Subject: Re: [Sip] RE: [Iptel] Calling Party's Category

From: Adam Roach <[email-masked]>
Date: Tue, 30 Nov 2004 13:27:19 -0600

David R Oran wrote:

>
> On Nov 30, 2004, at 10:42 AM, GARCIN Sebastien RD-CORE-ISS wrote:
>
>> As an fixed line operator we also are interested in this feature and 
>> would be happy that the IETF finally moves forward with this draft. 
>> This type of parameter is widely signalled in ISDN/PSTN networks. In 
>> SIP (for example) it is required in context of both:
>>
>> - pure SIP networks (e.g. in case of a SIP payphone), and
>> - interworking with legacy networks
>>
>> I think the uses case for this parameter will depend on the operator 
>> service portfolio. For example, in France, the calling party's 
>> category parameter is used for the Call Return service.
>>
> Could you explain a bit about how this is used? I, for one would find 
> it helpful and possibly a motivating use case.

I'm equally confused. I'm familiar with the calling party category in 
ISUP, which works only because of the walled-garden nature of the SS7 
network. Without that, there are really two major factors around this 
which need to be characterized:

   1. Who is authorized to assert a particular calling party category?
      This is much trickier than the identity problem; with identity, we
      can trust that a domain is the authority for the use of user names
      in that domain. For calling party category, there is no such
      relationship. For example, it would probably not be valid for a
      domain of "adamroach.com" to assert a calling party category of
      "priority," "operator," or "police."
   2. Under which circumstances is the calling party category required
      to be present? Is there some architectural mechanism that can be
      used to enforce this? (We don't need to define it, but there
      should at least be some idea about whether it's possible). If not,
      then there is no purpose in coming up with a protocol mechanism
      for conveying such information.

/a

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---

From: Mike Hammer <[email-masked]>
Date: Wed, 01 Dec 2004 11:22:39 -0500

At 01:27 PM 11/30/2004 -0600, Adam Roach wrote:
>>>would be happy that the IETF finally moves forward with this draft. This 
>>>type of parameter is widely signalled in ISDN/PSTN networks. In SIP (for 
>>>example) it is required in context of both:
>>>
>>>service portfolio. For example, in France, the calling party's category 
>>>parameter is used for the Call Return service.
>>Could you explain a bit about how this is used? I, for one would find it 
>>helpful and possibly a motivating use case.
>
>

The underlying assumption of the base peer-peer architectural model is that 
the peers have a mechanism to do end-end security and can establish direct 
trust between the ends.  But, this does not hold much water when one end is 
intentionally betraying trust.  That begs for middleman enforcement.

What happens when:
the calling endpoint can not be trusted,
a middle point proxy can be trusted to know the calling endpoint,
the called endpoint could trust the middle device?

The issue seems to be that we have an end to middle security requirements 
(draft-ietf-sipping-e2m-sec-reqs-04), but not a middle to end security 
requirements, whereby the called end does not trust the caller, but could 
establish trust of the middle with appropriate mechanisms.

Granted this leads back to a walled garden sort of approach to things, but 
walls may serve a purpose.  But, instead of thinking of this as an 
impedance to traffic, better to consider this as a truthful attribution of 
traffic as it is allowed to traverse domain boundaries.  Trust comes from 
authenticity of information and in some cases middlemen are needed to 
enforce that.  Otherwise, expect spam, spit, wormy, virus-sick networks.

Mike