AT&T MERLIN LEGEND System Reference Manual page 41

System Overview
1-14 Capabilities
1. Digital-to-Analog translates digital signals to analog signals for data calls
made from a digital data station to an inside or outside analog station. In this
configuration, the ISDN 7500B Data Modules are assigned to a DHG.
Analog-to-Digital translates analog signals to digital signals for data calis
2.
from an analog data station to an inside or outside digital data station. In this
configuration, the modems are assigned to a DHG.
Digital-to-Analog (Outgoing) on Dedicated Outside Lines translates digital
3.
signals to analog signals for data calls from a digital data station to an
outside analog station over analog dedicated outside lines. These lines are
used solely for data communications. In this configuration, the ISDN 7500B
Data Modules are assigned to a DHG.
4. Analog-to Digital (Incoming) on Dedicated Outside Lines translates
analog signals to digital signals for data calls from an outside analog data
station to an inside digital data station over analog dedicated outside lines.
These lines are used solely for data communications.
Configurations 1 and 2 (digital-to-analog and analog-to-digital) use system lines;
therefore, the modems and data modules must be connected directly to the
control unit. Each modem is assigned to a jack on a 012 or 008 OPT module,
and each ISDN 7500B Data Module is assigned to a 008 MLX module jack.
For configurations 3 end 4 (the digital-to-analog or analog-to-digital on a
dedicated outside line), only the ISDN 7500B Data Module connects to the
control unit via jacks on a 008 MLX module.
In all four configurations, a 440A4 terminating resistor is required when the
7500B is connected without an MLX telephone to the control unit.
Local Host Computer and LAN Workstation
Figure 1-4 shows data stations assigned to DHGs to provide access to a Iocal
host computer and a workstation on a LAN.
1. Local Host Computer configuration includes a local host computer and the
modems or ISDN 7500B Data Modules that connect the local host computer
to the control unit.
The modems and data modules are connected to RS232 ports of the host
computer. Each modem is assigned to a jack on a 012 module, and each
ISDN 7500B Data Module is assigned to a 008 MLX module jack.
2. Workstation on LAN configuration includes a data terminal or computer
(workstation) that is part of a LAN and modems and/or ISDN 7500B Data
Modules. The LAN is either an interconnected chain of terminals or PCs that
pass data to and from a mainframe computer or a network of interconnected
computers.
In Figure 1-4, the modems and data modules are arranged in DHGs to allow
a sharing of data communications equipment. Data station users
communicate with the local host computer or the workstation on the LAN by
using the extension number assigned to the DHG.