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PBX and SIP Trunk using PortSIP SBC

This topic describes how to configure PortSIP SBC to enable interoperability between a generic SIP trunk and PortSIP PBX. The SBC acts as a secure SIP signaling and media boundary, interconnecting the enterprise PBX deployed in a private network with a SIP trunk service hosted on a public network.

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1. Interoperability Topology

The interoperability testing between PortSIP SBC, a generic SIP trunk, and PortSIP PBX was performed using the following deployment model.

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Deployment Scenario

  • The enterprise deploys PortSIP PBX within its private LAN to provide internal voice communications.

  • The enterprise requires PSTN connectivity and enterprise calling services through a SIP Trunk provided over the public Internet.

  • PortSIP SBC is deployed at the network edge to interconnect the enterprise LAN with the SIP trunk provider and to protect the PBX from direct exposure to the public network.

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Key Concepts

  • Session A real-time voice communication session established using the Session Initiation Protocol (SIP).

  • Border The IP-to-IP network boundary between the enterprise LAN (where PortSIP PBX resides) and the public network hosting the SIP trunk.

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Call Flow Overview

The high-level call flow for this topology is:

This architecture ensures secure signaling, controlled media traversal, and protocol normalization between the PBX and the SIP trunk provider.

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2. Configuring PortSIP PBX

Before configuring the SBC and SIP trunk, ensure that the PortSIP PBX is installed and operational.

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Prerequisites

Complete the following PBX setup steps:

  1. Install PortSIP PBX

  2. Perform basic PBX configuration, including system and tenant setup

Refer to the corresponding PBX installation and configuration guides for detailed instructions.

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3. Configuring PortSIP SBC

Install and configure the PortSIP SBC according to your deployment requirements.

❗Note If WebRTC endpoints are used, ensure the SBC is configured for WebRTC support as described in the Configuring SBC for WebRTC guide.

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4. Adding the SIP Trunk to PortSIP PBX

This section describes how to add the SIP trunk to PortSIP PBX when the SBC is used as an outbound proxy.

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Assumed SIP Trunk Parameters

  • SIP trunk is reachable over the public Internet

  • SIP trunk IP address: 52.214.181.141

  • SIP signaling port: 5060

  • Transport protocol: UDP

  • Authentication mode:

    • IP-based authentication or

    • Register-based authentication

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Step-by-Step Configuration

  1. Sign in to the PortSIP PBX Web Portal

    • Use System Administrator credentials.

    • Navigate to Call Manager > Trunks.

  2. Add a New Trunk

    • Click the arrow button and select:

      • IP-based Trunk or

      • Register-based Trunk, depending on the SIP trunk type.

  3. Configure Basic Trunk Settings

    • Enter a friendly name for the trunk.

    • Set Host Domain or IP to the SIP trunk IP address:

    • Set Port to 5060, or to the actual port provided by the SIP trunk provider if different.

  4. Configure the Outbound Proxy (SBC)

    • Set Outbound Proxy Server to the private IP address of the SBC, for example:

    • Set Outbound Proxy Server Port to:

      By default, PortSIP SBC listens on TCP port 5069 for SIP traffic from the PBX.

  5. Select Transport Protocol

    • Select TCP as the transport.

    • Click Next.

    Note PortSIP PBX communicates with the SBC using TCP by default. Ensure the selected transport matches the SBC configuration.

  6. Configure Authentication (Register-Based Trunk Only)

    • Enter the Authorization Name and Password provided by the SIP trunk service provider.

    • Click Next.

  7. Advanced Options

    • Enable Trunk is located in same LAN with PBX.

    • Disable Rewrite the host IP of Via header by public IP when sending the request to trunk.

    • Click Next.

  8. Assign Trunk to Tenants

    • Since the trunk is created by the System Administrator, select one or more tenants that are allowed to use this trunk.

    • For details, refer to the Add the Trunk by System Admin section in Trunk Management.

Now you are ready to create the inbound & outbound rules for the call routing.

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