[SIPForum-discussion] FAKE RBT Scenarios

[Stephen James]

Some UAC if the receive 180 with SDP will still play local ring back rather than cut through media. Also, some UAC will not stop local ring back (started with 180 without SDP) even if 183 with SDP is received after 180. The choice then becomes send 183 with SDP which has the highest probability of getting media cut through and then 180 to signal that alerting has begun. So from a pure SIP specification point of view it seems unusual, from a practical interworking point a view it is needed. 

Sent from my iPad

> On Jan 29, 2014, at 8:35 PM, Shah Hussain Khattak <shahhusayn at msn.com> wrote:
> 
> Dear Stephen, 
> 
> First of all really appreciate your quick response! Yes the RBT comes from far end side, our proxy is just doing transparent signalling. Can you please explain your point in a little detail? Honestly i am not getting it very clearly and i want accurate understanding :)  
> 
> Regards, 
> Shah Hussain 
> 
> Subject: Re: [SIPForum-discussion] FAKE RBT Scenarios
> From: sjames_1958 at yahoo.com
> Date: Wed, 29 Jan 2014 20:31:10 -0600
> CC: discussion at sipforum.org
> To: shahhusayn at msn.com
> 
> Does the RBT come from the far end? Some systems won't cut through if SDP is in 180 and some systems won't cut through if 183 with SDP is received after 180 without SDP. If theming back is being cut through then the meaning of 180 ringing is less important. 
> 
> Sent from my iPad
> 
> On Jan 29, 2014, at 8:10 PM, Shah Hussain Khattak <shahhusayn at msn.com> wrote:
> 
> Dear Stephen, 
> 
> Thanks for your feedback. Please find below the call scenario, in which client hears RBT after a long interval, hence increasing the pdd at his end:
> 
>  <call-scenario-1.png> 
> 
> I think, i would better rephrase my question to delay before hearing PDD ( sorry for the misguiding title). So is above call flow normal, i think we should send 180 ringing before 183 Session in progress, as sending 183 before 180 ringing is causing the delay for the client to hear actual RBT. Your thoughts sir? 
> 
> Regards, 
> Shah Hussain  
> 
> 
> 
> 
> 
> 
> 
> Date: Wed, 29 Jan 2014 16:44:43 -0800
> From: sjames_1958 at yahoo.com
> Subject: Re: [SIPForum-discussion] FAKE RBT Scenarios
> To: shahhusayn at msn.com; discussion at sipforum.org
> 
> This is pretty normal for early media such as custom ringback or announcement from the far end. 
> Since the 183 doesn't have 100rel/PRACK then sending SDP twice is ok. If the 183 is sent reliably there shouldn't be SDP is later responses.
> 
>  
> Stephen James 
> sjames_1958 at yahoo.com
>  
> We are not princes of the earth, we are the descendants of worms, and any nobility must be earned.
> 
> From: Shah Hussain Khattak <shahhusayn at msn.com>
> To: "discussion at sipforum.org" <discussion at sipforum.org> 
> Sent: Tuesday, January 28, 2014 12:19 PM
> Subject: [SIPForum-discussion] FAKE RBT Scenarios
> 
> Hello All SIP Experts, 
> 
> Can you guys please confirm me is below scenario normal:
> 
> Call Invite ---------------->
> 
> 183 session in progress without SDP <----------------------------
> 183 session in progress with SDP      <----------------------------
> 
> then
> 
> 180 ringing with SDP <---------------------------------------------
> 
> i just want to know is above call flow normal? 
> 
> 2nd thing, is 180 ringing with SDP creating fake RBT for calling party side? 
> 
> 
> Regards, 
> Shah Hussain 
> 
> 
> 
> 
> 
> 
> 
> 
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