Philip,

There are many protocols you can use. It entirely depends on your
application.

Some common ones are
X.25, TCP/IP, UDP, MASC, SNAP, ROSSI

Generally, if you have larger amounts of data , your application would
likely segment these into smaller packets and reassemble them at the other
end. In this case X.25 and TCP would be better.

If it is small packets of data then UDP or SNAP would be better
(www.hth.com) .

Also, the medium has influence. For example, over radio - you would want to
keep your packets very small (say 32 bytes) and re-send only packets with
errors.

Hardwired applications with lots of data usually would use HDLC bit oriented
protocol.

We deal mostly with radio and use small scale protocol based on 3 layers of
the OSI 7 layer reference model.
We use 16 bit CRC for error detection and re-send if not ack from addressed
node, All our packets have destination and source address bytes and work
well in a networked environment of radio modems up to 256 devices.

The protocol shouls exhibit synchronization. In our application a sync byte
is sent. When over air, you need to send pre-amble before the data packet to
condition the receiver's data slicer.

Regards

David Huisman
Orbit Communications
www.orbitcoms.com

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