[Info-vax] Rethinking DECNET ?

[JF Mezei]

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.


>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).

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.

(our wholesale system on DSL called GAS uses layer2, while on cable,
called TPIA is based on layer 3 and has a huge differences in how they
are managed).

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

> 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).