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We ran into issues with our hosted conference bridges where calls were dropped, or conference participant lost audio and assumed the call was dropped, audio was interrupted but restored, participant heard fax tones, or conference system barged in with operator assistance or played menu option. I thought I would pass on our pain to hopefully help you from experiencing the same.
Issue 1: Conference participants were being dropped from conference calls, or losing audio and thinking they were dropped, losing audio and then regaining audio on the bridge, or hearing fax tones.
Issue 1 Cause found: The default notification tone for iPhone called "Note" plays a 2100Hz tone, the same frequency as a CED tone for faxing and modems. Callers that are connected from PBXs and systems that are listening for fax tones interpret this tone as a sending fax machine attempting to establish a connection and a T38 invite is created. The systems try to negotiate on T38 and the following was found:
1) the PBX would reject the received T38 invite and due to timing of trying to renegotiate the audio session fails and the PBX disconnects the call
2) the PBX would reject the received T38 invite and renegotiation back to the audio session is successful and audio is restored for the participant
3) the PBX would receive CNG and it would play on the participant's call, where this was in the RTP stream and nothing replies the audio continues after the CNG plays.
Here is the iPhone tone:
Here is a 2100Hz fax CED tone at 9 seconds:
Here is just a 2100Hz tone:
Apparently it can cause issues with regular calls as well, which makes sense, check out this guy's video
Issue 1 Solution: This is Avaya's solution for this issue:
Issue 2: The conference provider's system barges into the call and announce that you were being connected to the operator for assistance, or list all the DTMF controls (code for muting participants, locking the bridge, muting yourself, etc).
Issue 2 Cause found: The conference bridge interprets the default notification tone for Windows for new mail for Microsoft Outlook as a * press, for our provide 2 successive * tones close enough together invokes the conference bridge to provide a list of DTMF options. The default Verizon Android notification tone is interpreted as DTMF for *0, which, for our provider, invokes the request for operator assistance on the bridge.
Solution for issue 2: Unfortunately, this can only be resolved by the participants on the call by muting their PCs and their cell phones. There is no way to stop this from happening if these tones are played.
- Stinney
“The man who asks a question is a fool for a minute, the man who does not ask is a fool for life.” - Confucius
Issue 1: Conference participants were being dropped from conference calls, or losing audio and thinking they were dropped, losing audio and then regaining audio on the bridge, or hearing fax tones.
Issue 1 Cause found: The default notification tone for iPhone called "Note" plays a 2100Hz tone, the same frequency as a CED tone for faxing and modems. Callers that are connected from PBXs and systems that are listening for fax tones interpret this tone as a sending fax machine attempting to establish a connection and a T38 invite is created. The systems try to negotiate on T38 and the following was found:
1) the PBX would reject the received T38 invite and due to timing of trying to renegotiate the audio session fails and the PBX disconnects the call
2) the PBX would reject the received T38 invite and renegotiation back to the audio session is successful and audio is restored for the participant
3) the PBX would receive CNG and it would play on the participant's call, where this was in the RTP stream and nothing replies the audio continues after the CNG plays.
Here is the iPhone tone:
Here is a 2100Hz fax CED tone at 9 seconds:
Here is just a 2100Hz tone:
Apparently it can cause issues with regular calls as well, which makes sense, check out this guy's video
Issue 1 Solution: This is Avaya's solution for this issue:
Issue 2: The conference provider's system barges into the call and announce that you were being connected to the operator for assistance, or list all the DTMF controls (code for muting participants, locking the bridge, muting yourself, etc).
Issue 2 Cause found: The conference bridge interprets the default notification tone for Windows for new mail for Microsoft Outlook as a * press, for our provide 2 successive * tones close enough together invokes the conference bridge to provide a list of DTMF options. The default Verizon Android notification tone is interpreted as DTMF for *0, which, for our provider, invokes the request for operator assistance on the bridge.
Solution for issue 2: Unfortunately, this can only be resolved by the participants on the call by muting their PCs and their cell phones. There is no way to stop this from happening if these tones are played.
- Stinney
“The man who asks a question is a fool for a minute, the man who does not ask is a fool for life.” - Confucius