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CHAPTER 6: ASYNCHRONOUS DTE CONFIGURATION
Characteristics of Modems that can be Attached to the 7500
Modems that are to be used with the 7500:
Must be full duplex.
Must support 10 bit code (start bit, 8 data bits, plus at least one stop bit).
Must use the asynchronous RS-232C or EIA-232D interface.
Must support any or all of the following speeds: 300, 1200, 2400, 4800, 9600, 19200 bps.
Must autodial to support calls from digital to analog network.
Must turn on Clear-to-Send (or keep it on) in response to a Data Terminal Ready signal from
7500-DTE when it is ready to receive ASCII dialing sequences from the 7500-DTE.
Must not transition the Data Set Ready lead from On to Off during the transition from interactive
(dialing) mode to data mode.
Must terminate a data call or dialing sequence when the 7500-DTE turns off its Data Terminal
Ready lead.
Must turn off Data Set Ready or Receive Line Signal Detect for a minimum of 50 milliseconds
when going on-hook at the termination of a data call.
Must turn on Ring Indicator lead for at least 100 milliseconds in presence of incoming analog call.
Should support EIA signals CI and CI2 if the modem is multispeed modem.
Overview of 7500 Operation
In this application, users from both sides of the network will call through the 7500 in a modem
pool. A method for controlling option settings from the analog network side is provided. The user on
the digital side cannot change option settings.
7500 Modem Pool: Digital to Analog Network
We recommend that Local Mode be set to off for the 5ESS switch X.25 packet-data modem pooling
and digital to analog only circuit switched modem pooling.
The role of the modem pool for calls coming from the digital network is as follows:
1. The user dials the call:
A user with a ISDN voice/data terminal or other compatible data device dials the telephone
number that is associated with the modem pool (typically a hunt group).
2. The 7500 checks for the availability of the attached modem and answers:
When the 7500 receives a data call, it turns on Data Terminal Ready and checks for Data Set
Ready, Clear to Send, or Carrier Detect from the modem. If one or more of the signals are
present, the 7500 accepts the call. The Auto Answer function is always enabled.
3. The user dials through the attached modem:
The user trying to place the call must know what the procedure for using the modem is, for after
it connects the modem, the 7500 passes user information to the modem without interpreting it.
Most likely, a second stage of dialing will occur at this point, and the user will be connected
through the analog network to the desired far end.
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