Subject: Re: [alto] Authoritative status of costs

From: "Vijay K. Gurbani" <[email-masked]>
Date: Wed, 31 Aug 2011 13:23:31 -0500

<As individual>

Bill Roome says:
> Basically, I think adding a "quality" modifier to the cost -- be it
> a binary "authoritative vs non-" flag, or a continuous "reliablity"
> value -- is an exercise in futility.
>
> Why? At best, the cost reported by an ALTO server is an indication of
> the recent performance of the network. [...]

I think this depends on the type of cost being reported.

Clearly, if the cost is derived from some monetary agreements
between transit partners or some reciprocal agreement between
peering partners, then the ISP operating that ALTO server is
in the best position to act as an authority for the cost metric.

As such, I don't see why we would not indicate this.

On the other hand, if the cost is derived from some characteristics
of the network itself (instantaneous queue length at routers,
percent of network link in use, etc.) I agree that reporting
this has diminishing value, irrespective of whether or not
the ISP is authoritative or not.

A third-party ALTO server or even an ALTO server being operated
by an ISP will not have much knowledge about the topology and
any costs associated with the parts of the network it does not
"own".

Therefore, we need to make sure that the protocol can answer
a routing queries of the type we saw during the interoperability
event: wanting to know the routing cost from of a peer in a
peering network to another peer in a transit network.  In such
a case, both the ISP ALTO server and a third party ALTO server
are indulging in a guess.  And if so, this should be reflected
in the response.

My personal feeling is that we should not preclude an authoritative
qualifier on the response.  We can make it optional and leave
it to the server to insert one.

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-masked]
Web:   http://ect.bell-labs.com/who/vkg/