Abstract: A downhole data transmission system communicates data along a downhole string including a communications master selected from the group including a surface interface, a down-hole interface, and a node, and including a communications line including a plurality of trans-mission segments that carry signals along the downhole string, and a plurality of repeaters that periodically refresh and restore signals transmitted along the downhole string. To minimize power consumption and to improve communications efficiency, the surface interface, the node, and the downhole interface communicate over the communications line(s) using pulses of radiofrequency energy. These pulses may be organized in data frames that may include one or more wake-up pulses.