PDD

Rate this page:

Post-dial delay (PDD) is the measurement of how long it takes for a calling party to hear a ringback tone after initiating a call. Technically it is the delta between the SIP INVITE and a 180 Ringing or 183 Session Progress response. 

Post-Dial Delay Symptoms

Callers who experience post-dial delay will report long waits before hearing ringing. In extreme cases high post-dial delay will be reported as dead air, one-way audio, or dropped calls since the calling party has no indication that the call has been properly established, or whether or not the destination has answered.

Tolerance for post-dial delay varies widely by geography. In North America most users will notice post-dial delay of ~5 seconds, but in some locations like South Africa post-dial delay of 10 seconds or more is common and even 15 seconds of silence before hearing ringing can go without remark by callers.

Post-dial Delay Causes

Most post-dial delay is due to improper SIP signaling respones from destination networks due to different interpretations of the SIP RFC. For example, in general a 180 Ringing response from a destination indicates that the calling party network should play the caller whatever their local ringback tone is and a 183 Session Progress from a destination includes specific audio in the SDP to be played back to the caller; however, in some cases a destination may try to provide specific ringback with a 180 Ringing response, or neglect to provide one with a 183 Session Progress response. Further, in some cases the ringback provided may be silence.

Post-dial delay can also be experienced when calling geographically remote destinations from the caller. Non-geographic destinations like satellite phones are also prone to greater post-dial delay.

Monitoring Post-dial Delay at Twilio

Twilio's Super Network actively monitors our carrier partners for increases in post-dial delay and will proactively notify and resolve problems that are detected without action required from customers.

In some cases calls to a specific destination may encounter post-dial delay that is not significant enough in aggregate to alert Super Network to the issue; in these instances customers can reach out to Twilio Support for assistance in investigating the issue and escalating to carrier partners if appropriate.

Post-dial delay can be proactively monitored by customers using the Voice Insights Dashboard and Voice Insights Advanced Features Call Summary API.

Rate this page:

Thank you for your feedback!

We are always striving to improve our documentation quality, and your feedback is valuable to us. How could this documentation serve you better?

Sending your feedback...
🎉 Thank you for your feedback!
Something went wrong. Please try again.

Thanks for your feedback!

Refer us and get $10 in 3 simple steps!

Step 1

Get link

Get a free personal referral link here

Step 2

Give $10

Your user signs up and upgrade using link

Step 3

Get $10

1,250 free SMSes
OR 1,000 free voice mins
OR 12,000 chats
OR more