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In telecommunication, the term trunk has the following meanings:
1. In a communications network, a single transmission channel between two points that are switching centers or nodes, or both.
2. [A] circuit between switchboards or other switching equipment, as distinguished from circuits which extend between central office switching equipment and information origination/termination equipment.
Note: Trunks may be used to interconnect switches, such as major, minor, public and private switches, to form networks.
Source: from Federal Standard 1037C and from MIL-STD-188 and from the Code of Federal Regulations, Telecommunications Parts 0-199
3. In popular parlance and in the UK at least a Trunk call was a long distance one as opposed to a Local call. See Subscriber trunk dialling and Trunk vs Toll.
Derivation. From an early stage in the development of telephony, the need was found for thick cables (up to c. 10cm diameter). These were usually covered in lead. Thus, both in colour and size they resembled an elephant's trunk.
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