Section 150-441-124
June 12, 1997
Revision 01
Page 40
PairGain Engineering - Plant Series
HiGain HLU-D41
2
Do one of following:
Press the Choice Setup button to initiate an NLOC loopback.
Press the Mode Setup button advance to the next available loopback.
Follow this sequence to initiate the entire battery of available loopbacks. See Table 17 to
identify the loopbacks available for your system. Previously executed loopbacks remain
active until the Choice Setup button is pressed and a different loopback is activated.
24.5
Terminating Loopbacks.
Pressing both the Mode and Choice Setup buttons simultaneously for
three seconds terminates any active loopback, ends the Manual loopback session, and returns the
display to normal mode.
At the initial activation of any of the HiGain loopbacks, the HLU-D41 can
momentarily transmit excessive 0s to the D4 bank. This can cause a 1s violation,
which may cause some banks to momentarily lose sync.
25. Digital Data Service (DDS) NEI Test Access and Control
25.1
The front panel DDS test access jacks, identified as Logic In and Logic Out, provide for high speed
DDS test access. Figure 8 shows the metallic and logic Network Element Interface (NEI) and Office
Channel Unit (OCU) loopback codes as they relate to the HiGain FT1 loopback configuration. NEI
is a DDS in-band loopback. The interface is compatible with a TPI 108/109 RT II or Phoenix test
set, which fractionally provides 64/56 kbps splitting access to the first time slot of the physical slot
where the HLU-D41 is plugged in. Circuit signals are provided at the Logic In and Logic Out jacks,
while clock is provided to the test set by the Office Interface Unit (OIU) in the D4 channel bank.
Near and far access is also provided.
25.2
The HLU-D41 generates DDS control codes in the first DS0 channel of the FT1 circuit when
abnormal conditions occur. For any of the alarm conditions except for LOSW, the HLU-D41 sends
the Mux Out of Sync (0001 1010) code toward the channel bank and sends AIS to the Customer
Interface. When an LOSW occurs, the HLU-D41 is unable to communicate with the FT1 remote
unit and the HLU-D41 sends the Abnormal Station Code (0001 1110) toward the channel bank.
25.3
The HLU-D41 detects the NEI latching loopback code and remotely commands the HRU-512 to
activate its NREM loopback. The latching loopback code sequence can be applied to the HLU-D41
either through its front panel test access jacks or from a DDS test access unit located in the network.
The NLOC loopback can be activated by the OCU latching code sequence.
25.4
DDS Loopback Steps.
The HLU-D41 responds to DDS NEI and OCU latching loop up codes.
Latching loop up codes must be in the following sequence: x = Don’t Care Bit. Use the following
settings to initiate DDS loopbacks:
1
A minimum of 35 Transition In Progress bytes (x0111010)
2
A minimum of 35 Loopback Select Code bytes (x1000001 for NEI, x1010101 for OCU)
3
A minimum of 100 Loopback Enable bytes (x1010110)
4
A minimum of 32 far end voice bytes (x1011010)
The bytes in each group are adjacent.
A 25-second timer is started after using setting 2 above. Loop up is aborted if setting 3 and 4 are not
completed within this 25-second period. To loop down, setting 1 (above) must be transmitted.
