When do X2 or S1 handover is preferred?

Hi Experts.

When do X2 or S1 handover is preferred?

All handovers are X2, unless X2 down then S1 handover is done.

Setbacks when S1 interface is preferred?

In Inter PLMN handover (same operator but different telecom circle/market), can’t say S1 is preferred but configuration or network architecture wise only S1 is preferred.

For X2 to take place, both target and source eNB should be on same MME pool. But in our network 2 PLMNs have different MME pools each of 11 MMEs so only S1 takes place.

S1 based handover happens in below condition.

  1. There is no X2 connection to target eNB
  2. The target eNB notify the source eNB that the privious X2 based handover fail
    3.The source eNB receive dynamic information about S1 handover.

Hi All.

How eNodeB knows handover to be done via X2 Or S1?
Does MME controls this or some parameter in eNodeB itself?

  1. I have a case where source target has different PLMN (state boundary), both sites have totally different MME pooling. All X2 ho gets failed at preparation phase.

  2. In other PLMN boundaries, S1 handover takes place successfully.

Need to understand in first case why eNB attempts X2 HO while it should attempt S1 HO.

If X2 is defined between inter PLMN first X2 attempt will only be attempted.

What is use of X2 here?

X2 is defined because earlier both PLMNs have common MME pooling, now they are separated.

Better to delete all inter PLMN x2 then.

This is not the case in other PLMN boundaries, though X2 is defined and enabled, only S1 is happening in standard scenario.

You can blacklist X2 also I guess.

Without deletion, in other circles it’s only S1 takes place, problem is only for 1 inter PLMN boundary after pooling separation.

So my question is, without deleting X2, how can we priortise S1 for inter PLMN? Any switch at eNodeB or MME end?

After some HO preparation failures, X2 get blacklisted.

That might be the case.

Not blacklisted yet, from 2 months, all X2 attempts have 100 prcnt preparation fail still X2 is enabled.

Check if HO Allowed kind of parameter is there or not.

For X2 connection.

Issue resolved. Issue was at MME side. In MME, inter plmn MME cinfiguration was defined in SNET group1, after cleanup activity, S1 HO started taking place.

main reasons for x2 interface failure?