Simple network question

[Tom Cumming]

        I am confused. What is the difference between TCP/IP network
    "stacks", and the ISO network "stack". Ok, ok, I understand the
    differences between TCP/IP and ISO it'self. But I am confused in the
    implementation.

	The environment that I am have in mind is say, a bunch of unix
    machines all talking to each other though some type of network.
    It seems to me (from experiance) that the TCP/IP network "stack"
    (in above environment) is usually implemented as a module of some
    sort that is linked into the kernel, i.e., Application-Datalink
    layers are all "right there". For example, some applicaton running
    under X connected through sockets to TCP/IP, sitting on a datalink to
    ethernet hardware, are all in one "box".
  
	On the other hand, the ISO "stack", although having functionality
    almost identical to TCP/IP is almost always implemented differently.
    I almost always see ISO Layers 1-3 (Hardware - Network) implemented
    in something called X.25.1-3, and then maybe TCP/IP hacked on top of
    that. For example, some application running under X connected through
    sockets to TCP/IP, sitting on a datalink to a special modem that is
    connected to an X.25 "cloud". You are not *really* running ISO because
    "layers" are really inplemented on the far side of the modem!
     
	Why don't I *ever* see something like this (for example): Some
    application running under X, connected through the ISO session,
    transport, network, layers, with a datalink to a ethernet controler.
    Why is'nt there a top to bottom *ISO* stack floating around like the
    BSD TCP network stack (The one I'm most familier with)?

		Thanx, Tom C.

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