Bridging Fax Transmissions via TE212P

I have an asterisk box with a dual E1 (TE212P) card between our legacy PBX (Alcatel) and our provider. It is configured to forward all calls from the provider to the old PBX and to route voice calls from the PBX via SIP to a VOIP provider.All calls from the PBX on known fax extensions are bridged to the telco provider.

The problem is that fax transmissions in either way are very unreliable althought they are bridged from one E1 port on the card to the other. Is there any thing I must take care of when bridging? Echo cancelation is turned of and I can’t see any IRQ mises or anything else in the log. ZTTOOL tells me that both ports get there sync source from the telco provider.

Reading through the WIKI I found in (search for Zap and Digium card issues) that it is necesarry to use a “timing cable” for relible fax bridging. What is this “timing cable” and how can it be built or where to get it?

Needless to say that without the asterisk box in the path everything is working fine.

Any help is very apreciated