Selfish routing

Mike Lloyd drmike at routescience.com
Sun Apr 27 21:31:22 UTC 2003



alex at yuriev.com wrote:
>>But curiously, adding some 
>>incremental capacity to a network can, under some conditions, actually 
>>make it worse!
> 
> Oh, rubbish.

Hmm?  You dispute the result in Roughgarden's paper - that Braess' 
paradox can occur?  Or are you just saying that if the Internet is run 
solely by people at your intelligence level, it'll never come up as an 
issue?  (I've not said Braess' paradox is common; only that it's an 
interesting result.)

> Of course, the sales people of yet another equipment vendor trying to sell
> yet another useless technology that claims in a yet another way eliminate
> the need of people with a clue on staff in exchange for major $$$ do not
> want to admit it.

Glad to be accused of offering a technology that can only do what smart 
people can do (whether I agree or not).  Since the supply of clue in 
this world is limited ...

>>If you want an optimal network, you can:
>>   1/ sit in the middle and play at being the God of TE
>>   2/ have the various actors optimize "selfishly"
>>   3/ count hops and assume that's close enough
>>(Oh, and if you're into that sort of thing, I suppose you can try 
>>dropping some packets to speed things up.)
> 
> Oh how about "fire those who are ordering wrong size of interconnects, order
> right sized interconnects, count the moneys that you did not waste".

Certainly a reasonable addition to the list - I'd prefer it to those who 
believe smart packet loss will solve all our problems.  Trouble is, 
firing staff and buying big cross connects does rather assume that all 
the people you hand packets to are as smart as you are (or can be 
stopped from misbehavhing promptly).

>>And I wouldn't evangelize that faith, as stated.  I do happen to believe
>>in "special" (or if you prefer, "selfish") technology that measures
>>problems in networks I do not control, and if they can be avoided (say by
>>using a different network or a different injection point), avoid them.  In
>>practice, that extra "if" doesn't change the equation much, since:
> 
> So, the brilliant technology costs money but does not provide excellent
> results under all circumstances? Simply not making stupid mistakes
> designing the network *already* achieves exactly the same result for no
> additional cost.

I certainly feel no need to defend a technology as perfect in all 
circumstances; it only need bring useful, cost-effective improvement. 
If you inhabit a part of the network where all links are 
over-provisioned, and no phenomena occur for which you'd like automatic 
re-route, great.  I'm happy for you.

In your own parallel posts, you acknowledge all the murky reasons why 
other people don't build their networks in the way you'd like.  OK; so I 
can make my own network and interconnects Yuriev-compliant, but that 
still doesn't solve all the issues as long as I want to talk to people 
across fabric that is not Y-c.  It's a network of networks we live in.

Mike




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