Chapter 1. System Overview and Modes of Operation
11
Trunk Processing
When a local alarm, remote alarm, or system failure causes a Carrier Group Alarm (CGA) to
occur, trunk processing removes line cards from service in the D/I Mux III. When the problem is
cleared, service is restored. Disabling CGA is optional on some line cards. Refer to the individual
user manuals for further description of CGA operation with specific line cards.
T1 Interfaces - CSUs
There are three versions of Dual Channel Service Unit (CSU) interfaces available: T1/DSX-1, T1/T1,
and DSX-1/DSX-1. Each CSU provides slightly different options and capabilities for equalizing output
across twisted-pair cable. This process is called line build-out (LBO). This is required to compensate
for the characteristics of the twisted-pair cable so that the correct signal level and shape is received at
the DSX-1.
With the T1/DSX-1 version, LBO is provided on the T1-1 (network) side, and an equalizing network is
provided on the DSX-1 (terminal) side. This version can be used, for example, between a T1-2 network
and a digital PBX.
The T1/T1 version provides line build-outs on both sides as well as on both T1-1 and T1-2 to interface to
T1 carriers. This version is used in drop-and-insert or dual channel bank applications.
The DSX-1/DSX-1 version provides DSX equalization on both sides. This version is for private networks
which require T1 test capabilities. DSX-1 interfaces work well with transmission equipment such as
microwave radios and fiber optic modems.
Lightning Protection
When installed as an option with a CSU interface unit, lightning protection circuitry is included with the T1
inputs and outputs. It protects against high-voltage surges and spikes on the T1 line only; it does not
provide protection on the line card side.
T1 Testing With the CSU
The Dual CSU interface option provides integrated Channel Service Unit functions for the D/I Mux III T1-
1 and T1-2 transmission paths, along with limited test functions.
A Dual CSU interface installed in a D/I Mux III shelf operates in conjunction with the other common
control units to provide the integrated CSU features. The CSU features are provided for both T1-1 and
T1-2 transmission spans, and include the following:
• Test loopback, network loopback, and bypass
• Lightning protection
• T1 span line build-out equalization
• Keep-alive signal (channel bank mode loopback)
• Span power can be terminated, looped back, or sent through the shelf
• Jackfield, for ease of maintenance
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