Re: [PATCH 2/2] Send alive/byebye announcements three times.

[Sven Neumann <s neumann raumfeld com>]

On Thu, 2011-06-16 at 19:52 +0300, Zeeshan Ali (Khattak) wrote:
> On Thu, Jun 16, 2011 at 7:45 PM, Sven Neumann <s neumann raumfeld com> wrote:
> > On Wed, 2011-06-15 at 12:39 +0200, Jens Georg wrote:
> >> On Mi, 2011-06-15 at 09:18 +0200, Sven Neumann wrote:
> >> > On Tue, 2011-06-14 at 09:00 +0200, Jens Georg wrote:
> >> > > On Di, 2011-06-14 at 08:57 +0200, Jens Georg wrote:
> >> > > > UPnP recommends to send the whole batch of announcements more than
> >> > > > once "due to the unreliable nature of UDP".
> >> > >
> >> > > Since I have a really unreliable wireless and do have problems with not
> >> > > seeing announcements due to packet loss, I think it's a good thing to
> >> > > have.
> >> >
> >> > We've been using a patch for quite a while that does something similar.
> >> > I believe though that it is closer to what the spec suggests as it
> >> > actually delays the duplicate advertisement sets a little.
> >> >
> >> > You will find the patch attached to this mail. Sorry for not suggesting
> >> > this change earlier. I totally missed that I never submitted this patch
> >> > before.
> >>
> >> Hm, yes. That is indeed more clever than my version :)
> >
> > I will revert your change then and apply this patch instead. Is that OK
> > with you?
> 
>   Please dont! While your patch is cleverer, its also slightly more complex.

Well, it might be more complex, but it has been out in the wild on our
devices for more than a year now.

The UPnP spec recommends that UPnP devices send a total of 2 or three
advertisement sets within a 10 second transmission window. That doesn't
absolutely imply that there should be a delay between the transmissions.
But if you just send three advertisements directly one after another,
you do not improve reliability significantly. There needs to be a delay
so that you end up in a different time slot on your wireless network.

If you really want to improve reliability, then you should prefer the
slightly more complex approach.


Sven