I have a Merlin Legend 6.1 with a 100D card that was connected to an Acculink 3160 CSU/DSU that went bad. I had to replace the card with a new 100-DCD becuause the 100D is no longer in production. I was informed by my distributor as well as Avaya technical support that the 100-DCD card was compatible with 6.1 and that the Legend would just disregard the internal CSU/DSU and I should not have any problems. Everyone seemed to be correct except for one thing - all my analog fax/modem extensions hanging off my 016 cards can not negotiate with other external fax/modems. You can dial the extensions over the T-1 and hear the negotiation process perfectly, as well - you can dial out from the fax/modem extensions and hear the negotiation process perfectly but for some reason they can never complete the handshake. (As a matter of fact, on one of the more expensive fax machines - it complains of poor line quality). These fax machines (4 of them) can call each other as extensions and communicate perfectly so I know that the 016 cards are not an issue and it boils down to the new DCD card. I know there is no magical diagnostic tool to determine what is going on and I'm a little concerned with the answers that I'm getting from Avaya & Distributor. Has anyone heard of this before and what can I do - upgrade?