Subject: [alto] Multiple cost maps for the same cost-type?

From: Wendy Roome <[email-masked]>
Date: Thu, 18 Jul 2013 15:34:15 -0400

Unless I missed something, draft 17 allows an ALTO Server to provide more
than one full cost map resource for the same cost-type (and network map).
What would that mean?  I can think of a couple of possibilities:

* That should be illegal.

* The resources are equivalent, and they return the same cost map (at
least eventually :-)). The duplicates provide load balancing, so the
client should pick one randomly.

* The resources return different cost maps. Eg, the server has several
different versions of one cost-metric, and they are distinguished by the
resource id. This implies that a filtered map service that offers a
multi-version cost-metric should have a 'uses' attribute to indicate which
cost-map resource it's based on.

I think the last interpretation will cause a lot of confusion. Invent a
new cost-metric name instead!

As for the other two, I have a mild preference for outlawing duplicates,
but I'd support the separate-but-identical interpretation if the rest of
you like that idea.

	- Wendy Roome

---

From: Richard Alimi <[email-masked]>
Date: Fri, 19 Jul 2013 01:00:44 -0700

> What would that mean?  I can think of a couple of possibilities:

To set the stage properly, the protocol draft never prohibited two cost
maps of the same cost type with different data even before draft -17.

> but I'd support the separate-but-identical interpretation if the rest of

I agree with disallowing duplicates, with the caveat that extensions can
introduce distinguishing attributes in the future [will need to update the
draft to document how that is done].  For example, imagine an extension
introduced a 'granularity' attribute; it would be good to allow ALTO
clients to have routingcost at multiple granularities in the same IRD.

Rich

>
>         - Wendy Roome
>
>
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