Fibre Optic cable from the fibre node (basically a junction box) to the cabinet.
IIRC an exchange will start accepting orders once 10 cabinets are fibre enabled. Extra cabs are added as they are commissioned.
Sounds like they still have to lay a fibre connection from the aggregation node to the cab
So is the node my exchange building?
Also do you mean 10 cabinets need to be ready in groups before you can order from each individually?
No and No.
The node is usually in a pit near to the cab.
The exchange is flagged as accepting orders once the first 10 cabs are enabled (IIRC) then single cabs are added as soon as they are commissioned.