Technical data

524 Chapter 18
T1 Analyzer
Measurement Results
T1 Analyzer
responsible for equipment beyond this point.
CSU: A customer provided unit that is required by the TELCO as part of the tariffed
service agreement. This device may be looped back applying a specific loop-back
code.
Isolating Faults with Alarm and Errors:
Elements in a T1 facility are subject to failure. The most common failure is due to
inadvertent cable dig-ups. Fault conditions cause errors and errors cause alarms. The
alarms are often remotely monitored and can be observed by test equipment
attached to the circuit. The most common alarm is the Alarm Indication Signal
(AIS), also known as a ‘Blue Alarm’. This alarm can be generated by a network
element that not functioning or is receiving no signal. A CSU that is not receiving a
signal (from the end-equipment) might generate an AIS depending on its
configuration. When the CSU at the distant end sees AIS from the network it
responds by sending a ‘Yellow Alarm’ back to the network. Figure 18-8 shows a
typical circuit layout.
Figure 18-8 (Blue) and Yellow Alarm Diagram
The CSU is a customer-supplied device. The Network Interface Unit (NIU) is
provided by the network supplier. It may be a simple passive device with terminals
or an advanced electronic package such as an optical to copper interface. Some NIU
devices sense the presence or absence of the CSU and, if absent, send a Customer
Disconnect Indication (CDI) toward the network.