Outbound RTP packets dropped, but only for one user

FreeSWITCH
1

Hi all,

I have an FreeSWITCH problem that I’m unsure where to investigate next. I have a FreeSWITCH instance with 20-30 calls in progress during the day. One particular user has reported that when they make a call, the recipient hears choppy audio. Incoming calls are fine. I can confirm this with a trace - I can see RTP packets coming in from their handset just fine, but FreeSWITCH is transmitting only about a third of those packets on the oubound leg (the trace is captured by a permanently running tcpdump on the FreeSWITCH box). There is no transcoding going on, both legs are PCMA. The customer reports that this happens for every outbound call they make and that ‘it used to work’. Unfortunately I don’t have historical traces going back far enough to find out when the problem started happening.

This doesn’t feel like a load-related issue to me as this is the only customer reporting this issue, and the free CPU % in freeswitch.log is about 85% at the time of the call I examined. Something has clearly changed at some point to cause this behaviour, but I’m at a loss to think what that might be, or what would cause that FreeSWITCH behaviour. The FreeSWITCH version is 1.10.7, running on AWS.

Does anyone have any ideas on where I could look next?

Best wishes,

Martin.

2

Hi Martin,
Its difficult to say without seeing the capture. My initial thought is that it could be that the ptime on the A leg and B leg do not match. That would account for more packets on the A side, and less on the B. It would also help to explain why it is only happening to a single user, as it would make the most sense that something in their set up would be triggering the issue, if all other users are not observing the same thing.

3

@ShaneHarrell-SW That’s a good thought, thanks for that - I’ve checked the ptime and it’s 20 on both legs. I’ve also looked further into the RTP packets themselves - each outbound packet is identical to one of the inbound packets, but (as described above) there are more packets inbound than outbound. So it looks like it’s just packets being dropped and not passed through to the other leg for some reason.

I have a trace, but could I pass it to you privately?