An ASCII string containing response codes that may be
generated by a modem to report the reason why a connection
attempt has failed. The response codes are delimited by
the first character in the string, for example:
/NO CARRIER/BUSY/NO DIALTONE/NO ANSWER/ERROR/
If one of these response codes is received via this serial
interface while attempting to make a modem connection,
the agent will issue the hang up command as specified by
serialModemHangUpString.
A value that is appropriate for a wide variety of modems is:
'/NO CARRIER/BUSY/NO DIALTONE/NO ANSWER/ERROR/'.