The SONET State Dictionary includes a
certain number of primary states involving changes in the drawing
of the link base.
Although this set of states is independent
of OSI or Bellcore standards, it shares the following common
subset with the following three main states:
Disabled: the facility is Out Of
Service (OOS).
Inactive: the working facility is
in service, carrying No Traffic (NT).
Active: the working facility is
in service, Carrying Traffic (CT).
The other states determine the state of
the link in relation to the usage and state of the protection
facility:
Active and Protecting: the
working facility is carrying traffic and the protection
facility is enabled.
Troubled and Protected: the
working facility is troubled (failure conditions are reported)
and the protection facility is active (the failure conditions
triggered the protection switch).
Troubled and Unprotected: the
working facility is troubled and the protection facility is
unable to protect.