Can anyone explain - IPSec latency

Damien Elmes resolve at
Wed Feb 20 06:32:51 EST 2002

Howard Lowndes <lannet at> writes:

> Can anyone explain, or even guess, why the difference between ex-tunnel
> and in-tunnel ping times is so much more when the link is ADSL to PSTN -v-
> ADSL to ADSL.  I know why the base latency is greater, but that doesn't
> explain the difference in latencies.  All machines at the gateways are
> comparable (typically mid-range Celerons).
> Typically:
> ADSL to ADSL (3 cases) ex-tunnel=65msec in-tunnel=80msec diff=15msec
> ADSL to PSTN (1 case)       "    185         "    235      "  50

i've absolutely no idea, to be honest. however, if we take the pecentage
increase in latency for these first two:

15/65 * 100

50/184 * 100

we see that in both cases, we're getting an increase in latency of roughly 25%
i'm a hopeless mathematician, so i'm probably glossing over something here..

Damien Elmes
resolve at

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