 2021 - R16)

Data transmission is the physical transfer of data over a point-to-point or point-to-multipoint communication channel. It involves the movement of bits in the form of electromagnetic signals across a medium.

Key terminology includes:

• Guided Media: Physical paths like twisted-pair, coaxial cable, or fiber optics where signals are directed.
• Unguided Media: Wireless transmission using air, vacuum, or water, such as radio waves or microwaves.
• Simplex: Unidirectional communication (e.g., keyboard to CPU).
• Half-Duplex: Bidirectional communication but one direction at a time (e.g., walkie-talkie).
• Full-Duplex: Simultaneous bidirectional communication (e.g., telephone network).
• Bandwidth: The range of frequencies contained in a composite signal or the capacity of the link to transmit data.

For example, in a computer network, data is transmitted from a sender to a receiver. If a server sends a file to a client via a fiber optic cable, the data is converted into light pulses (signals) and travels through the guided medium, typically operating in full-duplex mode to allow for acknowledgments.

The ISO-OSI (Open Systems Interconnection) model is a seven-layer conceptual framework used to standardize the functions of a telecommunication or computing system. The layers are:

1. Physical Layer: Handles bit-level transmission and physical interface specifications.
2. Data Link Layer: Manages framing, physical addressing (MAC), and error control.
3. Network Layer: Responsible for logical addressing (IP) and routing packets across networks.
4. Transport Layer: Ensures end-to-end communication, segmentation, and flow control (TCP/UDP).
5. Session Layer: Manages sessions, dialog control, and synchronization between applications.
6. Presentation Layer: Handles data translation, encryption, and compression.
7. Application Layer: Provides network services directly to end-user applications (e.g., HTTP, FTP).

The model is visualized as a vertical stack where each layer provides services to the layer above it and receives services from the layer below it. Data flows down the stack at the sender (encapsulation) and up the stack at the receiver (decapsulation). A sketch would show these seven layers stacked vertically with arrows indicating data flow between adjacent layers and peer-to-peer logical communication between identical layers on different hosts.