Throttling calls-per-second to protect your carrier

To stay under your carrier's calls-per-second cap, ease how fast VICIdial places calls: lower the auto dial level, soften your pacing, and spread placement across more than one trunk. The goal is to smooth out the bursts so you never spike past the limit in any one second.

Why throttling matters

Your Carrier's Calls per second (CPS) cap rejects attempts the moment you exceed it, sending back 503s and CONGESTION. The fix isn't to retry harder — it's to pace your dialer so it never asks for more setups per second than the carrier will accept. A smoother call flow keeps the trunk healthy and your agents fed.

Lower the auto dial level

The dial level is the biggest lever. With Predictive dialing on adaptive pacing, VICIdial raises the dial level to keep agents busy — which means more calls placed per second. If you're hitting your CPS cap during launches, cap the maximum adaptive dial level lower, or switch to a gentler dial method like Ratio dialing with a fixed, modest ratio so the burst size stays predictable.

• Set a maximum adapt dial level the campaign won't exceed, so the dialer can't spike during a wave of free agents.
• Prefer a fixed ratio when you need a hard, predictable burst size rather than an adaptive one that climbs.
• Tune your Dialer pacing gradually — drop the level a notch, watch the 503s disappear, and only then push back up if you have headroom.

Spread placement across trunks

If one carrier's CPS cap is your bottleneck, divide the load. Send some calls down one Trunk and some down another, and each carrier sees only its share of the per-second rate. Two carriers at 5 CPS each give you 10 CPS of headroom without straining either.

flowchart TD
  A[Campaign wants to dial fast] --> B{Estimated CPS over cap?}
  B -->|No| C[Place calls normally]
  B -->|Yes| D[Lower max dial level]
  D --> E{Still over cap?}
  E -->|No| C
  E -->|Yes| F[Split load across trunks]
  F --> G[Each carrier under its CPS cap]
  G --> C

Watch and adjust

Throttling isn't set-and-forget. Watch your call logs for 503s and congestion during your busiest periods, not just the quiet ones — the bursts that break the cap happen when many agents free up at once. If you see a spike of rejections at the top of a campaign launch, your peak CPS is too high even if the average looks fine.

A trunk that runs clean all day is worth more than one that dials a fraction faster but burns leads on rejected attempts. Pace for the carrier you actually have.

Where this fits

Throttling is the practical answer to the limit explained in calls-per-second limits and your carrier. Splitting calls across providers is easier when you've already set up multiple carriers with failover. For the full carrier setup and where these settings live, see the VICIdial carrier integration guide.

VICIfast gives you a dedicated box with full control over dial level and pacing — provisioned in under 40 seconds — so you can throttle precisely to whatever your carrier allows. See pricing to spin one up.