Re: [Ecrit] call marking

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

Maybe it would be helpful to discuss requirements first and who would  
use the call marking for what.

The first usage is presumably for call routing. This matters only if  
a proxy needs to do something different to route emergency calls,  
such as invoke LoST, and if it sees something other than emergency  
calls. (For example, if we have hierarchical routing, the state proxy  
will simply forward calls to one of the county proxies, but all such  
calls need to be re-mapped. Or, alternatively, the URL identifies  
emergency calls for that destination, without any standardized  
convention, such as sip:some-local-string at esr.queens.ny.us)

A second usage is that the destination (PSAP) can tell if the call is  
an emergency or "business" call. One could argue that the destination  
URL is the appropriate marker for that, without any standardization.  
In other words, as long as a PSAP doesn't use its business E.164  
number or SIP URL as the service URL in the LoST record, there is no  
problem. Again, no standardization is needed.

Another, orthogonal, usage is to provide some kind of prioritization  
in call handling. This is more closely related to the SIP Resource- 
Priority header.

So, what are the goals and when precisely do we need this?

Henning

On Jan 4, 2007, at 2:42 PM, Andrew Newton wrote:

> I'm not sure where we left off with this issue, but it needs to be  
> resolved.
>
> Previously, I leaned toward the sos URN in the request URI (I  
> believe this was Henning's suggestion).  I no longer think this is  
> a good idea, because the request URI is actively used in emergency  
> calls today, many times containing psuedo-codes relevant to call  
> routing.  Admittedly, this is an artifact of gatewaying to the  
> PSTN, but picking another method that would remain compatible with  
> this practice seems to offer easier transition.
>
> For the clueless, why is the Priority header with the "emergency"  
> value not useable here?
>
> -andy
>
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