Clock and data recovery/Buffer Memory (Elastic Buffer)/Clock domains

Inside a clock domain all the clocks are locked to a master.
They may jitter with respect to the master and with respect to each other, but they do not drift.

The domain of a master clock

In general, the slave clock needs not run at the same frequency of the master.
There are cases where the frequencies are different (by the ratio of two integer numbers).
When the frequencies differ, since the jitter is measured in radian (i.e. as a fraction of 2 $\pi$ * clock period), the same jitter amount if measured in time (i.e. seconds) will represent, if measured in radian, an amount of jitter different at the slave than at the master, by the ratio:

$\frac{{\omega }_{slave}}{{\omega }_{master}}$

If a slave gets disconnected from its master, a new domain is created.

A slave creates his own domain

If two clocks exhibit a phase differenece because they have followed different paths inside the same clock domain, or because they belong to different clock domains, a buffer memory can be used to compensate that difference.
The figure below illustrates the second case, where, to compensate for the phase difference of two clocks of different domains, a buffer memory is used at the point of border connection.

A buffer inserted between clock domains

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