Operation Manual

FRITZ!Card on the ISDN Line
28 FRITZ!Card – 4 How Does Work FRITZ!Card
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.
No matter which interface your FRITZ!Card is connected to,
an internal or an external S
0
interface, the terminal device is
not the ISDN-Controller FRITZ!Card USB v2.1, but rather the
ISDN software on your PC: for instance, the FRITZ! modules
FRITZ!data and FRITZ!fax.
Whenever 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 trans-
mitted first. This service indicator distinguishes between a da-
ta call from a fax call, for instance. For incoming analog calls no
such differentiation is possible: telephone calls and G3 (ana-
log) faxes are both designated by the “voice” service indicator.
In order to route such calls correctly, different MSNs must be
assigned to the different terminal devices or FRITZ! modules.
See the section “Using ISDN Services with FRITZ!” on page 24
for more information.
Analog phone with
answering machine
ISDN phone
Fax
Cordless
phone
PBX
with analog
extensions
NT
NT
Computer with
FRITZ!Card
S
S
O
O
S
S
O
O
S
S
O
O
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