Chak,
"Special Cable"
I actually haven't seen one in a while. I work in our Remote Services Center servicing our Mitel product line so there isn't much need for me to touch one.
In the original 3300 controllers, if you wanted to statically set the IP address of the E2T card you had to remove one of those round metal plugs in the bottom of the controller and connect to it with a special DB9 to DIN (round end connector). From there you talked to it like you would the RTC.
We've only ever had a couple of customers that needed to set a static IP on the E2T so we only had a couple of cables that floated around with the field techs.
Ralph