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Generally if UE is in RRC Idle state, ENB will inform to UE via paging message about CS domain i.e incoming call.

My doubt is in LTE, when UE is in RRC Connected State, how network will notify to UE about incoming MT call ? In which Information element or message ?

Any help will be appreciated !!

Achal
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There's a NAS message called "CS Service Notification". Assuming the UE is "RRC Connected" and assuming it has a established NAS connection, that's what the MME uses to notify the UE. That leads the UE to reply with the "Extended Service Request" message, and then what follows is pretty similar to what would happen if the UE was being paged.

Gustavo Meira
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    Agree Gustavo. Thanks for reply. UE should have done combined CS & PS attach procedure before this. Am I right ? – Achal Jul 30 '18 at 13:13
  • @achal I imagine so, that's always required for CSFB – Gustavo Meira Jul 30 '18 at 13:18
  • After ESR it should receive rrc connection release, is that true ? What if it didn't receive rrc connection release ? My concern is regarding CSFB. – Achal Aug 30 '18 at 09:44
  • For sure if you're using handover between 4G and 3G, for example, then during the whole procedure the (source) MME would request a context release to the ENodeB at some point, which would probably trigger an RRC Context Release. If you're using redirection, then I'm not a 100% sure. I don't know how the ENodeB is going to be aware that the ESR is finished in order to terminate the RRC connection, but my guess would be it does send an RRC Connection Release. I guess you would have to read the 3GPP specs to confirm that. – Gustavo Meira Aug 30 '18 at 11:23
  • Thanks lot :) I have gone through 3gpp specs. One last doubt in some case I observe there is no RAT to be redirected info in rrcConnectionRelease, then to which RAT it will fall back or not ? – Achal Aug 31 '18 at 06:21