Subject: RE: TCP/IP Terms

From: "Michel Py" <[email-masked]>
Date: Sun, 6 Oct 2002 21:40:32 -0700

Vint,

> vinton g. cerf wrote:
> Michel,
> your drawing of TCP/IP is NOT the model I used in
> the design of TCP/IP.

[Thanks for the historical precisions]

My understanding is that the TCP/IP model is de-facto, opposed to de
jure for the OSI model.

Below are the top ten matches searching for "tcp/ip model" on google;
basically none is the same; some have four layers, some have five, the
names are not consistent.

Some years ago I tried to teach the TCP/IP model and I had to spend
hours explaining why "my" vision of the TCP/IP model was not the same as
they have seen somewhere else (you know, if they've seen it on the
Internet, same as they've seen it on CNN, it must be true).

I'm having trouble explaining to students why a reference model has
variable definitions. If this:
+---+-------------+
! 5 ! Application !
+---+-------------+
! 4 ! Transport   !
+---+-------------+
! 3 ! Internet    !
+---+-------------+
! 2 ! Link        !
+---+-------------+
! 1 ! Physical    !
+---+-------------+
Is what you define as being the TCP/IP model (I don't think anybody
would challenge *you* on this), would you please write an RFC about it
so we can avoid what is below?

http://www.pku.edu.cn/academic/research/computer-center/tc/html/TC0102.h
tml
http://www.indianest.com/computing/networking/n003.htm
http://www2.themanualpage.org/networks/networks_tcpip.php3
http://www.8052.com/tcpip/
http://www.microsoft.com/windows2000/en/server/help/default.asp?url=/win
dows2000/en/server/help/sag_TCPIP_ovr_model.htm
http://dast.nlanr.net/Training/DCWJuly99/kai_tcpip/sld005.htm
http://www.unm.edu/~network/presentations/course/chap2/sld018.htm
http://academic.regis.edu/jguhlke/osi.ppt
http://www.interex.org/pubcontent/enterprise/jul99/f1eltoft.html
http://www.linuxsa.org.au/meetings/1998-02/conflinux/tcpipmodel.html

Regards,
Michel.

---

From: Robert Elz <[email-masked]>
Date: Mon, 07 Oct 2002 23:38:32 +0700

Date:        Sun, 6 Oct 2002 21:40:32 -0700
    From:        "Michel Py" <[email-masked]>
    Message-ID:  <2B81403386729140A3A899A8B39B046405E352@server2000>

  | I'm having trouble explaining to students why a reference model has
  | variable definitions.

What you should be explaining to students is that reference models make no
sense as absolutes.

Models are useful only to analyse some particular situation; if you don't
know what the situation is, they just waste time (as this discussion is
showing).

For most purposes, there are only 3 layers that matter, the layer that is
of immediate interest, the layer below, which is used to implement whatever
is being implemented, and the layer above, which is going to make requests,
and consume whatever can be provided.  Occasionally 4 will be useful if
you're concerned about the boundary between 2 layers, and then need the
layers either side of those two.

Then that sequence can be placed into the overall stack as many times as
you happen to need it, and depending upon your magnification level when
you're looking, sometimes what appears as one layer to one observer will
be a whole complex stack of layers to another.

Attempting to give these things absolute numbers, other than for ease of
reference in some particular context is lunacy.  Even at what we consider
mostly to be the absolute bottom of the stack, I suspect that if you get
the physists involved, you'll find a whole complex set of stuff going on
down there that could be described by a set of layers.

The OSI model has its uses, when you understand that its purpose was to
break up the whole mass of protocols that they were wanting to create
into something manageable to actually work on.  Even then, with hindsight,
it is possible to see that they only just barely managed to get the
net and transport defined with some kind of meaning (those were
the ones whose role and function was pretty much known at the time).  The
complexity that would grow into the link level wasn't anticipated, and
the less said about the stuff above transport the better.

If you have need of a model to explain some particular situation, then
create on, just don't try and give that, or any other model, and
particular absolute status.   It doesn't work.

kre

---

From: Dave Crocker <[email-masked]>
Date: Tue, 08 Oct 2002 12:25:03 -0700

At 11:38 PM 10/7/2002 +0700, Robert Elz wrote:
>reference in some particular context is lunacy.

Not that I disagree with your primary point, it is worth noting that there 
is some basis for hovering about 7, for an *overall* model.

It's that memory limit thing (7, plus or minus 2.)  The plus or minus is 
statistical, so if you want to make sure that people really have no trouble 
grokking the total set, 5 is a better choice.

d/

Dave Crocker <mailto:[email-masked]>
TribalWise, Inc. <http://www.tribalwise.com>
tel +1.408.246.8253; fax +1.408.850.1850

---

From: "Bill Strahm" <[email-masked]>
Date: Tue, 8 Oct 2002 13:17:31 -0700

<Cynicism>
I always figured it was based on the number of managers that you have on
the project, one manager for each layer...  At least that is how it was
done at a previous company I worked for...

</Cynicism>

Models are very nice to help you get people to think about something the
same way.  Of course the best engineers that I know, understand the
model, but think way outside it... Letting unique solutions that break
the model, but deliver better results...

Bill

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Dave
Crocker
Sent: Tuesday, October 08, 2002 12:25 PM
To: Robert Elz
Cc: [email-masked]
Subject: Re: TCP/IP Terms 

At 11:38 PM 10/7/2002 +0700, Robert Elz wrote:
>Attempting to give these things absolute numbers, other than for ease 
>of reference in some particular context is lunacy.

Not that I disagree with your primary point, it is worth noting that
there 
is some basis for hovering about 7, for an *overall* model.

statistical, so if you want to make sure that people really have no
trouble 
grokking the total set, 5 is a better choice.

d/

---

From: John C Klensin <[email-masked]>
Date: Tue, 08 Oct 2002 20:19:51 -0400

--On Tuesday, 08 October, 2002 12:25 -0700 Dave Crocker
<[email-masked]> wrote:

>> Attempting to give these things absolute numbers, other than
>> for ease of reference in some particular context is lunacy.
> 
> Not that I disagree with your primary point, it is worth
> noting that there is some basis for hovering about 7, for an
> *overall* model.
> 
> It's that memory limit thing (7, plus or minus 2.)  The plus
> or minus is statistical, so if you want to make sure that
> people really have no trouble grokking the total set, 5 is a
> better choice.

I would suggest that this particular situation has almost
nothing to do with the Miller result.  In particular, that
hypothesis derives from work with short-term memory and the
number of things one can keep track of at a time.  The purpose
of layering is, to some extent, similar to that of
modularization of other types, i.e., to reduce the number of
things you need to think of at a time.  And, from that
standpoint, kre's observation to the effect that "the one you
are looking at, one up, and one down" is what is relevant is
exactly the right short-term memory analysis.  And that number
is lots smaller than seven.  Or even five.

But this is getting very far afield from anything relevant to
the  IETF or network modelling.

    john

---

From: Dave Crocker <[email-masked]>
Date: Tue, 08 Oct 2002 20:49:43 -0700

At 08:19 PM 10/8/2002 -0400, John C Klensin wrote:
>number of things one can keep track of at a time.

for serially related data, yes.  data that might be termed independent 
contexts probably is down to one for each of the information bits that he 
postulated, namely 3.  2 if you want to be safe.

At any rate, juggling a model, for doing real-time work -- like discussion 
-- seems to involve short-term memory issues.  Hence the limit still seems 
to apply.

>the  IETF or network modelling.

that was why I hadn't gone into citing Miller's paper, which is, by the 
way, a really fun read.  It was published in the preeminant psych journal, 
yet he open it with a discussion of his being stalked by a number...

d/

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