LANs: High-speed LANs

LAN protocols according to IEEE standard 802 are all based on copper transmission media (that is twisted pair or coaxial cable), which allows data rates of up to 15 Million bits per second (Mbps). This is too little if special applications (like picture or video processing) are running or mainframes or minicomputers should be integrated into the LAN. To get higher transmission rates (up to 100 Mbps and more) it is often necessary to switch to optical fibre media. This is often done in addition to copper media: according to the needed performance, devices are connected to different tiers of LANs, not to a single local network. These tiers provide the necessary performance for the devices connected to them. Thus, a device with low performance needs can be connected to a slower - and cheaper - LAN. The single LAN tiers are then interconnected, which is more cost-effective than using a single LAN fulfilling all possible performance needs.

There are a few network standards based upon this optical fiber technology, for example:

• Fibre Distributed Data Interface (FDDI and FDDI-II): can be used in the same way as the common LANs but is often used as a backbone to connect copper LANs because of its high speed. FDDI always uses the topology of a ring and a MAC protocol similar to token ring.
  A typical FDDI implementation may look like this:
  
  FDDI-II supports protocols for real time transmission of data.
• Fibre Channel
• Fibernet II
• S-Net
• Fasnet and Expressnet

100Base Fast-Ethernet

100VG-AnyLAN