High-Pitch Handshake
If you attempt to make a connection and the call gets answered
with a high-pitch tone that doesn't progress to a normal handshake, it may be a
problem at your ISP.
Ascend-Max equipment may be particularly susceptible. If the
ISP has more incoming phone lines than modems available to answer calls, the
call is directed to the Max's HDLC drivers (same as used for digital ISDN) so
you hear loud high-pitch digital tones instead of the friendly handshake.
This may happen more often that you would think due to the way
the Max operates even if the ISP doesn't have more incoming phone lines than
modems. The Max keeps a list of modems in several categories: free, busy,
suspect, disabled, and dead. The Max keeps track of how many bad calls a modem
takes, and when it reaches a threshold, it places it on the suspect list. At
this point, no calls will be assigned to it until no other modems are available.
If it continues to take bad calls, it will be placed on the disabled list and
will not use the modem at all until the modem card is reset. The modem card will
automatically reset once there are no active calls. Since a modem card handles
at least 16 calls, if only a single user is left connected to a modem card on
the disabled list, there will be 15 disabled modems on that card which will not
come back into service until that last user disconnects.
