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answering mode) channel.
After the incoming seizure the pool-modem is inserted into the call processing state. Over a
leased line NO dialling information can be received by the modem and call processing does
not receive any indialling information: the leased line behaves like a trunk line without DDI.
Normally the call will be routed to an operator A-queue (incoming route option) but with
digital information this will not be very useful. Another option is to assign a Permanent Line
Extension (digital party) to the `trunk' lines in this route. This PLE-data terminal (can also be
a group of terminals) answers the incoming calls over the leased line.
DDI with digit conversion to a complete number can also be used.
One data path is established through the switching network:
-
From the MLU to the PLE:
The analogue (modulated) signal now enters directly on the modem. The demodulated
user information is sent in V.24 format to the MLU and the data rate adaptor incorporates
the user information in the 64 kbps standard signal. The 64 kbps signal arrives at the
SOPHO-SET, SOPHO-LAM or LAM (via the switching network and the DLC circuit). This
device retrieves the user information from the 64 kbps signal and sends it to the data
terminal.
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 the analogue part of the MLU is not used the tone generation and detection circuits of the
MLU are not available: the modem must be able to generate and detect the necessary tones.
When the call is answered by the destination party (PLE), the pool-modem is activated:
-
CT111 (DSRS) is sent to the modem to indicate if the high or the low speed must be used-
depending on the projecting of the MLU-circuit;
-
CT126 (STF) is sent to the modem to indicate if the modem must receive in the high
frequency band and send in the low frequency band (calling mode) or receive in the low
frequency band and send in the high frequency band (answering mode)-depending on the
projecting of the MLU circuit;
-
The MLU circuit forces circuit CT105 (RTS) to on;
-
The modem starts waiting for the carrier from the remote party. If this carrier is detected
the modem knows the opposite party is on-line. The circuit CT109 (DCD) indicates to the
DTE that the DTE must be ready to accept data. Now the modem starts transmitting the
carrier in the opposite channel. The modem returns CT106 (RFS) to the DTE to indicate
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