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Hamed Nassar wonders:

>      ===  personal protocols: where do they fit in the big picture ===

> People have been asking me this question.  Personal protocols (such as
> kermit, xmodem, ymodem, <banana>modem, tlink, sealink, <banana>link,
>cis a, cis b, cis <banana>, etc..etc.(where banana = any thing)), where
>do they fit in the ISO reference model?

I would say they represent the application layer. There are two
applications at both sides communicating with each other, more or less
duplicating functions of the lower layers. If the lower layers provide
more functionality you can choose a more appropriate protocol. Eg. if
you use one of those ISDN-killing-modems which transport data
error-free at astonishing speeds then you can use a simpler protocol.
But if you have no error-handling what so ever then you should use a
protocol that handles this itself.
Modems as the Telebit trailblazer do 'protocol-spoofing'. They collect
packets ACKing each packet directly to the host and send them in one
long datapacket to the other modem which handles them one by one to
the receiving host. I have always thought you could see this as a
(confusing) implementation of the layers 1,2 and 7 (physical, data- and
application layer). Comments?

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                any official position of my employer.

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