Instruction manual

Data Services Overview
b. ASCII Data Terminal With Keyboard
This category can be subdivided into two classes: (1) basic terminals, and (2)
intelligent, programmable data equipment such as personal computers. Basic
terminals appear to the data port to be on-line and available whenever they
are turned on, thus ready to enter either the Data Terminal Dialing mode. or
to enter the Setup mode on calls originating from a voice terminal or on
auto-answered calls.
In the case of most personal computers, a communications program must be
executed in order for it to communicate with its own RS-232 port or built-in
modem. Once the communications software is running, further operation will
be similar to that of the basic terminal.
c.
Host Computer Endpoint
A host computer endpoint is very similar to a data endpoint with keyboard
except that the host has many ports and the interface is usually capable of
supporting multiple speeds and more of the RS-232 control signals. Front-
end communication software running in the host is typically supplied by the
computer vendor and is not designed to support the Data Terminal Dialing
feature. Such software typically supports call origination through Automatic
Calling Units (ACUs), which are not compatible with Data Terminal Dialing.
Thus, the primary means of communicating with the host is by calling from
data terminals or personal computers.
Groups of host ports with matching
characteristics may be members of hunt groups (referred to as host port
groups).
d. Analog Data Endpoint
Data endpoints with modems are referred to as analog data endpoints.
Modems connected via tip ring lines use PDCs as extension numbers rather
than Data Dial Codes (DDCs). Station-to-station data calls to (or from) this
endpoint from (or to) digital endpoints require a modem conversion resource
to convert the endpoint’s analog data to digital format. Calls from a digital
endpoint to an analog data endpoint (i.e., calls to a PDC), will automatically
have a conversion resource inserted in the calling path. If the called (analog)
endpoint should then invoke Transfer To Data, the conversion resource will
be released. Data calls originating from an analog data endpoint must first
enter a Modem Request Code before addressing a digital data endpoint.
This is required because the system assumes that a call originating from a
voice terminal will invoke Transfer To Data. If the originating station is not
going to transfer to data, it must indicate this so that a conversion resource
will be included in the connection.
2. DCE Devices
This group of data endpoints consists primarily of modems. The modems are
connected to a data port from their RS-232 side. The modem must be configured as
a DTE interface to connect to a System 25 data port. It is possible to simulate a DTE
interface from a modem with a cross-over (“null modem”) cable. This group of
2-131