Hi Experts.
When CSFB initiated with extended service request, it is expected for s1mme and other resouces to be released so there is UE context release request.
But right before it, it establishes a initial context.
If it will be released, why it is established beforehand?
Thanks in advance to all of you.
Good question.
No link exist b/w UE and network for it to make any request.
So even to process Extended Service Request, Initial Context has to be created.
Is DRB created on radio side after initial context request as usual?
If yes, isn’t it wasting the resource?
I am trying to remember but pretty sure in CSFB case no drb is created unless mechanism include sending measurement reports. Setting up initial context is required for RRC connection.
If this is CSFB with blind release, UE is released fairly quickly after network finds out that UE is raising request for voice and it has to be CSFBed.
RRC connection shold already be setup since extended service request message is present as you, right?
After initial context, rrc reconfug is sent for DRB I think.
Maybe initial connext is sent to assign mme s1ap ue address, an identifier on application layer.
Sorry you are right (getting old so cannot remember call flows any more 
).
There shouldn’t be initial context setup requests if UE was connected.
New S1AP may trigger if eNB somehow removed the context, has corrupted record etc.
But generally there shouldn’t be a need for a new S1AP initial.
Yeah i think so, but maybe because of the procedure of setting s1ap mme-id, it may sent, i dont know.
Normally there is already sctp connection setup.
It can send UE release request from there in fact.
