Re: [PATCH v2] mac80211: Jitter HWMP MPATH reply frames to reduce collision on dense networks.

[Johannes Berg <johannes@sipsolutions.net>]

Hi Alexis,

> This is loosely based on RFC5148, specifically event-triggered
> message generation as described in section 5.2.

I'm confused. I see how that generally seems to apply to any mobile
network, but it *does* state up-front that
    In some instances, these problems can be solved in these lower
    layers, but in other instances, some help at the network and higher
    layers is necessary.

I believe 802.11 *does* in fact solve these issues at lower layers.

Can you explain how you observed any problem in this area?

> The frames are not duplicated, but, hopefully offset enough so they
> don't collide at the receiver 

That wasn't my question - my question regarding duplicating was if this
was intended to *suppress* duplicates, but it sounds like not.

> (and, since, these are management frames, there is no retransmission
> and we may lose the information contained in them).

That statement isn't true in general, though it does seem that some of
the frames you're touching are actually *multicast* frames and as such
don't have any retries.

> If the two (or more) devices that reply are synchronized well enough,
> carrier sense will tell them that air is clear and messages will go
> out at the same time. It doesn't happen too often, but we found it
> noticeable enough in our testing.

I'm still curious how it happens at all, since NAV synchronisation
should prevent it at a much lower level?

johannes