Data Communication and Computer Networking
Domain 4 - Data communication and computer networking
Tests transmission, topologies, OSI/TCP-IP layers, devices, IP addressing and protocol choice.
Core rules
- Data communication needs sender, receiver, medium, protocol and message.
- OSI layers: Physical, Data link, Network, Transport, Session, Presentation, Application. TCP/IP maps to network access, Internet, transport and application.
- LAN vs WAN; topology affects cost and fault tolerance; a switch forwards by MAC address, a router by IP address.
- TCP is reliable and connection-oriented; UDP is fast and connectionless. Ports identify services.
- IPv4 address = network + host bits; subnet mask separates them; CIDR /n gives 2^(32−n) addresses.
Worked example
A network 192.168.10.0/26 is required. /26 means 26 network bits and 6 host bits. Mask = 255.255.255.192 because 128+64=192. Addresses per subnet = 2^6 = 64; usable hosts = 64 − 2 = 62 because network and broadcast are reserved. Number of subnets in the last octet = 2^(26−24) = 4. Ranges: .0–.63, .64–.127, .128–.191, .192–.255. For the .64 subnet, usable hosts are .65–.126 and broadcast is .127. Reasoning: subtract reserved addresses and count host bits.
Traps
Do not count all 64 addresses as usable. Do not confuse MAC (data link) with IP (network). A hub broadcasts; a switch learns MAC addresses. TCP is not always “better” - UDP suits live video. Check whether the question asks network address, first host or broadcast.