| 摘要 |
<p>A head-end station (1) for a passive optical network system arranged to transmit and receive TDMA frames comprising a header portion and a plurality of basic frames, each basic frame comprising traffic bits and control bits. The head-end station (1) includes a data transmitter which assembles and transmits downstream frames and also generates a diagnostic signal for transmission in a downstream frame, the station being switchable to a diagnostic mode in which it transmits the diagnostic signal in a downstream frame in the absence of other traffic, and also including a data receiver which receives upstream frames and detects a return of the diagnostic signal. In a preferred example, the head-end station (1) may transmit a diagnostic signal in the header portion (H) of each downstream frame. Also, in a test mode the transmit signal is looped back to the receiver to enable testing of the transmit/receive function. Loop back is provided at three levels, namely the transmitter drive level, the monitored output level and at the laser output/receiver input level.</p> |
