What is the difference between iRAT Handover and SRVCC for 4G & 5G?

Hmmm…what do you say about VoLTE to VoNR transition?

Or about mobility for data session from 4G to 5G?

I heated about the opposite way, not 4G to 5G transition…

I dunno if it is applied in any operator or defined by the 3GPP. This Need to be checked.

Chat GPT says: " …SRVCC comes into play if user moves out of the LTE coverage area and enters an area covered by NR"

That’s why I don’t believe in ChatGpt theory! :wink:

Don’t use chatgpt, please.

Sure, I don’t use. :wink: :point_down:

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While learning 3gpp functionalities or vendor specific implementation, at least.

Chatgpt may be good for surface level knowledge or things which are frequent on internet.

If it works out a state-machine with possibility from A to N only in reality…it will respond you that N to A is also possible which may not be the case in reality.

The best way to get answers is this forum here, with real experts. :slight_smile:

Yes. And you can also use sharetechnote, 3g4gforum, in addition many websites that are very useful while googling on any topic.


ShareTechNote is gem! Thanks @Jaeku_Ryu :clap:

Totally agree!

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Usually in 3gpp there is no smooth handover process defined from lower technology to higher technology.

It’s different and vendor tries different method to improvise.

These procedures are discussed in 3GPP TS 23.502 : Procedures for the 5G System (5GS) :point_down:

Very good info, but real use case would have no use because IMS is the same in VoLTE and VoNR.

After VoLTE call is finished, we can push handset to 5G.

If this transition is seemless, no interription in RTP , we can test this, if interription it is not worthy.

SRVCC is handover to 3G.

For the handovers between 4G 5G and wifi, Voice call continues over IP session.

5G to 4G HO, you mean to iRAT HO, right?

Yup! :wink:

So from 5G perspective, we can say 3 solutions to legacy:

  • EPS fall back
  • IRAT Ho
  • eSRVCC
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eSRVCC is defined in R10, not between 5G and 4G.

5G started with R15.

  • SRVCC is for Voice call continuity.
  • eSRVCC is for PS session continuity (in addition to the Voice).
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But even in SRVCC the PS session was handover to SGSN if it falls back to 3G network in LTE.

That’s an intermediate solution in evolution to VoNR.

VoNR is much advanced compared to VoLTE for marked differences like new codecs (3gpp IVAS) resulting in higher capacities than 3gpp EVS.

In this post there are also some good answer by @MOHAMED_SALAMA :point_down: