Specifications

December 2008 Page 5–3
Chapter 5. Alternate Path Mode (APM)
5
Where xxxx is the chassis address (terminal ID)
of the node which prevented APM to arm, and
yyyy is the reason the node at address xxxx
failed to arm. It will be one of the following:
• T1/E1 Bad
• Inactive Node
•Wrong XID
•Time Out
• Address Mismatch
Refer to Table 5-1 for help in troubleshooting
the problem.
9. Once APM is successfully armed, you can
perform the following test to verify that APM
is working.
Either shut down a chassis serving as a pass
through terminal for the channel module(s)
assignment(s) you have made or disconnect the
fiber receiver at the drop for your channel
module(s). The modules should experience a
momentary loss of communication and then
start communicating again. Look at the status
LEDs on the front panel of the FOCUS
Chassis. The APM FLIPPED status LED
should be on (red LED, left side, third row
from top).
5.1.1.1 Chassis with Two ARMed Loops
A FOCUS chassis with two ARMed loops works
as follows:
When a break occurs in one of the loops, the
chassis will sync into the broken loop and become
a master/slave appropriately. If, before the first
loop is restored, a break occurs on the second
loop, the FOCUS chassis will NOT switch its sync
or mode for the break on the other loop. Thus,
when both loops have a break, sync slips will
occur.
For best synchronization during alternate path
mode, we recommend that you program a chassis
with two ARMed loops as a master and include an
EAST or NORTH in each loop .
5.1.2 How to Disarm a Loop
The APM Loop may be disarmed at any time.
There may be a condition when one node is not
armed, but other nodes on the loop are ARMED
(probably with a status of FLIPPED or DOWN!).
When the disarm command is issued by FCS to
the local node, the command is sent out both sides
of the loop to ensure all nodes get the message,
even if there is a break in the loop.
(For complete instructions on specific FCS proce-
dures, please refer to the FCS online help.)
To disarm the loop:
1. Execute the “APM Disarm” command. Note:
the chassis must be unlocked.
2. After the command is sent, you may verify the
success of the command in one of the
following ways:
a) Receipt of a positive acknowledgment
from FCS.
b) Observing that the APM status LED on
the front of the FOCUS chassis is OFF.
c) The system target “APM Loop 1
Disarmed from Locally” is logged.
d) The APM status of all nodes changes to
“Ready for Arm.”
e) All other nodes on the loop should log the
system target “APM Loop 1 Disarmed
from Remote.”
5.1.3 Installing a New Maintenance
Module into an ARMed Loop
Whenever you install a new Maintenance Module
into a chassis that is part of an ARMed loop,
always follow the procedure below to ensure
proper operation.
(For complete instructions on specific FCS proce-
dures, please refer to the FCS online help.)
1. Pull the old Maintenance Module.
If the Maintenance Module is operational
before you pull it, you should save the chassis
configuration, so that you can download it to
the new Maintenance Module. The goal here