Subject: [Ecrit] Suggestion for "performance and reliability" section

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 02 Aug 2005 05:07:52 -0400

I would think capturing the known external requirements as such is 
helpful. For example, the NENA 2s (dial-to-ring) requirement, which is 
part of the 10s dial-to-pick-up I mentioned could just be captured as 
such external guidelines, possibly in a separate "performance and 
reliability" section. If early implementations, with reasonable 
assumptions on round-trip times and topology, can't satisfy those, we 
know we have a problem.

Henning

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From: "Byron Smith" <[email-masked]>
Date: Tue, 2 Aug 2005 09:21:27 -0500

Henning, where do you get the NENA 2s and 10s numbers?  The only thing I
have found in NENA documents is:

"  9 Call Set-up Time
     It is recommended that emergency call set-up time not exceed the
average call set-up time for any
     other type call made by the customers of that particular serving
office.

     It is also strongly recommended that in all circumstances the caller
hear either audible ring tone or a
     recording alerting them that their call is being processed."

The above is from NENA 03-501.   I have looked for other NENA
recommendations, but have not found them.

I would appreciate a reference if you have one.

Not that this is terribly relevant: But I would make a small wager that more
than 50% of the (rural) wireline 911 systems in the country fail to meet the
above recommendations.  (Probably closer to 80%) The observed call setup
time for systems that use CAMA trunks is usually 3-7 seconds dial-to-ring,
with 5 seconds being typical. Most digital end-office switches make local
dial-to-ring setups on the order of 1 second.

Byron

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From: Henning Schulzrinne <[email-masked]>
Date: Tue, 02 Aug 2005 11:57:03 -0400

I don't think I mentioned NENA. My source of the information was the 
LAPD PSAP (which I visited during the NENA meeting). The person in 
charge said that their goal was 10s in 95% (not sure about the 
percentage) from call to human answer. They apparently tracked this 
information. In their case, the concern was primarily human response 
time, not routing time. Call setup time in mobile systems often 
approaches several seconds.

Beyond these anecdotal numbers, I'm not sure that we'll be able to rely 
on existing performance standards and that we can draw much insight from 
any number we get, except that having a gnome looking up the information 
in an atlas is likely to be unsatisfactory and that faster is better.

I also suspect that the only protocol that would likely fail a 
reasonable lookup time test, except by pure implementor stupidity, would 
be one that walked a geo search tree with widely distributed servers for 
each query.