LANs: Transmission Media

There are three major forms of transmission media used for LANs:

• twisted pair: two insulated copper wires twisted together in a regular spiral pattern; one pair establishes one communication link; it transmits electromagnetic signals. Twisted pairs are distinguished between shielded and unshielded twisted pairs according to their protection against electromagnetic fields
  
• coaxial cable: a single insulated inner wire is surrounded by a cylindrical conductor which is covered with a shield; it transmits electromagnetic signals. Coaxial cable is classified into two categories: baseband (uses digital signals) and broadband (uses analog signals) coaxial cable
  
• optical fibre: consists of three concentric sections, the core (a fibre conducting optical rays), the cladding (reflecting optical rays) and the jacket (surrounding one or many fibres to protect them); transmitts optical signals, which must be transformed to electromagnetic signals
  

Which media to be chosen depends on three other characterization features of LANs: firstly, which topology is to be implemented. Secondly, which capacity and reliability are needed.