During the call today, we discussed error handling in SIP location
conveyance and identified two problems:
(1) With multiple locations, it is impossible to tell which error
(warning) refers to which location. Since location elements may be
inserted by proxies and are then invisible to the UAC, the UAC could
get an error indication which makes no sense since it refers to
another location.
(2) The current return-424 model is inappropriate if location-related
failures should not cause the call to fail, as will often be the
case. (Just because Domino's can't dereference my location URL, it
still wants to talk to me about ordering pizza, but I also want to
fix that URL.)
Thus, my proposal:
(1) Define a new Location-Error request (?) and response header, as in
Geolocation-Error: "Cannot
dereference" ;tag="xkauc" ;code=711 ;source="alice.example.com"
where tag is a new tag added to a location header. This error can
occur in a 424 or any other status code, including a 200. If included
in the request, it's used by the UAS in case location handling is
delegated to some other proxy. (I'm not sure whether the request
header thing is a good idea.)
(2) Define a new Accept-* header, as in
Accept-Geolocation: sip, http
which identifies the dereferencing protocols supported, to avoid the
current ugly overloading of the warning messages.
Henning
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