State Machines

The SEC contains a number of state machines, one for each outgoing port. The state machines are driven by incoming messages from the SEC of the neighboring switches or from HECs. The information needed to implement the distributed algorithm remains local to the State Machine at the relevant output port. At any given point in time, each state machines is in one of the following three states:

• Idle State : No establishment procedure is going on. The state machines are ready to initiate new connection establishment procedures.
• Wait_for_Pass2 : The SEC has processed an establish request message for a connection routed through the given output port. It is waiting for the establish reply message. This state machine is locked for subsequent establishment requests; these requests are queued in the Internal Queue of the SEC.
• Wait_for_Pass3 : The SEC has processed the establish reply message and us now waiting for the establish confirm message from the connection source. The state machine is still locked.

At system startup all the state machines are in the Idle state. Depending on the type of message and the connection identifier in the message header, the Dispatcher hands off the received message to the appropriate state machine. For an SEC, the identifying parameter would be the outgoing port of the message while in an HEC, it would be based on whether the host was acting as sender or receiver for that particular connection. The state machine performs the operations of the algorithm and forwards the message to the next daemon. It then sets itself to the appropriate state and returns control to the daemon process.