Dialogic PCI Linecard Installation and Replacement
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Aug 2001 Ericsson Enterprise AB
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Channel Service Unit
The Channel Service Unit (CSU) is usually the first piece of equipment on the customer
premises that connects to the T-1 line. A CSU is required any time metallic T-1 services
are ordered from a local exchange (all the Regional Bell Operating Companies) or
interexchange carrier (including long-distance carriers like MCI, Sprint, and AT&T).
Metallic T-1 uses wire to carry the signal instead of optical fiber or microwave radio. The
CSU connects a DS-1–level line to DSX-1–compatible customer equipment. The CSU
may be a standalone unit or it may be integrated into a PBX.
The CSU provides functions that are critical to the network. It provides loopback
capabilities for running diagnostic tests to locate where problems are occurring on the T-1
chain. Some CSUs have dial-in capability for performing remote diagnostics.
The CSU is the last point where the signal is regenerated as it leaves the network. It also
provides line equalization, provides voltage protection for telephone company and
customer premise equipment, monitors the T-1 line for violations, and generates “keep
alive” signals and error condition messages. (A “keep alive” signal is a bit stream of all
“ones” used to power repeaters in the circuit when there is no activity on the line.)
The CSU that you connect to the D/240PCI-T1 must support Superframe (D4) format.
Digital Service Unit
A Digital Service Unit (DSU) may be installed at some sites. The DSU traditionally
serves to encode user data from unipolar to bipolar format, frame user data, and interpret
some incoming bipolar patterns as network commands. The D/240PCI-T1 performs most
DSU functions. However, it cannot interpret some bipolar violations from the network as
commands to go into (or out of) loopback modes. Therefore, a DSU should be removed
from most sites when using a D/240PCI-T1. Further, DSU functions are generally
integrated into current CSUs.
D/240PCI-T1 Connection to Other Equipment
The D/240PCI-T1 can connect to certain other equipment without the need for an
additional CSU. For example, the D/240PCI-T1 can connect to a T-1 interface on a 4
ESS
(Electronic Switching System) or 5
ESS
telephone system without a CSU, provided that
the connecting cable to these devices is not over 655 feet (approximately 200 meters) in
length. Confirm these specifications with your carrier.
