This attribute is only used when the actualLinkMode is dce. It is
used to determine the clock to be used to recover the receive data.
Note that a V.11 DTE interface uses the S clock (see X.21 standard)
for both receive data and transmit data timing. The DTE interface
always loops the received S clock back to the DCE as the X clock
(see X.21 standard).
If the value of the attribute is fromDce, the DCE V.11 interface uses
the internally generated transmit clock as the S clock and for both
receive and transmit data timing. The X clock is ignored.
If the value of the attribute is fromDte, the DCE still uses the
internally generated transmit clock as the S clock and for transmit
data timing, but the receive data timing is derived from the X clock.
The fromDte mode is recommended when the DTE is far away from
the DCE interface.