DTMF detection is not functional on Norstar system

Owned by Nathaniel Halbrooks
Dec 27, 2023
2 min read

Issue

DTMF detection is not functioning when a local extension calls into a Dialogic 1000 Media Gateway Series (a “DMG1000 gateway”). The user presses keys but the gateway is not registering DTMF digits. External calls routed to the gateway detect DTMF digits without a problem. Any DTMF digits generated by the IP application are heard by the caller without any problems. 

Solution

The issue appears as defined in the diagram below: 

 

Calls that follow the red call path between the PSTN and the gateway allow DTMF detection, but calls following the yellow call path between local extensions and the gateway do not. 

This appears to be occurring as a result of a limitation of the Nortel Norstar key system. Specifically, the Nortel Norstar key systems do not pass DTMF tones between digital station sets. Because the DMG1000 gateway emulates a 7324 digital station set, the PBX is not providing the gateway with in band DTMF tones to detect. This can be reproduced by replacing the DMG1000 gateway with a Nortel Norstar station set and making the same type of call. 

 

Fix\Solution 

At present, there is no PBX configuration change that can be made to permanently address this issue. 
This limitation does not affect IP applications such as IVR systems or voice mail systems that take all their calls from external callers, since the DTMF on external calls always comes across in the voice path. 

Workaround 

Internal callers can make use of the 808 feature code form their phones to force the Nortel Norstar system to inject the DTMF tones in the voice path so they can be detected by the DMG1000 gateway. To do this, the user must press the ‘Feature’ key on its phone and then dial the code ‘808’. 

Several limitations of this workaround are: 

  1. The feature code needs to be entered each time the calling station changes state. If the caller starts out with their phone in speaker mode and then picks up the handset the feature code needs to be entered again. 

  1. This code enables a PBX feature called ‘Long Tones’. This feature forces the PBX to inject the DTMF tones in the voice path for the entire period of time that the user holds down its dial pad button. This means that if the user dials very quickly, the length and spacing between digits can be very inconsistent and in turn can lead to digit detection issues on the DMG1000 gateway. 

Glossary of Acronyms / Terms

DTMF - Dual Tone Multi Frequency

Return to Documentation Home I Return to Sangoma Support