Demand Priority
Demand priority has two basic network roles: the requester (client) and the granter (server).
The granter is a centrally located device that evaluates client requests to transmit.
When the granter determines that a request to transmit should be granted, the client is sent a grant signal to transmit on the wire.
Essentially, this is a star-bus network like 100BaseT, but without the collisions. The server is actually a special (and expensive) hub that grants access to the wire based on priority.
Special NICs that support demand priority are also required so this is a relatively more expensive architecture to implement.