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interoffice trunk issues


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We have two geographically distant, offices both running the same setup:


1- same firewall and same configuration

2- A site-to-site VPN with no restrictions in any direction

3- A PBX running at each location on a windows 2008 server



We created a trunk at each end as a SIP Gateway, each with the far ends internal IP (via the VPN) as their proxy address and have a dial plan sending all calls to each office according to their extension numbering (7xxx and 8xxx respectively)


The issue we have is the following:


1) When office A calls an extension on office B, we get the call through perfectly with good audio and all, but the call is always dropped at around the 2 minute mark.

2) When office B calls an extension of office A, the call goes through and can last hours without any issues.


These happens no matter what extension call or what extension is called.


Any ideas?


Firewall is not an issue (identical equipment and configuration on both ends)

VPN is clean and identical both ends (using Meraki MX90 appliances to do a site-to-site VPN)

all configuration of the PBX is almos identical, expect the extension numbering and local trunks.





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If you can "ping" each server without problems we can exclude NAT and firewall problems. Make sure that both trunks are gateway trunks and their outbound proxy is the address of the other PBX. You might want to specify the IP addresses of the other PBX in the "explicitly specify..." so that there is no mistake where packets are coming from (this makes it hard to register phones from the remote site in case that is an issue).


If the call gets dropped after 2 minutes check what IP address the PBX puts into the 200 Ok message for the INVITE. Maybe it puts the wrong IP address there and then the ACK does not make it. Also check who terminates the call. Is there a BYE message being sent? Maybe check the log. Who knows, maybe you have limited the call duration on the trunk or something.

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