Why don't I hear ringing after dialing? Post Dial Delay!
Posted by Bob Russo on 14 October 2014 07:21 AM

PDD - Post Dial Delay

What is it? - It is the delay experienced between the time you dial a number and receiving any audible signal. It is typically encountered when placing an outbound call on both SIP trunks and/or Hosted phone systems.

How Long? - The delay varies depending on the terminating destination’s response. It may result in a few seconds of perceived missed ringing to no ringing at all and just hearing the called party answering.

Why? - SIP signaling relies on the called (terminating) party to tell the calling (originating) party with a message instructing what kind of signal to relay. An example would be a return message of  “180 ringing” which would instruct the originating system to play a ringing signal. Without this information, the origination point doesn’t know whether to play a busy signal, ring signal or if a voice is supposed to be received from an auto attendant/voice mail. In cases of PDD, the termination end either delays, or never sends the message.

Remedy?  – If a customer is continually experiencing this condition, it is possible to try different call routing in case the missed messaging is due to one of the hops failing to pass the message along. If the termination point does not respond with the correct message at all, then little can be done. Arbitrarily assigning a result at the originating end would be counterproductive in most cases.

As the SIP protocol operates primarily on industry recommendations there is currently no way to force carriers to always provide the messaging required. As SIP evolves this may be an issue that is left behind however for the time being it is a fact of life when dealing with SIP.

Please note that on the Hosted Platform there is delay after dialing if the user does not press the # key to signify they have completed digit entry. The timer in place waits for 5 seconds from the last key press before actually placing the call. This is not part of PDD, but part of the inter digit delay logic and occurs both on outbound calls as well as any internal dialing.

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