Placing and Receiving Calls 2-15
Placing and Receiving Calls
This section illustrates how to place and receive a variety of
calls with your 3Com Impact digital modem. The digital
modem uses AT commands and S registers for call
management. See Appendix A, “AT Command Set
Overview,” for instructions on use of the AT command set,
and Appendix B, “AT Commands, Registers, and Result
Codes,” for a tabular summary of the AT command lines.

Placing ISDN Data Calls

When you need to place a call from your PC or Macintosh,
the 3Com Impact digital modem recognizes the AT
command ATD to dial a digital ISDN data call. Depending on
the setting of register S60, 56 Kbps (default) or 64 Kbps
B channel transmission speeds are used. Correct examples of
outgoing circuit-switched digital modem commands with
dial strings are:
AT D 1 908 555 7891
ATD19085555555

Multilink PPP Calls With Dynamic Bandwidth Allocation

The 3Com Impact digital modem supports Multilink PPP,
which allows the two B channels to be virtually linked, thereby
allowing a maximum digital connection of 128 Kbps. Note
that both your service and the one that you are dialing into
must support Multilink PPP, or the virtual linking will not
occur. Multilink PPP is enabled by default.
Multilink configuration is facilitated through registers S80,
S81, S82, and S83. Additionally, dynamic bandwidth
allocation (DBA) in multilink mode is configured in
register S70. Register S80 enables (the default) or disables
Multilink PPP operation.