Re: [p2pi] Information in an ALTO protocol

John Leslie wrote:
> Vijay K. Gurbani <vkg@alcatel-lucent.com> wrote:
>> I think that which parameters to gather will turn out to be an
>> interesting topic to nail down.
> 
>    Interesting, certainly; but IMHO unwise to nail down too tightly.

John: Agreed, and my intention was not to nail them down but
continue discussion on which pieces of information are useful to
guide work that will be done in the future.  After all is said and
done, one of the deliverables will be a schema document -- as
extensible as it may be -- to communicate information between
the pertinent entities.

>> At present, we have the following discrete pieces of information
>> mentioned in the post-BoF charter:
>>
>>   (1) Routing preferences
>>   (2) Priority values
> 
>    These are a bit amorphous...

Fair enough.  Folks have suggested that preferences and priorities
along the lines of:

   <local 1> _is_better_than_
    <external ASN 2> _is_better_than_
     <local 2>

How do you see that we can make these a bit more concrete?

>>   (3) AS numbers
> 
>    Sometimes very useful; sometimes not...

But arguably a low-hanging fruit that does indeed provide some
information that is helpful in the absence of any other guidance.

>>   (4) Geographic location
> 
>    Often wildly inaccurate, and even more often quite unrelated to
> network topology. Would be _very_ useful in an alternate universe where
> routing found next-hops _physically_ closer to the destination...

Probably needs a bit more discussion on whether or not this is
valuable before discarding it.

>> 6 can be provided by the network operator or approximated using
>> synthetic coordinate systems and the like.
> 
>    Actual topology is likely to change without warning; so you should
> be prepared for it to prove wildly inaccurate. More often than not,
> it turns out to be only roughly approximated or hopelessly optimistic.

Sure; synthetic coordinate systems have been designed with
approximations and opportunistic optimism in mind.  While the
active guidance of an ISP in imparting topological information
is best, we should not preclude third-party services from
approximating the same to the best of their abilities.

>> Information that has been deemed out of scope based on list
>> discussion is:
>>
>>   (1) Last hop bandwidth
> 
>    The most useful number yet listed, _if_ folks will give it to us
> and we interpret it correctly...

Hmmm ... so I suspect that it is premature to say that last-hop
bandwidth is out of scope?  What do others think?

>> What other sort of information should be a focus of ALTO?
> 
>    It would be rather useful to have "characteristics that indicate
> congestion" on a path. The applications are going to have to judge
> instantaneous congestion anyway, and basing that judgment on
> known characteristics rather than guesswork should speed progress
> towards an optimal mix.
> 
>    Jitter in the latency will be of interest to certain applications.

I believe that these will fall squarely in TANA, if not some other
TSV WG.

Thank you.

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
2701 Lucent Lane, Rm. 9F-546, Lisle, Illinois 60532 (USA)
Email: vkg@{alcatel-lucent.com,bell-labs.com,acm.org}
WWW:   http://www.alcatel-lucent.com/bell-labs
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