After the incoming call has been authorized by call filtering, the call type is determined.
There are two call types associated with modems:
Data over a modem
Fax over a modem
There are five call types associated with ISDN adapters:
Asynchronous data over ISDN
Synchronous data over ISDN
Fax over ISDN
Video over ISDN
Voice over ISDN
Refer to the Callservices(4bnu) manual page for more information.
Other types of call (for example, PPP connections) can be auto-detected using the /etc/ics/Autoacts file (see Autoacts(4bnu) and pppsh(1M)). This file contains a list of byte sequences and associated services. The port monitor uses Autoacts to discover which service to invoke by matching its entries against an incoming byte sequence.