Skype for Business with AudioCodes: Prevent disconnected calls

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If you use Skype for Business together with an AudioCodes gateway, there's a risk that calls can get disconnected in the middle of conversations.

If you change a few of the default settings in Skype for Business and AudioCodes, you can avoid that risk.

RTCP is a protocol that controls its sister protocol RTP, which is used for delivering audio over IP networks.

When Zylinc transfers a call to an agent, Zylinc updates the media stream so that the audio is sent directly between the caller and the agent. When that's the case, the RTCP sequence numbers are very likely to change.

In Skype for Business, the settings RtcpActive and RtcpOnhold are enabled by default. Skype for Business uses those settings to detect and terminate inactive calls.

However, when RTCP sequence numbers change, Skype for Business may not adapt. This can lead Skype for Business to wrongly conclude that no RTCP is received, and after 30 seconds it'll disconnect the call.

To prevent this, disable the RctpActive and RtcpOnhold settings in Skype for Business.

Once you've disabled the two settings, enable the session timers in Skype for Business. This will ensure that Skype for Business will still be able to detect inactive calls.

Skype for Business uses silence detection. This means that in order to minimize bandwidth usage, Skype for Business won't transmit any audio when the audio is below a certain level. You can't disable this.

In AudioCodes, a setting called DisconnectOnBrokenRTP is enabled by default. This means that if no audio is received for 15 seconds, the call will be disconnected, and a BYE message will be sent with the following reason header:

Reason: Q.850 ;cause=31 ;text="local, RTP Broken Connection"

This means that if the person who uses Skype for Business doesn't say anything for a period of 15 seconds, AudioCodes will disconnect the call.

To prevent this, disable the DisconnectOnBrokenRTP setting in AudioCodes.