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Collaboration, Voice & AV · Foundational

Tie Line

A dedicated private trunk that connects two PBXs or call control systems at different sites.

Definition

A tie line, or tie trunk, links two private telephone systems so that users can dial each other by extension without using the PSTN. Historically tie lines were leased analog or T1 circuits using E&M or QSIG signaling; in IP networks they are replaced by SIP or H.323 trunks across the WAN. Gateways can emulate a tie line with connection trunk or connection plar-opx commands.

Example

Site A dials 8-2xxx to reach Site B over a SIP trunk that replaced the old T1 tie line.

Exam tip

On exams a tie line or intersite trunk usually implies an on-net call, so no PSTN charges and no PSTN digit manipulation.

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