FCID addressing

Hi,

I need some clarifications on the FCID addressing,

consider the FCID 0x012b00,

Here 01 - Domain id

         2b- is  this a port number or area id, how does this second byte is calculated ?

      I knew that the switch can address only upto 255 ports if the no.of ports in a swtich goes beyond 255 , aread id comes in place.

        00 - mean that it is not connected to any ALPA.