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CHANNEL SERVICE UNIT (CSU)
The Channel Service Unit (CSU) provides the interface between the 100D module and the DS1 facilities.
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AT&T models are available for use on the Legend system: the ESF T1 CSU and the 551 T1 L1 CSU.
● Model 551-T1L1
Reg. Number G1 47226819-/DE-N
The 551 T1 CSU is a full-duplex modem, provides data terminal equipment (DTE) with
access to synchronous DS1, 1.544-Mbps lines. The CSU accepts data from the DTE
and transmits it to the serving central office. It also receives signals from the serving CO
and transmits them to the DTE. The CSU has three primary uses:
- To terminate a DS1 transmission system on a PBX
- To ensure that signals entering the public network from the DTE comply
with the transmission system’s requirements as defined in AT&T Technical
Reference 62411 and FCC Part 68 Requirements.
- To provide maintenance, diagnostic. and testing capabilities.
Model ESF-T1 Reg. Number GIC 47216544-DE-N
The ESF T1 CSU harnesses the real-time diagnostic capabilities inherent in facilities using
the Extended Superframe format (ESF), such as AT&T ACCUNET T1.5 Service. This
highly productive diagnostic tool evaluates circuit performance and records performance
data, without service interruptions. The ESF T1 transcodes DID through D4 formatted
signals into Extended Superframe format for transmission at 1.544 Mbps over T1 lines.
The Facility interface Codes for the CSUs are:
●
Digital D4 Framing 4DU9B
●
Digital ESF Framing 4DU9C
●
Digital ESF and B8ZS 4DU95
Note: If a non-AT&T CSU is used on a Legend system, AT&T will not accept the
responsibility for its installation, connection, or testing.
The ESF T1 CSU can connect the DS1 network by using the D4 or extended superframe format (ESF).
Also, it is the only CSU to provide the B8ZS line coding needed to transmit a 64-Kbps clear channel.
The ESF T1 CSU can be mounted in a relay rack or on a shelf as a stand-alone unit. Power can be provided
by plugging the CSU into a 117-VAC outlet.
Installation of the ESF T1 CSU involves setting the switch options. mounting the CSU as needed, and
connecting the wires from the l00D module and the DS1 network. The procedures for installing the CSU
can be found in Section 3 of the Legend Installation, programming and Maintenance Manual.