Sometimes I can't make inbound calls, just silence, no ring

[ingram]

Occasionally, I can't make inbound calls (calls from the public, to our 3CX system). When you call our number, you just hear silence and nothing ever happens. We can still make outbound calls, and internal calls, you just can't call in. This will last for about 30 minutes, and then start working again. We have a SIP trunk, and I've looked at the 3CX server when this was happening. Everything seemed ok. The SIP trunk status was normal, all the phones were registered, and there were no internet issues.

If I restart the 3CX services, everything starts working again, but I'd like to find out what the actual problem is.
Anyone have any idea, or have you seen something like this before?
Thanks

 

[leejor]

Re: Sometimes I can't make inbound calls, just silence, no r

Since the logs showed everything at your end to be "normal" and I'm assuming that there was no sign of the incoming call, you may have to consider a couple of possibilities.

When calls were silent, were you placing from the same location/ same provider / same device, etc.? if so, and there is something in common, the issue may be at the originating end.

If the silent calls happen from multiple origins, then you may have to enlist the help of your provider in tracing the calls. It is unusual to end up with silence. If the provider isn't able to contact the destination (your 3CX), the caller will usually get some sort of busy signal, a recording, or reach an alternate destination.

 

[lneblett]

Re: Sometimes I can't make inbound calls, just silence, no r

In addition -

Take a look at your VoIP provider requirements. Look at the registration section in particular and take note if they require a registration and if so, when. Many providers do not require a registration and will set 3CX to "registration not required". This will then cause the registration light to constantly indicate a green status which may be somewhat misleading. It could be that the provider is indeed off-line and is unable to handle the call thereby resulting in silence followed by a disconnect sometime thereafter.

While they may not require a registration, that does not necessarily mean that they won't/don't support registrations. I personally want the registrations as it allows me to have some feel for the reliability of the connection and/or provider. If calls suddenly stop I can go and check the trunk registration and if need be, try a manual refresh.

 

[ingram]

Re: Sometimes I can't make inbound calls, just silence, no r

In addition -

Take a look at your VoIP provider requirements. Look at the registration section in particular and take note if they require a registration and if so, when. Many providers do not require a registration and will set 3CX to "registration not required". This will then cause the registration light to constantly indicate a green status which may be somewhat misleading. It could be that the provider is indeed off-line and is unable to handle the call thereby resulting in silence followed by a disconnect sometime thereafter.

While they may not require a registration, that does not necessarily mean that they won't/don't support registrations. I personally want the registrations as it allows me to have some feel for the reliability of the connection and/or provider. If calls suddenly stop I can go and check the trunk registration and if need be, try a manual refresh.

Thanks, I spoke with our provider. They don't support registration. I don't think they were offline, because I can make successful outbound calls when this happens.
I also worked with my provider when the problem was occurring today. I call in, get only silence. They were monitoring the call when it happened. They said it looked like a normal call, but the 3CX server never responded back.

 

[lneblett]

Re: Sometimes I can't make inbound calls, just silence, no r

If indeed the provider was monitoring and the issue was no response back from 3CX, then I would start with the firewalls that are in play; both the hardware firewall facing the internet and the Windows or 3rd party firewall that might be installed on the server. I assume you ran the firewall checker and all was OK?

Restarting the services may only be a mask that causes the firewall to open for the outbound traffic that resulted from the restart. For some period perhaps the port is still open thereby allowing inbound traffic to pass as well. After a while, and perhaps triggered by a lack of activity, the port may close thereby preventing inbound to get past the firewall.

You may want to examine your settings with regard to advanced settings and if you have a fixed IP, set to use that rather than STUN.

You may also end up needing to use wireshark as we don't know at this point if the silence is caused by the SIP message not getting through or if it was the RTP stream, but start at the firewall and make sure that 1) any SIP ALG settings are disabled at the firewall and 2) USE PBX provides audio for the VoIP provider trunk.