Subject: Re: [alto] New draft on relay usage for ALTO

From: Sebastian Kiesel <[email-masked]>
Date: Tue, 29 Sep 2009 15:19:17 +0200

Hi Yu Meng,

On Tue, Aug 25, 2009 at 10:24:08AM +0800, [email-masked] wrote:
> Hi,
> We have submitted a draft on relay usage for ALTO. This document would 
> describe the background of Qos relay and design the mechanism of combining 
> ALTO service with relay. 
> 
> The draft can be found at 
> http://www.ietf.org/internet-drafts/draft-meng-alto-relay-00.txt. Comments 
> welcome. 

Your draft mentions two use cases: the first is the "Connectivity relay"
to connect users with limited Internet access (NAT).  I fully agree with
that use case and I think that ALTO should be able to assist in
selecting an "optimal" (in the sense of ALTO) connectivity relay.

However, I am very concerned about the second use case, on which your
document focuses: the "QoS relay".  With the goal of lower latencies you
are proposing an Application Layer-routing/forwarding mechanism that
diverts traffic from the path along which normal IP routing would send
the packets:

| Under the following two conditions, overlay 
| routing paths can be faster than the direct IP routing paths
| (1) An AS in a direct routing path is congested or failed.

Can you please explain which timescales we are talking about?

Do you want an ALTO-based solution to reroute around suddenly appearing
failures/congestion faster than the IP routing protocols can do?

Or is it all about routing around chronically congested links, 
which are known to the operators to be congested but which they 
do not want to upgrade for some reason?

| (2) Multi-homed customer ASes can further improve overlay routing.

If we look at Figure 1 of your draft, can you please explain how the
owner of the AS B can publish what kind of transit traffic he is willing
to relay through a "QoS relay" in his multi-homed stub AS (if he wanted
to relay all kinds of IP traffic, AS B could just become a transit AS on
BGP level)?  Should this policy-aware detection of candidate relays be
part of ALTO?

Thanks,
Sebastian

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