Advertisement
Note: Depending on the projecting of the MLU it can switch the CT111 circuit (DSRS) to off or
on to indicate to the modem that the low or the high speed must be used. For more
information: see projecting aspects.
B.2.2. Outgoing Call
Modem pool dialling with outgoing calls is usually only applied on trunk lines which support
DDO.
If a modem in the modem-pool is idle, all signals between the MLU and the modem are in the
off-condition.
If a party (internal) initiates a call request to a destination (trunk access code to a destination
via an analogue trunk line with CV), the compatibility check is used to find out that a modem
of a specific type must be used for that trunk line. Now a free circuit on a MLU with the
correct modem type is seized.
For an outgoing call, first the dial information is transferred over the trunk line in the applicable
signalling type (bundle dependent!). The V.25 Automatic Calling Unit of the modem is not
used.
Two data paths are established through the switching network:
-
From the destination 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.
-
From the MLU to the ATU circuit:
After modulation the analogue modem signal is digitised and sent in a 64 kbps signal to the
ATU circuit. Here the modulated user information is reconstructed back to analogue and
sent over the trunk line.
For full duplex data communication, the reversed path must also be established through the
switching network.
Now call processing starts waiting for the call to be answered. The call establishment is
guarded by timers.
When the call is answered by the destination party, the pool-modem is activated:
77
Advertisement
