Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

On 10/31/2009 05:46 PM, Richard Bennett wrote:
> the fact that IP is a very thin abstraction of the Ethernet layer 2 
> and that TCP is a vehicle for resolving problems that are typical of 
> the CSMA/CD Ethernet environment
This statement is nonsense. IP is not a very thin abstraction of 
Ethernet layer 2.  IP is carried over many protocols other than the 
Ethernet. TCP is an end-to-end protocol for in-order virtual circuit 
data delivery, designed to work over IP, and to handle problems that 
have nothing to do with CSMA/CD.

> In other words: does the success of Switched Ethernet suggest that 
> it's better to think of network protocols as units of recursion than 
> as collections of statically-placed functions that operate once and 
> only once in the lifetime of a packet?
No.  This is also nonsense, and begs the question.  Network protocols 
have never been described as not "collections of statically-placed 
functions that operate once and only once in the lifetime of a packet".  
Nor does the "success" of anything in the marketplace suggest how to think.

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

There definitely are lessons 
in the evolution from 
end-mediated contention to 
switch-mediated access
in ethernet-land.

The oft-perceived analogy
of the whole internet as a big ethernet,
a huge shared resource 
with contention mainly mediated
by end systems, is alluring.

So the move to 
net/switch-centric resource allocation/control
in the local, 
might suggest some similar move
in the wide area...
until you actually think about the
heterogeneity in the
topology, in capacity and in latency,
of the system - 

Plenty of enterprise nets and small ISPs
(e.g. UK size) can consider
a carrier-grade switched ether
control philosophy (e.g. 
esp. to replace
complicated MPLS setups:)
but it doesn't subsume/replace e2e
resource sharing - 

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

well to be specific,
TCP retransmission times
and 
TCP congestion control
were NOT designed in from day 1

early TCPs had fixed retransmit until the RSRE algorithm
and then it was still some time before the Karn/Partridge
improvements kicked in
plus 
early TCPs had no congestion control at all 
until '87

however, since then 
the adaptation of timers
and the adaption of flow rates 
makes the interweb
look very much like a giant contention ethernet - 
in fact for exactly the same reason as voice on ethernet
never  was a big deal, voice on the interweb
requires you to have a path running at releatively 
low utilisation otherwise delays diverge...and loss kicks in

one thing 
(van pointed this out in a talk here a couple of days ago)
that saves it from the same fate as pure contention systems
is that there's a packet conservation principle...
again NOT something designed in the original TCP

so that's 3 new principles within the end2end system that

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

David P. Reed wrote:
> On 10/31/2009 05:46 PM, Richard Bennett wrote:
>> the fact that IP is a very thin abstraction of the Ethernet layer 2 
>> and that TCP is a vehicle for resolving problems that are typical of 
>> the CSMA/CD Ethernet environment
> This statement is nonsense. IP is not a very thin abstraction of 
> Ethernet layer 2.  IP is carried over many protocols other than the 
> Ethernet. TCP is an end-to-end protocol for in-order virtual circuit 
> data delivery, designed to work over IP, and to handle problems that 
> have nothing to do with CSMA/CD.
>
Dave Reed is right, of course. Richard Bennett's declarative statement 
is so far into an alternate universe from the real world that one has to 
suspect he is baiting the list.  Dave used the word "nonsense" ... it 
seems to me to be difficult to deny the rightness of that word choice.

Bob Braden

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

Jon Crowcroft wrote:
> well to be specific,
> TCP retransmission times
> and 
> TCP congestion control
> were NOT designed in from day 1
>
>   

Jon,

It does not really matter, of course, but your quick summary is not 
quite accurate.
It depends upon what you consider to be "Day 1".  E.g., RFC 793 did NOT 
have a
fixed retransmit time.  And if you want to give RSRE credit for 
exponentially smoothed
RTT measurements (a fact I had forgotten, assuming you are correct), you 
ought to
give Van credit for finally figuring out how to do real congestion 
control, in 1987.

Bob Braden
> early TCPs had fixed retransmit until the RSRE algorithm
> and then it was still some time before the Karn/Partridge
> improvements kicked in
> plus 
> early TCPs had no congestion control at all 
> until '87
>

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

On Oct 31, 2009, at 2:46 PM, Richard Bennett wrote:

> Dave Eckhardt wrote:
>> So it's unclear
>> that CSMA/CD was a structural limit of Ethernet--the reality
>> is probably more like "It doesn't matter much how you contend
>> among a few hosts, but you can't build large networks unless
>> you limit contention domains to less than the size of the
>> large network", which is almost a tautology.
>>
> That's part of the story, but the implications of the switched  
> Ethernet killing off CSMA/CD Ethernet are much larger, and relate  
> the end-to-end arguments principle. CSMA/CD Ethernet was an end- 
> point managed system sharing a dump pipe, while switched Ethernet is  
> a system that deploys intelligence - switching, flow control,  
> buffering, QoS discrimination, VLANs - inside the network at  
> multiple points. Switched Ethernet is scalable, manageable,  
> diagnosable, and future-proof, while CSMA/CD Ethernet is none of  
> these things. So the competition of CSMA/CD and Active Switching for  
> markets demonstrates something about which approach to the design of  
> layer 2 networks is superior.

I think you left-out how Power over Ethernet will replace the global  
power grid and that it also juliennes fries :)

Color me a cynic, but I rather thought that today's switched  
"Ethernet" needed flow control and buffering precisely because CSMA/CD  
was removed from Ethernet when it went full-duplex?  I seem to recall  
that flow-control was not initially present in full-duplex Ethernet.   

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

There was a need for flow control as soon as full dupex was included in 
the 10BASET spec, but it became even more important with the addition of 
100BASETx to switches that were backward compatible with 10BASET. A 
collision is better than a silent drop, but neither is necessary. Full 
duplex Ethernet switches can transmit multiple frames at the same time, 
which is quite convenient in meet-me rooms at IXPs so I don't buy the 
routing vs. switching dichotomy; switching helps us do routing.

The point about the thinness of the IP layer doesn't have to do with 
routing as much as it has to do with what's in the IP header and what 
isn't. I would expect that a network layer protocol would have an 
unambiguous address for the host, like CYCLADES, DECNet, XNS, and ISO 
CLNP. But all IP has is an address that's a synonym for the LAN 
interface address, a point of attachment. So it's not fully separated 
from Layer 2. This is especially stark in IPv6 where they just throw in 
the whole MAC address into the IP header in order to bypass ARP.

In addition to IP lacking an actual host address, it doesn't do any 
protocol either - it's just a packet format and doesn't participate in 
any specific sequences of behavior, which is once again just like Blue 
Book Ethernet, AKA V2. It's perhaps worth noting that V2 is an odd MAC 
protocol  since most of its cousins have multiple frame types and state 
machines for each, even Switched Ethernet. Granted, there is a network 
address in the IP header, for what it's worth, but IP seems to be 
missing some function that would make networking a lot easier than it is 
in scenarios where a number of diverse applications contend for 
resources, and some of the function it's missing was also missing in V2. 
This is true in many universes, some of the alternates to this one.

Regarding Jon's comment on the rebirth of CSMA at the edge, there is 

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

On Nov 1, 2009, at 1:26 PM, Richard Bennett wrote:
> Regarding Jon's comment on the rebirth of CSMA at the edge, there is  
> some ironic truth to it, but Wi-Fi's not the same style as CSMA/CD  
> because with 802.11n we have a selectively acknowledged windowing  
> protocol, much more efficient than TCP where you have to discard  
> everything after a dropped packet and do it again.

My history with TCP stacks does not go back "to the  
beginning" (whatever that might actually be), and I did not start in  
the "PC" space so perhaps my life was charmed, but going back to 1988  
I'd not encountered any TCP where that was the case.

rick jones
there is no rest for the wicked, yet the virtuous have no pillows

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument

In missive <4AEDCCF6.3090600 <at> isi.edu>, Bob Braden typed:

 >>It does not really matter, of course, but your quick summary is not 
 >>quite accurate.

 >>It depends upon what you consider to be "Day 1".  E.g., RFC 793 did NOT 

absolutely - sorry - i was talkin about first cut at design - the RSRE
discussion predates the RFC and the result made it in to the spec..

 >>have a
 >>fixed retransmit time.  And if you want to give RSRE credit for 
 >>exponentially smoothed
 >>RTT measurements (a fact I had forgotten, assuming you are correct), you 

see  IEN160 for the discussion and credit - was a couple of years
before i was doin this sort of thing so you prob. know more about this
than me...
http://www.postel.org/ien/pdf/ien160.pdf

but the smarter smoothing happened in 87 
(using smoothed mean + mean squre difference
for retransmit rather than just EWMA)
and the late 80s stuff had input from Karn&Partridge

 >>ought to
 >>give Van credit for finally figuring out how to do real congestion 
 >>control, in 1987.

of course!

Re: Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument