[Starlink] [Cake] [Make-wifi-fast] [Cerowrt-devel] Due Aug 2: Internet Quality workshop CFP for the internet architecture board

[Dick Roy]

-----Original Message-----
From: Starlink [mailto:starlink-bounces at lists.bufferbloat.net] On Behalf Of
Leonard Kleinrock
Sent: Monday, August 2, 2021 5:38 PM
To: David Lang
Cc: starlink at lists.bufferbloat.net; Make-Wifi-fast; Bob McMahon; Cake List;
codel at lists.bufferbloat.net; cerowrt-devel; bloat
Subject: Re: [Starlink] [Cake] [Make-wifi-fast] [Cerowrt-devel] Due Aug 2:
Internet Quality workshop CFP for the internet architecture board

These cases are what my student, Fouad Tobagi and I called the Hidden
Terminal Problem (with the Busy Tone solution) back in 1975.

[RR] Also known as the "hidden node" problem!

Len 


> On Aug 2, 2021, at 4:16 PM, David Lang <david at lang.hm> wrote:
> 
> If you are going to setup a test environment for wifi, you need to include
the ability to make a fe cases that only happen with RF, not with wired
networks and are commonly overlooked
> 
> 1. station A can hear station B and C but they cannot hear each other
[RR] Lots of reasons for that in the wireless world of mobility.

> 2. station A can hear station B but station B cannot hear station A 

[RR] This is largely due to link imbalance. In TDD systems like Wi-Fi, time
variability of the RF channels is also an issue that is dealt with by having
turn around times that are much less than the "(de-)coherence time" of the
channel. Link imbalance is largely due to differences in tx power and rx
front end noise figure. Smart antenna technology makes this a bit more
complicated, but the essentials are still the same.

3. station A can hear that station B is transmitting, but not with a strong
enough signal to decode the signal (yes in theory you can work around
interference, but in practice interference is still a real thing)

[RR] Yes, energy can be detected at levels that are insufficient for
decoding.  That said, if you can't decode the signal, you generally cannot
know who sent it :^)))
> 
> David Lang
> 

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