Specifications

December 2008 Page 5–15
Chapter 5. Alternate Path Mode (APM)
5
Case
Number
1
2
3
4
Location and number of
FOCUS Chassis in the
Down/Flipped state
Two adjacent chassis in
the Down state, all other
chassis are in the Flipped
state.
One chassis in the
Down state
A chassis adjacent to
this Down chassis
(chassis 2) is Flipped,
but it first went to the
Down state before
flipping
All other chassis are in
the Flipped state
Three adjacent chassis in
the Down state, all other
chassis in the Flipped
state
Two chassis are in the
Down state, but the XCVR
directions of the Down
chassis are not toward
each other.
FOCUS reason* for
the APM event
Chassis 1
>
T1 Errors
Chassis 2
>
T1 Errors
Chassis 1
>
T1 Errors
Chassis 2
>
Adjacent chassis
Down
Chassis 1
>
T1 Errors or
XID Time-out
Chassis 2
>
T1 Errors or
XID Time-out
Chassis 3
>
T1 Errors
Chassis 1
>
T1 Errors or
XID Time-out
Chassis 2
>
T1 Errors or
XID Time-out
Probable causes
Alow signal, sync error, or yellow alarm
has been detected for a duration of 90 ms
due to:
Broken fiber(s)
Fractured fiber
FOCUS Transceiver Failure
The chassis which remained in the Down
state initiated APM after detecting 90ms
of low signal or out of sync due to:
Single fiber broke (Chassis 1’s
receive fiber)
FOCUS Transceiver problem with
Chassis 1’s receiver components
The middle FOCUS chassis in the Down
state has lost communications with both
adjacent nodes. Here, the failure is most
likely to be at the middle FOCUS chassis
and due to one of these:
Maintenance or FRAMER1Module
failure at the middle FOCUS Chassis
FOCUS Transceiver Pulled or Failed
at the middle FOCUS Chassis
All four fibers from the middle FOCUS
chassis pulled or broken.
This case indicates two separate loop
failures, which most likely occurred during
the same 90–200ms time span. This is
not an APM supported scenario, and
conflicting maps may be present.
*As recorded in the target buffer by the FOCUS chassis in the Down state(s)
Table 5–4. Alternate Path Mode Failure Scenarios.