On Mon, 10 Aug 2015, Stephens, Adrian P wrote:
[Adrian P Stephens]
This problem is nothing new. We know about the relative performance of
multicast vs unicast.
Saying it "sucks" is not very helpful. Unlicensed spectrum is free. You are
getting more than you are paying for :0).
I don't see how it's relevant that the spectrum is free? Even if this was
done in a licensed spectrum I would still get 10% packet loss because
multicast isn't ACKed, right?
The technical solution is surely to add a class of service specification to
multicast packs that indicates their sensitivity to loss.
The point is that the AP is in possession of a lot of data about individual
nodes that may help it make an informed decision
between unicast and multicast.
Moving the duplication into the IP layer ensures uninformed decisions.
That's my opinion as well. Thanks for confirming it.
> From what I read below, one way out of this is the IETF making a clear
> statement that multicast is an integral part of IP networking, and if a
> medium doesn't support delivering multicast frames in a similarily
> reliable fashion to unicast, it's not suited to carrying IP based
> protocols (or any other protocol that uses L2 broadcast/multicast).
[Adrian P Stephens]
<irony type="british; very-subtle">
I'm guessing you will be the first to turn off the 802.11 networking on your
devices when the IETF makes such a statement.
</irony>
Well, since it seems 802.11 has mechanisms to make multicast delivery
decently reliable, it seems it would be suited if the implementation
actually included that mechanism. If it's omitted by the implementor, it's
not. Currently I have no idea if my home network includes GCR or not. I
also don't know if GCR needs client support.
[Adrian P Stephens]
As I indicated in my earlier post, there are multiple actors here.
The odds are pretty good that 802.11 will respond to a clear requirement to
handle multicast specially.
If has, after all, already done this twice.
What do you mean "specially"? What I've been bringing up is not to treat
it specially, it's to treat it so that it works similarily to unicast.
From my point of view, without the GCR or similar mechanism, multicast is
treated specially, ie it's being treated worse than unicast.
What are the odds that the WFA will create a new certification?
What are the odds that it is successful in the market?
These are presently unknowns, and will remain that way until tried.
I have no history on this kind of subject, someone who has been involved
in 802.11 perhaps could make an educated guess and share an opinion on
what might be the path that has the best odds to succeed?
http://eprints.networks.imdea.org/275/1/L.%20Eznarriaga-MsC%20Thesis-September%202011.pdf
Btw, could you confirm that GCR in 802.11aa is something that is needed in
both AP and clients to work? It seems like it would need to be. How widely
implemented is it in clients? Is this a hardware issue or driver issue?
Does the operating system need to support it as well?
--
Mikael Abrahamsson email: swm...@swm.pp.se
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