Computer Networks and Data Communication
Core concepts
Master the layered models: OSI's seven layers and the TCP/IP four-layer stack, with the function and example protocol of each. Know transmission media (twisted pair, coaxial, fiber, wireless), topologies (star, bus, ring, mesh), switching (circuit, packet, message), and multiplexing (FDM, TDM, WDM). Address the addressing scheme: IPv4 classes, subnetting and CIDR, private ranges, NAT, and the shift to IPv6. Understand TCP vs UDP, ports, DNS, DHCP, HTTP, and routing basics (static vs dynamic, distance vector vs link state). Error detection (parity, checksum, CRC) and flow/error control (sliding window, ARQ) appear regularly.
Traps to watch
OSI has seven layers; TCP/IP has four - do not count session and presentation separately in TCP/IP. TCP is connection-oriented and reliable; UDP is connectionless and faster - questions reverse these. A /24 mask (255.255.255.0) yields 254 usable hosts, not 256. Private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Switches operate at layer 2 (MAC), routers at layer 3 (IP). Bandwidth is capacity; throughput is actual delivered rate; latency is delay.
Worked example / rule of thumb
For 192.168.10.0/26: mask 255.255.255.192, block size 64, subnets at .0, .64, .128, .192, each with 62 usable hosts (2^6−2). Rule of thumb: usable hosts = 2^(host bits) − 2; subtract network and broadcast addresses.