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channel in the 2B+D line to the DLC/DTX. The signalling information, such as the called
number, is transferred as a message in the D-channel of the 2B+D line.
If the call set-up information indicates an access code towards a destination which can be
reached via a DTU/DTX route, the ISPBX searches for a free circuit (timeslot) in the route
and sends a message to the external network in the signalling channel. After acknowledgement
the transparent 64 kbps path between the DTE and the external network is established.
With an incoming call the ISPBX receives an incoming seizure of a DTU/DTX circuit. It
receives further dial information in the signalling channel and this information is analysed in the
DDI-tree related to the route. If there is no DDI-traffic on the route the call is directed to the
operator or to a PLE related to the trunk line. After call set-up is completed a transparent 64
kbps path between the external network and the internal user is established.
The opposite DTE can be connected to the external network by a digital interface or by a
modem. This gives rise to the following configurations:
-
Opposite DTE connected to a digital interface.
No modem connection in the ISPBX has to be used. The 64 kbps data signal from the
DLC/DTX can be transparently switched through to a circuit of the DTU/DTX. Here the
64 kbps signal (with the user data incorporated) is inserted in a free timeslot in the 2 Mbps
link to the external network. For full duplex communication the reversed path must also
be established between the DTE and the DTU/DTX circuit.
V.24
DCE-SOPHO-SET,
SOPHO-LAM or LAM
1
2B+D, B=64kbps, user channel.
2
2B+D, (DTU-BA or DTX-I) or 30B+D (other DTUs). B=64kbps user channel.
Figure 3-10 Digital Connection to a Digital Trunk.
A fully digital connection between the ISPBX (internal) DTE and the external DTE is
established.
The internal DTE must be allowed to dial the applicable trunk access code or the incoming
call must be allowed to dial the DLC/DTX-DNR. The allowance between the
compatibility value of the internal DTE and the compatibility value of the DTU/DTX-route
must be set to allowed (3).
-
Opposite DTE connected to a modem.
44
1
IMP
64 kbps
2B+D
DLC/
DCE
DTX
SN
IMP
64 kbps
DTU/
DTX
2
Trunk
Trunk
line
line
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