outbound ring tone
drgeoff:
Quote from: CoalMinerRetired on August 05, 2015, 06:23:38 am
It's a worldwide standard that the ringing you hear when placing a call is generated by the called party's equipment, not by the calling party's equipment. I don't believe there is any mechanism, in an OBi or otherwise, that intercepts a call being setup and generates a tone, a beep or any signal.
No, that is not totally correct.
Yes, it is the way that pure POTS/PSTN calls generally work. But it may not apply when VoIP is involved. For example when a call is purely SIP, the ringing tone heard by the caller is generated in the caller's terminal when the SIP 180 'Ringing' message is received. See for example Fig 1 at http://pbx-solutions.blogspot.co.uk/2010/06/overview-about-session-initiation.html. That message comes in the signalling channel, there is no audio path existing at that point in time.
ianobi:
I'll see if I can make this even more complicated :)
Where the ringback tone is generated depends on "early media" and how the OBi device handles that. "Early media" is any audio and/or video that is sent in either direction before the call is actually answered. This might be an information message or a tone etc.
With regard to SIP the "180 Ringing" message is sent from the callee SIP equipment back to the caller SIP equipment (OBi in this case) to indicate that the callee is actually being called. The OBi device handles this as follows:
1. If "early media" has been established and an RTP path has been established between caller and callee before the "200 OK" message (call answered), then the OBi will ignore the "180 Ringing" message and pass the early media to the caller. So a voip provider may send its own ringback tone via early media.
2. If no "early media" has been detected by the OBi, then when it receives the "180 Ringing" message from the callee it will generate its own ringback tone locally and send that to the caller.
In my own setup I have tested one provider (sipgate) that uses early media to supply ringback tone, so case 1 applies. Another provider (sip2sip) does not provide early media, so case 2 applies.
Of course, GV uses XMPP not SIP, but I believe that XMPP behaves the same with regard to early media as SIP. Also, I believe that GV does not provide early media, so it is likely that it's the OBi providing the ringback tone locally. This could be proved by changing the relevant tone pattern in the OBi. However, I would say that I am very much NOT an expert when it comes to GV, so maybe our resident GV expert would like to comment on that.
I trust that's helped anyone who managed to stay awake to the end of this post :D
Edit: There is another scenario where a voip provider who wishes to use "early media" does not send the "180 Ringing message" back to the caller at all, but instead sends a "183 Session Progress" message which contains all the information (connection ip address, codecs to use etc) back to the caller SIP equipment (OBi in our case). This enables an audio channel to be opened for sending tones, IVR announcements etc before the "200 OK" message confirms that the call is connected and call charging can begin.
CoalMinerRetired:
Quote from: drgeoff on August 06, 2015, 02:36:49 am
Quote from: CoalMinerRetired on August 05, 2015, 06:23:38 am
It's a worldwide standard that the ringing you hear when placing a call is generated by the called party's equipment, not by the calling party's equipment. I don't believe there is any mechanism, in an OBi or otherwise, that intercepts a call being setup and generates a tone, a beep or any signal.
No, that is not totally correct.
Yes, it is the way that pure POTS/PSTN calls generally work. But it may not apply when VoIP is involved. For example when a call is purely SIP, the ringing tone heard by the caller is generated in the caller's terminal when the SIP 180 'Ringing' message is received. See for example Fig 1 at http://pbx-solutions.blogspot.co.uk/2010/06/overview-about-session-initiation.html. That message comes in the signalling channel, there is no audio path existing at that point in time.
Thanks. My understanding is from 20 years ago (all landlines). However, what you said and what Inaobi added sums up to: the ITU standard doesn't apply to sip to sip calls, and for sip to sip in some cases it may not.
So I think there's still a mystery, because GV is not SIP, and on top of that GV does not support early media unless something has changed very recently.
I'll also add I see no OBi settings (202/110/100) that hint at controlling this, however since it's happening and it's never been mentioned here might mean it's one of those unexplained 'magic number configuration fields' that are right in front of us.
azrobert:
Quote from: ianobi on August 06, 2015, 03:28:07 am
2. If no "early media" has been detected by the OBi, then when it receives the "180 Ringing" message from the callee it will generate its own ringback tone locally and send that to the caller.
I set the following:
Tone Settings -> Tone Profile A -> Ringback Tone -> Tone Pattern:
480-18,620-18;10;(.25+.25) (Fast Busy)
I called a GV number and heard a fast busy tone instead of the ringback tone. I think this confirms what ianobi posted above.
drgeoff:
@ianobi
I've never had a need to understand the "early media" stuff so I've never investigated it. Do you know for a fact that Sipgate UK use it or is it a conclusion you have come to?
I ask because most calls placed via Sipgate UK are not SIP end to end. In a pure SIP to SIP call the audio flows directly between the two endpoints. However many ITSPs do not work that way but remain "in circuit". I suspect that there is SIP between your OBi and Sipgate and then there is POTS/PSTN/cellular or another SIP between Sipgate UK and the callee. Thus it appears (to me) that tones you hear could come from Sipgate equipment, or anywhere else on the route to the callee. And that would be possible without "early media" between Sipgate and your OBi; merely that the "call" from your OBi to Sipgate is answered immediately and any call progress tones (Sipgate to callee) you hear are coming to the OBi as audio in the ordinary way.
I'm not saying you are wrong and I am correct. I'm just interested in knowing exactly what is going on and whether you or anyone else has hard evidence which clarifies matters.
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