Now I would like to set up a digital data link using RS232C.  To speed
    up the link I think about some sort of data packaging, compression and
    correction. All this would be burried into PIC (16C84) acting as a
    link controller.

    Do you have any suggestions and/or ready made examples?

I would think the PIC arcitecture would be particularly unsuitable for
implementing any of the currently popular compression algorithms.

BillW