ATT System 25 Reference Manual

Data Services Overview
Data Services Overview
System 25’s data features provide switched data transmission at up to 19,200 bps (RS-232
interface), and a 212A modem compatible conversion resource capable of handling data at
300 and 1200 bps.
The system provides switched connections between data endpoints. These endpoints
include data terminals, personal computers, multiport computers, and modems.
Data
endpoints are either digital data endpoints or analog data endpoints.
Analog endpoints are connected to...

FEATURES AND SERVICES
The following describes the categories and attributes of each:
1.DTE Devices
This group of data endpoints have one thing in common: their interface configuration
(although RS-232 control signal utilization varies significantly from terminal to
terminal). Some data equipment do not use any RS-232 control signals; these
require only BA (Transmitted Data Ready-Tx), BB (Received Data Ready-Rx) and AB
(Signal Ground) to function,while others require more RS-232 control signals to...

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...

FEATURES AND SERVICES
endpoints is important for users who provide their own modems, connected to
dedicated trunks or private lines, for internal modem pooling.
Data Endpoint States
The data endpoint may take on three states: (1) off-line, (2) on-line (on-hook), and (3) on-line
(off-hook). Off-line is when a data terminal is out of service (turned off, disconnected, etc,).
The on-line (on-hook) state occurs when the terminal is turned on, is available to answer a
call, but is not on a data call. Finally,...

Data Services Overview
e.Data Terminal Dialing Mode
Data Terminal Dialing is a data feature accessed via Command Mode. It provides a
procedure to establish data calls without the use of a voice terminal. Data Terminal
Dialing supports both on-premises and off-premises data calls (with the support of
the System 25 Modem Pooling feature).Dialed digits are entered from the data
terminal keyboard or host computer (using a program compatible with Data Terminal
Dialing protocol). Call progress text messages...

FEATURES AND SERVICES
b. Data Terminal Dialing
Data Terminal Dialing provides call setup from terminals and host computers
c. Transfer To Data
Transfer To Data is the preferred method of data call origination from multiline voice
terminals equipped with Transfer to Data (DATA) buttons and associated digital data
endpoints. The DATA button is associated by DDC with a near end data endpoint. A
unique DATA button must be provided for each DDC that the voice terminal is
capable of controlling.Associated with...

Data Terminal Dialing
Data Terminal Dialing
Description
This feature allows users to onginate (place) data calls from a data terminal. Voice terminal
dialing and call progress tones are replaced by keyboard dialing and call progress messages.
The message “DIAL:”’ prompts the user to enter the called number from the keyboard, and
“RINGING” or “DIALING ... COMPLETED” informs the user that the dialed number is being
called.
Table 2-1 provides a list of the call progress messages.
Note:The following dialing...

FEATURES AND SERVICES
Pause characters may be used consecutively if a longer pause is required. Note that System
25 cannot detect tones, such as a second dial tone for end-to-end signaling.
End-to-End Signaling:
Data connections to off-premises destinations require that a conversion resource (pooled
modem) be inserted into the connection.Occasionally it is necessary to send additional
tones to the remote endpoint after the connection is established to signal the remote
equipment. A “mark” character ($)...

Data Terminal Dialing
Table 2-1.
Call Progress Messages for Data Terminal Dialing
Displayed
MessageApplication
DIAL:Placing a call
RINGINGPlacing a call
BUSYPlacing a call
ANSWEREDPlacing or
receiving a call
TRY AGAINPlacing a call
INCOMING CALL-*Receiving a call
PLEASE ANS-Placing a call from
a voice terminal
DISCONNECTED*Call is terminated
CONNECTED,Call is connected
SPEED = NNNN
INCOMPATIBLEPlacing a call
FAR END
DIALING . .Placing a call
COMPLETED
PLEASE WAITPlacing a call
BAD NUMBERPlacing a call
NO...

FEATURES AND SERVICES
Answering Endpoint:
When the dialed endpoint is alerted, the user receives “INCOMING CALL-”. (The called
terminal will auto-answer if it is turned on.) If the handshake succeeds, a data connection is
established and the “CONNECTED” message is displayed if so optioned. If the handshake
fails, the user receives “INCOMPATIBLE FAR END, DISCONNECTED” and the data endpoint
returns to idle mode.
Considerations
Data Terminal Dialing allows users to place data calls from their terminals...