How VICIdial Detects Fax Machines and What to Do

Fax machines still answer outbound calls, and a fax tone is no good to anyone on your team. VICIdial can identify a fax answer during detection so you handle it automatically instead of routing screeching tones to an agent. Fax detection (Fax detection) is part of the broader call progress detection (CPD (call progress detection)) picture, sitting alongside answering machine detection (AMD (answering machine detection)).

How a fax answer gets flagged

When a call is answered, the detection step classifies what is on the line: a human, an answering machine, a fax, or another outcome. A proper call progress engine separates a fax answer from a human one, which Asterisk's basic AMD cannot always do on its own. Engines like the Sangoma and KHOMP gateways classify fax answers directly, and VICIdial records that result so you can act on it.

That classification then lands in a Status (lead status), which keeps a fax out of your live-contact numbers and out of an Agent queue. The built-in Asterisk AMD is mostly tuned to tell humans from answering machines, so a clean fax category is one of the clearer wins you get from a dedicated call progress engine. If your lists never contain fax numbers it may not matter, but most outbound data has a few hiding in it.

Hanging up faxes automatically

The cleanest action for a fax answer is an immediate hangup. Inside the AMD Agent Route Options settings container there is a FAX-Hangup-ENABLED option that triggers an immediate hangup on calls detected as fax. There is a matching FAS-Hangup-ENABLED option, and a NOAUDIODATA-Hangup-ENABLED option for calls that arrive with no audio data at all. Turning on FAX-Hangup means a detected fax drops right away instead of tying up a line.

flowchart TD
  A[Call answered] --> B{Detection result}
  B -->|Human| C[Route to agent]
  B -->|Machine| D[Play message or hang up]
  B -->|Fax| E{FAX-Hangup enabled}
  E -->|Yes| F[Hang up immediately]
  E -->|No| G[Log fax status]

With the gateway-based engines, a fax answer can also feed the CPD AMD Action handling, where DISPO can disposition and hang up the call before it ever reaches an agent. Either way, the goal is the same: no human hears a fax tone, and no fax counts as a real contact.

Why bother flagging faxes

• Cleaner reporting: a fax never inflates your live-answer count.
• Better agent experience: nobody picks up a call only to hear tones.
• Smarter retries: a fax-coded Lead does not get dialed like a missed human.

On lists that came from web forms or old databases, fax numbers sneak in more often than you would expect. Letting detection catch and drop them keeps your dialing focused on numbers that can actually convert. It also protects your reporting from a quiet form of inflation: without fax handling, a fax answer that counts as connected makes a list look more responsive than it is, and you keep retrying a number that will never become a sale.

One caution: do not enable the immediate-hangup options blind on day one. Run with fax results logged for a short while first so you can see how often faxes really show up on your data and confirm the engine is calling them correctly. Once you trust the detection, turn on FAX-Hangup so those calls drop the instant they are identified rather than after a person has already been bothered.

Where this fits

Fax handling lives inside your AMD and CPD routing, so it helps to understand the engine first. See how VICIdial AMD detects machines and the full AMD and CPD complete guide for the surrounding settings.

We tune fax and machine handling so your agents only ever talk to real people. See VICIfast pricing to get detection set up the right way.