Subject: Re: [Sip] Need for RPH in SIP Responses

From: ken carlberg <[email-masked]>
Date: Tue, 27 Nov 2007 11:04:44 -0500

Janet,

sorry for the tardy comments on the thread.  when I read the draft, a  
couple of other use cases outside of the GETS model came to mind that  
would seem to prompt a need for an R-P header in a SIP response.  In  
the land mobile radio arena, we have bridging architectures/ 
technologies like the ISSI that use SIP as a foundation to bridge  
autonomous subnets of P25 systems.  These tend to be resource  
constrained systems of multi-level precedence, and so having a  
corresponding R-P header in SIP responses would fold in nicely with  
what is being built today and planned for the near future.

outside of that, there are also some efforts to bridge ISSI with Push- 
to-talk over Cellular (PoC) with SIP, though this is quite preliminary  
so I don't know if I'd list this as another use case.  But in any  
event, I think it would be helpful if you could broaden the problem  
statement in your draft so that it is not strictly focused to just  
GETS.  Subsequent to this broader statement, you could then provide a  
more in-depth discussion of the GETS *example*.

also, is it your plan to progress your draft in the SIPPING WG given  
that it deals with a requirement?  I see its on the SIP agenda along  
with James' related draft, which is helpful, but I assume that further  
progress would be shifted to SIPPING.

-ken

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From: Janet P Gunn <[email-masked]>
Date: Wed, 28 Nov 2007 17:01:03 -0500

Ken,

Could you expand on these other use cases, and how they would benefit from 
RPH in responses?

Thanks

Janet

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From: ken carlberg <[email-masked]>
Date: Thu, 29 Nov 2007 12:43:29 -0500

Janet,

I'll expand a bit, but I think anything more would probably be best in  
the form of text+references,  and an offline discussion if needed.

land mobile radio, commonly used by police/ambulance/first- 
responders,  has been the poster child for NON-interoperable systems.   
They operate within Radio Frequency Sub Systems (RFSS) using a common  
air interface (CAI) and the fixed station interface (FSI) -- using TIA  
as an example.  The inter sub-system interface (ISSI) is used to  
extend interoperability between RFSSs, and here is where SIP is being  
incorporated  for call control between RFSSs.  Initially, the system  
uses stateful SIP proxies, but later on stateless proxies are expected  
to be incorporated in the architecture.  In addition, there is a  
desire to incorporate RPH and replace TIA's current approach of  
overloading the SIP Priority value with TIA-specific values (this is  
very aggravating, but hopefully reason will win out).  Hence, adding  
RPH to responses would be constructive given the potential for  
stateless proxies in the sample calling segments below

Calling <------->Calling <-------->Called <------>Called
serving            home                 home             serving
RFSS              RFSS                 RFSS             RFSS

with respect to PoC, there are efforts to build bridging architectures  
that provide interoperability between the ISSI/RFSS and PoC systems  
using SIP in order to seamlessly extend the push-to-talk feature of  
the different architectures.  Some designs for these bridges advocate  
stateless SIP proxies that just map calls of one system to the next.

-ken

On Nov 28, 2007, at 5:01 PM, Janet P Gunn wrote:

>
> Ken,
>
> Could you expand on these other use cases, and how they would  
> benefit from RPH in responses?
>
> Thanks
>
> Janet
>
>