ANSI INCITS 332-1999 pdf download Information Technology – Fibre Channel Arbitrated Loop (FC-AL-2) Amendment 2
The maximum delay of a Transmission Word through an L_Port in the MONITORING or ARBITRATING state should not exceed twelve (12) Transmission Word periods. See 8.2.2 for maximum round trip latency and annex A for L_Port Elasticity buffer management.
The following steps provide an example for how an L_Port transfers one or more ANSI X3, FC-PH-x frames on a Loop:
(1) The L_Port requests the LPSM to obtain access to the Loop.
(2) The LPSM enters the ARBITRATING state and transmits its ARB(AL_PA) in place of the appropriate received Fill Word (see 7.1) until a matching ARB(AL_PA) is received. When the matching ARB(AL_PA) is received, the L_Port opens the Loop (i.e., stops retransmitting received Transmission Words).
(3) The LPSM transmits OPNy to establish a point-to-point Loop circuit on the Loop with another L_Port. OPNy may be followed by ANSI X3, FC-PH-x frame(s). The number of frames that can immediately be transmitted is based on BB_Credit (see 8.3.4).
(4) Either L_Port (of the Loop circuit) may transmit CLS when the L_Port desires to close the Loop circuit. When an L_Port receives CLS, it completes transmitting its frame(s), retransmits the CLS, and closes its end of the Loop circuit. When the CLS returns to the L_Port that originated the CLS, this L_Port closes its end of the Loop circuit.
NOTE — Since either open L_Port may transmit CLS, an L_Port must be prepared to handle CLS simultaneously with or on the next Transmission Word after entering the XMITTED CLOSE state.
8.1 History variables
8.1.1 Access fairness history
The access fairness algorithm requires four memory elements that shall be maintained and used by each L_Port (see 8.4 for management requirements of each memory element):
a) ACCESS — the value of this variable is used by an L_Port to determine the status of the fairness window (i.e., whether the L_Port may arbitrate for access to the Loop). If ACCESS is FALSE(0), then an L_Port that is using the fairness algorithm, shall not arbitrate for access to the Loop; if ACCESS is TRUE(1), then an L_Port may arbitrate for access to the Loop and the L_Port may use the TRANSFER state to open a Loop circuit with another L_Port.
b) ARB_WON — the value of this variable is used by an L_Port to indicate that this L_Port has won arbitration. If ARB_WON is FALSE(0), then the L_Port did not win arbitration; if ARB_WON is TRUE(1), then the L_Port won arbitration.
ANSI INCITS 332-1999 pdf download
PS:Thank you for your support!
