How Does the ADSL/ISDN-Controller FRITZ!Card DSL Work?
FRITZ!Card DSL – 5 Basic ADSL/ISDN Information
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5.4 How Does the ADSL/ISDN-Controller
FRITZ!Card DSL Work?
FRITZ!Card DSL connects your computer with ADSL technolo-
gy and ISDN. The cable included in the package is used to
connect to both ADSL and to the S
0
bus, and thus to the local
exchange of the telephone network.
All services in ADSL technology and ISDN are implemented
using protocols. These protocols define how data transfer
between the subscribers takes place. They facilitate smooth
communication and adjust such parameters as transmission
speed and data compression during transfer.
For the ADSL line, transmission is regulated by the protocols
TCP/IP, PPP, PPPoE and ATM. These define that data can only
be transmitted between two fixed locations – what is known
as broadband POP and the user. It is not possible to estab-
lish a direct ADSL or PPP connection to another ADSL sub-
scriber. The ATM (Asynchronus Transfer Mode) transport pro-
tocol defines how user data are transmitted on the ADSL
line. The data are packed in “ATM cells” then are fed in and
transported to the ATM network of the ASDL provider.
I
n both ADSL and ISDN both of the communicating parties
must support the selected protocol to enable smooth data
transfer. For ISDN these are the protocols T.30 for G3 fax, for
example, or HDLC transparent for Internet communication.
The driver software for the ADSL/ISDN-Controller
FRITZ!Card DSL must support the right parameters in real-
time for every connection and pass them on to both local ap-
plications and the remote station. Transfer to the communi-
cations software takes place in the computer via the COM-
MON-ISDN-API interface, CAPI for short. CAPI establishes the
connection between FRITZ!Card DSL and the installed appli-
cations. The driver software for FRITZ!Card DSL thus is also
known as the CAPI driver.
While every FRITZ!Card DSL has a special CAPI driver for each
operating system supported, the applications work identi-
cally and can be used universally with CAPI 2.0. The FRITZ!
communications software modules, the FRITZ!web DSL pro-
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