OXE to OT SIP going to sleep

[huntsman]

Hi.
I have an OTMS and OXE in a virtual environment, and seem to have an issue with the communication between them if it has not been used for a while. I find that if it is not used overnight, you can try and ring from OXE to OT or visa versa and it comes up congestion. After trying for a few minutes, it comes back to life and keeps going all day without any problems until that night again.
Has anyone else seen this problem or have any suggestions?

thanks.