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Re: [Ecrit] Emergency Call Framework for Canada; Questions on draft-ietf-ecrit-framework-09
At 05:36 PM 6/2/2009, "François D. Ménard" wrote:
Actually, I think BCP would be: "Proxies MUST provide location on
behalf of devices ONLY if the device does not provide it's own location."
That's a good statement, but it is not sufficiently precise.
has anyone ever heard of a default route?
the call only has to be to _A_ PSAP --
preferrably in the same country (or
state/province or county or city)... The call can
be transferred from that PSAP to the appropriate
one once the location of the caller is determined
(when they tell the dispatcher). This transfer
ought be nearly on speed-dial, considering how few PSAPs there are.
The question is 'how can proxies (which are by definition stateless),
well, this statement is false. Proxies can merely
choose to become transaction stateful (because
the request and response go through the same
proxies), and can inject a Record-Route into a
SIP request to becomes dialog stateful. This
means all subsequent requests go through this
proxy also (all BYEs, REFERs, INFOs...)
inspect an S.O.S. call and try to look for the presence of a PIDF-LO
by way of SIP LOCATION CONVEYANCE',
well, perhaps all you need to look for is the
presence of the Geolocation header, because that
has to be present in order for there to be a
Location URI or a PIDF-LO message body (i.e.,
this header's presence in the SIP request is a
dead giveaway that location is not
there). Something can be done upon realizing that header is not present.
and upon that not being there,
decide to inject it.
This seems like a violation of the mother-rule-of-SIP, which is that
proxies do not modify SIP message contents, which is where Lby? lies.
possible correction -- proxies aren't to modify
or delete message bodies, but they can certainly
add or change the contents of any SIP header,
though some aren't recommended to be changed
(like Via, From or To, for example).
Some people are claiming that adding Location-by-reference does not
violate the rule, however location-by-value would violate the rule.
so long as the SIP server is operating strictly
as proxy, but many SIP servers don't limit
themselves to only operating as a proxy -- many
are B2BUAs and SBCs -- which by definition, *can* modify SIP message bodies.
What's the latest take on that?
see above
"If the device does not provide location and the proxy can't find
location OBO the device, then the call MUST be routed to a 3rd party
call centre for verbal location and routing."
personally, I think OBO shouldn't be done, given
how often I believe this will be incorrect
location information, but I've been out-argued on
this point. That said, routing to the 3rd party
call center (as written above) would be my recommended 2nd step.
What mechanism will a PROXY use to make this determination?
local configuration, clearly...
even though that won't taste too good to some.
it's the way SIP generally operates.
f.
Regards,
--
John Lange
http://www.johnlange.ca
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