Hi Kai and all, On Fri, Jul 15, 2016 at 10:27:14AM +0800, Gao Kai wrote: > On 13/07/16 05:09, Sebastian Kiesel wrote: > > On Tue, Jul 12, 2016 at 02:55:52PM -0400, Wendy Roome wrote: > >> My comments on draft-kiesel-alto-xdom-disc-02: > >> Section 3.2: > >> > >> If a client wants the cost from X => Y, why just do cross-domain discovery > >> on address X? Why not do it for Y instead? Or do it for both X & Y? > > This is again to cope with the not so well-defined "routingcost" metric. > > > > Our assumtion is that XDOM-DISC(X) will discover one ALTO server, > > which will be able to express costs (X,Y) and costs (X,Z) using a > > (locally) consistent routingcost metric, i.e., with the meaning that > > a lower value indicates a higher preference. > > > > If we used XDOM-DISC(Y) and XDOM-DISC(Z) we would probably discover > > two servers, which could use completely incompatible definitions. > > > > > > In other words, the example query given in sec. 11.5.1.7. of RFC 7285 > > should be sent to the server yielded from XDOM-DISC(192.0.2.2). > > > > If the "srcs" list contained more than one IP address, the query > > should be split up in several queries, each containing only one > > IP address in "srcs" (but keep all in "dsts"), and each of these > > "sub-queries" would need its own call to XDOM-DISC. > > I had the same question as Wendy because for me, sources and > destinations are somewhat symmetric
if src/dst and the costs between are really symmetric, it doesn't make a difference. > so it is tempting to think there > should be something like XDOM-DISC(X, Y), which might be overcomplicated > though. That would be too complicated indeed. > I think whether to use the source/destination or to split up queries > depends on the application. If it is selecting a destination for a > given source, it certainly can choose XDOM-DISC(SRC). If the selection > is about sources, probably XDOM-DISC(DST) is more reasonable. I agree. So the idea is, that we call XDOM-DISC(X), in oder to find an ALTO server that can answer both ECS queries, whether routingcost(src=X, dst=Y) > routingcost(src=X, dst=Z). and whether routingcost(src=Y, dst=X) > routingcost(src=Z, dst=X). In other words, we use the common address X that appears in all the tuples we want to compare as parameter for the XDOM-DISC. For the Endpoint Cost Service ECS, queries may have to be split in a way that either the "srcs" or the "dsts" list in the query contains only one IP address - and this address is used for XDOM-DISC. What that means for the other ALTO services we still need to define. > If the > application wants to pick the best source-destination pair, maybe the > queries should never be split up. Not splitting the queries would be the best thing to do from an optimization perspective. It would be great if there were a bunch of ALTO servers all with the same knowledge, so we could just discvover any one of them (e.g. using RFC7286) and ask it arbitrary questions or download a comprehensive NxN cost map. But for various reasons I believe that this is not going to happen on an Internet scale (and after all, we are the Internet Engineering Task Force ;) ). So we need to find a solution that works if knowledge is partitioned. Thanks Sebastian _______________________________________________ alto mailing list [email protected] https://www.ietf.org/mailman/listinfo/alto
