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B.3.1. Outgoing Call
For an outgoing call over a leased line, the procedure is the same as the seizure of a free trunk
line when making an outgoing -voice- call. Therefore the MLU-circuits with the modems
connected, are assigned a line number and related to a bundle, route and destination. When
an internal data party wants to have access to the external data party, only the trunk access
code to the destination is enough (CV connection allowance: allowed) to seize a free line
(including modem) to the external data party.
If the modem is idle, the MLU circuit still forces the modem on-line using CT108.1. The
modem returns the signal CT107 to indicate that the modem is ready for operation.
Guarding of the line:
In some cases the remote data party offers a constant carrier on the line. In this case the signal
CT109 from the modem indicates that the carrier is being received. If this carrier is not
present, it may indicate a problem with the line and the MLU circuit is set into the ABL-FAIL
condition. The guarding of the line can be enabled or disabled in the projecting data. For more
information: see Projecting aspects.
If the send and receive frequency of the modem is controlled by the MLU by signal CT126
(STF), the constant carrier can only be in the high frequency band. If the modem is idle the
signal CT126 is in the off-condition. The modem is set in the calling mode and only detects the
carrier in the high-frequency band.
If the send and receive frequency is controlled by the modem itself (switchess and/or straps)
the constant carrier can be in the high (modem in calling mode) or in the low (modem in
answering mode) channel.
If a party initiates a call request to a destination (trunk access code), the compatibility check
allows the connection. Now a free circuit on a MLU in the correct route is seized.
One data path is established through the switching network:
-
From the calling party to the MLU:
The V.24 user data is incorporated in a 2B+D 64 kbps signal by a SOPHO-SET, SOPHO-
LAM or LAM and transferred to the MLU circuit via the DLC-circuit and the switching
network. The V.24 user data is retrieved from the 64 kbps signal and sent to the modem.
For full duplex data communication, the reversed path must also be established through the
switching network.
The outgoing route option `direct switch through' must be yes. As no answer signal can be
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