This object sets the source of the E1 transmit clock for this line: internal, slave, recovered from the receive line, or manual, defaulting to internal. Admins configure it to establish correct network timing hierarchy, such as slaving a branch office's E1 clock to the timing recovered from an incoming line from the central office. For example, setting wfE1ClockMode to slave(2) makes this E1 interface derive its transmit clock from the received line signal instead of its own internal oscillator.