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TRUNKING
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Trunks are the transmission medium through which voice and data signals travel from one switch to
another. Studying the variety of ways trunks can differ can help simplify your decisions when you
implement and administer a network. Trunks can vary according to:
• Application
• Connectivity
• Administration options
• Interface circuit
APPLICATION
Trunks can be classified according to the type of switch with which they communicate:
• Local exchange trunks carry transmissions between private communications systems, like the System
75, System 85, and DEFINITY systems, and the switch at a central office.
• Tie trunks carry transmissions between private communications system switches.
• Special-access trunks carry transmissions between private communications systems and the point-of-
presence (POP) of the interexchange carrier (IXC).
• Auxiliary trunks link facilities on a single switch with each other.
• Miscellaneous trunks perform functions that do not neatly fit with the above applications. Included
among miscellaneous trunks are release link trunks, remote access trunks, and host access trunks.
See Administration Options later in this chapter for an explanation of the signaling used in each of these
trunk types. In addition, tables 1-10 through 1-13 specify the administration for all of these trunk types.
Local Exchange Trunks
Local exchange trunks connect the switch to a central office. Among local exchange trunks are the
following varieties.
• Central office trunks — 1-way outgoing, 1-way incoming attendant-completing, or 2-way trunks
connecting the switch to a central office (CO).
• Foreign exchange (FX) trunks — 1-way outgoing, 1-way incoming attendant-completing, or 2-way
trunks connecting the switch to a CO that is outside the local exchange area. These trunks give a caller
direct access to a central office outside the local exchange area without using the public network.
• Wide Area Telecommunications Service (WATS) trunks — 1-way outgoing trunks connecting the switch
to a CO equipped to handle WATS calls. The outgoing trunks allow a customer, for a monthly charge,
to place outgoing station-to-station calls to telephones in a defined service area. The service area has
one or more geographic areas known as WATS bands. Incoming trunk calls are completed by an
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