We often get the chance to work directly with our customers designing their SIP trunking solutions. We sit with them and come up with a design that lines up with their underlying data network and business continuity requirements. Once we have that design we work with our carrier partners to get solutions from them that we can integrate with our design.

A key design point we want to touch on in this blog is inbound SIP trunking fail over. The inbound fail over is controlled by the SIP trunk carrier where the outbound fail over is controlled by the phone system or PBX. Many carriers have limitations when it comes to how we can fail over inbound calls.

Types of inbound SIP fail over

Manual Forwarding

Some carriers will offer a one to one mapping where you forward a number on a SIP trunk to a new number on some other trunk. This requires 2 direct inward dial numbers for each user that needs inbound fail over. We always try to steer our customers away from this option because it requires maintaining a forwarding database with the SIP carrier directly on top of managing the on-premise phone system.

Automatic fail over between SIP trunks

Ideally we will have a primary SIP trunk that will take all of the inbound calls, if this trunk were to go down we want to automatically send calls to an alternative route. The automatic fail over of inbound calls is the key design principle. We recommend a secondary SIP trunk that the SIP carrier can fail calls over to automatically. The fail over by the carrier is usually triggered by a loss of connectivity to the primary SIP trunk path.

Since the inbound fail over is automatic we can set it up at the time of deployment and not have to worry about maintaining a forwarding database with our SIP carrier.

Check out this cool video showing a visual demonstration of SIP trunk fail over in action