[Info-vax] Rethinking DECNET ?

[Johnny Billquist]

Look, you are making a huge mistake when you try to use the OSI 7 layer 
model when talking about TCP/IP. I've tried to say that a number of 
times now, but I guess I will have to be more explicit.

On 2014-09-03 06:18, JF Mezei wrote:
> On 14-09-02 22:12, Johnny Billquist wrote:
>
>> No. The 7 layer model is specifically the OSI model.
>
> It is a generic model developped to allow comparison/compatibility of
> network stacks.  It may not map precisely to  TCP but the concept is
> still useful.

No. The OSI 7 layer model is the OSI 7 layer model. You can develop 
other models if you want to. Those other models might have more or fewer 
layers. You might also throw different things into the different layers. 
And this will not be the OSI 7 layer model.

It will still be a model, but a different model.

So why do you think that the OSI 7 layer model is somehow universal and 
generic? It is not. It is one explicit model.

>> There is no
>> universal rule that you have to have 7 layers,
>
> Of course not. Those 7 layers are there to try to be able to compare
> stacks are more or less compatible layers. For instance, DECNET 4 is
> compatible with IP on layers 1 and 2 (physical and ethernet).

Indeed. And those two layers are obvious for anything that uses 
ethernet. If you do some other physical medium, the story might be 
different, though.

But I fail to see the point. If you use ethernet then of course any 
network protocol stack would be the same at the ethernet layer.

> Another example: whebn discussing networking, you can have switches that
> handle layer 2, or routers that work at layer 3. A layer 2 network is
> oblivious to what happens at higher levels, so it can switch IP, DECNET,
> PPPoE , LAT, SCS etc. So the discussion of layers is useful here and is
> used often at regulatory discussions in Canada.

Are you aware that an IP router covers both layer 3 and layer 4, if you 
want to talk about the OSI 7 layer model?

> The 7 layer model defines all the way to the application, but one can
> still use it when dealing with only the lower levels.

The OSI 7 layer model is a specific model with a specific division 
between the layers. Other separations can be done, and are done. TCP/IP 
do *not* fit in the OSI 7 layer model.

So it do not make sense to use this model when we talk about TCP/IP.

>> Not sure why you want to exclude protocols like ftp from the TCP/IP stack.
>
> I guess they could be included to fill the top layers if you wanted. But
> generally, IP is though of as layer 3 in networking terms since this is
> where routers generally stop. (although many routers will look at layer
> 4 (TCP) for additional network management and DPI equipment go even
> higher to look inside data payloads to then perform throttling).

No. IP is both layer 3 and layer 4, if you want to use the OSI 7 layer 
model as the reference. And TCP is also layer 4, but might also be 
considered to cover part of layer 5.

And ftp is a protocol, which runs on top of TCP, so of course you could 
include it in whatever model you want to think of.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol