About Modem Connections; Configuring Your Modem - Digi PortServer II User Manual

About Modem Connections

If you use a modem or similar device on a connection to a remote host or system, you
must configure the serial port to operate with the modem. This Chapter describes how
to configure PortServer II for communications between the PortServer II and the
modem. You will also have to configure your modem settings for communication with
PortServer II and should refer to your modem documentation for details.
Note: Configuring communications by the modem over telephone or data lines is
outside the scope of this User's Guide. Refer to your modem documentation
for assistance.
You will also need to configure PortServer II for the protocol to use over the modem
connection after you have configured the modem. Information on this is given in
Chapter 8, Configuring WAN Connections.

Configuring your Modem

The configuration procedure for your modem depends on the type of modem and your
system arrangement. However, to ensure that the modem operates with PortServer II,
set your modem to meet the requirements listed below:
• Make sure signals TD, RD, DCD, DTR and GND are wired in the cable between
PortServer II and the modem. Refer to the cabling diagrams in Chapter 3, Instal-
lation.
• Configure the modem so that DCD goes high when it receives an incoming
connection request. For Hayes-compatible modems, this command is AT &C1.
• Configure the modem to answer an incoming call only when DTR is high, and to
drop the line when DTR goes low. For Hayes-compatible modems, this command
is AT S0=1 &D3.
• For the best results in bidirectional mode, configure the non-volatile parameters in
the modem for incoming calls. Also, configure the modem to reset to these
parameters each time DTR is dropped. For Hayes-compatible modems, this
command is AT &D3.
• PortServer II cannot switch the baud rate of the serial line for different
connections. You should configure the modem to lock the serial line speed at the
highest baud rate the modem will accept for reliable data transfer.
• Generally, use hardware flow control on modem lines, and set software flow
control off.
Note: UUCP and XMODEM protocols do not work with software flow control.
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