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Re: 95th Percentile again (was RE: C&W Peering Problem?)

  • From: Richard A. Steenbergen
  • Date: Sun Jun 03 15:42:50 2001

On Sun, Jun 03, 2001 at 01:41:08PM -0400, Alex Rubenstein wrote:
>
>
>
> > No its not obvious. The SNMP byte counters are odometers - as long as
> > you get two clean samples per counter wrap you can accurately count
> > bytes. The trick is to ensure that you get a minimum of two clean
> > samples of the odometer reading per counter wrap - for high speed
> > interfaces that typically implies reading the MIB2 64 bit interface
> > counters, or triggering an SNMP poll at relatively tight time
> > intervals.
>
> 2^64 is 1.844 * 10^19
>
> at 2.5 gb/s (OC48 line speed) (2,500,000,000 bits/sec), you transfer
> 312,500,000 bytes/sec, or 298 megabytes/sec.
>
> 2^64 / 312,500,000 = 6.189 * 10^16 seconds per rollover.
>
> or, 1.719 * 10^13 hours
> or, 1,962,741,057 years.
>
> My point: at least for the near future, 64 bit counters won't roll.

Or thought about another way:

2^64 = 18446744073709551616 bytes/sec = 147573952589676412928 bits/sec.

Which means a 64 bit counter will roll over in 5 minutes at
491913175298921376 bits/sec, or 491Pbps (Petabits/sec).

Under the current naming scheme, this will be OC-9444732864. Better start
planning for 128 bit counters, we wouldn't want to be stuck in something
which doesn't scale. :P

-- 
Richard A Steenbergen <ras@e-gerbil.net>       http://www.e-gerbil.net/ras
PGP Key ID: 0x138EA177  (67 29 D7 BC E8 18 3E DA  B2 46 B3 D8 14 36 FE B6)





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