Configure PBX passthrough for a BYOC or External SIP trunk

AI-generated summary

Genesys Cloud's PBX passthrough feature enables PBX systems to route PSTN calls through the platform using BYOC or External SIP trunks, eliminating the need for separate PSTN connections. The feature leverages the Site's Number Plan and Outbound Routes to intelligently route inbound calls when the destination is not a Genesys Cloud object such as a user, station, or IVR flow. Calls are processed in two distinct legs—PBX and carrier—with each subject to applicable usage fees and number normalization operations. The system supports routing external calls through multiple trunk types including BYOC Cloud carriers, External SIP, or Genesys Cloud Voice trunks. Configuration requires at least one PBX trunk, as passthrough between two carrier trunks is not supported. Proper SIP Access Control configuration is essential for implementation. Multi-site BYOC trunk configurations are not recommended due to unpredictable routing behavior; however, implementing identical Number Plans and Outbound Routes across all sites can enable consistent functionality across deployments. Security considerations include disabling PBX passthrough on External trunks connected to carriers to mitigate toll fraud risk. Users require Telephony > Plugin > All permissions to configure this feature. Administrators access external trunk configuration through the Menu > Digital and Telephony > Telephony > Trunks interface, where they can navigate to the External Trunks tab to select and modify specific trunks. SIP Access Control settings provide PBX Passthrough functionality that manages trunk access parameters and is critical for security posture. The platform supports multiple deployment models including BYOC Cloud and BYOC Premises options, with capabilities to create trunks under either deployment type or convert between hybrid media configurations. Detailed external trunk settings documentation is available for administrators requiring comprehensive configuration guidance.

PrerequisitesClick to expand

When you configure a BYOC PBX trunk or an or External SIP trunk, you can enable the PBX passthrough feature to allow your PBX to pass calls intended for the PSTN directly through Genesys Cloud. This feature eliminates the need to maintain a separate PSTN just for PBX calls, thus reducing cost, simplifying configuration, and improving call efficiency.

More specifically, the PBX passthrough feature allows Genesys Cloud to use the Site’s Number Plan and Outbound Routes configurations to route inbound calls when the destination address is not a Genesys Cloud object: user, station, or IVR flow.

For example, a third-party PBX user can dial an E.164 number for a customer and the call routes to Genesys Cloud. Genesys Cloud recognizes the call as an external destination and routes the call out a BYOC Cloud carrier, an External SIP, or a Genesys Cloud Voice trunk.

Note: When a PBX passthrough call occurs, there are two call legs – one for the PBX leg and one for the carrier leg. Genesys Cloud performs the number normalization operation for each leg. Once for the carrier (inbound) leg and once for the PBX pass through leg. Each leg is subject to any usage fees that are applicable to that particular trunk type.

Best practiceClick to expand

Genesys recommends that you not enable the PBX passthrough feature on BYOC Cloud trunks that are associated with multiple sites. The reason being that inbound calls route to any of the potential sites without predictability. However, if your configuration can support it, you can configure each of your sites with identical Outbound Routes and Number Plans. That way the PBX passthrough is consistent across all of the sites.

PBX passthrough requires that either the inbound or outbound trunk must be a PBX trunk. PBX passthrough between two carrier trunks is not supported.

Warning: While you can enable PBX passthrough on a premises-based Edge appliance, do not enable PBX passthrough on External trunks that connect to carriers. Doing so leaves you at risk for toll fraud.

If you need more information about any of the settings on the Create/Edit External Trunk page, see External trunk settings.

Click Menu > Digital and Telephony > Telephony > Trunks.
Click the External Trunks tab.
Click the trunk you want to configure.
Under SIP Access Control, enable PBX Passthrough.

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