[e2e] Historical question: Link layer flow control / silent discard

John Day jeanjour at comcast.net
Tue May 28 14:02:57 PDT 2013

Just for the record and then I will let this discussion go on, but 
X.25 was not at the core of the OSI Model.  It is true that there 
were some people Bob's age (we called them the old guard) who thought 
they wanted to X.25 products and say it was OSI, but no one else had 
any intention of doing OSI products with X.25.  Nor was it at the 
core of OSI Network Layer.  Most of those people would have said CLNP 
was the core of the OSI Network Layer.  In fact, OSI was designed to 
handle multiple network technologies, which is why the Network Layer 
was structured the way it was.  OSI allowed both connection-oriented 
and connectionless operation.  The fact that no one ever defined for 
OSI a connection-oriented network layer protocol but did define a 
Connectionless Network Layer Protocol (CLNP) speaks for itself.

End of myth-busting.

Take care,

At 9:51 AM -0700 5/28/13, Bob Braden wrote:
>On 5/25/2013 4:34 PM, Lachlan Andrew wrote:
>>However, perhaps that isn't the link layer. I've always wondered 
>>why switched ethernet (which does the ISO layer-3 tasks of 
>>addressing, routing over multiple point-to-point links and 
>>buffering) is called a "link layer" by the internet community... 
>>Cheers, Lachlan
>Ah, interesting point. Of course an Ethernet, whether switched or 
>bussed, is a network. It has addressing, routing,
>and flow control. Ethernet, or rather its predecessor X.25, was at 
>the core of the OSI  7 layer model.
>But the pesky internetwork crowd came along and said, we need a 
>network of networks, so we need a new end-end
>INTERnetwork protocol, let's call it IP."
>So what are the poor OSI devotees, who believe in One Network to 
>Rule them All, to do?
>We IETFers are pragmatists, not layer model purists. (as illustrated 
>by our lack of
>embarassment about splitting the layers with MPLS, IPsec, TLS, etc.) 
>We became careless and smudged over
>the network/internetwork distinction. So, IETFers generally refer to 
>the Internetwork layer as the "network layer." Then the Internet
>protocol stack sort of looks like the OSI stack, and there is an 
>illusion that the OSI stack has something to do with reality.
>If IP is the "network layer" (we are too lazy to say "internetwork 
>layer"), then what is the Ethernet? In IP land, it is a 
>subnet(work). But
>for those who believe that IP is really our network layer, then the 
>next layer below IP was dubbed  the Link Layer, because it
>seems to correspond to the OSI Data Link Layer. That is the answer 
>to your question.
>Note that the Internet's Link Layer should not be (but often is) 
>confused with the OSI Data Link Layer. It co ntains
>"everything" in Vint's famous phrase " I  P  over everything".
>Section 1.1.3 of Host Requirements RFC 1122 defines the internetwork 
>layer model carefully.
>And MAP was the only internet community member who bothered to 
>straighten this out.
>(You are an Internet pioneer iff you know who MAP was).
>Bob Braden

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