X2 Handover preparation failure in LTE (unknown-MME-code)

Hi Team,
We recieve X2 Handover preparation failure in LTE.
After analysis, its cause is “unknown MME-code”.
What does it mean?


Which message do you check?
Is it handover required message from source eNB to target eNB via X2?
Seems your X2 is down. That’s why MME come in picture through S1.

Is this X2 handover or S1 handover?
Please check external cell TAC/MCC/MNC configuration?

Is there an Handover Preparation failure that occur with the Cause Value = “unknown -MME code”?
Also what is UE-X2AP-ID=1925?
What does it mean?


MMEs are not defined in Pool.

Can you give me more info on it?

Sure. Some cases…

One case, we identified 3 sites in network with only 6 termptoMME’s defined, and it should be 8.
(Use commands st mme, st termpointtoMME)

Another case: In CTR we find out that the preparation failure were happening due to “unknown-MME-Code”
(Use commands get . mmeCodeListLTERelated , get . mmeName)

And another case: 25 sites were upgraded and connected to new MME (2 New MMEs are added), other sites were still connected to with previous 2 MMEs.

Thank you, let me analyse one by one.
These cases belong to Core end, to defined MME in pool.

Check if S1 interface removed from sites & if eNBs S1 interfaces are following design.

unknown-MME-code.xlsx (99.3 KB)