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Routine Maintenance Procedures
555-233-123 5-70 Issue 4 May 2002
Configurations Using Fiber Multiplexers
Use the loopback jack when customer premises DS1 wiring connects to an on-site
fiber multiplexer (MUX) and allows wiring to the network interface point on the
MUX to be remotely tested. This requires that ICSUs be used on DS1 wiring to the
MUX.
Fiber MUXes can take the place of Interface termination feeds as shown in Figure
5-11 on page 5-64 , Figure 5-12 on page 5-65 , Figure 5-13 on page 5-66 , and
Figure 5-14 on page 5-67 . Test these spans using the same procedures as
metallic spans. Note the following points:
1. Fiber MUXes may have loopback capabilities that can be activated by the
service provider from the CO end. These may loop the signal back to the
CO or back to the DS1 board. If the MUX provides the equivalent of a line
loopback on the “problem” DS1 facility, this may be activated following a
successful loopback jack test and used to isolate problems to the wiring
between the loopback jack and the MUX.
2. Be aware that there are installations that use repeatered metallic lines
between the MUX and the “dumb” block. Theses lines require DC power for
the repeaters and this DC power is present at the “dumb” block interface to
the CPE equipment. A loopback jack is required in this configuration to
properly isolate and terminate the DC power.
To check for the presence of DC, make the following 4 measurements at the
network interface jack:
1. From Transmit Tip (T, Pin 5) to Receive Tip (T1, Pin 2)
2. From Transmit Ring (R, Pin 4) to Receive Ring (R1, Pin 4)
3. From Transmit Tip (T, Pin 5) to Transmit Ring (R, Pin 4)
4. From Receive Tip (T1, Pin 2) to Receive Ring (R1, Pin 4)
All measurements should read 0 (zero) volts DC. For pin numbers and pin
designations, refer to Integrated Channel Service Unit (ICSU) Installation and
Operation, 555-230-193.
Operating Characteristics
If a TN464F or TN767E and a 120A2 were installed in a system running pre-G3V3
software and the software is later upgraded to G3V3 Release 3 or later, reseat the
DS1 circuit pack so that the ICSU administration fields will appear on the DS1
administration form.