JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV Year INDUSTRIAL DATA COMMUNICATIONS Previous Question Paper (July/August - 2022 - R16)

The ISO-OSI model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers, facilitating interoperability between diverse communication systems.

• Physical Layer: Handles the transmission and reception of raw bit streams over a physical medium, defining electrical, mechanical, and functional specifications.
• Data Link Layer: Provides node-to-node data transfer, error detection, and correction for frames, often divided into MAC and LLC sublayers.
• Network Layer: Manages packet forwarding, routing, and logical addressing to ensure data reaches the correct destination across multiple networks.
• Transport Layer: Ensures end-to-end communication, flow control, and reliability through segmentation and reassembly of data.
• Session Layer: Establishes, manages, and terminates connections (sessions) between local and remote applications.
• Presentation Layer: Acts as a data translator, handling encryption, decryption, compression, and formatting to ensure the application layer can read the data.
• Application Layer: Provides network services directly to end-user applications, such as HTTP, FTP, and SMTP.

The EIA-485 (also known as RS-485) standard defines the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. It is widely used in industrial automation due to its robustness against electrical noise and its support for long-distance communication.

• Differential Signaling: Uses two wires (A and B) to transmit data, where the signal is determined by the voltage difference between them, providing high common-mode noise immunity.
• Multipoint Capability: Supports up to 32 unit loads on a single bus, allowing for multidrop configurations where one master can communicate with multiple slaves.
• Range and Speed: Capable of operating over distances up to 1200 meters (4000 feet) and data rates up to 10 Mbps (depending on cable length).
• Voltage Levels: The standard specifies a differential voltage of at least 200 mV between lines to represent a valid logic state, with a common-mode voltage range of -7V to +12V.
• Termination: Requires a termination resistor (typically 120 ohms) at both ends of the bus to prevent signal reflections.