VoIP glossary · Post-Dial Delay
What is PDD?
PDD (Post-Dial Delay) is the time between finishing dialling and hearing ringback or an answer, typically measured from the INVITE to the first 180 Ringing or 183 Session Progress.
PDD explained
Callers notice long PDD as silence after dialling. A few seconds is normal on international calls, especially to mobiles, but consistently long PDD can mean a route is trying several carriers in turn before one accepts the call.
For diallers, PDD matters as much as ASR. If the dialler gives up before ringback, the attempt is counted as failed even though the route would have connected. Set dialler timeouts with real PDD measurements in mind.
Example
Calls to Nigerian mobiles show a PDD of 7–9 seconds. The dialler’s 6-second "no answer" timeout is cutting them off, so ASR looks far worse than it is.
Put it into practice
Prepaid SIP trunks and wholesale routes from $200. Ask sales for rates or the NOC for a technical answer.