tdh@frog.UUCP (T. Dave Hudson) (10/27/87)
I did not receive any informative responses to my question as to why IEEE 802.4 Head Ends don't simply remodulate, but Kevin Strietzel referred me to Ken Jones of Concord Communications. Ken said that: 1) The pseudo-silence pattern is used to avoid the need for a longer preamble and allow cheaper receivers, since the modems can remain in sync with the signal. 2) The remodulation (not simply frequency translation) reconditions the signal. 3) The error bit (set on bad checksum discovered by the head end) is used for isolating errors. Now (2) and (3) are obvious, but their justification, according to Ken, is that the protocol depends upon a low error rate. He admitted that the head end did seem to be doing a link layer function with (3). David Hudson