ring concentrator (TR)
The ring line distributor (RLV) belongs functionally to the group of cable concentrators or workgroup hubs. It is used to connect terminal devices in a token ring network and contains connection positions for a maximum of 8 connectable terminal devices, for which it forms an internal ring.
The devices are connected in point-to-point connections to the ring line distributor, which is also called a Multistation Access Unit( MSAU), and form a star-shaped network topology. The cables connecting the terminal equipment to the ring line distributor are called lobe cables. There are passive and active ring line distributors. The passive ones do not need any power supply, their functions are controlled by the connected terminal devices. A terminal device is only switched into the ring when it triggers the access relay in the ring line distributor by feeding in a DC voltage, which briefly interrupts the ring to admit the terminal device into the ring.
If errors occur at the terminal device or if the supply line is interrupted, the access relay falls back into its idle state due to the missing voltage supply and automatically takes this connection from the ring.
The addition or removal of a terminal device or an error case causes the loss of tokens or frames. These errors are detected and corrected by the token access procedure.
To increase the size of the network, up to 33 ring line distributors can be interconnected to form a ring. The output socket( RO, Ring Out) of one distributor is connected to the input socket( RI, Ring In) of the following distributor.
These connectors are different in operation from the connectors for the end devices. IBM provides two ring line distributors for connecting end devices, the 8228 passive ring line distributor for up to 8 end devices and the 8230 active distributor, to each of which up to four line connection units can be connected. Up to 20 terminal devices can be connected to the Token Ring at each of these connection units.