Re: [Sipping-tispan] Advice of Charge (AoC)

[Miguel Garcia <[e-mail]>]

Inline discussion.

GARCIN Sebastien RD-CORE-ISS wrote:
> Miguel,
> 
> First it may be true that there has been some discussion in the past about this but I think it is still interesting to list the conclusions of those discussions in order for readers (including me) to understand if there was indeed a real problem with piggy-backing solution. Please note the solution is not exaclty "piggy-backing" because in some flows (e.g. AoC-S service) the AS generates the 183 answer and does not wait for a 183 answer from the terminating side (see figure 1/ WI3030).
> 
> Looking at your points: 
>  
> 1/ IMS Charging problem and creating artificial SIP message
> ------------------------------------------------------------
> I am not sure to undertand the problem. The AS is perfectly entitled to create and send 183 answers downstream, such message is needed anyway for the service and this has nothing to do with "preconditions or sending charging information". Could you please clarify ?

So here we go... the AS need to create artificial 183 messages when 
there might not be a need to send 183 at all. Think for example that you 
call someone who happens to be an automata, such as an answering 
machine, you will get 200 OK immediately. This does not require a 183, 
but you need to create it artificially and delay the session just for 
sending the AoC information. It would be more natural to create a 
separate side-by dialog for sending the required information.

Second: 183, as any other provisional responses, apply only to INVITE 
transactions. So you would never be able to apply the AoC service than 
any INVITE generated service, that is, video, voice, and MSRP sessions.

> 
> 2/ Breaking end-to-end signalling
> ---------------------------------
> The AS does not break anything, it simply adds service information to messages. This behaviour is very common in the work we are doing in TISPAN.

If the 183 has to split the dialog between the calling and the called 
party, it is breaking the end-to-end signalling. While this situation 
can't be avoided in some cases, in general it is desired to get away 
from it. It breaks any possible end-to-end security, as a starting 
point. If the service can be implemented while the AoC AS behaves as a 
proxy, that would be an advantage for the implementation of the service 
and the future compatibility of services.


BR,



     Miguel

> 
> Regards
> sebastien
> 
> 
> 
> -----Message d'origine-----
> De : Miguel Garcia [mailto:[e-mail]] 
> Envoyé : lundi 30 janvier 2006 09:55
> À : GARCIN Sebastien RD-CORE-ISS
> Cc : [e-mail]
> Objet : Re: [Sipping-tispan] Advice of Charge (AoC)
> 
> GARCIN Sebastien RD-CORE-ISS wrote:
>> Hi Miguel
>>
>> First I have some problems with the service definition as expressed in the draft-jesske-requirements-draft. The draft seems to indicated the AoC service is always invoked by the served user. Although this might be a valid case, this is not the only way to invoke the service since it can be a permantent invocation. I suggest that you copy and past the service definition as documented by TISPAN in WI3030 instead of the text at the beginning of §3.4.
> 
> 
> True, there is a permanent service indication that does not require any SIP signalling, thus, it does not have any protocol impact. In the requirements we listed only those which we believe they may have protocol impact.
> 
>> In other words the requirement "to signal to a network that the service is invoked" is optional. Additionnal I believe that it should be optional for the UA to indicate whether it is capable of understanding an AoC information sent by the network (note that this is different from "invoking" the service). It is important that the capabilities required from terminal is kept to a minimum so as to make the AoC service possible for a wide range of terminals.
> 
> I agree.
> 
>> With regards to the delivery of the information, I don't agree the piggy backing solution has been demonstrated as "bad", in my view it is the most elegant way I have seen and has the advantage to require minimum capability to terminals.
> 
> Here I disagree. I am aware of two contexts where piggyback has been 
> discussed: one is the IMS charging information, and you know what? When 
> 3GPP wanted to remove the usage of preconditions, all the problems where 
>   around the fact that "hmmmm... if we remove preconditions, there 
> aren't enough messages to transport charging information, so we can't 
> remove preconditions". This is crap: creating artificial SIP messages 
> just to transfer required information.
> 
> The other context where this was discussed was in the Session-dependent 
> policies. After some comparisons and analysis, the SIP WG decided to 
> create a sideby channel for providing information of the policies (the 
> slides were presented in an IETF meeting, perhaps in Seoul, don't quite 
> remember exactly).
> 
> Additionally, breaking the end-to-end signalling just to provide sideby 
> information is, in general, a bad idea. It should be avoided.
> 
> 
>> Also I am surprised that you don't mention "MESSAGE" as solution since you advocated this solution in TISPAN meeting ??
>>
> 
> Yes, MESSAGE is also an alternative to transport the information. So we 
> have the SUB/NOT, REFER, and MESSAGE.
> 
>> Regards
>> sebastien
> 
> BR;
> 
>      Miguel
> 
> 
>>  
>>
>>
>>
>>
>>  
>>
>> -----Message d'origine-----
>> De : [e-mail] [mailto:[e-mail]] De la part de Miguel Garcia
>> Envoyé : lundi 30 janvier 2006 08:41
>> À : '[e-mail]'
>> Objet : [Sipping-tispan] Advice of Charge (AoC)
>>
>> Hi all in the list.
>>
>> I would like to get opinions on solutions for implementing the Advice of Charge service.
>>
>> Requirements for this service are listed in the TISPAN requirements I-D, Section 3.4:
>> http://www.ietf.org/internet-drafts/draft-jesske-sipping-tispan-requirements-02.txt
>>
>> When we discussed this service in Vancouver, Jonathan suggested to take a look at the SIP Interaction Framework to get ideas. They are very good ideas in the SIP Interaction Framework, but still I would like to get opinions.
>>
>> This service presents two problems to be solved:
>>
>> 1) How to signal to a network node that the service is invoked
>>
>> 2) How to transport the required information to the User Agent.
>>
>>
>> According to the interaction framework, invocation could be signal by a combination of protocol elements, specifically: Allow REFER, Accept-Types with some specific XML format, Contact with schemes: http, Contact with GRUU, Supported with "tdialog", ... don't know what else.
>>
>> While that is valid, I think it presents three problems. First, it is not possible to distinguish between "this is what the UA supports" from "this is the invocation to the service". Second. it makes the configuration of the initial filter criteria (to trigger to the AoC Application server) a nightmare, because instead of searching for one "item", we need to create comparisons for four or five items. Third, this works as long as there is some unique item to the service, which could be the type of body declared in the Accept-Types, but as soon as we wanted to reuse this body for some other service, we would run into trouble.
>>
>> One proposal to invoke the service was to define a new specific header, let's call it P-AoC, that contains some parameters that define the service behavior. For example, it could contain some preference of the reporting time or something like that. Another alternative could be to use a subscription to an event package, in which case, we are determining not to use a REFER to an HTTP URI for conveying the information. A third possibility is to define a specific feature tag, but I think this isn't really a feature, but a whole service.
>>
>> On the delivery of information, we can think of a REFER to an HTTP URI or a SUB/NOT type of notification. Some folks have been thinking of piggy-backing the information to SIP requests or responses that "happens to pass by", but this solution is bad, as it has been demonstrated with the charging stuff in IMS, besides it does not meet the requirement of delivering information "a few seconds after the communication has ended" 
>> (REQ-AoC-1). So I guess the choices are just REFER + HTTP URI or SUB/NOT.
>>
>> I am willing to hear comments that can provide the needed guidance to TISPAN.
>>
>> Best regards,
>>
>>            Miguel
>>
> 

-- 
Miguel A. Garcia           tel:[phone]
sip:[e-mail]
Nokia Research Center      Helsinki, Finland


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