On Tuesday, September 2, 2003, at 11:10 AM, Harald Tveit Alvestrand wrote:
[note - the 2 sets of expectations for VoIP rollouts is a very true obsevation. however....]
paradox? what paradox?
the fact that VoIP has two largely orthogonal qualities at the same time is not a cause for calling it paradoxical; only if they have to have two incompatible values of the same metric should the "P" word be applicable.
the metric is availability.
--On 31. august 2003 02:04 -0400 S Woodside <[EMAIL PROTECTED]> wrote:internet
The public internet. Availability on the public internet is /best
effort/ which means that other factors (such as price and bandwidth)
can be more important than availability.
"best effort" means that you get no better service than what you pay for.
Why shouldn't that achieve five nines?
Because it's local-network reliability only. The remote party and everyone in between would also need to pay for the higher availability as well to ensure edge-to-edge availability at five nines. My assumption is that is a non-goal of the "best effort" network.
telephony
The public and private branch exchanges of the telephone network.
Availability in telephony is counted as /five nines/. So, 99.999% of
the time when you pick up the phone you get a dialtone. That's all
but five minutes per year.
and one has to carefully tune the measures of "availability" to achieve that figure.
for instance (personal experience from Norway, mostly):
- pabx availability is dependent on the janitor not tripping over the power cord, and not measured
- a cell phone that is out of range is not counted (of course!)
- a subscriber line that is down is not counted until the time the subscriber reports the error.
- "acts of God" like fires in telephone exchanges (and even some "backhoe fade" cable faults) are not counted.
- if you try to call Liberia, all bets are off.
in practice, five nines is a shared illusion between the operator and the regulator.
Perhaps, perhaps not. I live in Ontario Canada and in the recent blackout, my phone kept working. It was as one might say an "object lesson" in the difference between best-effort and five nines.
simon
Conclusion:
statistics always lie. what exists, exists. paradox is in the mind of the beholder.
-- simonwoodside.com -- openict.net -- 99% Devil, 1% Angel