Background

There are times where it is necessary to delay the out-pulsing of DTMF digits on analog trunks in order to allow the far end equipment enough time to be ready to receive the digits.

Scenario 1

Some analog trunk interfaces provided by PSTN service providers take longer to be ready to receive DTMF digits from customer equipment such as the UCX. When this happens, outbound callers may experience hearing stutter dial tone and hang up believing that the line is busy, or their calls may not complete as dialed since the central office only heard the latter portion of the incoming digits. This scenario is typically true for many older, rural central office facilities.

Scenario 2

Some external paging equipment can accept DTMF digits from the UCX analog trunk interface to identify the intended zone where the paging should be sent. However, the paging equipment may require a small delay after the initial connection before it is ready to receive the digits.

Solution

Step 1 – Configure Inbound and Outbound Routes

Configure the analog trunk inbound and outbound routes following the procedures outlined in Adding DAHDI Trunks and in Configure Analog Trunks.

Step 2 – Update Trunk

1. Go to PBX / PBX Configuration / Trunks page.
2. In the list of trunks presented on the right hand top corner of the page, select the Dahdi trunk associated with the connection to the far end equipment that requires the delay in outpulsing DTMF digits.
3. In the Outbound Dial Prefix field, enter one or more “w” characters. Each “w” will cause the system to delay the sending of the DTMF digits by one half second. Adjust as necessary for the response time of the far-end equipment.
   
4. Click Submit Changes. You may get a warning recommending to define the outbound Caller ID. However analog lines cannot send outbound Caller ID, so click OK.
5. Apply Changes.