ADC-2: Topology Auto configuration

Kevin D Butt kdbutt at
Mon Mar 27 13:15:09 PST 2006

Formatted message: <A HREF="r0603273_f.htm">HTML-formatted message</A>

In ADC-2, 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 
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?
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

More information about the T10 mailing list