 If an acknowledgment was not received from the Menehune after the prescribed number of automatic retransmissions, a flashing light was used as an indicator to the human user.Also, since the TCU's and PCU's did not send acknowledgments to the Menehune, a steady warning light was displayed to the human user when an error was detected in a received packet.Thus it can be seen that considerable simplification was incorporated into the initial design of the TCU as well as the PCU, making use of the fact that it was interfacing a human user into the network.