Post Dial Delay Timer

The SBC Core supports Post Dial Delay (PDD) for SIP-SIP call on a per-trunk group basis by implementing a configurable PDD timer on the ingress/egress trunk group. If not satisfied, the call is released by sending release messages on both the ingress and egress call legs with the disconnect cause code configured on the associated trunk group.

A PDD time-out (expiry) value and disconnect reason code (response) is configurable on the SIP Trunk Group object.

The disconnect reason code, CPC_DISC_PDD_TIMER_EXPIRED, is created for PDD Timer expiration-related call release. This code is logged in the existing "Call Disconnect Reason" field in the associated ATTEMPT record. The disconnect reason code configured on the ingress and egress trunk groups is included in the release message independently.

The Ingress PDD timer is activated when the configured value on the ingress trunk group is greater than zero, and the incoming SIP call reaches address complete state. The PDD Timer is not activated if the configured value on the ingress trunk group is zero. Priority calls like High Probability Completion (HPC) or emergency calls will not be released due to PDD time out.

The Egress PDD timer is activated when the configured value on the egress trunk group is greater than zero, and upon receipt of the 100 Trying message from the egress peer. The timer is canceled upon receipt of a 18x/200/3xx/4xx/5xx message from the egress peer. The PDD Timer is not activated if the configured value on the trunk group is zero.

A PDD Timer Cancel action occurs in the following scenarios:

• The SBC cancels the ingress PDD timer when the 18x/200/3xx/4xx/5xx/6xx message is sent from the SBC in the backward direction to the ingress peer.
• The SBC cancels the egress PDD timer upon receipt of 18x/200/3xx/4xx/5xx/6xx from egress peer.
• Call crankbacks have no effect on a running PDD Timer.

During the PDD timer expiry, the following behavior is possible:

• If the ingress PDD timer expires, the SBC cancels the call in the forward direction (egress peer) and cranks back to the ingress peer, then sends PDD response code configured on ingress trunk group.
• If the egress PDD timer expires, the SBC cancels the call in the forward direction (egress peer) and cranks back within the SBC; if an alternate egress route exists, it is used if crank back does not occur to the ingress peer, and PDD response code which is configured on ingress trunk group is sent.