On the web site it says
Cisco X2-10GB-ZR: Supports link lengths of up to about 80 km on SMF. This interface is not part of the 10 Gigabit Ethernet standard but is built according to Cisco optical specifications.
I have a need to connect my 4507 chassis with the X2-10GB-ZR module to a Nortel switch at another site. Can anyone tell me if the Cisco ZR module is standards compliant, Nortel claim theirs to be, but don't want to waste a lot of money on a module that won't communicate ?