Verilink APS 2000 T1 Line Protection (880-502411-001) Product Manual - Manual (Page 73)

Diagnostics
Verilink APS 2000 User Manual 5-9
T1 and DSO Loopback and Test Functions
The Craft interface provides for selection of various loopback and
test modes. These functions may also be controlled via SNMP.
Loopbacks may be accomplished for either the aggregate T1 signal
or for a portion of a T1 (one or more DSO channels). Test patterns
may be sent in, and extracted from, either the entire aggregate T1
bandwidth or in one or more DSO channels on a drop and insert
basis. This section describes the various loopback and test modes.
Figure 5-6 CSU Loopbacks
All of the following loopbacks activate the LED indicators on the
CSU front panel.
Local Loopbacks Local loopbacks include the Payload Loopback (PLB) and the Line
Loopback (LLB).
T1 Payload
Loopback (PLB)
This command causes the T1 payload (exclusive of framing bits,
CRC bits and FDL bits) to be looped back toward the far end when
asserted at the near end of a circuit. It also automatically forces
both ends of a circuit to switch to the protection line so as not to
disrupt traffic. Because the APS communication channel is not
looped back (since it is carried in the ESF FDL bits), the APS
functionality does not recognize the loopback condition
automatically. For this reason, the payload loopback command also
asserts the MANUAL APS control mode in order to force a switch.
When the payload loopback function is turned off, the APS control
mode reverts to whichever control mode it was in prior to the
payload loopback state.
Line Loopback
(LLB)
This command causes the entire T1 signal (including framing bits,
CRC bits, and FDL bits) to be looped back toward the far end when
asserted at the near end of a circuit. The APS functionality
recognizes its own unique network code on the ESF FDL and forces
a switch to the protection line. The APS control mode currently in
effect will operate normally while the circuit is in the LLB state.
CSU
Signal
Processing
Circuits
To/From
DS-1
Equipment
ELB PLB LLB RLB
Repeate
To/From
Networ
LBO