JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DATA COMMUNICATION AND COMPUTER NETWORKS Previous Question Paper (October - 2020 - R16)

The OSI model is a theoretical, vendor-neutral framework developed by ISO, while the TCP/IP model is a practical implementation that forms the basis of the modern Internet. Key differences include:

• Layer Structure: The OSI model consists of seven layers (Physical, Data Link, Network, Transport, Session, Presentation, Application), whereas the TCP/IP model simplifies this into four layers (Network Access, Internet, Transport, Application).
• Approach: OSI follows a vertical, layered approach with strict boundaries between layers. TCP/IP is more flexible and less rigid, often combining functions of multiple OSI layers.
• Service/Protocol Distinction: OSI explicitly separates services, interfaces, and protocols, making it easier to replace protocols. TCP/IP does not clearly distinguish these, making protocol replacement more difficult.
• Development: OSI was developed before the protocols were defined, leading to a more academic model. TCP/IP was developed after the protocols were established, prioritizing practical functionality.

ATM (Asynchronous Transfer Mode) and Frame Relay are both WAN technologies designed for high-speed data transmission, but they differ significantly in architecture and application:

• Data Unit: ATM uses fixed-size cells of 53 bytes (48 bytes payload + 5 bytes header), which allows for predictable switching and low latency. Frame Relay uses variable-length frames, making it more efficient for bursty data traffic.
• Switching Mechanism: ATM is connection-oriented and uses virtual circuits (VPI/VCI) to ensure Quality of Service (QoS). Frame Relay also uses virtual circuits (DLCI) but relies on simpler packet switching.
• Quality of Service: ATM provides robust, guaranteed QoS support for voice, video, and data integration. Frame Relay offers limited QoS, primarily focusing on best-effort delivery with basic congestion management.
• Complexity: ATM is highly complex due to its cell-based nature and extensive management overhead. Frame Relay is simpler and less expensive to implement, making it a popular choice for interconnecting LANs over a WAN.
• Speed: ATM was designed to scale to very high speeds (Gbps range), while Frame Relay is typically deployed at lower speeds (up to T1/E1 or T3/E3 rates).