Trunks and Multiplexing

Computer NetworkComputer EngineeringMCA



Trunks are a large-bandwidth communication channels connecting switching centres, forming the core of the telephone network. A trunk comprises of a cluster of broadcast frequencies that are suitable for long haul communication of many voice and data signals simultaneously.


The characteristic features of a trunk are −

  • They carry digital information as opposed to analog signals carried by local loops.

  • They are designed for both voice and data transmission.

  • They can carry millions of calls simultaneously over long distances.

  • They have very high bandwidth.

  • They generally comprise of a cluster of fiber optic cables bundled together to maximize bandwidth.

  • Another method of achieving high bandwidth is to use a single high capacity link that can carry many signals multiplexed together.

Trunks used in Telephone Networks

  • Toll connecting Trunk − Lines that connect end offices with toll offices. Fiber optic cables are used here.

  • Intertoll Trunk − Very high bandwidth channels that connect either two toll offices via intermediate switching offices. Fiber optic cables and microwaves are used here.

Trunks used in Telephone Networks

Multiplexing in Trunks

Trunks are required to carry a huge number of calls simultaneously. An option is to provide a large number of low-bandwidth trunks. However, the cost of installation and maintenance of a low-bandwidth trunk is almost same as cost of installing a higher bandwidth counterpart. So, installing a large number of low-bandwidth trunks is not an economic decision.

A feasible solution is to use a high bandwidth channel and use multiplexing for simultaneous transmission of several signals. Multiplexing is a method of combining more than one signal over a shared medium. The commonly used multiplexing techniques in trunks are time division multiplexing (TDM) and frequency division multiplexing (FDM). In TDM, the users are allowed the total available bandwidth on time sharing basis. In FDM, signals of different frequencies are combined for concurrent transmission.

Updated on 30-Jul-2019 22:30:23