[time-nuts] wifi with time sync
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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