Troubleshooting Post Dial Delay (PDD) and Delayed Ringing on Twilio Calls

This guide is intended to help troubleshoot any issues with Twilio Programmable Voice calls that display post dial delay (PDD), or have a long delay before the call begins ringing. This guide covers the following topics for diagnosing and resolving your issues:

Please start at the top, and walk through each of the troubleshooting steps as you work your way down the page. 

Check for Twilio Incidents

Check the Twilio Status Page to see if there is an active incident, or an incident during the timeframe you reported issues, that could be causing your issues. For full details, please see Checking Twilio Service and API Status with the Status Page.

No incidents are listed that may be affecting calls: If you don't see an incident posted that may affect calls, then there is likely an issue elsewhere. Continue reading for additional troubleshooting.

An incident may be affecting calls: If you see an incident posted that may affect outgoing Twilio calls, please monitor the status, and then test again once the incident is resolved.

Identify the Issue

Attempt to ascertain the full details surrounding this issue:

  • For Elastic SIP Trunking or SIP Domain calls, do you see a delay of 6 seconds or more between the 100 Trying and 180 Ringing or 183 Session Progress responses in the Packet Capture?
  • Does the call log show any Debug Events?
  • Is your TwiML URL or Application SID showing a delayed response?
  • For Voice Insights users, do you see PDD of over 6 seconds?
  • Does this issue only occur with specific phone numbers or number types (landline, mobile, VoIP, etc.)? Mobile phones generally have higher PDD times, due to the nature of the technology they use.
  • Does this issue only occur when calling or receiving calls from a specific region or country?
  • Do other callers/callees report similar issues?

Once you are able to answer these questions, continue reading for additional troubleshooting.

Attempt to Replicate the Issue

Attempt another test call or two between the same phone numbers, and then try using the same Twilio phone number with different caller/callee phone numbers. The goal is to determine if this was a one-off, if the issue is limited to specific phone numbers or service providers, or if there may be a larger issue that requires investigation.

Issue is always replicated: If you are able to replicate the PDD issues on all calls in the same direction (to or from) with your Twilio phone number, we need to perform additional testing. Continue reading for additional troubleshooting.

Issue is sometimes replicated: If you are able to replicate the PDD issues only some of the time on calls in the same direction, check for any patterns:

  • If PDD is only seen from incoming callers using a specific service provider (or a small group of providers), then escalate to the caller's service provider.
  • If PDD is only seen from outgoing callers using a specific service provider (or a small group of providers), then continue reading for additional troubleshooting.
  • If no pattern can be found, collect additional examples, and then continue reading for additional troubleshooting.

Unable to replicate this issue: If you are unable to replicate the PDD issues, it's unlikely we will be able to address this report. Continue to monitor, and restart troubleshooting as needed if additional reports are received.

Escalate to Twilio Support

If you can rule out all of the above issues, Twilio's Support team can help investigate what went wrong. Please collect 3 or more examples of calls to or from the same Twilio phone number that have reported PDD issues from the last 24 hours, and include the following information:

  • Call SIDs
  • Description of issues
  • Variance of issues
  • Frequency of issues
  • Replication pattern

When you have collected this information, please share it with our Support team.

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