All things related to multicast

[Stig Venaas <>]

Dan Pritts wrote:
> On Sat, Jan 12, 2008 at 01:21:04PM -0500, Alan Crosswell wrote:
> > - What do we do about multicast over WiFi networks?  We are looking at
> >   systems that distribute entertainment content to students in their
> >   dorm rooms, and, as we all know, students don't use wired networks
> >   anymore.  What are the issues with various vendors' WiFi products and
> >   multicast snooping, pruning, rate limiting, etc.?
>
> I tried this back in the 802.11b days with a mix of apple airports
> and cisco 350s.  Even when i rate-limited multicast to 512kbps the
> network was unusable.
>
> I believe this was because 802.11a/b/g all drop down to the speed of
> the slowest client associated to the AP when sending broadcasts, and
> they made no attempt to do anything more intelligent with multicast.
>
> the slowest data rate in the 802.11b spec is 1Mbps; I guess the 512k of
> multicast i sent plus all the 802.11 MAC layer stuff was just too much.
> if i recall correctly, 802.11 is pretty chatty to prevent stations from
> stepping on one another.
>
> Looks like the lowest rate in 802.11g is 6Mbps (assuming you disable b 
> compatibility).  Probably not good enough for IPTV, i assume you'd need
> to support several 2-4Mbps streams?

Right. I wish it was possible to configure the minimal rate somehow, and
just say that any clients below that speed won't get it.

I have the impression that somehow both multicast and IPv6 is
problematic with some of the controller based solutions. I have however
not tried to study this myself. It would be great to hear what
experiences people have in such environments.

Stig

> I should be able to attend the BoF.
>
> danno
> --
> Dan Pritts, System Administrator
> Internet2
> office: +1-734-352-4953 | mobile: +1-734-834-7224