Post-Dial Delay

Post-Dial Delay (PDD) is the time elapsed between when VICIdial sends a call request (SIP INVITE) to the carrier and when the caller hears the first ringback tone or receives a response indicating the call is progressing. PDD represents the call setup time through the telephony network — encompassing SIP signaling, carrier processing, number translation, and PSTN routing. Normal PDD ranges from 1-5 seconds, while excessive PDD (over 7-10 seconds) indicates carrier or network issues.

How It Works in VICIdial

When VICIdial’s Asterisk server initiates an outbound call, it constructs a SIP INVITE message and sends it to the configured carrier trunk. The carrier receives the INVITE, validates the account, routes the call through its network to the destination carrier, and eventually the destination phone begins ringing. At that point, a SIP 180 Ringing or 183 Session Progress response is sent back to VICIdial, and the PDD period ends.

Several factors contribute to PDD in VICIdial environments: Carrier processing time — the primary carrier validates credentials, checks routing tables, and forwards the call; Inter-carrier routing — calls may traverse multiple carrier networks before reaching the destination; Number portability lookups — the network checks if the dialed number has been ported to a different carrier; International routing — calls to international destinations typically have longer PDD due to additional gateway hops.

VICIdial’s dial_timeout setting defines how long the system waits for the call to be answered after initiation. This timeout includes PDD — meaning high PDD effectively reduces the ring time available for the called party to answer. If PDD consumes 5 seconds of a 30-second dial timeout, the phone only rings for 25 seconds.

Why It Matters

PDD directly impacts predictive dialer efficiency and call throughput. Every second of PDD is a second that a dialer channel is occupied but unproductive. On high-volume campaigns dialing thousands of calls per hour, even 1-2 seconds of additional PDD can measurably reduce calls per hour and increase the number of concurrent channels required to maintain agent utilization.

Excessive PDD also causes false timeouts. If VICIdial’s dial timeout expires before the destination phone rings long enough for someone to answer, the call is logged as “no answer” when it may have been answered given adequate ring time. Monitoring PDD by carrier helps identify underperforming routes and provides data for carrier negotiations. Compare PDD across your carrier connections and consider routing high-priority campaigns through the carriers with the lowest PDD.