DS1/T1 CPE loopback jack
555-233-116
156 Issue 4 October 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 in terface point on the
MUX to be remotely tested. For a G700 Media Gateway, this requires that the
MM710 CSU be set so it can be used on DS1 wiring to the MUX.
Fiber MUXs can take the place of Interface termination feeds as shown in
Figure 24 through Figure 31. Test these spans using the same procedures as
metallic spans. Note the following points:
1. Fiber MUXs may have loopback capabilities t hat can the service provider
can activate from the CO end. These may loop the signal bac k to the CO or
back to the DS1 board. If the MUX provides the equiva lent of a line
loopback on the “problem” DS1 facility, activate it after a successful
loopback jack test, and use it to isolate problems to t he wiring between the
loopback jack and the MUX.
2. Be aware that there are installations that use repeate red metallic lines
between the MUX and the “dumb” block. These 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, P in 1)
3. From transmit tip (T, Pin 5) to transmit ring (R, Pin 4)
4. From receive tip (T1, Pin 2) to receive ring (R1, Pi n 1)
All measurements should read 0 (zero) volts DC. F or pin numbers and pin
designations, refer to Integrated Channel Service Unit (I CSU) Installation and
Operation.