Subject: Re: [homenet] 802.11 is just fine for IPv6 [was: Despair]

From: Toerless Eckert <[email-masked]>
Date: Mon, 10 Aug 2015 01:36:27 -0700

sorry, address typo. again.

IMHO, a better place for this discussion than homenet is Mboned,
for example in conjunction with evolving draft-mcbride-mboned-wifi-mcast-problem-statement.

I do not particularily like the scope either of the discussion in homenet
or in the draft in MBoned, because both only look at the problems, not
the opportunities/benefits. If we stay that line of thought, it will just
lead to further removal of multicast. Multicast is necessary for
discovery, it is necessary for most efficient airtime use in multipoint
delivery and it is the most flexible multipoint deliver API we've come 
up with so far in the IETF. It is not necessarily equally beneficial 
for a bunch of signaling procedures where we've  been using it so far
in wired LANs. Especially in IPv6 signaling.

The IPv6 and routing protocol signaling use of IP multicast are IMHO
most easy to solve because they really don't need a serious amount of
airtime when done right. And it would be lovely if not every routing
protocol would have to come up with its own scheme but if we could define
an appropriate set of procedures ONCE that all protocols we want to use
could plug into equally. Babel, IS-IS, RPL, what have you. I think
ISO called this subnet adaptation layer ;-)) We (IETF) did this for some
other technologies if i remember correctly. And IMHO it also applies
to non-multicast issues in WiFi.

What would be cool, but where i see little hope to do something useful
unless the IEEE actually helps us to prioritize the use-cases is to
automatically do protected (reliable)  multicast vs. replicated-unicast
streaming of multipoint data via WiFi. And its easy to see when one
approach is better than the other (based on #receivers and per-receiver
channel characteristics). It just takes a lot of WiFi specific logic
to make the right choice.

Cheers
    toerless

On Fri, Aug 07, 2015 at 09:36:07AM +0200, Juliusz Chroboczek wrote:
> > However, I do think that 802.11 needs to point out to its members that if
> > they don't implement assured multicast replication, IP doesn't work
> > properly.
> 
> That's an overstatement.  IPv6 works just fine over 802.11, it just
> suffers from increased multicast packet loss and lower rate.  I don't
> think there's anything in the IPv6 architecture that requires (link-local)
> multicast performance to match unicast performance.
> 
> While it would be nice to have better multicast performance, I don't think
> it's productive to be overly alarmist ("IPv6 obsolete before it gets
> deployed, according to IETF spokesperson.  News at eleven.").
> 
> -- Juliusz
> 
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-- 
---
Toerless Eckert, [email-masked]