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MODEM POOLING
Description
Allows switched data connections between digital data endpoints and analog data endpoints.
(Refer also to the description of the system’s data features provided in the “Data Services
Overview’’ subsection.)
Data transmission between digital and analog endpoints requires a conversion resource since
the digital format used by the data module is not compatible with the modulated signals of
an analog modem.
The conversion resource translates the digital signals from the digital
endpoint into analog signals and vice versa.
The modem pool is a single group of up to 12 conversion resources (3 Cabinet system) with
the characteristics of a 212A full duplex asynchronous modem that can operate at speeds of
300 and 1200 bps.
The Modem Pooling feature operates transparently to the user whenever possible. The
system adds a conversion resource to a connection when a digital endpoint is connected to an
analog trunk or port without any explicit action by the user.
A voice terminal user who plans to use an analog modem to call a digital endpoint must first
enter the Modem Request Code before dialing the digital endpoint. This is because the
system assumes that a voice call to a digital endpoint will be transferred to data via the
Transfer To Data feature.
A DID call terminating on a digital endpoint will reassigned a modem resource, if available.
Otherwise, the call receives Reorder tone.
For each situation that requires a conversion resource, the system:
1. Determines if a resource is required by examining the types of endpoints that are
to be connected together or by user indication.
2. Once it is determined that a conversion resource is needed, it is reserved. The user
receives Reorder Tone (or the
“NO MODEMS - TRY AGAIN” message) if a
resource is not available. The system queries the data port to determine whether
its options are compatible with those supported by the modem pool. If they are not
(e.g., 9600 baud and Permit Mismatch is not enabled), the originating user receives
intercept treatment (i.e., INCOMPATIBLE FAR END) and call setup is abandoned.
3. At data connection time, the conversion resource is seized and placed in the
connection.
4. The call is disconnected within 15 seconds if the conversion resource does not
successfully handshake with both endpoints.
Conversion resources are required for:
●
Data Terminal Dialing: To establish a data connection for calls originated via
Terminal Dialing to intrapremises analog data endpoints.
● Incoming Trunk Calls: To establish a data connection between an incoming trunk
call and a digital endpoint.
Incoming trunk calls that are answered at a voice
terminal can be transferred to a data endpoint using the Transfer To Data feature.
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