Re: [alto] Discussion II: Unifying cost-mode and cost-type to a single type

[Wendy Roome <[e-mail]>]

Okay, I can avoid the IANA registration requirements by using "priv:" or
"exp:" for custom Cost Types.

But that doesn't answer the question of *why* we should register Cost Types.
What's the advantage? How does that benefit us? That's a serious question.
To me, registration looks like an annoyance without any redeeming benefit.

I realize that the goal might have been to make costs interoperable, but I
don't think registration accomplishes that. Take "routingcost". I believe
all the IANA registration says is that "routingcost is a non-negative
number, and lower is better". I don't think that's enough. To make
routingcost interoperable, I'd like to know what "40" means. Better yet, I
think "interoperable" would mean that I could compare routingcost values
between different ALTO servers, so 40 on one server means roughly the same
as 40 on another server.

That's clearly not true.

Here's a sample use-case. I want to select a host for new VM. The VM manager
gives me the CPU load (0.0 to 1.0) for several hosts. I then ask an ALTO
server for the routingcosts between my client and each of those hosts. I run
a function to blend the alto cost and the cpu load into an overall cost,
using the appropriate weighting and scaling factors, and I select the host
with the lowest overall cost.

So how do I determine those scaling factors? The IANA registry doesn't help.
I have to talk to the folks who provide that ALTO server, or else just look
at the values it returns. If I switch to a different ALTO server, I'll have
to start over again.

To me, that is not "interoperable". To me, "interoperable" would mean that I
could determine the scaling factors just from the central registry, and use
the same factors with any ALTO server.

As it stands now, "routingcost" values are only meaningful in the context of
a specific ALTO server. So even though "routingcost" is registered, it's
still a custom cost that varies widely from server to server. So what's the
benefit to registration?

Sorry to be a pest, but it seems that a while back, someone just declared,
"Well, of course we should to register cost types!" Since then we've all
accepted that on blind faith. All I'm asking is for is why registration
helps.

- Wendy Roome


From:  "Reinaldo Penno (repenno)" <[e-mail]>
Date:  Thu, February 21, 2013 12:16
To:  Bill Roome <[e-mail]>, "[e-mail]"
<[e-mail]>
Subject:  Re: [alto] Discussion II: Unifying cost-mode and cost-type to a
single type

This is what you need. A private cost you can use within your ALTO servers
and domain.

"Identifiers prefixed with ¹priv:¹ are reserved for Private Use"