Re: PHY Layer Protocols


dsp_stap@...
 

--- John Hays K7VE wrote:
>Raw TCP/IP packets will need some kind
> of synchronization training sequence at
> the beginning.

Right.  Each lower layer wraps the previous upper layer in its own header and trailer before sending.  The PHY layer's header is for synchronization and error correction.

> Right now we have two Amateur protocols
> that provide framing around TCP/IP and
> handle the synchronization as part of their frames.
>
> TCP/IP runs within a UI AX.25 frame.
> TCP/IP runs within Ethernet Frames inside of D-STAR frames.

> ... create more robust and efficient air protocols,
> e.g. forward error correction, header compression ...

Really? D-Star has no FEC??  I'm shocked!!  (And horrified!)  If it were possible, I would now have an even lower opinion of D-Star than I had in the past.

The ARETF needs to develop a PHY layer protocol, or perhaps even more than one.  We should look to 802.1x for ideas.

All PHY layer protocols should do FEC, and synchronization.  Perhaps we need a very simple PHY layer that does only that, for simple point-to-point links.

Then perhaps we need more complex PHY layers which handle media access (to minimize collisions and thus maximize throughput).

How fast will Xmit/Recv switching be?  Will it be fast enough for TDMA?

Finally, I'm thinking we want more complex LINK layer which would handle discovery, link establishment, ad-hoc networking, etc.

It is not clear to me how to handle frequency selection. It is clear to me that if we can solve the problem of using multiple chanels simultaneously in a network, it has the potential to increase aggregate network throughput. Frequency selection is part of the physical layer, but perhaps it should be controlled at the link layer.  On the other hand, how do you tell all nodes who might want to talk to node X that he has moved to channel Y?  What about the choice to QSY? Should that control be centralized?  That seems like a bad idea, but it is also not clear how to do it in a distributed fashion.  What happens when node Z didn't get the message, and continues to waste bandwidth on channel X, talking to node X, when node X has QSYed to channel Y?

I think there is possibly a Ph.D. thesis lurking in the problem of channel selection controlled at the link layer. I note that NOBODY has done it yet.  I've never read any academic papers on the subject.  And it is such an obvious solution; hams have been doing it on nets for passing traffic for almost 100 years -- maybe longer.

All of a sudden, ham radio is fun again.

73,
Ken N8KH

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