On Mon, Oct 31, 2011 at 9:29 AM, Y. Richard Yang <[email protected]> wrote: > On 10/31/11 11:27 AM, Richard Alimi wrote: >> >> On Mon, Oct 31, 2011 at 7:51 AM, Vijay K. Gurbani<[email protected]> >> wrote: >>> >>> On 10/31/2011 08:49 AM, Bill Roome wrote: >>>> >>>> I don't have complaints, but I do have an observation: A client >>>> cannot distinguish between "pids are invalid" and "pids are valid but >>>> this server doesn't have reliable cost data for that pair." >>>> >>>> Does that bother anyone? >>> >>> The problem, at least as I understand it, is not predicated on a PID >>> being valid or invalid. >>> >>> The validity (or lack thereof) of the PIDs is a function on whether >>> they appear in the network map and cost map. Presumably, if they >>> appear there, the PIDs are valid. >> >> I agree with Vijay and Ben that looking at the Network Map should be >> sufficient (presumably the ALTO Client already has it in order to >> interpret the Cost Map). >> >>> However, the greater question is this: does the ALTO provider know >>> authoritatively the cost between all PIDs? That is the issue >>> under discussion. >>> >>> Clearly, the ALTO provider cannot know the costs between all PIDs. >>> Again, consider our sample topology we used for the bakeoff [1]. In >>> that topology, the ALTO provider had authoritative costs for >>> >>> mypid{1,2,3} -> mypid{1,2,3} + >>> peeringpid{1,2} + >>> transitpid{1,2} + >>> defaultpid >>> >>> However, asking the ALTO server to provide a cost between defaultpid >>> (Internet) and transitpid1 is useless, since at best, the server will >>> be indulging in a guess (and at worst, it'd be lying). >> >> I agree - so, just to be sure I'm understanding correctly, do you >> think that letting the Cost Map be a sparse matrix solves this issue? >> Or do you think there is something else that should be done? > > In a "typical" understanding, a sparse matrix means that the missing > elements have a value of "0" and hence do not need to be explicitly > represented. In our context, then we may need to make clear the > semantics that the cost is unknown or not revealed. This can be > important in that a client may use a sparse matrix library (database) > which may use the "standard" interpretation and then generate some > wrong results.
Yes - good point. The actual language in the draft (to be posted today) is along the lines of omitting entries that are not defined by the ALTO server -- "sparse" is not mentioned at all. I should have been more specific in my reply above. Rich > > Thanks. > > Richard > > >> Thanks, >> Rich >> >>> [1] http://www.ietf.org/mail-archive/web/alto/current/msg01147.html >>> >>> Thanks, >>> >>> - vijay >>> -- >>> Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent >>> 1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60566 (USA) >>> Email: vkg@{bell-labs.com,acm.org} / [email protected] >>> Web: http://ect.bell-labs.com/who/vkg/ >>> _______________________________________________ >>> alto mailing list >>> [email protected] >>> https://www.ietf.org/mailman/listinfo/alto >>> >> _______________________________________________ >> alto mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/alto > > _______________________________________________ > alto mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/alto > _______________________________________________ alto mailing list [email protected] https://www.ietf.org/mailman/listinfo/alto
