Dropped or Lost Connections
Phone line quality or features such as call waiting can cause lost connections.
As described above, if the connection keeps dropping, you might want to
contact the telephone company. However, you may first want to try a connection
with another remote system or try using the modem from a different phone
connection altogether. In addition to phone line problems, two other things
might cause loss of connection. These are Call Waiting and Automatic Time-out.
Call Waiting
The call waiting feature available on some dial-up lines momentarily
interrupts a call, causing a click, to inform voice call users that another
call is coming through. This process effectively interrupts the carrier
signal and may cause some modems to drop the connection.
One way around this is to set S10 to a higher
value so the modem tolerates a fairly long loss of carrier signal. Data
loss may still occur, but the connection will not drop. Of course, the remote
modem must be similarly configured. When originating the call, a special
prefix can be issued as part of the dialing string to disable call waiting
for the duration of the call. The exact procedure varies from area-to-area;
contact the local telephone system for details.
Automatic Timeout
Some Hayes modems offer an automatic timeout feature, to prevent an
inactive connection from being maintained. This inactivity delay can be
set or disabled with S30. This feature prevents
occurrences such as undesired long distance charges for a connection that
was unintentionally maintained.
System Lock-up
There are situations in which systems do lock up, but in many cases
it is simply that one or the other of the DTEs has inadvertently sent a
character that stops data transfer. This can happen during error-control
connections if the wrong kind of local flow control has been selected. For
an explanation of local flow control options, see the &Kn -
Select Flow Control Option command. In addition, the problem could be
the result of incompatible RS-232/ITU-T V.24 signaling. The section below
provides some situations and tips that help if the communication link seems
to lock up.
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