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Old April 26th 06, 02:02 AM posted to rec.radio.amateur.digital.misc
psyshrike
 
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Default Newbie, questions on AX.25, theory, hardware etc.

Howdy,

I'm interested in low level portability. The end-user portion the
transmission standard is expected to be implimented in chips. But the
the data-originator should optimize existing infrastructure. From that
standpoint:

Browser-net-WebServer-Database-net-proxy-radio-wireless-client.


The segment between the database and the proxy really wants to be able
to use IP as a network layer. If I was looking for a one-off solution I
could cronjob an RCP. I would rather have a protocol instead because I
want intercompatability between implimentations.

As a transmission standard I am thinking more layer 2 and up. Bandwidth
usage should scale with the layer 1 medium. I don't need much
band-'width' but would happily encode the bits on whatever frequency is
most appropriate. 56Kbps would be nice but I could probably get away
with 4.8Kbps

The actual frequency range I settled on will be dependent primarily on
associated hardware costs. (on the client side, not the publisher side)
I am guessing the L-band might be servicable considering there are
already buku recievers units built for consumer GPS. Feel free to
enlighten me if I'm totally off the mark there.

This service doesn't compare to GSM or equivilant. The protocol should
not disclude terrestrial transmission, though sattelilte would be
prefered due to fact that the customer base is global, potentially
rural in many cases, and generally atypical of the GSM customer. I do
have unique identifiers (for the data, as well as a client-id) that
must be transmitted. These unique bits are expected to be read by a
chip on the client side.

I am guessing that one of the issues here is that FEC seems to
intigrate layer 4 and layer 1 of the OSI model into a single service.
So wireless transmission and terrestrial transmission are a bit
backwards. On copper, bits are reliable so error correction is mostly
just CRCs. Dropping a frame is rare. With wireless the frequentness of
dropped frames makes heavy error correction and transport control part
of layer one. This makes following the OSI model from a development
standpoint at least a little redundant past layer 1? Am I seeing that
part of the issue clearly?

Thanks for the Ref to the ATSC, that will probably clear up a lot of my
questions. You are correct, I do need to learn more about wireless
communications. That is why I posted here. :-)

I'm guess what I'm looking at is writing a presentation layer protocol,
encapping it in UDP, the proxy then strips the UDP header and reencaps
my protocol into some form of ATSC protocol, which is then dumped into
a modem buffer. Whalla, IP to end user.

(if only it was that easy)

-Matt

 
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