What CHANUNAVAILABLE means and why it's usually a line-count problem

CHANUNAVAILABLE looks like a carrier problem and almost never is one. It means the dialer intended to place a call but did not have a free line to send it on. The call never even reached your carrier — it stalled on your own box for lack of an available channel.

That is the key contrast. CHANUNAVAILABLE is a local line-count limit; the carrier was never asked. Compare it with CONGESTION, where the call did leave the box and the carrier could not place it. Same symptom — calls not completing — opposite cause.

Where the call runs out of road

Every outbound call needs a free Channel on the way to the Trunk. If the dialer is trying to fire more calls at once than there are lines configured, the surplus calls have nowhere to go and come back as CHANUNAVAILABLE. The carrier never sees them.

flowchart TD
  A[Dialer wants to place call] --> B{Free line available}
  B -->|Yes| C[Call sent over trunk to carrier]
  B -->|No| D[No channel to use]
  D --> E[Logged as CHANUNAVAILABLE]
  E --> F{Cause}
  F -->|Trunk channel cap| G[Raise channel count]
  F -->|Dial ratio too high| H[Lower lines per agent]

It comes down to arithmetic. Your trunk has a fixed number of simultaneous channels. Your dialing tries to use a certain number of lines at peak. When the second number exceeds the first, the overflow is CHANUNAVAILABLE.

This is why the problem grows as you add agents. A ratio that fit comfortably with five agents can blow past your channel cap with fifteen, because every agent multiplies the lines the dialer wants at once. The box was sized for the old headcount and nobody resized the trunk when the floor grew. The code shows up gradually, tracking your agent count, which is the tell that it is capacity and not a carrier event.

How to confirm and fix it

1. Confirm the calls never left the box. If the carrier has no record of them, it is a local channel shortage, not a carrier reject.
2. Check the channel cap on your trunk. CHANUNAVAILABLE rising as your agent count climbs means you are hitting that ceiling at peak.
3. Look at your Lines per agent setting. A high ratio multiplied across many agents can demand more simultaneous lines than the trunk allows.
4. Either raise the channel count on the trunk to match peak demand, or lower the dial ratio so you stop asking for lines that are not there. Pick whichever you can change cleanly.
5. Re-run a slice after the change and watch the count. If CHANUNAVAILABLE falls and your connects rise, you sized the lines correctly.

CHANUNAVAILABLE is a sizing problem you own. Match your channels to your peak dialing and it disappears.

For how this sits next to the carrier-side codes, see the troubleshooting playbook. For the carrier-side twin of this problem, read what CONGESTION means. If you would rather not size channels and dial ratios by hand, VICIfast runs the box so you are not chasing line counts on a self-managed install → see plans and pricing.