Solved Random call/registration failures

[ITSP]

At random times, we suddenly get a flurry of 403 errors resulting in people not being able to call outside

Call or Registration to 02xxxxxx@(Ln.10003@SIP Provider) failed.
sip:203.1bb.1cc.1dd:5060;lr replied: Forbidden (403)

At first, the provider told us it was because of congestion and we had too many calls with all channels occupied. I challenged them on that by logging into their own portal and showing that at the time the error occurred, there were only 5 calls active (we have 15 channels). They said they'll keep monitoring. A month later, they came back and said they couldn't find anything wrong.

We use a username/password to register calls to them and it hasn't changed in 3CX so it can't be because of a bad username/password. Also, what confuses us is that it randomly starts and stops throughout the day. As my telco is useless, anyone have any ideas what else I can do? I could try doing a wireshark but I am hesitant to do so because I think it'll just give me the same error (403 forbidden). But what's causing them to be forbidden won't be indicated.

 

[BrunoI_3CX]

Hello ITSP

A 403 Forbidden response from the provider indicates that the call is being correctly routed to the provider, but the request is being rejected on their side.

To further investigate, we recommend capturing a packet capture while reproducing the issue and sharing it with the provider for analysis. This will allow them to identify the reason behind the rejection.

 

[ITSP]

Just to close this, the telco finally admitted they incorrectly set the wrong number of simultaneous calls for our service (we subscribe to 15 calls and they have configured us for 12).