Subject: [alto] Comments on draft-kiesel-alto-xdom-disc-02

From: Wendy Roome <[email-masked]>
Date: Tue, 19 Jul 2016 15:18:24 -0400

draft-kiesel-alto-xdom-disc-02 has this (Sect 3.2, Endpoint Cost Service):

If an ALTO client wants to query the Endpoint Cost Service (see Section
11.5 of RFC 7285 [RFC7285]) for the costs from source address X to
destination address(es) Y (and Z), it has to invoke the crossdomain ALTO
server discovery procedure with parameter X. The result will be the IRD
URI of the ALTO server to query for the costs from X to Y (and Z).

My first comment was why do cross-domain ALTO server discover on X, rather
than Y or Z?

Then I realized there is a good reason. I believe most ECS queries will be
either 1->N or N->1. That is, costs from many sources to one destination
(client selecting server from which to download a file) or one source to
many dests (client selecting server for upload).

So if the query is 1->N or N->1, do cross-domain discovery on the one
address. That is probably the address of the real client - the one which
needs ALTO guidance. So use the ALTO server which has the best data for
that address.

	- Wendy Roome

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From: Sebastian Kiesel <[email-masked]>
Date: Tue, 19 Jul 2016 23:13:39 +0200

Hi Wendy,

> needs ALTO guidance. So use the ALTO server which has the best data for

exactly!

This does not only save on the number of transactions with different
ALTO servers, it helps also to deal with our (deliberately)
not-so-well-defined "routingcost" default metric.

Thanks
Sebastian