How can I figure out why some of our incoming calls are not getting through?

This is a totally random issue that has come up. When calling in, sometimes the call goes through and sometimes it does not. I seems totally random to me. sometimes 4-5 calls will get through fine, others its one in then one failed. I was told this was a DNS issue but I don’t think that is the case. We have our correct DNS servers in the system and we aren’t having any other problems on the network relating to DNS.

SIP I assume? If so, the best way is probably a packet capture - start one and then keep calling in until you have a failure, stop the capture and look at the call in Wireshark - the sip breakdown should show you what is going wrong.

We are on a PRI if that makes a difference. We have SIP Trunks set up in PBX. It looks to me from the call log that all inbound calls use ZAP/1-1, ZAP/2-1, ZAP/3-1, or ZAP/4-1. I’m far from an expert with phone systems so any help would be great.

The only thing I can think of that has changed was we went from 2 PRI to 1 PRI a few months ago. Could this have anything to do with it? We didn’t make any changes as I was told there was no need by our provider.

Also there is a pretty long delay before we get a ring. This is both internal and inbound. Outbound works perfectly.

Also from from what I can see in the call log, The problem is when more than one call in coming in at the same time.

That is much harder - to really see what is happening you will need a TBerd - a T1 Signal Analyzer - you can ask the carrier, but they will ALWAYS tell you it’s your equipment even when it’s not - you might want to talk to the people who put the system in and see if they have one, or if there is anywhere you can rent one.

Digium paid support can also do some PRI troubleshooting - they did it for me once, but that was years ago, so I don’t know if they still do.

It’s hard because most of the T1/PRI signalling for Asterisk is “Under The Hood” - it’s really hard to see what is going on (and going wrong).

Thank you. You have been very helpful.