From: Chris Leishman (eqbrrau@mail.dy.fi)
Date: Thu Jan 04 2001 - 06:43:03 EET
Hi all,
According to the AX.25 Link-Layer Protocol Description, it is possible to do
"multicast" style transmission, where the destination callsign is a code word
that the receivers listen for.
----------------------
2.4.3.6 Connectionless Operation
In Amateur Radio, there is an additional type of operation that is not
feasible using level 2 connections. This operation is the round table, where
several amateurs may be engaged in one conversation. This
type of operation cannot be accommodated by AX.25 link-layer connections.
The way round-table activity is implemented is technically outside the AX.25
connection, but still using the AX.25 frame structure.
AX.25 uses a special frame for this operation, called the Unnumbered
Information (UI) frame. When this type of operation is used, the destination
address should have a code word installed in it to
prevent the users of that particular round table from seeing all frames going
through the shared RF medium. An example of this is if a group of amateurs are
in a round-table discussion about packet radio,
they could put PACKET in the destination address, so they would receive frames
only from others in the same discussion. An added advantage of the use of
AX.25 in this manner is that the source of each
frame is in the source address subfield, so software could be written to
automatically display who is making what comments.
-------------------------
I'm trying to work out how you can configure the linux device to receive
packets destined for that callsign (in addition to it's normal callsign) and I
can't seem to see it in the HOWTO's, etc.
Please note that I don't actually have any equipment as yet - I'm just trying
to determine if linux & AX.25 will be suitable link-layer for a broadcast
style ad-hoc wireless network protocol I'm thinking up..
Thanks,
Chris
--
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Knuth: premature optimisation is the root of all evil.
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