DS3/E3 signals are not required to be synchronous. However, it is acceptable for their clocking to be generated from a synchronization source. The 7750 SR and the 7450 ESS allow E3/DS3 physical ports to be specified as a central clock input reference.
DS3/E3 signals do not support an SSM channel. QL-override should be used for these ports if ql-selection is enabled