In message <CAA93jw627Q12XkZy3CFuV81CLbJc5D9oX6LK1=cgetwsop1...@mail.gmail.com>
Dave Taht writes:
> >
> > BFD, Hellos, or any form of probe traffic over wireless has the speed
> > of detection vs overhead issue. At nominal 10 Mb/s (low end today for
> > wireless) a small probe would take about 0.1 msec (for example, 125
> > bytes including all overhead is about 1000 bits). Not bad if running
> > 100 probes/sec (30 msec detection) unless there are a very large
> > number of stations using the AP and doing the same thing. In that
>
> You are thinking about it wrong. Wireless-g is only capable of roughly
> 1300 TXOPs total per second. Bandwidth has NOTHING to do with it.
>
> I don't have the figure in my head for n or ac, but it is not a lot, and
> in the presence of g, falls back to the above figure.
>
> losing 10% of the bandwidth - per station - to run BFD is not an option.
>
> > case 10 probes per second might be better. A very high collision rate
>
> Still too much. Next question?
Oops yeah. You are right. Forgot about TXOPs.
How about a PPP LQM / MPLS-TP LM OAM equivalent?
Briefly:
"A" sends pkt/byte sent to "B".
"B" notes pkt/byte recv and adds that to the packet.
"B" adds its pkt/byte sent and sends that back to "A".
"A" notes its pkt/byte recv and sends back to "B". "A" saves this.
"B" simply receives and saves this.
Save prior packet, wait some time, and then repeat:
Now subtract the two sets of counter (new - old packet).
Each side compares other side sent to their own received.
Difference is number of packets dropped.
Repeat forever using prior result to update drop rate.
If any of the control packets drop, drop a partial result, repeat
later, and compare to the last complete result.
Is one cycle per neighbor too much? How about one cycle per neighbor
each 5 seconds? If "B" is the AP it sends only one packet per cycle
but both sides get accurate drop rate for both directions.
Curtis
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