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Barracuda Phone System

Detecting Faxes

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The Barracuda Phone System is capable of reliable fax receipt and delivery. It is very important to remember, however, that the ability to send and receive fax messages using the Barracuda Phone System is also determined by network quality and provider support. Local and Public Network problems such as dropped packets, latency, and jitter will significantly affect the ability to properly handle facsimile messages. Telephone Service Provider support is also critical to reliable fax message handling, and one of the most important steps in setting up fax handling is ensuring that the provider fully supports fax messaging.

Use only one fax detection method at any given time in a call flow. Using multiple methods will result in unexpected behavior.

This method listens to an answered call, intercepts the call if it hears fax tones (the CNG tone), processes the fax, and delivers it to an email address. This method listens to an active line, so it requires the call to be answered by another action. This method cannot use a dedicated fax number as it does not answer the call itself, and delivers all faxes to a statically assigned email address.


When a modern analog fax machine seizes a line to place an outbound call, after it dials the destination number it automatically starts to send a CNG tone even when there is ringback from the called party's fax machine. The CNG tone cadence is 1100Hz played for ~0.5 seconds followed by a ~3 second silent period. Fax detect is an option on a call router or via Find Me Forwarding that listens for a CNG tone from a calling party's fax machine. Once the CNG tone is detected, the call is processed as a fax call and delivered via email similar to a Wait for Fax action. The Barracuda Phone System inserts five seconds of simulated ringback tone while it attempts detection of the CNG tone.

If fax detection fails to detect the CNG tone, the call proceeds as defined in the call flow of the advanced call router / Find Me Forwarding. Typically the failure is a result of jitter or packet loss on the link from the ITSP/SIP provider, under/over voltage on an analog trunk or PRI trunk (if equipped), B-channel timing errors/line code violations on a PRI circuit or the calling party fax machine does not support or has disabled CNG tones.

Fax Detection Scenarios

Typical scenarios where fax detection is employed are when you need to conserve DID/external numbers due to cost or technological needs. An example deployment might be:

  • On a 270b or 'a' unit that utilizes analog trunks either via direct hardware connections or via an Analog Telephony Adaptor / Analog FXO gateway. For more information, see Supported Phones and Features.
  • Calls are delivered to an Advanced Call Router that sends voice calls to an Automated Attendant or diverts inbound faxes directly to email if the CNG tone is detected.

Sample Call Flow Utilizing Fax Detection

This section describes an example call flow that utilizes fax detection, including:

  • When a call is placed from the PSTN to (408) 867-5309 during business hours (Monday-Friday 8:00AM-5:00PM), the Barracuda Phone System answers the call from the analog trunk.
  • Send the call to the Advanced Call Router called Main Inbound at extension 200.
  • The calling party hears five seconds of simulated ringback while fax detection occurs.
    • If the CNG tone is detected, the fax is emailed to faxes@example.com. Once the fax is successfully received, hang-up.
  • If the CNG tone is not detected or if it is a voice call, try calling the Automated Attendant at extension 190 called Main Inbound AA.
  • If the calling party does not enter any digits because they are either unable to or unwilling to, transfer the call to the receptionist at extension 150 (Jane Doe).
  • If the call is received outside of business hours:
    • If the CNG tone is detected, the fax is emailed to faxes@example.com. Once the fax is successfully received, hang-up.
  • Send the call to the receptionist's voicemail at extension 150 (Jane Doe).
Step 1. Create an Automated Attendant

For complete details on creating an Automated Attendant, refer to Setting Up Automated Attendants. For this example, the attendant is at extension 190 and is named Main Inbound AA. Ensure that the Repeat value is set to 1.

Step 2. Create a New Advanced Call Router
  1. Navigate to the EXTENSIONS > Advanced Call Routers page.
  2. Click Create New Advanced Call Router in the upper right of the page.
  3. Type the name in the Router Name field (e.g., type Main Inbound).
  4. From the Extension Type drop-down menu, select Single Extension, and then type 200.
  5. From the Default Action drop-down box, verify (New Action Set) is selected.
  6. Type a name for the new action set (e.g., type After hours Callflow).
  7. Click Create.
Step 3. Edit the Call Router
  1. While editing the call router from Step 2. Create a new Advanced Call Router above, click Add a Rule, and then select in the Time/Number Rule column with the conditions Monday-Friday, 8:00AM-5:00PM.
  2. (New Action Set) is already set. Type Business Hours Callflow in the empty Action Set name field, and then click Add.
  3. Click either Manage Action Sets buttons.
  4. Click the row for the newly created action set ( Business Hours Callflow ) . 
  5. Click Create an Action. 
  6. From the Action drop-down menu, select Try Calling an Extension, and then click inside the Extension box to the right and type 190. 
  7. When finished, click Add.
  8. In the Options section, select Detect and Email Faxes. Type in the email address faxes@example.com. 
  9. In the If the call is not answered field in the Final Action section, select Transfer to an Extension or Number and type 150 in the resulting text field that appears.
  10. Navigate back to the previous screen ( Manage Router Action Sets ) using the bread crumbs at the top of the page.
  11. Click on the row button for the default action set (configured in Step 2. Create a new Advanced Call Router, called After hours Callflow).
  12. In the Options section, select Detect and Email Faxes. Type in the email address faxes@example.com. 
  13. In the If the call is not answered field in the Final Action section, select Transfer to a Person's Voicemail, and type 150 in the resulting text field.
Step 4. Configuring the hardware Analog ports
  1. Navigate to the PROVIDERS > Hardware Providers page.

  2. Click the requisite Analog port where calls are to come in from the Central Office.
  3. In the Send To field, type 200.

Frequently Asked Questions about Faxes Received by a Wait For Fax or Detect Fax Action

  1. How long does the Barracuda Phone System retain retained fax messages when the fax is successfully received but not queued for delivery to the mail server?
    • The Barracuda Phone System retains faxes for seven days if the message is not queued by the message transport agent (MTA) on the Barracuda Phone System.
  2. How can I view the faxes if the mail server is misconfigured?
    • You can view the non-delivered faxes in the Call Detail Records page. For each successfully received fax, there is a PDF download link in the Recorded File/Fax column on the far right of the web interface.
  3. Once the inbound fax is delivered to the mail server via Wait for Fax or via Detect Fax, what happens to the fax on the Barracuda Phone System?
    • The fax is deleted from the Barracuda Phone System.


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