EXFO FTB-8500 Series for FTB-500 - Manual (Page 161)

Port Tabs
Ethernet and Fibre Channel Application 147
Interface Setup (Fibre Channel)
Buffer-to-Buffer Flow Control

Enable: The Enable check box is forced selected when Login is
selected. The FTB-8500 Series and FTB-8120NGE/8130NGE will send a
Received Ready (R_RDY) automatically after receiving a frame when
the Enable check box is selected.
Note: Since R_RDY are inserted between frames and have higher priority, in
certain condition they may affect the TX throughput.

Available BB_Credit is the number of frame buffers that the remote
port has available to receive frames from the local port. Available
BB_Credit is not editable when either the Enable or Enable login
check box is selected. Choices are from 1 to 65535. The default setting
is 10.
Note: After a Login process, the Available BB_Credit displays the value received
from the remote interface through the login process.
World Wide Name
Only available when Enable Login is enabled.

Source: Enter the World Wide Name source address.

Destination: The destination Worldwide Name will be displayed and
grayed-out after the Login process when Point-to-Point is selected.
Enter the Worldwide name destination address.