Selfish routing

Sun Apr 27 21:09:04 UTC 2003

alex at yuriev.com wrote:
>>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.
> 

And what, pray tell, governs stupid mistakes designing the network? For 
that matter, which network? I've run traffic through some networks for 
years without a problem. Then one day, that network makes a mistake and 
clobbers the traffic I send through it. Naturally, I redirect traffic 
via other networks, but the spare capacity via the other networks does 
not equate to the traffic I'm shifting, so while improving QoS for my 
customers, I have still shorted them.

It could be argued that more spare capacity should have been allotted 
for the other networks, yet then if the first network hadn't had a 
problem, money would have been wasted on capacity that wasn't needed. It 
is an art to establish enough bandwidth to handle redirects from 
networks having problems and yet keep costs at a reasonable level.

Hypothetical: You are interconnected with 3 networks pushing 100Mb/s 
through each. Slammer worm appears and makes 2 networks untrustworthy 
because of their internal policies. The third network is fine, but your 
capacity to it probably won't hold 300Mb/s. Do you a) spend the money to 
handle your full capacity out every peer and pay two - three times what 
your normal traffic is to the peer, or b) allot reasonable capacity for 
each peer, and recognize that there are times when the capacity will 
fall short?

Network planning is not just about whether you make a mistake or not. 
Performance is dependant upon the networks we interconnect with, issues 
they may have, and how well we can scale our network to circumvent those 
issues while remaining cost effective. My hypothetical is simplistic. 
Increase the number of peers, as well as the number of peering points to 
said peers, determine the cost and capacity necessary during multiple 
points of failure, plus the cost within your own network of redirecting 
traffic that normally takes more diverse routes, apply chaos theory and 
recalculate.

-Jack