Ok, there may be some misinterpretations of what I wanted to say. When I see a Central controller, I see an entity. I don't see a single or a group of machines, I see a concept. For me a central control system is still central, even if behind it, there are hundreds of machines executing instructions in parallel. If inside, it aggregates all services and decisions, then its a single entity that does it all.
Andrew spoke of one thing that is where I see multiple controllers, and it's when there are different domains (ex: different ISP's networks). If the "Master" is different, then so controller shall be (unless they are Virtual ISP's, but that's just a network virtualization). Interesting chat :) On 21 October 2013 16:20, Andrew Ferguson <a...@cs.brown.edu> wrote: > hi Carlos, > > On Oct 21, 2013, at 8:34 AM, Carlos Ferreira <carlosmf...@gmail.com> > wrote: > > I don't really understand why would anyone want multiple controllers, when > there could be only one controller and over it, multiple apps implementing > different services. Its a much more simple layered approach. > > > multiple controllers are important for the same reasons one would want > multiple instances of any piece of critical infrastructure: scalability, > redundancy, fault-tolerance, the ability to upgrade without impacting the > running network, to protect yourself from software bugs or operational > mistakes, to completely isolate different domains except via an > intern-domain protocol (eg, BGP), etc. > > of course, this makes the controller a distributed system, so now you have > two problems. :-) > > > cheers, > Andrew > -- Carlos Miguel Ferreira Researcher at Telecommunications Institute Aveiro - Portugal Work E-mail - c...@av.it.pt MSN Contact -> carlosmf...@gmail.com Skype & GTalk -> carlosmf...@gmail.com LinkedIn -> http://www.linkedin.com/in/carlosmferreira
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