ASR, ACD and PDD: measuring wholesale route quality

Wholesale voice is bought and sold on price, but kept or dropped on quality. These are the numbers carriers watch.

ASR — Answer Seizure Ratio

ASR is the percentage of call attempts that are answered: answered calls ÷ total attempts × 100. It reflects both the route and the callers’ behaviour — busy subscribers, unreachable mobiles and wrong numbers all lower ASR. Compare ASR for the same destination and traffic type over time rather than against a universal target.

ACD — Average Call Duration

ACD is total billed minutes ÷ answered calls. Very short ACD on a route can indicate poor audio (callers hang up), one-way audio, or false answer supervision — where a call is marked answered before anyone picks up. Sudden drops in ACD are worth investigating quickly.

PDD — Post-Dial Delay

PDD is the time between sending the call and hearing ringback. Long PDD frustrates callers and often reflects many routing hops or slow signalling. Lower is better; acceptable values vary by destination.

CLI delivery

Whether the caller’s number arrives intact matters for business and contact-center traffic — and is required by law in some markets. Routes are commonly separated into CLI and non-CLI products for this reason.

Reading the metrics together

• Normal ASR, falling ACD: possible audio problems or false answer.
• Falling ASR, normal ACD: capacity or reachability issues on the far end.
• Rising PDD: routing changes or congestion upstream.
• Unusually high ASR with very short calls: a classic sign of fraud or artificially inflated traffic.

Good practice

• Test new routes with real test calls before production traffic.
• Monitor per destination and per supplier, not just overall.
• Share call examples (date, time, A- and B-number) when raising issues.
• Agree thresholds and review periods in your commercial relationship.