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From: Dave Taht <dave.taht@gmail.com>
To: Juliusz Chroboczek <jch@pps.jussieu.fr>
Cc: bloat <bloat@lists.bufferbloat.net>
Subject: Re: [Bloat] tiny monsters: multicast packets
Date: Sun, 29 May 2011 09:57:24 -0600	[thread overview]
Message-ID: <BANLkTin_G+s3ycMt-Ajy6_g3ML1YjNO7wQ@mail.gmail.com> (raw)
In-Reply-To: <7ipqn1bkhy.fsf@lanthane.pps.jussieu.fr>

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On Sun, May 29, 2011 at 9:21 AM, Juliusz Chroboczek <jch@pps.jussieu.fr>wrote:

> > And the irony is that the lower speed is specifically chosen for
> > multicast in order to make sure all clients in range can hear them
> > reliably.
>
> It was my understanding that it was done for compatibility with older
> devices, since 2 Mbit/s is the fastest rate supported by pre-B
> spread-spectrum hardware.
>
>
And thus, everybody loses. I doubt there is much 802.11b gear still active
in the field.


> > 2) Unicast the packet to each attached host in turn,
>
> Both DVMR and the multicast part of BATMAN-adv do that for router-router
> links.
>
> A better link-layer solution, IMHO, would be to multicast (with ARQ) the
> packet at a reasonably high rate (say, the median of the STAs subscribed
> to the multicast group),


I'm not deeply familiar with many of the  multicast protocols in use today,
such as MDNS. I AM under the impression that IGMP has not been well used or
tested recently.

I did start building uftp which I think I understand, and lets me have very
tunable rates, and definately uses igmp.


> and then unicast it to all STAs that failed to
> return an ACK.  Interestingly, if the new multicast frame format is
> incompatible with the normal 802.11 format, then this scheme is
> compatible with legacy devices, which won't ever see the multicast frame
> and hence won't return an ACK.
>
>
While I can see this helping for many protocols ARP seems a problem, in that
you'd like to stop broadcasting after you get a good response, and that's at
a higher layer.

> So the workaround is to isolate the broadcast domains of wired
> > networks and wireless networks by making the home router into...
> > a router.  Wireless on one subnet, wired on another, and so ARP
> > between the two turns into ARP to the router alone - much more
> > scalable.
>
> OpenWRT is your friend.
>
>
It certainly is! I would never have got this much insight into these
problems, so fast, had I not poked into the depths of the linux kernel,
patched it up (with the help of many here on this list) and tried to build a
version of openwrt based on everything we've learned about bufferbloat so
far, and setup a lab to stress it out.

Future directions are becoming apparent, rapidly.


> -- Juliusz
> _______________________________________________
> Bloat mailing list
> Bloat@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat
>



-- 
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://the-edge.blogspot.com

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  reply	other threads:[~2011-05-29 15:41 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-05-29 13:23 Dave Taht
2011-05-29 14:10 ` Jonathan Morton
2011-05-29 15:10   ` Dave Taht
2011-05-29 15:33     ` Juliusz Chroboczek
2011-05-29 15:44       ` Dave Taht
2011-05-29 15:51         ` Juliusz Chroboczek
2011-05-29 16:07           ` Dave Taht
2011-05-29 16:07             ` Dave Taht
2011-05-29 16:53               ` Dave Taht
2011-05-29 16:33             ` Eric Dumazet
2011-05-29 17:02               ` Dave Taht
2011-05-29 17:17                 ` Eric Dumazet
2011-05-29 17:40                   ` Dave Taht
2011-05-29 17:47                     ` Jonathan Morton
2011-05-29 19:14                     ` Eric Dumazet
2011-05-29 15:21   ` Juliusz Chroboczek
2011-05-29 15:57     ` Dave Taht [this message]
2011-05-31 14:58       ` Jim Gettys

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