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Collaboration, Voice & AV · Foundational

Private Branch Exchange (PBX)

A privately owned telephone switch that connects internal extensions and shares a pool of outside lines to the PSTN.

Definition

A PBX switches calls between extensions inside an organization and provides features such as transfer, hold, conference, voicemail integration and hunt groups. Traditional PBXs use TDM and digital or analog handsets, while an IP PBX performs call control in software and uses IP phones and SIP or proprietary signaling. Cisco Unified Communications Manager is an example of enterprise IP call control that replaces a PBX.

Example

A legacy TDM PBX is connected to CUCM with a QSIG PRI during a phased migration to IP telephony.

Exam tip

Distinguish an on-premises IP PBX from a hosted or cloud PBX (UCaaS such as Webex Calling or Teams Phone) where the provider runs the call control.

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