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Fibre Channel for Mass Storage by Ralph H. Thornburgh

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3.3. Hubs

Hewlett-Packard’s implementation of FC-AL for a private loop includes a hub. FC-AL hubs connect devices to the loop. It is a simple way to connect participants in a private loop. There are two types of hubs:

  • Passive, which only reacts to ports being inserted into or removed from a loop

  • Active, which are able to do configuration changes dynamically, based on some controlling protocol.

Some hubs can sense or manage configuration changes in the loop, including:

- knowing when NL_Ports are added

- knowing when NL_Ports are removed

- knowing when address changes occur for an entire set of NL_Ports

- switching NL_Ports into or our of a loop

Hubs also provide port bypass circuits to “heal” a loop when a device is removed or fails This allows ...

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