Re: Equal-cost path

["Naidu, Venkata" <Venkata.Naidu at MARCONI.COM>]

-> >  If we assuming all nodes in an area have same
-> >  capabilities (like, line rate forwarding etc), fewer number
-> >  node path performs better in the average case.
-> >
-> 
-> I do not believe that you can make this claim, except in a 
-> simulation, which has little to do with reality.

 I don't think so...[please read on]
 
-> In real networks, with reasonably fast routers and links, the 
-> performance of the routers and per-link serialization are greatly 
-> overwhelmed by other issues (such as the speed of light and queue 
-> lengths.)

 That is why I said, "in the average case", where the assumption
 is all the routers in an area have equal capabilities. In such a
 a case, simple queuing theory would suffice to prove that 
 shorter paths minimizes delay (if link costs are all same).

 Practically, any service provider buying bunch of routers, never
 going mix routers from different providers in an IGP area. Simply,
 can't justify for non-technical reasons. The assumption that
 an IGP area has equal capable routers is a valid assumption.
 If not, why don't we have a router metric in Router LSA ?

-> One could just as plausibly posit that, on average, a random 
-> assignment 
-> in the case of equal path costs could improve performance by 
-> spreading 
-> the load more effectively across the infrastructure, but it totally 
-> depends on the particulars of equipment, topology, and traffic.
 
 Most of the cases, a deterministic algorithm performs better than
 non-deterministic algorithm. Randomized selections of equal-cost
 paths can bring instability. 
 
 Take this for example: If IGP is flapping between equal-cost paths 
 in a non-deterministic manner would increase out-of-order IP packets. 
 This makes overhead for higher layers waiting for all IP datagrams
 to make out a transport packet. It is always better to send all IP
 datagrams of an application packet on a single deterministic path.
 
 That said, non-determinism and randomized algorithms are good for 
 proving theorems like probabilistic checkable proofs etc.
 
Venkat.