Verilink APS 2000 T1 Line Protection (880-502411-001) Product Manual - Manual (Page 10)

Overview
1-2 Verilink APS 2000 User Manual
Theory of Operation
Protection
Groups
An APS Protection Group is comprised of a T1 protection line and n
working T1 lines.
T1 Prioritization To eliminate the possibility of cross switches, switching priority is
built into the APS 2000 system.
Prioritization ensures that, during multiple line failures, both ends
of the same line switch to the protection line. That line will be the
failed line with the highest priority, as determined at the time of
installation.
If a lower priority line has switched to the protection line and,
subsequently, a higher priority line fails, the lower priority line is
“bumped” back onto its original line, which is forced to carry
service as best it can. By definition, the protection line has the
lowest priority and cannot be switched if it has failed.
Figure 1-1 Prioritized sequence of CPEs = 1, 2, 3, 4
The priority system may also be overridden for maintenance
purposes by placing higher priority lines in the Inhibit control
mode. Then lower priority lines can access the protection line.
Switching
Criteria
There are four types of abnormalities which may cause a working
line to switch to the protection line. These criteria are:
• Errors and alarms
• Abnormal network codes
• Switch code
• Removal of the CSU module
CPE 4
CPE 3
CPE 2
CPE 1
CSU 4
CSU 3
CSU 2
CSU 1
APS 2000
Protection
CSU
#4
#3
#2
#1
Switch Circuit
Protection
Circuit
in
in
in
in
out
out
out
out
T1 #4
T1 #3
T1 #2
T1 #1
T1 Protection Line
Low Priority
CPE