Method of and apparatus for determining time origin of timer for modem

A method of and apparatus for determining a time origin of a timer for a modem which is adapted for training in a parallel channel transmission system. A transmitter during a first period of time in a training procedure transmits a channel signal to a receiver except for a signal in at least one channel, while the receiver during the first period of time activates an AGC to receive the channel signal, whereafter the transmitter during a second period of time transmits the channel signal without excluding any channel and the receiver sees presence/absence of received signal power in a specific channel in which the received signal power in the first and second periods has been adjusted to a predetermined value.