Verilink 1558D (34-00255) Product Manual - Manual (Page 22)

Operation 3-6 1558D APS CSU/DSU
TEST LED
This LED (tri-color amber, red, green) will indicate when
the DSU portion of the 1558D has been placed in a TEST
state either via remote loop command (V.54, Lp DTE Fac or
DTE Eq) or by placing the front panel manual loop switch
to either the RL or LL positions. The LED will be off when
the unit is not in a test state (no active loops either locally or
remotely). The LED will be ON (yellow when the manual
loop switch is in the LL position). The LED will be On
(yellow) when the manual loop switch is placed in the RL
(remote loop) position. In ð5 seconds, the yellow LED will
change to green if the far-end looped (V.54) or RED if the
far-end did not loop.
Loopbacks
The 1558A unit supports several local and remote loopback
diagnostic capabilities allowing the user to quickly deter-
mine both facility and equipment problems. The types of
diagnostic loops that can be performed by the 1558 unit are:
• Manual Local Loop
• Manual Remote Loop
• Inband CSU Line Loop
• ESF Line Loop
• ESF Payload Loop
• V.54 Equipment Loop
The following sections will describe the operation and usage
of these loops. The reader should refer to Figure 3 on page
3-13 for additional information concerning the location of
these loops.
Local Manual Loop/Unloop
The 1558D unit provides a three position manual loop
switch located on the front panel. This switch allows the
user to initiate either a local 1558D loop or a remote loop of
a far-end 1558D unit.
To initiate a local 1558 loop, simply move the loop switch
from the NORM position to the LL (local loop) position.
The unit responds by; (1) looping back the transmit T1 sig-
nal (Tx towards the facility) back to the receive T1 signal
path (Rx from the facility) and, (2) turns on (yellow) the
front panel TEST LED indicator. Note that the manual local
loop forces a loop condition on both the A and B paths.
Once the loop is activated, any signals coming from the CPE
equipment are looped back to the CPE equipment. If a
BERT test set is attached to the 1558 DTE port, the user can
BERT test and verify the operation of either the A or B path
circuitry by moving the Path Select switch to either the A or
B positions.
To remove the local loop condition, move the manual switch
from the LL position back to the NORM position. The unit
will immediately remove the loops from both the A and B
paths and turn off the front panel TEST LED indicator.
Manual Remote Loop/Unloop
The near 1558D can initiate a manual remote 1558D loop
of a far-end 1558D unit using an industry standard inband
V.54 loop code pattern. To initiate a far 1558D equipment
loop, manually operate the front panel loop switch from the
normal position to the RL (remote loop) position. The unit
responds by performing the following:
1. Generates a V.54 loop pattern towards the far-end unit.
2. Turns on (yellow) the front panel TEST LED indicator
3. The far unit, after detecting the V.54 code for approxi-
mately 2 seconds, will initiate a V.54 equipment loop
(loops DTE port receive data back to send data plus
passes receive data to CPE equipment). See Figure 3.
4. After approximately 2 seconds, the near end unit stops
sending V.54 loop code and begins running a ten second
BERT test.
5. After running the BERT test for several seconds, the
front panel TEST LED indicator either turn GREEN if
the BERT test ran error free or turn RED if the BERT
pattern ran errors. Note that the errors could be caused
either by facility problems or by failure of the far-end
unit to loop.
To deactivate the remote loop, simply move the front panel
loop switch from the RL position back to the normal posi-
tion. The 1558D responds by sending the V.54 unloop pat-
tern to the far-end for approximately 2 seconds, afterwhich
the far-end unit will unloop and the both the near and far
unit TEST LED will turn OFF.
Anytime the 1558D has been manually placed in
a test state, the front panel TEST LED will be on.
Also note that the TEST LED will be on when
either a remote V.54 loop command has been ini-
tiated or when the unit has been commanded by
the 1559 to perform a CPE Equipment loop.
(V.54/CPE Equipment loop).l
Inband CSU Loop/Unloop
The 1558D will respond to industry standard inband CSU
loop/unloop codes. Operation of a CSU LLB (line loopback)
results from the 1558D receiving either a framed or
unframed repeating T1 pattern of (10000) for
≥
5 seconds.
Upon receipt of this pattern for the prescribed time, the
standby path will loop the receive T1 signal (from the net-
work) back to the transmit signal (to the network) and pass
the receive signal to the CPE (see Figure 3). Note that the
1558D will not allow a CSU loop of the active path. Also
note that when a loop is active on a given path, the associ-
ated front panel Loop LED indicator (yellow) will be on.