North American Network Operators Group

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Re: Traffic engineering tools

  • From: Jerry Scharf
  • Date: Tue Oct 26 16:09:27 1999

While I fully agree with Tony's comments on damped control systems, we
also have to ackowledge the desire for fast failure recovery. When a
person talks about recovery times measured in the same units as link RTT,
it is very difficult to create well damped systems. Many systems that work
fine in simulation and in "normal operation" die a horrible death as
circuits start to fail. Those people pointing to theoretical complexity
tend to be proven correct, in my experience.

I will also point to an idea that Vadim has championed for a long time
that fast lines should go down quickly and up slowly rather than up
quickly and down slowly as they do now. It doesn't solve the damping
problem, but it does allow you to be more aggresive in taking failed lines
down without destabilizing current algorithms. Someday YFRV may offer this
as an option, perhaps some of them do already.

I do believe that some of the TE folks are punting the general case
solution by only attempting to do TE and protection on a small potion of
their traffic. If you have a glut of web traffic that acts as a sponge,
you can get away with nonoptimal management of the subset without causing