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LTE HO : Why two MME UE S1AP IDs present within the S1-AP HO Request message ?

+1 vote

I found two MME UE S1-AP IDs i.e. MME UE S1AP ID (Mandatory) and MME UE S1AP ID 2 (optional).
I got why mandatory one is present but what's use of optional one.

Can someone please explain it ?

posted May 30, 2014 by Harshita

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By the way nice question ...

1 Answer

0 votes

Yes i also came under same question when i was going through Handover Request message .

This optional id importance is there when ENB (HeNB) and MME connected through Gateway instead of Directly .

Here GW creates two context one towards ENB and another towards MME.

See If Source ENB is connected to MME through Gateway (see figure) .

So during Handover the Target ENB should know two ids.
1>The MME UE S1-AP Gateway id (so that he can use Target ENB and Gateway connection ) as
2> The MME UE S1-AP id which is the generally we send.

So the 2nd ID is needed and it is optional as it is used in this case only.

For more description u can refer

enter image description here

answer May 30, 2014 by Sachidananda Sahu
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