Quality Metrics
Ref: ITU-T Recommendation E.600
PDD
Post-Dial Delay
Direct Telecom Definition • Carrier Industry Standard
The elapsed time between the sending of the last dialed digit and hearing the ringback tone.
Technical Definition & Carrier Engineering Standards
Post-Dial Delay measures the latency experienced by the caller before the destination network indicates the call is ringing (SIP 180 Ringing or 183 Session Progress). Carrier-grade VoIP routes target sub-second PDD (under 1.5 seconds) through direct MNO interconnections.
Standard Formula / Protocol Algorithm
PDD = Timestamp(Ringback / 180 Ringing) - Timestamp(SIP INVITE)