A unique value for each PORT within a given SMT.
Its value ranges between 1 and the sum of the
values of snmpFddiSMTNonMasterCt
{ snmpFddiSMTEntry 6 } and snmpFddiSMTMasterCt
{ snmpFddiSMTEntry 7 } on the given SMT. The
value for each PORT must remain constant at least
from one re-initialization of the entity's network
management system to the next re-initialization.