Verilink T1 ESF CSU (34-00309.B) Product Manual - Manual (Page 20)

8 T ESTING
Network
Position SW1-6 sets network loopback functions. NET LOOP
can be set to Auto or Manual. “Auto” enables the unit to respond
to network loop requests (a 1-in-5 pattern) and remain looped
until it receives a 1-in-3 pattern. Setting the switch to “Manual”
forces the unit into a manual network loopback until the switch
is returned to Auto or loopdown code is received from the
network. The unit sends an unframed all ones pattern to the
equipment end unless the equipment is also in loopback.
Figure 3-2 Line or CSU Loopback
The following paragraphs describe other loops that may be
initiated on the unit. Refer to the looping diagrams below for
further information.
CSU Inband LLB: Each unit can be looped remotely by
generating towards it a standard CSU line loopback code (00001
repeating for
≥
5 seconds, framed or unframed). Once looped,
the received signal from the T1 facility (NET IN) is regenerated
and transmitted back to the T1 facility (NET OUT).
CSU Inband Unloop: Each unit can be unlooped remotely by
generating towards it a standard CSU line unloop code (001
repeating for
≥
5 seconds, framed or unframed).
T1.403 LLB: The unit supports the T1.403 line loopback
command (the FDL LLB format is 00001110 11111111). Once
looped, the received signal from the T1 facility (NET IN) is
regenerated and transmitted back to the T1 facility (NET OUT).
T1.403 LLB Unloop: The unit supports T1.403 FDL line
loopback unloop command messages (00111000 11111111
repeating).
T1.403 / 54016 PLB: The unit supports T1.403 FDL payload
loopback command messages (00010100 11111111 repeating).
Figure 3-3 Payload Loopback (with Frame and CRC
regeneration)
Equipment Network
AIS
Equipment Network
AIS
CRC
FRAME