Yes, MPEG3 uses compression. But I think the compression is on the delta of the next frame to the current frame. (For those who are reading and wondering what delta means, it's the difference between the two frames in this case.)
I think that compression algorithm also contributes to the varying transfer rate that you see on the display.
I'm sure fibre optic in your home environment suffers from little interference, just as coax would. When I first had cable installed, I complained that the picture is not clear and sharp. The cable company technicians (a few of them came down) said that it's my computer network causing it, that it's the area I'm in, that my flat-ribbon TV antenna cable is causing it...None of that is true. The truth: they have a faulty part installed on the connection out on the street!
Computer networks using T-pieces don't use gold-plated t-pieces. And data is not corrupted.
Take modems for example. You can use the best cables for your best modem, or you can use cheap cables for your cheapest modem. If your telephone is noisy, nothing is going to stop you from getting a bad transmission.
