Computer Communication Channels and Cables

Definition

• In a network, a communication channel is the physical path the transmission signals travel.
  • It is the path information travels from computer to computer.
  • How do the computers in a network “connect” to each other.

The 5 communication channels

• twisted pair cables
• coaxial cables
• fibre optic cables
• terrestrial stations
• communication satellites

Twisted pair cables

• Signals are transmitted using pairs of independently insulated wires that have been physically twisted together
• Used by older telephone networks
• Network cables use an RJ-45 jack for four pairs of twisted pair cables.

Coaxial cables

• Core of the wire is copper
• High frequency signals can be carried on a single cable – used for video transmission
• Used when twisted pair cabling is not adequate to carry the required amount of data.

Fibre Optic Cables

• Digital signals are sent as light pulses which are translated back into electrical signals

• Composed of fine glass strands
• Centre core is composed of: Fine glass strand surrounded by glass cladding and protective layer
  • Glass cladding reflects light back into the core, guiding the light along the wire

• Thousands of transmissions can be carried on a single strand
• Can transmit signals faster than twisted pair and coaxial cables

Terrestrial Stations

• Information is sent via microwaves from ground based transmitting and receiving stations
  • Text, sound, and graphics are converted into microwave pulses and transmitted

• Microwave stations (a.k.a. repeater stations)  must be placed every 50 kilometres to receive, amplify, and then pass the signal along
• Transfer information at much higher speeds than cabling

Communication Satellites

• Orbiting around earth
• Avoids cost of cabling and repeater stations
• Minimum of three satellites are needed to provide world-wide communication
• Transfer information at much higher speeds than cabling