Computer Networks
Core concepts
Know the OSI and TCP/IP models and which protocol sits at each layer. Study framing, error detection (parity, checksum, CRC), and flow control (stop-and-wait, sliding window). Cover Ethernet, IP addressing and subnetting, routing basics, TCP vs UDP, and application protocols (HTTP, DNS, SMTP). Link budgets, propagation delay, and throughput calculations are common. Security basics (encryption, firewalls) appear in modern papers.
Traps examiners set
- CRC detects burst errors but is not encryption; it does not correct errors.
- TCP is connection-oriented and reliable; UDP is connectionless and unreliable.
- Subnet masks borrow host bits; usable hosts = 2^h - 2.
- Propagation delay depends on distance and medium, not on bandwidth.
- Switches operate at layer 2; routers at layer 3.
Worked rule of thumb
For a /26 subnet, host bits = 32 - 26 = 6, so 64 addresses and 62 usable hosts. Example: 192.168.1.0/26 gives subnets at .0, .64, .128, .192. Always subtract two for network and broadcast addresses.
Practice strategy
Convert addresses to binary before subnetting; it prevents mask errors.