Subject: Re: [TE-wg] TE use in today's networks

From: Jennifer Rexford <[email-masked]>
Date: Mon, 28 May 2001 13:49:01 -0400 (EDT)

> I suspect that one of the papers referenced is:
>
>	http://infocom.ucsd.edu/papers/744.pdf

Two other papers (posted on the TE-WG list back in December 1999) include

  - A. Feldmann, A. Greenberg, C. Lund, N. Reingold, and J. Rexford,
    "NetScope: Traffic Engineering for IP Networks," IEEE Network 
    Magazine, March/April 2000.
      http://www.research.att.com/~jrex/papers/ieeenet00.ps

  - B. Fortz and M. Thorup, "Internet Traffic Engineering by
    Optimizing OSPF Weights," Proc. IEEE INFOCOM, March 2000.
      http://www.ieee-infocom.org/2000/papers/165.ps

> There are serious considerations to be overcome before this is
> practically implementable (ie, 10 significant digits on routing
> metrics).

The techniques in the papers listed above work with integer weights.
Experimental results seem to suggest that a small number of different
weight values are often sufficient in practice.

> Additionally, there are subsequent ops problems with implementing it
> (ie, dramatic impact when one link drops).

Depending on which link fails, the network load after the failure
isn't all that bad.  Although some failures can cause problems, often
one or two weight changes after the failure is enough to bring the
network back to a happy place (analogous to the need to fail over to
backup paths in MPLS).

> I suspect that this issue has been hammered to death on a mailing
> list somewhere, anone have pointers?

There has been some discussion recently on the IRTF-RR list...
Another reference listed there is

  http://www.eng.tau.ac.il/~shavitt/pub/DIMACS01-17.ps

-- Jen

---

From: Ben Black <[email-masked]>
Date: Mon, 28 May 2001 11:53:55 -0700

> network back to a happy place (analogous to the need to fail over to

The difference in the MPLS case is that the backup paths can be
configured in advance.  With TE using link metrics, you may be forced
into changing the configuration when you least want to: during a
failure situation.

Ben

---

From: "Xipeng Xiao" <[email-masked]>
Date: Mon, 28 May 2001 15:08:58 -0700

Two authors of this much discussed paper:
http://infocom.ucsd.edu/papers/744.pdf
Yufei Wang and Leah Zhang, are my colleagues at Photuris.
We had a long discussion on the practical issues 
of the paper some time back.  Yufei told me that:
THE APPROACH PRESENTED IN THE PAPER IS INTENDED FOR
NETWORK PLANNING, NOT FOR REAL-TIME TRAFFIC ENGINEERING.

You may also find the discussion on the 
[email-masked]' mailing list during 5/7/01-5/9/01
helpful. It clarified some common misunderstandings 
about the paper. See the following thread:
RE: interesting Infocom paper on traffic engineering via routing metrics

XiPeng

---

From: "Dmitri Krioukov" <[email-masked]>
Date: Tue, 29 May 2001 13:56:58 -0400

...Or, with MPLS-OMP, you don't configure backup
LSPs in advance -- OMP dynamically establishes them
(http://www.fictitious.org/omp/fail.html).
The trade-off is slower convergence, of course.
--
dima.

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On
> Behalf Of Ben Black
> Sent: Monday, May 28, 2001 2:54 PM
> To: Jennifer Rexford
> Cc: [email-masked]; [email-masked]; [email-masked];
> [email-masked]; [email-masked]; [email-masked];
> [email-masked]
> Subject: Re: [TE-wg] TE use in today's networks
> 
>