MiVoice Business 8 with MiCollab 8 for teleworkers.
There is a separate MBG for the SIP trunks.
Both MBGs are at release 10.0
Problem: Teleworker users experience one-way audio part-way during a call. It is intermittent. There are 12 teleworkers and the issue happens once every 1-2 days.
I captured traffic on the SIP trunk MBG and found that, on calls that experience the problem, the service provider changes the RTP sequence number on the incoming RTP stream. The result is that teleworker user don't hear the caller (calling in through the SIP trunks) but the caller can hear the teleworker user. The call starts with two-way audio, but after a minute or so it will turn to one-way audio. It's intermittent. Some calls are fine, others are not and it doesn't matter if its an inbound call or outbound. Inbound and outbound calls have the potential to experience this.
I opened a ticket with Mitel and this is how I learned that the RTP sequence number was changing during the call. I learned how to do an RTP stream analysis in Wireshark and I can clearly see that the RTP sequence number changes even through the SSRC stays the same. Mitel says that the service provider shouldn't be changing the sequence number like that.
During the call, the MiVB sends an INVITE and the service provider sends back an OK SDP. After that the sequence number changes for the RTP stream inbound from the service provider. The RTP stream from the SIP trunk MBG to the TW MBG stops. It stops at the sequence number just before the jump. I only get reports of this happening to TW users. Many report that it happens after they retrieve a parked call. Mitel says that parking and retrieving the call shouldn't matter.
I'm waiting to hear back from the service provider. They don't think that the sequence number changing is an issue, but they opened a ticket with their support.
In the SIP Peer Profile in the MiVB, I disabled the Session Timer and that seemed to help. I used to get reports of this happening 3-4 times per day and now it's once every 1-2 days.
Has anyone experienced something like this? Any ideas or suggestions?
