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The technology for T-1 is moving rapidly. The encoding system and components are not always
upgradable to the newer innovations.
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If the customer application requires maximum network reliability, automatic dialing back-up in case of
digital facility failure could prove costly.
Do GBS Customers Need T-1?
Consider this: a standard T-1 circuit consists of 24 analog voice circuits. The cost of 24 long distance
circuits is more expensive than a T-1. Within the same Central Office a T-1 line is less expensive than the
use of 5-to-7 voice grade lines.
This may also be true where only 2 voice grade lines are involved,
depending on the local traffic. Where fractional T-1 (FT1) is available, the cost break point is even more
favorable.
In fact, some GBS sized customers are losing money by not converting to T-1 service.
With a MERLIN LEGEND CS, a customer can use the T-1 lines as Loop-start, Ground-start or Tie (4-wire
E&M lines). This means the lines can be programmed to emulate, or look like, these facilities. (DID is also
available on T-1 service, but this is not supported on the LEGEND system.) When the 100D module is
programmed for T-1, it can be set to emulate which ever type of tine is needed (GS/LS/Tie - or OPX). The
programming must, however, match the settings for a given line assigned to it by the Central Office.
Complete details for administering the correct T-1 settings can be found in Section 4 (page 4-44), of the
LEGEND system Installation, Programming, and Maintenance Manual (555-410-140).
In order to use T-1 services the LEGEND system is connected to the network by a data communications
device called a Channel Service Unit (CSU). The next section explains the purpose of the CSU and the two
types available. It also covers the use of multiplexers used to increase the efficiency of the T-1 channels.
DATA COMMUNICATIONS EQUIPMENT
This section is an overview of various equipment which is used to enhance the capability of data
communications and or Integrated Services Digital Network- Primary Rate Interface (ISDN-PRI)
operations. The Channel Service Unit is necessary to connect the MERLIN LEGEND system to the Digital
Signal One (DS1) or PRI facility. The Multiplexer is designed for use on large systems where it is
necessary to combine the B channel input into a single digital stream for significant cost savings.
A hypothetical customer has installed a LEGEND system and is subscribing to MEGACOM service to
handle voice traffic. The question is, Which CSU should you order?
The LEGEND system will operate properly on either of the AT&T CSU's identified below. They both can
transmit up to 1.544 Mbps. While the Model 551-T1L1 is the lowest price unit, the ESF-T1 model
provides a more extensive range of features and diagnostic tools. The ESF-T1 should be the unit of choice
if the customer is capable of performing diagnostics on the circuits, and if the network smite will also be
used to transmit data. The 551 model should be used if the transmission speed is 56Kbps and clear
channels are not a primary concern.