ADC-2: Topology Auto configuration

[Kevin D Butt]

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ADC WG,
In ADC-2, 6.2.2.3.3 Fibre Channel descriptor parameter format, there is 
defined the topology lock bit.
<<<
A topology lock (TOPLOCK) bit set to one forces the DT device primary port 
to operate only in the mode selected by
the P2P bit. A TOPLOCK bit set to zero indicates the DT device primary 
port may negotiate the topology (see FC-FS).
If the TOPLOCK bit is set to zero in a MODE SELECT command (see SPC-3), 
the P2P bit shall be ignored.
A point-to-point (P2P) bit set to one indicates the DT device primary port 
is configured to operate in point-to-point
mode. If the P2P bit is set to one and the TOPLOCK bit is set to one, the 
RHA bit, LIV bit, and FC-AL LOOP ID field shall
be ignored in a MODE SELECT command. A P2P bit set to zero indicates the 
DT device primary port is configured
to operate in arbitrated loop mode.
>>>
IBM drives have had the option since FC2G devices were implemented, to 
select configurations of N-Port, L-Port, LN-Port, and NL-Port in our 
terminology.  That is, 1) N-Port (force Fabric Topology), 2) L-Port (Force 
Arbitrated Loop), 3) LN-Port (Auto-Configure tryin L-Port or Arbitrated 
Loop first), and 4) NL-Port, (Auto-Configure trying N-Port or Fabric 
Topology first).  There is no way in the ADC to distinuguish between 
LN-Port and NL-Port.
It is IBM's desire to add the capability to distinguish between LN-Port 
and NL-Port to ADC-2.  If FC-AL-2 is strictly followed, a device will 
attempt FC-AL and then, if unsuccessful, fall into OLD_PORT state (i.e. 
port operating as an N-Port).  This would match our LN-Port.  However, it 
is not known that all current implementations interpret the settings this 
way.
The are two possible solutions that I am contemplating proposing:
1) Use the P2P bit when the TOPLOCK bit is set to zero.  If P2P is set to 
one use NL-Port, if P2P is set to zero then use LN-Port.
2) Use a new bit from the reserved bits to indicate NL-Port.
Any comments?
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com