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Direct In-Bound Fax Routing Utilizing DTMF Tones

Direct In-Bound Fax Routing Utilizing DTMF Tones with Dialogic® Brooktrout® Loop-Start Fax Boards

This document is intended to highlight some system characteristics for implementing a direct inbound fax routing solution using:   
    -  DTMF tones generated by telecommunications equipment; 
    - a Dialogic® Brooktrout® loop-start Fax Board; and
    - a suitable LAN Fax application.

A general outline will be presented, followed by technical details of certain notable features and characteristics for each element of the system. This document is intended for use by VARs and system integrators; however, it may be of use to developers unfamiliar with this method of routing. This implementation often uses features of a PABX and fax application software that were not intended for this purpose, and thus the installation can require a degree of improvisation. Inbound routing using a Dialogic® Brooktrout® BRI-ISDN Fax Board or an analog Fax Board (or, for higher volume situations, a Dialogic® Brooktrout® T1 Fax Board) can provide a faster, more reliable service.

IMPORTANT NOTE: All Dialogic ® Brooktrout® loop-start Fax Boards - including the Brooktrout® TR1034 Fax Boards and RoHS Dialogic®Brooktrout® TruFax® Fax Boards - are capable of performing DTMF routing. However, the enabling and control of DTMF routing is handled through fax application software. Questions about configuring Brooktrout Fax Boards for DTMF routing should be directed to the fax application software provider. The fax application must support inbound routing by DTMF tones; please double-check this with the provider of the software you choose.

'Manual' Sending of DTMF Tones

This option requires extra steps on the part of the person sending the fax, as no telecom equipment is generating DTMF digits to the Brooktrout Fax Board.

1. The sending fax machine dials the number for the Brooktrout Fax Board.

2. The Brooktrout Fax Board answers the call (goes off-hook); typically the fax application instructs the board to play a tone (or, in the case of Brooktrout TR1034 Fax Boards, there is an option of playing a voice prompt) alerting the sender that the fax board is ready to accept DTMF digits.

3. The sender types in the extension of the person to which the sender wants to send the fax; if sending through a desktop fax program, the sender would type in the number followed by a series of pauses so as to allow the call time to reach the Brooktrout Fax Board. The Brooktrout Fax Board would accept the digits, then answer the call and receive the fax.

DTMF Routing with a PABX

1. The sending fax machine dials the number for the Brooktrout Fax Board. 

2. The PABX rings the Brooktrout Fax Board, and plays ringing tone to the sending fax machine.

3. The Brooktrout Fax Board answers the call (goes off-hook).

4. The PABX senses this, and sends down the last few digits of the dialed number as DTMF tones (usually the last 3 or 4 digits of the phone number).

5. The application software collects these digits and looks them up in a table to determine to whom or where to route the incoming fax.

6. The PABX connects the sending fax machine to the Brooktrout Fax Board. 

7. The fax is then received and routed to the correct location.

System Requirements

The PABX should:

- Provide a standard loop-start line for the Brooktrout TR1034 or Trufax Fax Board. Loop-start is often referred to as "POTS", for Plain Old Telephone Service.

- Be capable of assigning a sub-group of numbers to a single port. When any number within the subgroup is dialed, the call is automatically routed to the same port.

- Be able to send down the dialed number, or part of the dialed number to the port as DTMF digits after the call has been answered. This is commonly called 'after-dialing', and is a feature provided for the PABX to communicate with other peripherals, such as voice mail.

- Send the first DTMF digit no earlier than 200ms after the call has been answered by the Brooktrout TR1034 or Trufax Fax Board. This parameter should be programmable, or significantly longer than the 200ms required by the Brooktrout Fax Board, to allow for delays within the application.

Many systems are capable of sending down a pre-defined number of digits, and stripping off any leading digits. For example, a typical system can be programmed to send down the last 4 digits.

Fax Software Developer Note:

If your end user will use a Brooktrout loop-start Fax Board behind a piece of telco equipment (like a PABX) and will have that equipment generate the DTMF tones, then there should be a way in your application to enable tone detection quickly (i.e., immediately after answering the call) on the Brooktrout Fax Board. For example, the Dialogic® Brooktrout® API sequence would be:

- BfvLineAnswer
- BfvToneDetectEnable


See also:
Ordering T1-PRI (Primary Rate ISDN) Service
Ordering T1/RBS Service


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First published: 05-Sep-2008
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