[Sip] SIP location conveyance: error indication

[Henning Schulzrinne <hgs at cs.columbia.edu>]

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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