Subject: [Sipping] draft-ietf-sipping-location-requirements-00

From: Henning Schulzrinne <[email-masked]>
Date: Fri, 13 Feb 2004 18:05:48 -0500

I think it would be helpful to do a back-of-the-envelope calculation for 
a typical message exchange and geo value as to what delay a reasonable 
(GPRS, say) wireless channel would impose for the case that the proxy 
provides location information.

My back-of-a-grocery-bag calculation (even rougher than 
back-of-the-envelope) is:

100 kb/s data rate (optimistic)
10000 bit per message with location information

= 100 ms per transit of a location object across the air interface.

In the proxy-provides-location case, we'd need roughly 3 messages 
(INVITE-redirect-INVITE), two of which have location information, for a 
total of 300 ms, not counting the TLS setup time (which may or may not 
be required for each emergency call). This is close enough to the E-1 
requirement limit that somewhat more precise calculations are called for.

I also found it peculiar that the draft does not mention the 
signature-only (unencrypted) mode for S/MIME, which would not interfere 
with proxy inspection. (The chain of reasoning should probably be: need 
privacy + can't use S/MIME for privacy since proxies need to peek -> 
TLS, rather than the current non-sequitur.)

Henning

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