Network Architectures & Physical/Logical Topologies
Analyzing physical topology layouts, fault tolerance, collision vs broadcast domain boundaries, and hardware device layer processing.
1. Physical & Logical Topologies
A Physical Topology defines how nodes and cables are physically laid out, whereas a Logical Topology defines how data frames travel across nodes regardless of physical cabling.
Bus Topology
Nodes connect to a single central backbone cable terminated at both ends with resistors (50-ohm terminators).
- Pros: Low cable usage, simple setup for small rooms.
- Cons: A single cable break drops the entire network; high collision rate (CSMA/CD).
Star Topology
Every node connects directly to a central hub or switch via dedicated point-to-point links.
- Pros: High fault isolation—one cable cut affects only that single node. Easy to expand.
- Cons: Central switch represents a single point of failure.
Ring Topology
Nodes are connected in a closed loop. Data frames or tokens travel sequentially from node to node in one direction.
- Pros: Deterministic access—no packet collisions.
- Cons: Unidirectional ring break disrupts all nodes unless dual counter-rotating rings (FDDI) are deployed.
Mesh Topology (Full vs Partial)
Every node connects to every other node (Full Mesh: $N(N-1)/2$ links) or to multiple selected nodes (Partial Mesh).
- Pros: Maximum redundancy, zero single points of failure, guaranteed link throughput.
- Cons: Extremely expensive cabling and port requirement for large $N$.
2. Collision Domains vs. Broadcast Domains
Understanding domain separation is a vital skill tested in university examinations and required for network switch deployment.
Collision Domain
A network segment where simultaneous transmissions from two nodes cause electrical signals to collide and corrupt.
- Hubs (Layer 1): All ports share 1 single collision domain!
- Switches (Layer 2): Every individual port forms its own isolated collision domain!
Broadcast Domain
A network region across which a broadcast frame (Destination MAC: FF:FF:FF:FF:FF:FF) is forwarded to all nodes.
- Switches: All ports belong to 1 broadcast domain (unless partitioned into VLANs).
- Routers (Layer 3): Routers block layer 2 broadcast frames by default—every router interface bounds a broadcast domain!
3. Network Scale Classification
LAN & PAN
PAN: Personal Area Network ($\le 10\text{m}$, Bluetooth).\nLAN: Local Area Network spanning a room, office floor, or campus ($\le 2\text{km}$). High throughput ($1\text{Gbps} - 10\text{Gbps}$).
Metropolitan Area Network
Spans an entire municipality or city ($5\text{km} - 50\text{km}$). Interconnects city municipal offices, university campuses, or regional fiber backbones.
Wide Area Network
Spans countries or global continents ($>50\text{km}$). Utilizes leased fiber lines, submarine cables, and satellite links (e.g. The Internet).