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'Broadcasting data over radio'
1997\09\08@001416 by Dave Mullenix

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Paul B.  (VK2BZC) wrote:

>  The problem of error correction in a broadcast mode is a thorny one
>indeed, generally implemented by serialising broadcast packets with non-
>cylic (non-modulo at least) identifiers and individual receivers issuing
>numbered NAKs after a timeout rather than ACKs.  Even this is limited.
>But I had best ask first, is this what Jason was asking, or does he just
>want a "connected mode" Packet protocol?

Paul probably already knows this, but for the benefit of non hams, some
amateur radio packet satellites use a broadcast mode that lets many people
receive files simultaneously.  Many files are too long to be sent in a
single 10 minute satellite pass.  It would also be wasteful to have many
hams downloading popular files over and over, so a broadcast protocol was
devised.  I don't know the details, but the files are sent in blocks with
enough extra information to allow ground stations to reassemble the blocks
of data received over many passes into a single file.  If a block is missing
or contains errors, protocols exist that allow the ground stations to
request single blocks to fill those holes.

I don't know exactly where to find information on this protocol, but

http://www.amsat.org

should be a good starting point.

Dave, N9LTD

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