[Babel-users] some thoughts towards babel-1.9

[David Schinazi]

Dave,

Thanks for writing this up, it's an interesting read.
I agree with you on the topic of multicast. My implementation sends
everything unicast, with the exception of Hellos. I'm interested in
working on a way to allow unicast Hellos. I read your thoughts here:
https://github.com/dtaht/rabeld/blob/master/babel_unicast_hello.md <https://github.com/dtaht/rabeld/blob/master/babel_unicast_hello.md>

and was thinking that we might be able to make this even simpler,
by adding a new "I support unicast Hellos" bit in the IHU Reserved field.
That way when a node appears on a link, they send a multicast Hello,
and get IHUs in response. If all the IHUs have this bit, then the router
can go into unicast Hello mode. Similarly, when a node sees a new
neighbor, it sends it an IHU with this bit and if it receives a unicast
Hello from that node it knows they are supported, otherwise falls back
to multicast. You could then have different intervals for multicast and
unicast Hellos, with the multicast one being potentially much higher.

This proposal stays in the spirit of current Hellos as a measure for
packet loss rate. If as you describe this isn't a great metric, we
could take this thought process even further and simply get rid of
Hellos for link quality estimation. You would still have multicast Hellos
to detect new peers, but you can estimate by-directional reachability
simply by noticing of you receive any Babel packet from a host, and
IHU for the reverse direction. This makes particular sense if you were
able to query your link-layer for information on how many
retransmissions are required on average to reach that host, and what
rate the Wi-Fi chip is operating at.

Thoughts?
David


> On Dec 12, 2016, at 09:25, Dave Taht <dave.taht at gmail.com> wrote:
> 
> I've long been testing a few out of tree patches for babel and long
> have had the intent to try a few more once the first phase of the
> make-wifi-fast work was completed - which it mostly is, so far as lede
> is concerned ( https://lwn.net/Articles/705884/ ) - and babel-1.8
> stablized.
> 
> I wrote up some of my thinking then in:
> 
> https://github.com/dtaht/rabeld/blob/master/rabel.md
> 
> back when we were having powersave issues affecting multicast (which I
> hope is now fixed), but I've partially deployed the "mo' unicast"
> patch around my testbed with no ill results.
> 
> Another thing that has come up a lot lately is the default gateway
> failing for some reason or another, tighter integration with
> babel-pinger might help.
> 
> And lastly, I had a chance to look at some packet captures from the
> wlan-slovenia network, which is essentially flat, and is sending 14
> packets worth of route information on a regular basis. Finding ways to
> attenuate and create covering routes, and make DV more DV would be
> nice.
> 
> I'd also written up some partially crazy thoughts towards a unicast
> hello extension in the same repo.
> 
> -- 
> Dave Täht
> Let's go make home routers and wifi faster! With better software!
> http://blog.cerowrt.org
> 
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