Question

Does the S1-handover procedure always has to be change in MME ? As per spec it is mentioned MME changes during the S1 handover. But in a case where the source and target enodeB is served by same MME , but let say because of some network problem X2 interface is not available and source enodeB initiates a S1 handover procedure. How do we validate this scenario, as I don't see any call flow in the spec for this?

Answer 1

In short , answer is "No".
If you look into the "S1-AP based handover required" message, there is an IE "target Id". Based on the Target Id , source MME get to know whether it has S1-connection with target eNodeB or not. It may have S1-connection with target eNodeB or the MME may not aware about the target eNodeB . In case of S1-connection availability, MME triggers "Handover Request" towards target eNodeB . As result, there is no change in MME.

Now consider the another scenario, in which source MME doesn't know about the target eNodeb. MME creates S10 interface based forward relocation request (having target Id information ) and sends to target MME. This is the scenario where MME gets changed.

Comments

Thanks Ganesh for your helpful reply.