Seagate Fibre Channel Interface User Manual
Page 54
40
Fibre Channel Interface Manual, Rev. D
Loop Initialization Soft Assigned (LISA)
20-byte payload
The loop master transmits the bit map resulting from the LIHA.
The L_Port checks to see if there are any free addresses left in the bit map by checking for the first available
‘0’. The L_Port sets it to ‘1’. If there are no zeroes in the bit map, all 126 NL_Port addresses have been taken
and the port is not allowed to actively participate in the loop.
The L_Port then retransmits the LISA frame.
Loop Initialization Report Position (LIRP)
132-byte payload
The LIRP and LILP sequences build a mapping between AL_PA values and participating L_Port positions. This
allows all L_Ports to know where all of the other AL_PA addresses are physically located on the loop.
To build this address map, the loop master primes the 128-byte position map with ‘FF’ in each position. The
loop master then sets byte 0 (the “counter” byte) of the position map to ‘01’ and places its own AL_PA in byte 1
and then sends the position map around the loop.
Each port increments the position counter (byte 0) by one and places its AL_PA at the map position indicated
by the counter. For example, the second device on the loop (with the loop master counted as the first device)
increments byte 0 by one to make byte 0 have a value of ‘2’ and then places its AL_PA in position 2 of the posi-
tion map.
Each port retransmits the LIPA frame until the map completes its journey to each of the devices on the loop
and gets back to the loop master. At this point, the LIRP process results in a position map containing the phys-
ical location and AL_PA of every device on the loop.
11050100
16-byte bit map of AL_PAs
Bit position
0
1
2
3
4
5
6
7
8
...
128
AL_PA positions
--
00
01
02
04
08
0F
10
17
...
EF
Switch address
--
7E
7D
7C
7B
7A
79
78
77
...
00
Bit map content
L
1
0
0
1
0
0
0
1
...
0
Example
The L_Port saw that the first ‘0’ occurred in bit position 1, so it
changed that bit to a ‘1’ to effectively select ‘1’ as it’s AL_PA.
First available ‘0’
changed to ‘1’.
11060000
128-byte map of AL_PA physical positions
Byte map content 06 E8 D6 E2 6A 5F 08 FF
...
FF
Example
This example position map shows that there are 6 ports on
the loop. The loop master has AL_PA ‘E8’. The first port after
the master on the outbound fibre has AL_PA ‘D6’ and the last
port on the loop before getting back to the master has AL_PA
‘08’.