Timers are hardware components or software routines that provide the time reference for controlling and monitoring processes
. Such an electronic timer generates time signals
bycalculating the time for hours, minutes, seconds and milliseconds from a reference frequency. High-precision pointers use temperature-stabilized oscillators or crystal oscillators, or derive their time signal from the GPS time reference. A timer can also perform the function of a real-time clock
. A software timer routine works with routines for timing applications. Timers are used in all systems and architectures, for example, in cellular systems the timer controls the time between successive updates ofdirectories. And in TCP protocol, various timers are used such as retransmission timer, window size timer and reconnection timer.