Seagate Fibre Channel Interface - Manual (Page 378)

364 Fibre Channel Interface Manual, Rev. D
Arbitrated loop topology
A topology where L_Ports use arbitration to establish a point-to-point circuit. A configuration that allows multi-
ple ports to be connected serially.
Attenuation
The transmission medium power loss expressed in units of dB.
Available BB_Credit
Also called “Available buffer-to-buffer credit.” A transmitter uses this variable to determine permission to trans-
mit frames, and if so, the allowable number of frames to transmit. The transmitter may transmit a frame when
the Available BB_ Credit value is greater than 0. The rules for modifying Available BB_Credit are:
(a) in an OPN Initiator, Available BB_Credit may be initialized to a value less than or equal to the
Login_BB_Credit of the OPN Recipient upon transmission of any OPN;
(b) in an OPN Recipient (acting as a Sequence Initiator), Available BB_Credit may be initialized to a value
less than or equal to Login_BB_Credit of the OPN Initiator (acting as a Sequence Recipient) upon receipt
of a full duplex OPN;
(c) Available BB_Credit is decremented upon transmission of a frame;
(d) Available BB_Credit is incremented upon receipt of R_RDY, except that following an OPN to or from a
Sequence Recipient with Login_BB_Credit>0, one R_RDY is discarded for each frame sent until the num-
ber of R_RDYs discarded equals the Login_BB_Credit value.
Available_receive_buffers
In class 3, the number of buffers in a receiving port which are available for receiving frames at link rate. Equal
to the largest number of R_RDYs an NL_port can issue immediately upon transmission or receipt of an OPN.
BB Flow control rules keep this number greater than or equal to the Available BB_Credit variable in a transmit-
ting port. The number of available receive buffers must be greater than or equal to Login_BB_Credit upon
receipt of any OPN.
Bandwidth
Maximum effective transfer rate for a given set of physical variants such as communication model, Payload
size, Fibre speed, and overhead specified by FC-PH.
Base address
The address of the lowest address byte to be transferred to or from an application client buffer.
Baud
The encoded bit rate per second.
BB Credit_CNT
Buffer-to-buffer Credit_Count.
BB_buffer
The buffer associated with buffer-to-buffer flow control.
BB_Credit
Buffer-to-buffer Credit.