In article .com writes:

I've touched wireless systems before but not enough to be dangerous. My
background is in software and IPv4.

I have an applicaction in mind for wireless transmission. It would be
very narrow band and low bit rate (obviously), multicast transmission.
The client side is reciever only.

In this case AX.25 is overkill, as none of the collision management is
required. As I understand it, what I need is modem, a radio, and a OSI
Layer 2 frame type suitable for wireless transmission. Would PPP or
HDLC work as a frame type? Is there something better suited to
narrowband wireless?

I don't really understand the actual signal modulation too well. If I
said I wanted to span a particular frequency range, doesn't that
frequency dictate the amount of asynchronous bits than can be modulated
into it? So the modem would have to be tunable right? It would have to
modulate specific to the spectrum in use. So I'm taking it there is a
standard, or do the modems you guys use have a knob to control the
modulation rate? Say the modem buffers 300 bps on the RS232 port but
only has the spectrum to transmit say 200 bps through the radio? Or am
I running into "why the hell would you do that?" territory?

So what the minimum hardware/software required to drop one ip datagram
onto a wire and get it transmitted in say a 10Khz wide band?

Several things come to mind.

1. Does it have to be an IP datagram? Does it need error detection?
Error correction? Maximum/minimum size?

2. What sort of data rate can you deal with? Is one bit per second
fast enough? Do you need 10 megabits/second?

3. What sort of coverage do you need? What signal to noise ratio
can you expect? Given the bandwidth you gave, one expects sort
of slow, but...

4. How does it compare to cellular transmissions?

5. How about ATSC (much bigger bandwidth and data rates, but you could
have a bunch of separate PIDs for the different info.)

You need to address several levels of the communications model -- from the
basic modulation, to framing of packets or data, to meaning of the content.

You need to learn more about data communications. There are some good books
out there. Unfortunately, if you want to develop something commercial and
not tell people what you are doing on usenet (a good idea, that), you will
have to learn a bunch, or pay someone who knows a lot about it.

Alan