Post Dial Delay (PDD) measures the amount of time that passes before a final response is received for a SIP Invite. PDD starts counting time as soon as the caller enters the last digit of a phone number (the SIP Invite is received) and ends when a SIP 2xx, 3xx, 4xx, 5xxx or 6xx response is received.)
The default time frame is 30 seconds for Max PDD when the value field is left empty.
B-Timer acts as an extension of PDD and is designed to work as a smaller subset timer to roll over to the next trunk if no response is received from the vendor or customer. The B-timer is activated when the INVITE is sent to the outgoing trunk, and if no provisional response (i.e. SIP 18x) is received within the allocated time it will expire and roll over to the next Trunk or Trunk Group if available. B-timer values can be between 1-10 and must always be smaller than the PDD value. The default value entry field for B-timer is empty, which means it will not be considered unless an integer value between 1 to 10 is set for it.
Note:
PDD = (sum of all PDDs from CDRs) / (sum of all completions)where PDD is the defined above