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The internal DTE must also use a modem. In this case the normal modem pool dialling as
discussed earlier is used. The 64 kbps signal from the DLC/DTX is sent to a MLU. The
digital information from the DTE is retrieved from the 64 kbps signal and sent to the
modem. The analogue signal from the modem is digitised and the resulting 64 kbps signal
transferred to the DTU/DTX. Now the digitised modulated carrier signal from the
modem is inserted into a timeslot in the route. For full duplex communication the reversed
path must also be established between the DTE and the DTU/DTX.
A modem-modem connection between internal and external DTE is established although
the signal is transferred between the ISPBX network and the external network in digital
format.
V.24
DCE
DCE-SOPHO-SET,
SOPHO-LAM or LAM
1
2B+D, B=64kbps, user channel.
2
Digitised modulated carrier in a 64kbps user channel.
2B+D, (DTU-BA or DTX-I) or 30B+D (other DTUs). B = user channel.
Figure 3-11 Digital Connection to a Digital Trunk (with Modem).
The internal DTE must be allowed to dial the relevant access code or the incoming call
must be allowed to dial the DLC/DTX-DNR. The connection allowance between the CV
of the internal DTE and the CV of the route must be set to `allowed with convertor' (2).
The relation between the CVs must indicate which type of modem is to be used.
For more information: see the modem pool dialling part with the analogue trunk or tie-
lines.
3.3.
DIGITAL ROUTES
There are two types of digital routes supported in ISPBX:
-
30B+D (Primary Rate).
A 2 Mbps digital trunk or tie-line offering 30 user channels (timeslots) of 64 kbps each.
Timeslot 16 is used for the signalling information for all user channels. Timeslot 0 is used
for synchronisation purposes.
-
2B+D (Basic Access).
1
IMP
2B+D
64 kbps
DLC/
DTX
SN
IMP
64 kbps
MLU
IMP
64 kbps
IMP
64 kbps
DTU/
DTX
MODEM
V.24
1
Trunk
2
line
45
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