[time-nuts] wifi with time sync

jimlux jimlux at earthlink.net
Fri Jan 13 18:00:19 EST 2017

On 1/13/17 2:19 PM, Chris Caudle wrote:
> On Fri, January 13, 2017 3:17 pm, Bob Camp wrote:
>> It just so happens that I'm trying to track down an issue with my WiFi
>> as I type this.
> This is getting off topic for time-nuts very quickly,

well, wireless distribution of accurate time is, I think, on topic..

Wifi, in general, has really poor diagnostics - probably because while 
they had IP (in the TCP/UDP sense) when Unix was written, or shortly 
thereafter, so there are things like ping and traceroute..

WiFi has always had idiosyncracies with the Media Access and Link layer 
- all stuff that is "beneath" the sort of idealized network driver level.

It's like asking for generalized utilities to measure disk access time 
and error rates.. There aren't any, because every disk drive is 
different (originally.. now they tend to have the same interface, which 
hides most of the timing, but they also expose things like SMART)

802.11 performance is affected by oh-so-many things - your basic node is 
actually half duplex, so you have the whole access point/user timing 
cycle to deal with.  Then there's the whole infrastructure vs ad-hoc 
thing - the latter which is very poorly supported by a lot of drivers 
and OSes. Doesn't everyone just run their computer talking to an access 
point? That's what all the software focuses on.

802.11 changes the data rate on the fly according to conditions, which 
will change the time it takes to send the message over the air.

I'm sure there's probably some registers that count the number of bad 
packets and number of good packets, but knowing whether the packet was a 
2 Mbps or a 54 Mbps packet or something else is generally not available.

Most 802.11 devices have tons of configuration and status registers of 
one sort or another, but very sketchy documentation.

The fact that there are even tools like net stumbler is a credit to 
people who reverse engineered, or figured stuff out.

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