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Date: Fri, 9 Mar 2012 17:21:37 +0100
From: Andrew Lunn <andrew@lunn.ch>
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Subject: Re: [B.A.T.M.A.N.] [Battlemesh]  Diversity in BATMAN
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On Fri, Mar 09, 2012 at 05:07:37PM +0100, Benjamin Henrion wrote:
> On Fri, Mar 9, 2012 at 4:43 PM, Andrew Lunn <andrew@lunn.ch> wrote:
> >> With such metric, you don't make any difference between a 56K
> >> telephone line and a 10Ge NIC.
> >>
> >> If you 10Ge has 5pc packet loss and your 56K line has 0pc, your TQ
> >> will be prefer the 56k link.
> >
> > If my 10Ge has 5% packet loss, its broken. I don't want to use
> > it. Falling back to the 56K link is the right thing to do.
> >
> > There is a general rule of thumb. The higher the bandwidth, the less
> > packet loss there is. This is because high bandwidth links are
> > generally not wireless and so don't suffer high packet loss.
> >
> > As a side effect, BATMAN will tend to favor wired links over wireless
> > links, because wired links tend to be reliable, wireless links drop
> > packets.
> 
> So compare a 1Mbits wireless link with a 54Mbits one.

The 54Mbps link probably has a very low packet error rate. Otherwise
it would not be running at 54 Mbps. The automatic rate selection
algorithm would take it down to a lower rate if it had high packet
loss.

On the other hand, any link running at 1Mbit probably has quite a high
packet error rate. It must be a bad link, otherwise it would not be
using the lowest possible coding rate.

So when comparing a 1Mbps and a 54Mbps link, probably the TQ for the
54Mbps link will be better than the 1Mbps link.

       Andrew