Dropped calls - looking for some help/ideas

[Allen_Miller]

I'm on my continuing education journey here.
I've got a customer that is experiencing dropped calls. This is not happening on all calls. Just using one SIP trunk provider for this customer.
PBX is on premises and behind a firewall. Firewall checker passes all tests.
I have swapped the firewall with a second firewall and getting the same results.
I have gotten the provider to show me their pcap for a sample problem call and we compared it to my pcap.
I can see where they are sending ACK after receiving 200 OK.
However, my capture (run from pbx machine) is not showing ACK, it just keeps repeating 200 OK and eventually the call gets dropped.
Let me interject that I have just exhausted my knowledge of this level of the communications.
If someone of you has some pointers I would really appreciate it.
Allen

 

[eddv123]

Hi,

Please confirm your setup and network topology in more detail. I have known dropped call issues in the past to be related to lack of bandwidth or QoS related issues so please confirm you have enough bandwidth to support your System call count.

Also check your PCAP trace, another time I saw dropped call issues it was Provider related. If this is only occurring with one provider this is your most likely cause.

Check in the PCAP if you are getting a "403 Forbidden" from your Providers IP address as you would normally see something like this if it was a Provider problem.

 

[YiannisH_3CX]

Hello @12494

From your description it sounds like the calls drop because the PBX does not receive an ACK which causes the call to drop after 32 seconds. If the provider sends the ACK message but it never arrives to the PBX then it could mean that something between you and your provider is blocking the signalling. Make sure that in the captures you are looking the call id is the same and you are looking at captures for the same call. You could also check the port and IP the ACK is sent to in case the signalling is sent incorrectly.

 

[Allen_Miller]

Update:
On about 1% of calls provider sends ACK but it does not get received by PBX. PBX sends another 200 OK but provider refuses to respond to these. Eventually call times out and disconnects. Provider (Vitelity) confirms that they do not follow the RFC on this and that they do not plan to change any time soon.
We have changed the SIP routing from UDP to TCP and so far it looks like we are not dropping calls.