JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II DATA COMMUNICATION Previous Question Paper (November/December - 2020 - R13)

The OSI model consists of seven layers, each providing specific services to the layer above it:

1. Physical Layer: Transmits raw bit streams over the physical medium, defining electrical, mechanical, and procedural specifications.
2. Data Link Layer: Provides reliable node-to-node data transfer, handling framing, physical addressing, and error control.
3. Network Layer: Manages logical addressing and routing of packets across multiple networks.
4. Transport Layer: Ensures end-to-end communication, flow control, and error recovery for data segments.
5. Session Layer: Establishes, maintains, and terminates sessions between communicating applications.
6. Presentation Layer: Handles data translation, encryption, decryption, and compression to ensure compatibility between different data formats.
7. Application Layer: Provides network services directly to user applications, such as HTTP, FTP, and SMTP.

Digital modulation is the process of converting digital data (binary signals) into analog signals by varying the characteristics of a carrier wave, such as amplitude, frequency, or phase, to represent digital information.

Quadrature Amplitude Modulation (QAM) is a high-efficiency modulation technique that conveys data by changing both the amplitude and the phase of a carrier wave simultaneously. It utilizes two carrier waves of the same frequency that are 90 degrees out of phase with each other, known as the in-phase (I) and quadrature (Q) components.

The principle involves:

• Representing data as a combination of I and Q signals, which are summed to produce a single modulated output.
• Mapping binary data points to a constellation diagram, where each point represents a unique combination of amplitude and phase.
• Increasing the number of points in the constellation (e.g., 16-QAM, 64-QAM) allows for higher data throughput within the same bandwidth by encoding more bits per symbol.