Computer Networking
Basics
A network links devices to share data and resources. By span: PAN, LAN, MAN and WAN. Topologies are bus, star, ring, mesh and tree; star dominates because a single cable failure affects only one node.
Devices and models
- A hub broadcasts to all ports; a switch forwards frames by MAC address; a router routes between networks by IP address; a modem converts signals; a repeater regenerates a weak signal.
- OSI has seven layers (physical, data link, network, transport, session, presentation, application); TCP/IP has four.
- TCP is connection-oriented and reliable; UDP is connectionless and faster.
- IPv4 is 32-bit in four octets; IPv6 is 128-bit.
Worked example
“A device sends a frame only to the port of the destination MAC address. Which device is it?” A switch, because it builds and maintains a MAC address table. A hub would flood every port, and a router works with IP addresses at layer 3, so neither fits the description.
Traps that cost marks
- Saying a router forwards by MAC address; it routes by IP.
- Mixing the transport layer (end-to-end delivery) with the network layer (logical addressing).
- Confusing bandwidth (capacity) with latency (delay).
- Assuming every cable in a star topology carries the whole network’s traffic.
- Forgetting that a MAC address is 48 bits written as six hexadecimal pairs.