The Zinwave Unitivity 5000 Transport Module creates a fiber link between two cascaded Primary Hubs. While it looks like an Optical Module, it’s built to also act like a Service Module to pass the service connection between the Hubs.
A pair of Transport Modules is required for the setup; one hooks up to the front of the first Primary Hub while the other hooks up to the back of the second Primary Hub. Up to 8 Transport Modules can be installed in the front of a Primary Hub, or up to 4 in the rear. Transport Modules cannot be installed in both the front and rear of the same Primary Hub.