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Re: AW: [Ecrit] Solution Approaches


On Apr 17, 2007, at 11:36 AM, Liess, Laura wrote:


I can not give you a feedback which is agreed within DT (the internal agreement process would probably take some time). But I roughly discussed the approaches with people working on emergency calling. If we understood the proposal correctly, we have a strong preference for the approach number 8), which could work as follows:

The ASP/ISP provides to the client the LbyR, the country code (or country and state codes)and the local EC dial string (at login and whenever these data change).

Once you have the country code (via some location mechanism, including L7 or DHCP), LoST will provide you with the dial string, so I see no need for yet another mechanism to convey that.


The client queries LOST and gets back an ESRP URI.
When the caller dials the emergency calling number, the client queries again the ASP/VSP for the LbyR and the country code and LOST query for the ESRP URI. The VSP routes the call to the ESRP. The ESRP has a shared secret with the LIS, gets the user location and the correct PSAP and routes the call with the location info to the PSAP (TLS required). (ESRP or a local LOST does load balancing for PSAPs an all this stuff).

Alternatively, the VSPs SIP proxy can do the LOST queries. 

While this works in some way, this has clear drawbacks and consequences:

- It requires a national ESRP.

- It does not allow the caller to verify, even roughly, its current address, thus making misroutes more likely. I suppose you could fix this by having the test function for emergency dialing read back the address to the caller, assuming that doesn't violate the ISPs strict confidentiality requirements on the customer's own address.






8) Country Code Routing

LIS provides country code to the end host. The end host
routes the SIP
emergency message via the VSP towards a ESRP that corresponds to the
country code. Then, ESRP fetches more detailed location
information todo
routing within the country.

CONSEQUENCE: No changes to the protocol mechanisms.
Deployment of ESRPs
that work this way are needed. Establishment of ESRP <->
ISP/ASP is more
difficult than with PSAP <-> ISP/ASP since there are far more
nodes to
consider.



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