Verilink APS 2000 T1 Line Protection (880-502411-001) Product Manual - Manual (Page 44)

Configuration
3-16 Verilink APS 2000 User Manual
While a switch is in process (service transferred to the protection
line), the original working line may be tested either locally or
remotely to verify that the trouble still exists or to ascertain the
nature of the trouble. Since traffic is operating on the protection
line during these tests, no service degradation will occur during
testing of the effected T1 line.
The Normal/Reset mode may be affected by failures of higher
priority T1 lines. If the protection line is not available, either
because it is also failed or because a higher priority T1 line has
failed, any lower priority lines will not attempt to transfer and will
reset automatically to the original circuit if already transferred.
The Normal/Reset control mode may be selected for both working
and protection lines, but is more appropriate for working lines. For
example, if a lightning storm in the middle of night, caused the
protection line to fail when no maintenance personnel were
available to reset it, it would remain unavailable to other lines until
reset in the morning.
Manual switch
mode
The Manual Switch control mode forces an otherwise normal circuit
to switch service to the protection line and remain switched as long
as manual is asserted.
MANUAL need only be selected at one end (either end) of the
system but may be selected at both ends. The end (or ends) where
MANUAL is selected is forced to switch to the spare (within the
constraints of the priority system as discussed above) and sends
the switch code BOP to the far end to force it to also switch to the
spare. This manually forced switch will remain in effect, regardless
of errors or lack of errors, until another control mode is asserted or
the protection line becomes unavailable due to a failed protection
line or failure of a higher priority working line.
The MANUAL mode may be used so that routine testing may be
accomplished on a working T1 line without disrupting service. It
also may be used to eliminate “ping-ponging” of an intermittent
line. If a line is experiencing intermittent error bursts, it may be
desirable to leave it on the protection line full time. Conversely, if
the error bursts are of very short duration, it may be desirable to
prevent the effected line from switching at all so that any lower
priority lines with more severe problems may have access to the
protection line without being intermittently “bumped.” Use the
INHIBIT function, described next, to prevent a line from switching.
Inhibit mode The Inhibit Inhibit Inhibit Inhibit control mode prevents a line from switching to the
spare or restores an already switched circuit back onto its working
line. INH must be asserted at both ends of the selected line to
prevent the possibility of a “half switch.”
INH may be used to prevent a “priority bump.” For example, if
routine testing is to be performed on the priority #2 line, INH
asserted on the priority #1 line will prevent it from bumping off the
priority #2 line in the event of a failure on #1.