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13. ISDN CAPI Port Device Driver 201
The modem "ISDN SoftCompression X.75/V.42bis":
Using data compression according to V.42bis for X.75 connections
Using the virtual modem ISDN SoftCompression X.75/V.42bis connections can be
established with activated data compression. This allows data to be transmitted at
a rate up to four times higher, depending on the type of data to be transmitted.
Some basic conditions must be met, however:
• The latest CAPI 2.0 device drivers are required:
The CAPI 2.0 device drivers for your ISDN-Controller must support V.42bis. If
this is not the case, the virtual modem ISDN SoftCompression X75/V42bis is
not available for selection in the installation window.
• Only for X.75 connections:
Data compression according to V.42bis can be used only for X.75 connections.
Possible applications include ISDN Point-to-Point connections and
connections to ISDN BBSs. According to CAPI 2.0, a secured data link is
imperative for V.42bis connections. As only the X.75 protocol guarantees this
feature, V.42bis can be used only with this protocol. For connections to ISPs,
HDLC is (nearly always) used as an ISDN B2 protocol. For this reason, a
connection with data compression is not possible on ISDN protocol level.
• Automatic negotiation
When a connection to an X.75 remote site is established, the system
automatically tries to negotiate V.42bis. If this does not succeed, e.g. because
the remote site does not support V.42bis, a connection without data
compression is made automatically.
Keep in mind that the V.42bis data compression algorithm of passive ISDN-
Controllers is processed on the host's CPU and thus demands more powerful
hardware. In the case of active controllers of the B1 family, the algorithm is
processed completely on the Controller.
Note: With the command ATS42=8, V.42bis can be activated manually for X.75
connections as well.
Remote access service (RAS)
The ISDN CAPI Port Device Driver can be used for RAS connections to Windows
95/98/NT and Windows 2000 computers. The virtual modem ISDN RAS (PPP
over ISDN) is provided for this purpose.
In Windows 95/98 Dial-Up Networking requires an additional server module to
serve as a remote site. Windows NT computers can use the "NDIS WAN CAPI
Device Driver for Windows NT" or the ISDN CAPI Port Device Driver for
Windows NT to make WAN connections over ISDN.
Windows 2000 users can use the ISDN CAPI Port Device Driver or the NDIS
WAN CAPI Device Driver installed with the CAPI 2.0 device drivers
ISDNmst.fm Page 201 Wednesday, January 15, 2003 9:22 AM