Re: About UTS#6: SCSU - 10. Possible Private Extensions: why not a "COBS" TES?

From: Doug Ewell (
Date: Sun Aug 15 2004 - 12:07:47 CDT

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    Philippe Verdy <verdy underscore p at wanadoo dot fr> wrote:

    > I know that this is not part of the SCSU standard, but the reference
    > section 10 about private extensions of SCSU seems to forget some other
    > wellknown transport encoding syntaxes that allows transporting SCSU
    > content within streams where usage of control bytes (like the null
    > byte) is restricted.
    > One well-known method is to apply a "COBS" encoding.
    > See reference and implementation details in
    > It is MUCH better than the proposed method in section 10.1 that uses
    > "DLE escaping", and the method is generic enough to allow escaping ANY
    > byte value (not only the 0x00 byte):

    The examples in Section 10 of UTS #6 are just that, examples. They are
    not intended to preclude other ways of solving the same (or different)
    problems. As you said, they are not part of SCSU, and in fact very few
    implementations actually support them (to paraphrase my paper, "nobody
    uses them because nobody uses them," i.e. they would introduce
    interoperability problems).

    That said, COBS does look like a useful general technique for solving
    the forbidden-byte problem, and might be a good fit with SCSU to solve
    the oft-stated "MIME-incompatibility problem." Perhaps it would be
    appropriate to mention COBS in Section 10.1 as a more general solution
    than the DLE-based scheme (which should still remain in the UTS, though,
    because it is easily explained and does not require a reference to an
    outside paper).

    -Doug Ewell
     Fullerton, California

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