EtherCAT includes a distributed clock mechanism, giving it a low jitter that meets the specifications of IEEE 1588 without additional hardware.
The mechanism is possible because of the timestamps each node includes in the EtherCAT frame. Each node attaches a time stamp to the EtherCAT frame twice, and the master receives the frame with two time stamps per slave.
With the time information, the master can calculate the delay for each node. The master repeats the calculation for every frame it sends. As the network operates, the enormous sample size means the master has incredibly accurate data. The inherent ring topology creates an incredibly efficient clock mechanism that is increased in accuracy with every message.