LANs, MANs, WANs

          

  • LANs : Local Area Networks

  • Typically connects computer in a single building or campus.
  • Developed in 1970s.
  • Medium : optical fibres, coaxial cables, twisted pair, wireless.
  • Low latency (except in high traffic periods).
  • High speed networks (0.2 to 100 Mb/sec).
  • Speeds adequate for most distributed systems
  • Problems : Multi media based applications
  • Typically buses or rings.
  • Ethernet, Token Ring

Network Type

Ethernet
FDDI
Token Ring
Apple LocalTalk
Wireless

Data Transfer Rate

10 (up to 100) Mbits/s
100 Mbits/s
4 or 16 Mbits/s
0.23 Mbits/s
1-3 Mbits/s

  • MANs : Metropolitan Area Networks

  • Generally covers towns and cities (50 kms)
  • Developed in 1980s.
  • Medium : optical fibres, cables.
  • Data rates adequate for distributed computing applications.
  • A typical standard is DQDB (Distributed Queue Dual Bus).
  • Typical latencies : < 1 msec.
  • Message routing is fast.

 

  • WANs : Wide Area Networks

  • Developed in 1960s.
  • Generally covers large distances (states, countries, continents).
  • Medium : communication circuits connected by routers.
  • Routers forwards packets from one to another following a route from the sender to the receiver. Store-and-Forward
  • Hosts are typically connected (or close to) the routers.
  • Typical latencies : 100ms - 500ms.
  • Problems with delays if using satellites.
  • Typical speed : 20 - 2000 Kbits/s.
  • Not (yet) suitable for distributed computing.
  • New standards are changing the landscape.