Datasheet

1.4 Drive Operation on the Loop
C141-C008 1-29
1.4.2 Arbitration
For information to be exchanged between the ports connected to a loop, generally
the two ports (send side and receive side) must occupy the loop (placed in point-
to-point connection state).
Arbitration is a process to win access right on the loop and must be done before
communicating with another port.
When the arbitration is finished, only a pair of a initiator and a target can
communicate each other on the loop.
The drive supports the method called “Access fairness”.
The process on the port supporting fairness movement is below.
a) If two or more ports request to arbitrate, the port with the highest priority (the
port with smallest AL_PA value) wins the arbitration.
b) The port once won the arbitration cannot participate in the arbitration until
other port wins the arbitration and release the loop.
This method protects that the same port uses the loop consecutively.
1.4.3 Communication between initiator and target
This section shows the figure of the protocol using FC-4 Device Data on Fibre
Channel layer.
The following procedures are followed to send FC-4 device data.
• Issue ARB by which the source of FC-4 device data asserts the occupation of
the loop.
• After occupying the loop, the source issues “Open” to the destination.
• The receiving station responds by R_RDY by the count by which it can
receive FC-4 device data.
• The sending station sends FC-4 device data.
• The sending station sends CLS to terminate the occupation of the loop.
A description of each FC-4 device data follows.