Our fax is done over VoIP, and today it was brought to my attention that the fax was not working. So in checking it out, I discovered that there was no issue with the line; Off-hook worked fine and I heard a dial tone, the number was dialed, a connection to the other machine was established, yet when it came time to transfer any data the line would go dead and after a ~15 second wait, the fax would give a message of trying to re-send.
Looking in our PBX's log, I can see that the "call" was properly established, and the fax line is Active.
Has anyone else seen this type of issue?