On 3/13/08 11:59 AM, Dean Willis wrote:
> We could fix this by having gateways encode their identity using a  
> reserved userpart. This has to have the  property of saying "Do not  
> display this as caller-ID". Using "sip:domain" or "sip:ipaddress" does  
> not work, as those might actually be valid URIs that be be displayed  
> as IDs.
>   

That's the problem I have -- if the calling party reported by the PSTN 
has been completely pulled out of the "From" header field, then you'll 
have very bad interaction with currently deployed phones. I don't think 
that's a reasonable trade-off. That's why I think this...

> It might work to have the gateway use a reserved value, like "sip:[EMAIL 
> PROTECTED]".
>   

...is a non-starter.


> Or it might work to extend RFC 4474 to have a "strength of assertion"  
> indicator.
>   

You mean something like:
  From: <sip:[EMAIL PROTECTED];user=phone;trusted=no> ?

Or something more like:
  Identity: "LotsOfBase64EncodedGunk==";trusted=no

(I acknowledge that this can be more nuanced than yes/no, but let's 
decide where the bike shed goes before we begin the argument about its 
color).

> It's certainly easier to add guidance in DTLS-SRTP about what gateways  
> should do and about how UASes should interpret various header fields  
> than it is to change RFC 4474.
>   

That would argue for some indication on the *From* header field that 
indicates a level of trust. I'm not sure it's really the proper place to 
place that information, from a semantic perspective -- but it does seem 
to be a potential way to get through this maze of thorns without losing 
too much blood.

/a
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