Re: [87attendees] IETF wireless

On Mon, Aug 5, 2013 at 5:48 AM, Tim Chown <tjc@ecs.soton.ac.uk> wrote:

> Hi,
>
> Others have given the wireless network at this IETF due praise.  Indeed
> the wireless has been excellent for many IETFs now, such that we pretty
> much take it for granted.  Well done to everyone involved.
>
> Is there any information available on the solution that was delivered?
>  From memory the APs were Cisco Aironet, but it would be interesting to
> know about density, controllers, etc.  Usage info, especially for IPv6,
> would be interesting too.
>
> If the info isn't available, so be it, but it might be of interest to
> many...
>

Bufferbloat kills you in many/most conference venues; IETF is one of the
few where it does not.   I first noticed at the Denver NANOG a working
wireless network; but the same people are involved in both NANOG and
IETF.So I poked into the topic to understand why. I was amazed to see a
room of 500 heavy duty network people and observe latencies from Denver to
California consistently under 50ms under load, and investigated why the
network was usable.

At past IETF's I've urged the operation teams that they should document
what they do.  I did not have time in Berlin to repeat the request again.

Besides the layout of AP's that other good operators do, there are a
number of "tricks" that they play:

1) the AP's have minimal internal buffering, and forward their packets back
to a big router.
2) the big router, having lots of aggregated traffic, is able/does run
(W)RED to keep the wireless traffic queues from being too much of an issue.
 This is hopeless in a home environment where you have little aggregation
of traffic (but there, you can now get help from fq_codel if you run
OpenWrt/CeroWrt on your home router; but to fix the situation properly will
still take a lot of work in Linux's WiFi stack).
3) There is some QOS/Diffserv tricks being played to prioritize certain
operations (e.g. DNS lookup, TCP opens, acks, and so on).   An early
version of the marking they do was documented at a NANOG meeting; but I
gather some later rules have been added since then. Those of you who have
looked at fq_codel in detail might recognize that fq_codel happens to have
similar behavior (without needing the hair of such explicit
marking/classification rules).

Anyone setting up an large event today should take a careful look at what
is being done, and it would be good to get the knowledge captured in enough
detail for others to reproduce their work, as it can be done today.
                             - Jim

> Tim
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