sing music as an analogy. Frequency Synchronization T&=1/f2 Tn=19 1A=f8 Phase Synchronization TA=1/A Tg=1/lg fa=f8 Time Synchronization 01:00:00 01:00:10 Tg=1/fg fa=f8 01:00:00 01:00:10 Figure 1-3 Frequency Versus Phase Versus Time Synchronization According to this analogy, frequency synchronization is the process of ensuring that two vibrating sources of sound in an instrument are playing the same note. An example would be where a musi- cian plays the note "A above middle C" on an instrument (sound waves carrying A above middle C, or A4, oscillate at 440.00 Hz). Playing the same note on another instrument such as a piano should generate a sound wave at that same frequency. On the other hand, phase synchronization is concerned with ensuring that two or more separate processes execute a planned action only when it is supposed to happen. Another way to think of this would be when the second hand of a clock actually "ticks" over. Two clocks can be running at the same speed (frequency synchronized), but if they do not tick over the second at the same time, their phase is not aligned. Processes that are phase synchronized (or phase aligned) understand time in a way that guarantees the correct sequence is followed, and simultaneous events occur at the same instant. In the music portion of this analogy, a metronome or orchestral conductor would be responsible for ensuring that the musicians play to the correct beat or tempo and that the same passage of music is simultaneously played by each musician-the choir needs to be "singing off the same sheet." If the musicians do not play the notes at the correct time or tempo, then the music will immediately be- come jarring and unmelodic. When two processes are phase synchronized, the term phase accuracy describes how far away the two processes are from each other in their understanding of when an event should happen. Phase accuracy is generally expressed in fractions of a second, SO you might say, for example, that two clocks are phase aligned within 100 milliseconds (100 ms) 