Excerpts from Christian Vogt on Sat, Jan 31, 2009 11:49:46AM -0800: > I think we should experimentally compare ALT with other mapping > systems before we decide whether pull-based or push-based mapping > systems are better. Dismissing push-based mapping systems without > corroborating data would be a bit premature in my opinion.
I don't believe push-based mapping systems have been dismissed. They are still a valid option, and one that could be pursued at any time. Some of us made an initial evaluation that pull-based systems are better, but with experience that might change, and it can. Push-based and pull-based systems can coexist as long as their protocols aren't too constrained. A push-based system can act as a representative for the sites it serves and inject mapping information for them into a pull-based system, and so on. APT default mappers are something like hybridization points between push and pull, but there are control messages which bypass them, so the parallel isn't really exact. > In the absence of experimentation results, I would actually argue in > favor of push-based mapping systems based on some analytical reasoning: > Pull-based mapping systems have two important disadvantages compared to > push-based mapping systems: > > - Performance penalty, i.e., additional propagation latencies for some > packets, and higher loss probabilities for packets that take a sub- > optimal path > > - Robustness penalty due to a new online dependency on components off > the actual transmission path. (FWIW: All pull-based mapping systems > have this penalty. Mapping requests must be routed via overlay > infrastructure because the direct route is unknown at that time.) And a push-based system is either very "chatty" or its state is decoupled from operational reality. With a pull-based system you can have the authoritative sources of information be directly coupled to the operational liveness of the ETRs -- they can be the ETRs themselves. You can get this with a push-based system but only at the cost of a lot of messages sent without actually knowing if the information will be used. A push-based system has extra equipment, and administration, as well. They all do. But this is all initial evaluation. Scott _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
