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@us.ibm.com
http://www-03.ibm.com/servers/storage/