Prerequisites – Network Configuration & Public Address

This guide assumes your Mitel OpenScape Session Border Controller (SBC) is already installed, licensed and working, with its network, certificates and phone system connection in place. It provides guidance on how to add a Voice AI SIP trunk - but you should establish the best route based on your own requirements.

Before configuring the SBC for Voice AI, the SBC must be reachable from the public internet on a publicly routable IP address, preferably with a DNS name that resolves to it. This is a fundamental networking requirement and is not specific to Voice AI — it applies to any external SIP trunk requiring connectivity across a network boundary.

Voice AI is delivered over a SIP trunk from a cloud platform. The platform sends transfers (SIP REFER) and any new call back into your phone system to the address the SBC presents in its SIP Contact header, so that must be a public address. An internal private address (RFC 1918) is unreachable from the public internet, and signalling, transfers and media would fail. If the SBC sits behind a device that translates addresses (NAT), such as a cloud provider's public IP address mapping, the SBC must be told its public address so that it presents that address to the Voice AI platform. Enter the public address in Security → Firewall → Firewall Settings: select the row for the access IP address and choose Edit. Tick External Firewall and enter the public address in Firewall external IP. Leave the other fields in that section at their defaults unless your signalling and media use different public addresses. With this set, the SBC puts the public address in the From header, the Contact header and the audio connection address that it sends to the platform. Before continuing, also check the following.

• A DNS (Domain Name System) server is configured on the SBC so that it can resolve the domain name that you are given for the Voice AI trunk.
• The phone system side is ready. For OpenScape 4000 this means a SIP trunk gateway board that is dedicated to the Voice AI trunk, as described in the OpenScape 4000 setup guide.

Firewall Requirements

You are given the signalling and media addresses of the Voice AI platform for your trunk, with the ports and transport it uses. Allow all of the signalling and media ranges you are given, because a call can use any of them. Apply the rules below to whatever firewall or security group sits in front of the SBC.

Gateway Boards (Clustered Servers)

The SBC connects to your phone system in one of two modes, set by Comm System Type under VoIP → SIP Server Settings. In Simplex mode the SBC connects to a single gateway board. In Clustered mode it connects to several, and each one is listed as a node.

Voice AI uses its own gateway board (see the prerequisites above), so the SBC connects to at least two boards: the one that carries your existing trunks and the one that carries Voice AI. Set the SBC to Clustered and list every board that has a trunk to the SBC, including the Voice AI board.

If the Voice AI board is not listed, calls to Voice AI can still connect, but the messages that the platform sends later in the same call are delivered to the wrong board. That board has no record of the call and answers 500 Server Internal Error. The transfer (SIP REFER) fails, and the platform's hang-up message (SIP BYE) is refused.

1. Open VoIP → SIP Server Settings and set Comm System Type to Clustered.
2. Select Clustered servers, then Add, and enter one row for each gateway board, including the board that carries your existing trunks.
3. Select OK, then select Apply Changes on the General page. Applying changes ends any calls in progress, so do this when no calls are active.

To check the result, take a network capture on the SBC while you place a test call that Voice AI transfers. The platform's transfer message should be delivered to the address of the Voice AI board, not to the other board.

Trunk Setup