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Chapter 1: Features of the Fibre Channel Hub
Fault and Error Management
The digital architecture of the Fibre Channel Hub eliminates all signal jitter and provides
automatic clock speed matching on every port. As a result, two hubs can be cascaded,
providing flexibility in network design and extending potential cabling distances.
Fibre Channel Hub error management improves the reliability and availability of fibre
channel arbitrated loops by isolating faults that could damage the rest of the loop, and
correcting error conditions that could cause loop downtime.
•
Loop initialization procedure (LIP) F8 bypass isolates faulty nodes, allowing the
loop to operate normally while cabling problems and other errors are diagnosed
and corrected. LIP F8 character streaming is described in greater detail in
“Automatic LIP F8 Word Substitution and Bypass.”
•
Synchronous cut-in and cut-out ensure that only complete words are forwarded
through the hub. Character integrity control ensures that only valid Fibre Channel
words are forwarded through the hub. Thus, recovery issues in remote devices are
avoided.
•
Automatic LIP insertion notifies all loop participants when nodes are added or
when active loops are combined. Automatic LIP insertion is described in greater
detail in “Automatic Loop Reconfiguration” on page 13.
Automatic LIP F8 Word Substitution and Bypass
If a hub port receives three consecutive LIP F8 primitive sequences from an attached
device, the port automatically enters bypass mode.
LIP F8 sequences slow the loop or make it nonfunctional. However, by default, the Fibre
Channel Hub automatically bypasses a port that is streaming LIP F8 characters. The
port’s status is shown as auto-bypass in the Hub Port Status screen and in the output of
the
show port
command.
When LIP F8 bypass occurs, the hub transmits LIP F0s and IDLEs to keep the loop alive.
Thus, LIP F8 sequences do not enter the loop.
The attached device is determined to be functional again when the LIP F0 sequence can
be propagated. When the device no longer sends LIP F8 sequences and the port receives
valid data again, the hub software reinserts the port into the loop by sending LIP F7 F7.
