Re: [PATCH RFC 0/2] Better throughput estimation on half duplex interfaces

[Marek Lindner <mareklindner@neomailbox.ch>]

On Thursday, 28 September 2023 21:16:36 CEST Remi Pommarel wrote:
> > > $ batctl o
> > > Originator     last-seen ( throughput)  Nexthop         [outgoingIF]
> > > * Orig0-Main-Mac   0.220s  (        110)  Orig1-mesh0-Mac [  mesh0 ]
> > > Orig0-Main-Mac   0.220s  (        100)  Orig1-mesh0-Mac [  mesh0 ]
> > > 
> > > So best path for Orig2 to Orig0 would go through Orig1 with an expected
> > > throughput of 110Mbps. But such a throughput cannot be reached because
> > > Orig1 has to forward packet from and to the same WiFi interface.
> > 
> > Correct. Looking at your example where is the problem with the store &
> > forward penalty?
> 
> The problem is that the wrong path is selected.
> 
> The best one should be the direct one. Because going through Orig1, 110Mbps
> would never be bereached due to the store & forward penalty on Orig1 and
> the real throughput will be below the direct path (around 80Mbps).

To summarize the problem you see: A path traversing a half duplex node might 
not be penalized enough when the weaker throughput link lies before a stronger 
throughput link because the half duplex penalty is not be applied before the 
packet is forwarded.

The underlying assumption is that this indeed is an issue in terms of 
(measurable) throughput. Are there any numbers / papers / experiments you are 
basing this on? Is the store & forward throughput limit determined by the 
throughput of the weakest link?

Cheers,
Marek