I have a customer who has 3 of these switches stacked in Data Center. He has one switch Nortel 470-48T with 2 GBIC ports which they want to connect to the stack through fiber. The connectivity is not going through due to some reason. We have tried changing the GBIC ports both sides, fiber patch cables too many times but no luck. Is there any interoperability problem between the two switches. Pls help. The customer is having connectivity through copper on another switch for the time being.