Questions
8 MCQs per paper
Difficulty
Medium
Importance
Core — never skip
Overview
Computer Networks is a high-yield core subject in Indian PSU exams, focusing on the fundamental communication architectures and protocols that govern data transmission. Understanding the layered OSI model and specific protocol behaviors is essential for solving technical MCQs asked in exams like GATE and PSU recruitment tests.
OSI and TCP/IP Models
These models serve as the framework for network communication, defining how data travels from application to physical transmission. PSU exams frequently test the mapping of protocols to specific layers and the functions of devices like repeaters, bridges, and routers within these models.
- OSI Model: 7 Layers (Physical, Data Link, Network, Transport, Session, Presentation, Application)
- TCP/IP Model: 4 Layers (Link, Internet, Transport, Application)
- Physical Layer: Hubs, Repeaters, Cables
- Data Link Layer: Switches, Bridges, MAC Address
- Network Layer: Routers, IP Address
- Transport Layer: TCP, UDP, Ports
IP Addressing and Subnetting
Subnetting is a calculation-heavy area where aspirants must determine network addresses, broadcast addresses, and valid host ranges from given CIDR notations. Mastery of binary conversion and mask arithmetic is vital for the 1–2 numerical questions typically found in every paper.
- Class A: 1.0.0.0 to 127.255.255.255
- Class B: 128.0.0.0 to 191.255.255.255
- Class C: 192.0.0.0 to 223.255.255.255
- CIDR Formula: Number of hosts = 2^(32-n) - 2
- Private IP ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
Routing Protocols
Routing protocols determine the path data packets take across an internetwork, categorized into interior and exterior gateway protocols. Exams often focus on the underlying algorithms, such as Distance Vector versus Link State routing.
- RIP: Uses Bellman-Ford algorithm, hop count as metric
- OSPF: Uses Dijkstra's algorithm, cost as metric
- BGP: Path vector protocol, used between Autonomous Systems
- Link State protocols are faster to converge than Distance Vector
- OSPF supports authentication and VLSM
Transport and Application Protocols
This section covers the end-to-end communication and user-facing services. Memorizing port numbers and the specific handshake mechanisms of TCP versus the efficiency of UDP is a standard requirement for these exams.
- TCP: Connection-oriented, reliable, includes flow/congestion control
- UDP: Connectionless, unreliable, low overhead, suitable for streaming
- DNS: Port 53, translates domain names to IP addresses
- HTTP: Port 80, SMTP: Port 25, FTP: Port 21/20
- DHCP: Port 67/68, assigns dynamic IP addresses
Formula Sheet
Total Subnets = 2^x (where x is borrowed bits)
Usable Hosts = 2^(32-n) - 2
Transmission Delay = L / R (where L is packet length and R is link bandwidth)
Exam Tip
Memorize the standard port numbers and the specific layer-to-device mapping, as these are the most common source of 'easy' marks in PSU technical papers.
Common Mistakes
- Confusing the layers where specific devices operate, such as placing routers in the Data Link layer.
- Miscalculating the number of usable hosts by forgetting to subtract the network and broadcast addresses.
- Assuming TCP is always preferred over UDP without considering latency-sensitive application requirements.
More Revision Notes
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