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Collaboration, Voice & AV · Foundational

IP Private Branch Exchange (IP PBX)

A PBX that performs call control over an IP network, registering IP phones and soft clients instead of using TDM line cards.

Definition

An IP PBX separates call signaling from media: endpoints register to the call control server, which handles dial plan and features, while RTP media usually flows directly between endpoints. It connects to the PSTN through voice gateways or SIP trunks and to legacy systems through TDM gateways. Examples include Cisco Unified Communications Manager, Asterisk-based systems and many hosted platforms.

Example

Two IP phones registered to an IP PBX exchange SIP with the server but send RTP directly to each other.

Exam tip

Remember that signaling goes to the call agent but media is endpoint-to-endpoint unless a media resource such as an MTP, transcoder or conference bridge is inserted.

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