On Thu, Nov 13, 2008 at 08:54:35PM +0300, Mikhail Kuzminsky wrote: > Sorry, is it correct to say that fat tree topology is equal to > *NON-BLOCKING* Clos network w/addition of "uplinks" ? I.e. any > non-blocking Clos network w/corresponding addition of uplinks gives fat > tree ? > > I read somewhere that exact evidence of "non-blocking" was performed for > Clos networks with >= 3 levels. But most popular Infiniband fat trees has > only 2 levels. > > (Yes, I know that "non-blocking" for Clos network isn't "absolute" :-))
Since Infiniband routing is static I suspect that the topology may match but the behavior will not. http://en.wikipedia.org/wiki/Clos_network#Strict-sense_nonblocking_Clos_networks_.28m_.E2.89.A5_2n_-_1.29_-_the_original_1953_Clos_result See the bit: "If m ≥ n, the Clos network is rearrangeably nonblocking, meaning that an unused input on an ingress switch can always be connected to an unused output on an egress switch, but for this to take place, existing calls may have to be rearranged by assigning them to different centre stage switches in the Clos network [2]. To prove this, it is..." The key word is "rearrangeably nonblocking". If 30 seconds of homework is sufficient the key to Clos topology research is that it is focused on teleco switching where a call is 'routed' when it is made and torn down on disconnect. This is not the same problem space as a packet switched network at a couple of levels. -- T o m M i t c h e l l Found me a new hat, now what? _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
