Q:Why router with ATM interface comes out earlier than pure SONET interface?

Sean M. Doran smd at clock.org
Tue Aug 4 01:40:00 UTC 1998

Here is my sole contribution to this conversation.

Christian Kuhtz wrote:

| That is, if somebody can figure out a way to do private line (circuit
| emulation) through an IP cloud.  ATM will be an interim step, in my opinion.

Done.  Essentially what you do is emulate a connection-oriented
network over a connectionless one [jnc bait], and prioritize this
emulated connection-oriented service.   This entails a design
constraint: the aggregate input rate for this emulated CO network
to any interface must be less than or equal to the output rate,
and traffic shaping must be done to avoid the "bunch up" effect.
This also requires a resource reservations mechanism of some
nature, ranging from manual configuration coordinated by email/phone
to fully dynamic "bandwidth brokerage", and a means of identifying
the emulated-circuit traffic at each router where it will receive
special treatment in terms of queueing, shaping or both.

Please see Van Jacobson, Sally Floyd et al's interesting work
on this front at http://www-nrg.ee.lbl.gov/nrg-talks.html
and in particular Van Jacobson's presentation 
"Towards Differentiated Services for the Internet" 

Also very interesting and related to your question is
the research and practical work on Class-Based Queueing at
and in particular Dr Floyd's "Notes on CBQ and Guaranteed Service"

Van Jacobson also did an excellent NANOG presentation, the video clip
of which lives at


(search down to the RealVideo Broadcast beginning at 10:45 am
on Monday, June 8)

While you are looking at tasty research notes, please also
take a moment to consider the wonderful world of best-efforts
services (rather than circuit-emulation) and examine the delicious
TCP Friendly page at


and study the paper by Jamshid Mahdavi and Sally Floyd intently.
These are among the best things you will read for a while.  Please
send all your network application developer friends -- especially
the multimedia ones -- to that document and to the page in general.

The followup paper at http://www-nrg.ee.lbl.gov/floyd/end2end-paper.html
and the related links at http://www-nrg.ee.lbl.gov/floyd/tcp_unfriendly.html
are also wonderful.  Heap scorn on the bad guys, or be prepared
to police people's congestion-avoidance.

For those of you who don't mind doing some digging and who
want to see some practical engineering thinking behind alot
of this theoretical stuff, please investigate the IETF 
diff-serv mailing list.  Curtis Villamizar <curtis at ans.net> has
made some excellent contributions there (from an operator's
perspective) that are worth some study, although many others
have had useful things to say.  (Many others have not, however, but
any operator, or anyone else, who reads NANOG is probably pretty
good at scanning for content).

Ten minutes with Noel Chiappa [the jnc being baited] is also
very worthwhile.  If you can't arrange that, I believe Gordon 
Cook did an interview with him in 1997ish that I remember was
well worth reading.

Finally, the ESNET people have recently done some proofs-of-concept
that the equivalent of CBR can be done across a small-i internet and
in principle the big-I Internet in the presence of a mix of traffic.
This should encourage those people who maintain that the good bits
of ATM -- and yes, even I admit that there are some --  can be
subsumed into the Internet if and as actually needed.


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