IP Trunk Issue

[inkfid]

Hello,

I have an IP trunk set up between an office in London and an Office in Sydney.
But every few calls seems to fail with Denial Event 1220. From looking at other posts this has generally been related to port issues or firewall but we cannot find anything being blocked.
It looks like the calls only fail when dialling from London to Sydney (approx. 1 in 2 calls work).
Everything seems fine from the Sydney end when dialling back to London. Any suggestions?

 

[nohuhu]

inkfid,

1220 means "recovery on timer expiry". most probably either setup packet from london or return acknowledge packet from sydney got lost en route, so calling system never get an answer and tore down this call due to timer expiry.
i'm afraid that the only way to fix this is to fix the network link.