Maximum Post Dial Delay (PDD) Timer

The Maximum Post Dial Delay (PDD) timer can be configured between 1 and 30 seconds.  If the timer is not configured a value of 30 seconds will always be used. 

For Termination Vendor Trunk Groups, the purpose of the Max PDD timer is to route advance the call to the next available vendor when the vendor does not provide a provisional (180/183) or a final (2XX - 6XX) response before the timer expires. The Max PDD timer starts when the Orchestrator sends the SIP Invite to the vendor. The Max PDD timer stops when a provisional (180/183) or a final response (2XX -6XX) is received from the vendor. The Max PDD timer expires when a provisional (180/183) or a final response (2XX -6XX) is not received during the configured time. If the timer expires, a cancel message will be sent to the vendor. The Orchestrator will then check if the Termination Customer Trunk Group's Max PDD Timer has expired.  If Termination Customer Trunk Group's Max PDD Timer has expired, then a SIP 504 Local PDD Timeout final response will be sent to the customer. If the Termination Customer Trunk Group's Max PDD timer has not expired, then the call will route advance to the next Termination Vendor Trunk Group (a SIP Invite will be sent to the next vendor selected based on the matched routing rule from the termination route plan). If there are no more vendors to route the call to then a SIP 503 Routes Exhausted message will be sent to the customer. 

For Termination Customer Trunk Groups, the purpose of the Max PDD timer to terminate the call when the the timer expires and the current Termination Vendor Trunk Group's Max PDD timer has also expired. The timer starts when a SIP Invite is received on the Termination Customer Trunk Group. The timer only stops when the call is established (i.e. a 200OK received by the vendor). No immediate action is taken when the Termination Customer Trunk Group's Max PDD timer expires.

Note: When  Termination Customer Trunk Group Max PDD timer expires the call will not be canceled unless the current Termination Vendor Trunk Group's Max PDD timer has also expired.

Example of a Termination Customer Trunk Group Max PDD expiration:

The Termination Customer Trunk Group's Max PDD timer is set to 30 seconds.

All Termination Vendor Trunk Group's Max PDD timers are set to 30 seconds.

A SIP Invite arrives at the Termination Customer Trunk Group which starts the Termination Customer Max PDD timer. Seven potential vendors trunk groups are identified, based on the routing rule matched using the termination route plan assigned to the Termination Customer Trunk Group .

A SIP Invite is sent to the first selected Termination Vendor Trunk Group.  The vendor initially responds with a SIP 100 Trying followed by a SIP 503 six seconds later.  Since the Termination Customer Trunk Group's Max PDD has not expired (14 seconds remaining) and the Termination Vendor Trunk Group is configured to route advance on a SIP 503 response, a SIP Invite will be sent to the second selected Termination Vendor Trunk Group.

The second vendor initially responded with SIP 100 Trying followed by a SIP 183 provisional response. 43 seconds later the second vendor responds with a SIP 480 Temporarily Unavailable. Since the Termination Customer Trunk Group's Max PDD had expired 19 seconds ago, the call will be terminated (no SIP Invite will be sent to the remaining five vendors) and a SIP 504 Local PDD Timeout final response will be sent to the customer.

Example of a Termination Vendor Trunk Group Max PDD expiration:

Termination Customer Trunk Group's Max PDD timer is set to 30 seconds.

All Termination Vendor Trunk Group's Max PDD timers are set to 15 seconds.

A SIP Invite arrives the Termination Customer Trunk Group which started the Termination Customer Max PDD timer. Four potential vendors are identified based on the routing rule matched using the termination route plan assigned to the Termination Customer Trunk Group.

A SIP Invite is sent to the first selected Termination Vendor Trunk Group.  The vendor responds with a SIP 100 trying and 6 seconds later with a SIP 503.  Since the Termination Customer Trunk Group's Max PDD has not expired (24 seconds remaining) and the Termination Vendor Trunk Group is configured to route advance on a SIP 503 a SIP Invite will be sent to the second selected Termination Vendor Trunk Group.

The second vendor initially responded with SIP 100 Trying followed by a SIP 183 provisional response, but no other responds are received.  15 seconds later the Termination Vendor Max PDD timer expires. Since the Termination Customer Trunk Group's Max PDD has not expired (9 seconds left), the call route advances to the third vendor.  The third vendor initially responds with a SIP 100 Trying followed by a SIP 183.  After 12 seconds the third vendor responds with a SIP 200OK.  Note: The Termination Customer Trunk Group's Max PDD had already expired but since the current (third) Termination Vendor Trunk Group's Max PDD had not expired, no action was specific to the expiration of the Termination Customer Trunk Group's Max PDD timer.

For Origination Customer and Origination Vendor Trunk Groups, the Max PDD timer is not used and has no impact on call processing.

Note: See  B-Timer for an explanation of how the B-Timer and Max PDD work together.