Hello, I have a coursework where you are required to build a laser communications system. At the transmit side, you will have the usual PCM codec chip, multiplexer and laser to send data (which comes from an anlog signal like MP3 player). At the receive side you have the DPLL, photoamplifier and PCM decoder, etc to decode the signal for a speaker. Both devices are separate so the PCM chip TP3054/3057 will be operating in asynchronous mode. We will be using the same master clock, and our frequency divider will give use the Bit clock and FSYN. In the lecture slides (Attachment FRAME1.jpg), there are 2 methods to identify the start of a data input. First is to send a few frame markers to "prime" the receiver to prepare for data input. The second will be to add a frame marker in front of a data byte, which will enlarge the output stream. Our group has also secured some design reports by our seniors. As we got them from 2nd hand sources, we are unable to ask them when something unexpected comes out. There is where I am turning to this forum for help Please read FRAME2.jpg. Is it a new technique of sending PCM data? The red line is the part which is most confusing, because it does not tally with the information of the lecture slides (FRAME1.jpg). Why is the Training frame imposed over the data signal in Figure 6? For my part, I suspect it is just a miswording of the 2nd method mentioned in the lecture. However, it might as well be some other method known to the people here, but not to learners like me.