150-402-102-01, Revision 01
Appendix A: Additional Technical Information
HRU-402 List 2
July 27, 1998
51
The simplex sealing current flow is blocked if it is used with HDU-451 List
1, 2, 3 or 3B doublers. These doublers are only compatible with the metallic
sealing current of earlier remote units. To provide a path through which the
simplexed sealing current can flow, the following doublers must be used with
the HRU-402 List 2:
•
HDU-451 List 4, 4B
•
HDU-437, HDU-439 List 1 or 1B
•
HDU-409, HDU-404, and HDU-407
Loopback Design Description
Loopbacks permit you to perform isolated diagnostic tests at specific points
of the circuit. The transmitted signal is returned to the sending device after
passing through a data communications link or network. This allows you to
compare the returned signal with the transmitted signal and to determine if
there is a problem with the circuit. Ideally, personnel performing loopback
testing are in direct communication with each other in order to correlate
messages displayed at both the HRU and HLU during the test.
The HRU-402 List 2 supports four types of loopbacks (
).
•
Network Remote (NREM): The DSX signal is looped back to the DSX
at the HRU.
•
SmartJack (SMJK): Loopback at the HRU towards the network initiated
by a 2-in-5 in-band loopback code or out of band ESF facility data link
(FDL) code.
The SmartJack loopback shown in
is the standard NID metallic
loopback. It has two modes of operation as determined by the SAIS user
option settings at the HLU (ENA or DIS). The ENA option causes the
HRU to transmit the AIS signal towards the CPE. The DIS option
transmits a quiet signal to the CPE. To send the AIS pattern to the CPE
during SmartJack or NREM loopbacks, set the SAIS to ENA before the
loopback is initiated.
•
Customer Local Loopback (CLOC): Signal from CI is looped-back to
customer at HRU-402 List 2.
•
TLOS: Initiated by a DS1 LOS condition at the HRUs DS1 input port if
the TLOS option is enabled.
