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The

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supports PSTN connections through its FXO ports and connections to analog phones through its FXS ports. It provides a low-cost long distance connectivity solution for enterprises that have PBXs in geographically separated locations. It also provides Survivability capabilities. A softswitch can also use the

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FXO ports as an enterprise gateway to route calls.

A Private Branch eXchange (PBX) can be connected to the

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for Session Initiation Protocol (SIP) trunking applications. A PBX is a private telephone switch that provides local phone service for an office or building. A PBX typically contains both FXS and FXO ports.

For more information about FXS ports, choose VoIP > SIP > SIP UA and refer to Configuring SIP UA.

Two-Stage Dialing for Inbound IP and PSTN Calls

You can enable two-stage dialing for inbound calls from the IP network and the PSTN:

• Inbound IP network calls—For calls that come into FXO/line ports on the

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  from the IP network, dial tone is provided to the caller to enable the caller to dial a number and connect through the PSTN.
• Inbound PSTN calls—For calls that come in from the PSTN, the SIP/FXO line port provides dial tone when the PSTN call is answered. This enables the caller to dial an extension to complete the call or hang up.

Priority Calling Support

Priority calling services route priority calls as defined in the VoIP ALG SIP trunking plan. Calls made to a priority calling number from any FXS port are routed and connected on a priority basis.

The following rules determine the treatment of an incoming priority call:

• If a free FXO port is available, the priority call is routed and connected.
• If all FXO ports are busy, a non-priority call on one of the ports is dropped to allow the priority call to be routed and connected. The PSTN live connection to the FXO port must support 3-way calling.
• If all FXO ports are busy with priority calls, the incoming priority call is not accepted.

To configure priority calling, enable the feature on the SIP FXO/Line Port Configuration Page and then define priority rules on the ALG Trunking Configuration page. Choose VoIP > SIP > ALG and refer to Configuring Bandwidth Settings for H.323.

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Priority calling services cannot be configured when WAN Link Redundancy is enabled.

Transmit/Receive Gain

FXO port TX/RX gain settings are adjusted at the WAN interface. TX adjusts the gain from the FXO port to the IP WAN. RX adjusts the gain from the IP WAN to the FXO port.