[e2e] Lost Layer?

Joe Touch touch at isi.edu
Tue Feb 11 11:24:12 PST 2014

On 2/11/2014 10:47 AM, Fred Baker (fred) wrote:
> On Feb 11, 2014, at 6:29 AM, Joe Touch <touch at isi.edu>
>   wrote:
>> On 2/11/2014 1:09 AM, Fred Baker (fred) wrote:
>>> In real operational networks, in 2014, we have at least three common
>>> sub-layers within the network layer. One is what we call the
>>> Internetwork Layer and should be called, perhaps, the Inter-network
>>> sub-layer.  It provides the end to end datagram service that TCP and
>>> other transports ride atop.  ...
>> The layer that TCP rides over that spans heterogeneous network technologies is IP, the Internet(working) layer.
>>> ...Another might, by analogy, be called the
>>> Intra-network sublayer. It connects systems that are not necessarily
>>> directly connected, but use the same technology and are operated by a
>>> common administration.Switched Ethernets, 802.11 networks, MPLS,
>>> ATM, Frame Relay, and X.25 are all examples of Intra-network
>>> protocols.
>> In ISO that's the link layer (the Internet originally called these
>> subnetworks), the homogeneous network technology span.
> Actually, no.
> In IEEE/ANSI politics circa 1985, there was an understanding that
> thenetwork layer belonged to ANSI, and the link layer belonged to IEEE.

Neither of which being the ISO.

Now you're just adding yet another set of groups that use terminology 

> IEEE 802 started work on 802.1 through 802.5, including two different
> ways to build networks out of what at the time were called Packet
> Repeaters or Bridges. They bypassed the understanding by calling them
> MAC Layer bridges, and they justified the appellation by noting that the
> bridges operated on the link layer header, whether transparently or by
> source-route bridging.

To the Internet, that's all subnet, not network.

> X.25 was a place where the nomenclature battle was fought heavily.
> InEurope, X.25 was, at the time, *the* network, and the definitive network
> layer.

Sure, and there's also ATM folk who entered the fray in the late 1980s 
too. Not to mention SONET, which is a network too (it has a multihop path).

> To the ARPA folks, it was an API that allowed someone to inject a
> packet into a network; it might come out a different API that was not
> X.25.

Sure, because what IP thought of as a subnet included translation 
gateways rather than using strict layering. All bets are off when you 
"cross the streams" that way (conceptually, as well as literally).

> In CSNET, IP ran atop X.25, and IP was the API that allowed
> someone to select which X.25 destination they might go to.

IP decided which IP destination they went to. Somebody mapped that to 
X.25 locations (either dynamically, ala ARP, or statically), but they 
were selecting IP addresses. If the API involved selecting X.25 
destinations, then they served two different purposes (and could easily 
have had different values): something like DNS names (that translate to 
IP address), and something like ARP (to map back to X.25 for layering).

> Get over it. X.25 is a network, and the Internet is a Network, and
> oneoften runs over the other. As in X.25/TCP/IP/CSNET and other bizarre things.

Sure. They're all "networks". But when we talk about the "network layer" 
in the Internet architecture, it refers to IP. The stuff IP runs over is 
the subnet layer, and the stuff that runs over IP is the transport layer.

> ISO had nothing to do with that.

Sure - I was mapping the Internet layer names and ISO names; throw more 
organizations into the mix and the translation matrix gets more complex 
and more overloaded.


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