56K modem - distinctive ring (AT+VDR parameters)

Hello !

My 56k modem uses the +VDR AT command to set it's distinctive ring
options.

My modem answer to an AT+VDR=? hyperterminal session is (0,1)(0,60)

I understand the first parameter is used to "enable/disable" the
function, but I can't find a reference on the second one's meaning or
usage.

Any help (or reference on the subject) would be appreciated.

Thanks.