[Serusers] SER + Prepaid = Old discussion

[Klaus Darilion]

You can not set the maximum call duration with Session-Timer. 
Session-Timer is a keep-alive mechanism, not a session-termination 
mechanism.

Quick answer: go with Asterisk. There are dozens of existing, well 
working calling card functions.

regards,
klaus


Ricardo Poppi wrote:
> 
> Hi all.
> 
> This list had a long discussion for the last two months about how to use 
> SER with prepaid applications, since it does not participate into the 
> media path. I´ll try to put things together in a easy way - at least for 
> me... - for trying to solve some doubts about how this feature can work 
> with SIP without creating new problems. And, of course, I´m assuming 
> that we WILL NOT use b2bua, but try to make this work in a proxied 
> environment.
> 
> As mentioned before, one way to do so, is using the session timer 
> (RFC-4028)  definitions.
> The main reason those definitions were created, is for using when a BYE 
> message don´t reach one of the UAs involved into a SIP dialog, that 
> without those definitions would be virtualy connected "forever" since it 
> did not receive any SIP signaling to disconect. With session timer 
> working, even if a BYE message never reaches the other point, the 
> maximun time that the "not-reached" UA would stay connected is the time 
> setted into the session-timer parameter.
> 
> Ok. But let´s use it to work with the prepaid environment. We implement 
> a logic into our sip proxy (SER), that record-route all signaling 
> messages between all UAs of our SIP network. Then we put our proxy to 
> analize all re-invite messages that goes into our  SIP dialogs and, if 
> the customer credit (in seconds) is below that the time into the 
> session-timer parameter, it rewrites the "seconds-credit" into the 
> message session-timer position, decrements the last session time into 
> the customer seconds credits table, and counts on the UAs to 
> disconecting the call, since it - the proxy - will drop/block the next 
> re-invite(s) to this especific dialog.
> 
> In this aproach, we need to check the first invite as well, because if 
> the customer credit is below that the value of the first/default 
> session-timer, the SIP message needs to be rewriten too.
> 
> Problems on this aproach:
> 
>  - If a re-invite from the caling user - the one that will be billed - 
> never reachs the proxy, the UA will disconect the call sending a BYE, 
> and, if the BYE never reachs the proxy either,  the seconds of the last 
> session won´t be billed, correct?
> 
>  - Thinking about security issues into a environment that just one UA 
> support session-timers, It would be very easy for a malicious UA - the 
> one that supports session-timers - when it runs out of credit, to send 
> its last re-invite - the never answered one -  withouting disconecting 
> the media path. In this case, the proxy will "think" that the call is 
> off, but it would be not true.
> 
> 
> Does anyone work with a true proxied prepaid environment using session 
> timers?
> 
> There is any aproach, other than using RFC-4028 - session timers,  for 
> doing this?
> 
> 
> Any clue will be welcome.
> 
> Thanks in advance for the list.
> 
> Regards,
> 
> Ricardo Poppi
> 
> 
> 
> 
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