The ISDN Line
38
FRITZ!Card DSL – 5 Basic ADSL/ISDN Information
Typical configuration of a point-to-multipoint ISDN line.
Some PBX systems provide both analog and digital exten-
sions. ISDN terminal devices may be connected directly to
these digital extensions. Digital extensions are also known
as “internal S
0
interfaces” as they present an alternative to
external S
0
interfaces.
When a call arrives on your ISDN line, it is necessary to de-
cide who will answer it: a FRITZ! module, the ISDN telephone,
or the PBX. For incoming ISDN calls, a service indicator is
transmitted first. This service indicator serves to differentiate
between data calls and fax calls, for instance. For incoming
analog calls no such differentiation is possible: telephone
calls and G3 (analog) faxes are both designated by the
“voice” service indicator. In order to direct such calls correct-
ly, different MSNs must be assigned to the different terminal
devices or FRITZ! modules. See the section “Using ISDN Ser-
vices with FRITZ!” on page 35 for more information.
Analog telephone with
answering machine
ISDN telephone
Fax
Cordless
phone
PBX
with analog
extensions
NT
NT
PC with FRITZ!Card
S
S
O
O
S
S
O
O
S
S
O
O
FCdsl-e.book Seite 38 Freitag, 17. Mai 2002 11:55 11
