Is it possible to receive RTP packets in MO device during VoLTE call ringing phase?

4G LTE
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1

Hello Experts.

Is it possible to receive RTP packets in MO device during VoLTE call ringing phase?

2

There isn’t voice during ringing so there shouldn’t be any RTP unless the ringing tone itself is classed as RTP.

3

Exactly.

So its based on configuration, no hard rule right?

4

Yes I believe.

Standard configuration is for non voice packets to be sent on QCI-5 and that includes RTCP.

5

I don’t think there is any other scenario which make it possible during ringing.

6

Early media supported during sip signalling.

7

Hey,

Yes, your phone can get RTP during the ringing stage of the VoLTE call, but only if the network sends early media. If it doesn’t then RTP will start only after the call answered.

8

Hi this is how it happens.Lets say A party calling B party and both are IMS registered subscribers.First when A calls B SIP invite will come to PCSCF or SBG with the SDP offer which carries A party UE prefered media information.By this time only IMS default bearer is established between.UE and SBG so SIP invite is flowing inside it.SBG has a component named SGC ,If you watch closely in IMS sip trace you might notice this.What this SGC will do is SGC will talk to its configured BGFs via H248/Megaco to book a media resource.Media Resource is IP and a Port for RTP and IP and a port for RTCP.BGF will check its MGW resource and send back this allocations to SGC.After receiving that information.SBG can act in two ways.If call setup time is critical to its network it can send the full IP port information to A party or if network is mpre concern about the media resource it can send only half of information usually the BGF IP only and keep the port information until it receives the SDP offer anser from B party either via 183 or 200 OK.Modern day networks are so focussed on quality usually SBG sends complete information to UE asap to establish the media as early as possible.How it will happen is SBG sends AAR/AAA and receive RAR/RAA with PCRF via Rx interface.and PCRF will communicate the same via Gx interface towards PGW.This is called Gx/Rx session binding.Once PGW receives those information it will immidiately setup the dedicated beaerer between UE and BGF/MGW anchoring it on PGW itself.From that point onwards.A party can send trffic towards BGF and some handsets actually will send some dummy RTP traffic towards BGF.If you want to cross verify this phenomena via prepaid call.You may know PGW triggeres the CCR-I via Gy interface for any dedicated beaerer only after receiving the first packet.But For a call real charging is not done by Gy it is done by Ro.The internface between MTAS and OCS..But if you check those two CDRs the PGW CDR via Gy and MTAS CDR via Ro you will see a time difference.this is because of this phenomena which I have explaind above.It is commonly refered to as Media Gating Function of SBG.

Thank you