Short-Duration Traffic and CC Routes: What Dialer Operators Need to Know

What counts as short-duration traffic

There is no single industry definition, but most carriers look at three ratios on a destination over a rolling window:

• Short-call ratio: the share of answered calls under a threshold, often 6, 10 or 30 seconds.
• ACD: average answered call length. Many standard routes expect ACD above 2–3 minutes.
• Attempts per answer: how many INVITEs you send for every answered call. Dialers commonly send 3–6.

A route sold for conversational traffic might tolerate a short-call ratio of 10–15%. A predictive campaign can easily run at 40% or more, because the dialer hangs up on answering machines, customers decline quickly, and agents disconnect wrong numbers. None of that is improper. It is simply a different shape of traffic.

Why carriers restrict it

Each call attempt consumes signalling capacity, session state on border controllers and, on some interconnects, a per-attempt fee. A carrier paid by the billed minute earns very little from a stream of 4-second calls while carrying all of that cost. Short calls also resemble patterns associated with fraud and nuisance calling, so terminating networks may apply extra scrutiny to them.

The result is that a standard CLI route may start returning 503 Service Unavailable or 403 Forbidden once your short-call ratio crosses its threshold, or the provider may silently move your traffic to a lower-quality path. Either way, your ASR collapses mid-campaign.

How CC routes are different

A CC (call-centre) route is a CLI route built with carrier partners that have agreed to carry dialer traffic. The differences are mostly commercial and operational rather than technical:

Billing increments matter more than most buyers realise. On 60/60 billing every 4-second call is charged as a full minute; on 6/6 it is charged as six seconds. Your rate deck in the portal shows the increment per destination. Read more on the CC routes page.

Keeping your short-call ratio healthy

Even on a CC route, traffic quality affects how long routes stay stable. These settings make the biggest difference on VICIdial and similar platforms.

1. Tune the dial ratio. An aggressive adaptive ratio creates abandoned calls that are answered and immediately dropped. Most regulators also cap abandonment (3% in the UK, for example).
2. Set a realistic ring timeout. 22–26 seconds is typical. Very short timeouts inflate attempts per answer without improving agent utilisation.
3. Use answering-machine detection carefully. AMD that disconnects after a 2-second greeting produces exactly the short calls carriers watch. Consider leaving voicemail-friendly campaigns on agent handling.
4. Clean your lists. Invalid and disconnected numbers create 404 and 484 responses that count against network ratios. Validate numbers with an E.164 formatter before loading them.
5. Respect calling hours and DNC. Calls placed outside permitted hours are both a compliance risk and a source of quick rejections.

Dial Method ............... RATIO
Auto Dial Level ........... 2.0
Dial Timeout .............. 26
Drop Call Seconds ......... 5
Available Only Tally ...... Y
AMD (Answering Machine) ... Agent-handled for new lists
Max Drop Percentage ....... 3

Short calls and capacity planning

Short-duration traffic is limited by calls per second (CPS) far more than by concurrent channels. A campaign with 50 agents at a ratio of 3 might only need 150 channels, but it can burst to 20+ CPS when agents become available together. Size both. Our guide to SIP Channels & CPS Sizing for Dialers walks through the maths, and the channel and bandwidth calculator does it for you.

Answering machine detection in more depth

AMD listens to the first seconds after answer and guesses whether a person or a machine picked up. People usually say a short greeting and pause; machines speak longer before a beep. Every AMD setting is a trade-off between false positives (hanging up on real people, which creates silent or abandoned calls) and false negatives (connecting agents to voicemail).

Regulators count a call where a person answers and hears silence or is hung up on as an abandoned call. In the UK the persistent misuse policy expects a short information message to be played on abandoned calls and the abandoned rate to stay at or below 3% of live calls per campaign over 24 hours. Start with conservative settings, measure, and tune.

Retry strategy

Retries are the hidden multiplier on short-duration traffic. A list where each number is retried six times a day generates six times the attempts for a modest gain in contacts, and the extra attempts are almost all short or unanswered. They also teach analytics engines that your numbers call people repeatedly without connecting.

• Retry busy numbers after 10–20 minutes, no-answers after several hours, and spread retries across different times of day.
• Stop retrying numbers that return 404, 484 or 604: they are invalid.
• Cap total attempts per number per week, and lower the cap for numbers that have never answered.
• Track contacts per 100 attempts by retry number; when the fourth or fifth attempt adds almost nothing, stop there.

What we monitor on CC routes

On CC routes we watch short-call ratio, ACD, attempts per answer and the share of 6xx responses per campaign, in near real time. When a ratio moves sharply, our NOC contacts you before the route is affected, usually because a dialer setting changed or a new list was loaded. That early conversation is what keeps CC traffic welcome on good carrier paths. See the CC routes overview and country pages such as CC routes for the Philippines.

How billing increments change the picture

Take 10,000 answered calls with a mean length of 22 seconds, where 40% last under 6 seconds. On 1/1 billing you pay for about 3,667 minutes. On 6/6 billing, each call is rounded up to the next six seconds, adding roughly three seconds per call on average: about 4,170 minutes. On 60/60 billing, every call is charged as at least one full minute: 10,000 minutes or more. The per-minute rate on a 60/60 route would need to be well under half the 6/6 rate just to break even on this traffic.

Compliance considerations for dialer traffic

Dialer campaigns are subject to telemarketing rules in most markets: abandoned-call limits, calling-hour windows, do-not-call registers and caller-ID presentation requirements. In the US that means the TCPA, the FTC Telemarketing Sales Rule and state rules; in the UK, Ofcom's persistent misuse policy and the TPS. We review campaign type and calling hours at onboarding so that routes are matched to traffic that is lawful in the destination. Country pages such as CC routes for Spain summarise the local rules.

Good compliance is also good routing. Traffic with low complaint rates keeps the reputation of your numbers clean, which keeps answer rates up and routes stable.