Which entity triggers X2-Setup?

Question

Its seen that X2 setup is not working, both enodebs can ping each other but no sctp assocation seen.

It is successful only sometimes when both nodebs are rebooted, What could be the reason.?

Answer 1

There may be various methods to trigger X2 setup.
1. OAM may trigger.
2. Due to ANR (Automatic Neighbor Relationship), which is one of the SON feature.
3. By using static configuration, eNodeB knows its peer in advance and at the time of bring up it makes connection with neighbor eNodeB.

I know only few of them, there may be another ways to do so.

Answer 2

From what I know this happen automatically between eNBs.

When one will notice the other one, and the first one is configured to use X2 then it tries to establish the X2 with the second/other eNB.

Comments

"When one will notice the other one"
> Does eNB keeps on checking it to notice it? please elaborate.

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UE is measuring and reporting continuously the signal level from different eNB in its Line of Sight or Non-LoS in some "common channel".
This is how eNBs are aware they have neighbors, or at least this is my understanding of this procedure.

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I just had a quick look on the ANR and it seem I'm mistaken.