Network Communications.

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Network Communications

The main features of a range of transmission media and modes of data transmission on a network


The form of communication link used to communicate between two or more stations.  EG.  Radio/TV broadcasts, copper cable (twisted pair/coax), fibre optic (FDDI), microwave, infra-red, satellite, cellular telephone network.

Each device on a network is connected to a transmission cable to allow messages to be sent from one device to another.

LANs typically use:

  • Twisted pair
  • coaxial
  • fibre optic

The differences between these media relate to:

  • cost
  • ease of installation
  • speed/capacity
  • distance
  • resistance to interference
  • reliability

Networks can also use wireless media such as:

  • microwave
  • radio frequencies

which do not require a physical link.


There are several configuration settings which affect the mode of transmission.

Flow control and cable provisions affect the type of exchanges between stations.  Simplex is a one-way mode of transmission; duplex is two way; half duplex enables two-way transmission but not for each station simultaneously; asymmetric duplex is two-way but with different speeds each way. Asynchronous transmission sends a character at a time with markers either end; synchronous systems are used to speed up this process and send whole blocks of data at a time by timing the start and end of the block.  Cable types and facilities affect the type of transmission. Serial transmission sends each bit of data down the same cable in sequence; parallel transmission enable the eight data bits to travel along separate cables simultaneously.

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SIMPLEX:  only allows the transmission of data in one direction between two devices

DUPLEX (sometimes called Full Duplex) 
Allows transmission of data in both directions simultaneously.

Allows bothway transmission of data between two devices but only in one direction at a time. (2-wire).

Irregular or not synchronised. In computer communications, the term is usually applied to data transmitted irregularly rather than as a steady stream. Asynchronous communication uses start bits and stop bits to indicate the beginning and end of each data block.

SYNCHRONOUS: Regular. Most communication within a computer system is synchronous, controlled by the computer's own internal clock, ...

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