Netopia 435 Reference Manual page 44

Configuring ISDN Connections 2-29
Calling Number Authentication (CNA), is an application of caller ID.
It is a method of verifying that an incoming call is originating from an
expected site. Using CNA, you can increase the security of your
network by requiring that callers not only possess the correct PAP or
CHAP information, but also that they are calling from a particular
physical location. CNA should be available where caller ID services
are available, but you will need to consult with your ISDN service
provider to find out if your ISDN line is provisioned for caller ID.
CNA works by checking the calling number that the Netopia ISDN
Router receives during the initial setup phase of an incoming call
against the stored Calling Number defined in each connection
profile. When a match occurs, the incoming call is handled by the
connection profile containing the matched number.
Using CNA can also provide cost saving because calls are not billed
during the CNA phase. With CNA, a caller can set up a connection to
the Netopia ISDN Router without incurring any charges by accessing
a dial-back connection profile. If the callers rates are higher than
those charged to the Netopia ISDN Routers return call, then using
CNA has saved the difference.