Hi Huawei Experts.
Needs suggestions on improving the LTE QCI-6/9 eRAB Setup Success rate and eRAB Drop Rate.
For data users
Any good parametric suggestions are welcome.
What problem you are trying to fix?
What is highest cause for setup failure and session drop?
L.E-RAB.FailEst.MME this is the highest cause right now, around 95% failures are due to this cause.
Upon checking traces found that each time failure observed due to the “interaction with other procedure”.
Right, this failure happens when handover and session setup are happening at same time, or call setup and handover happening at same time.
If you search Hedex, Huawei introduced a parameter to prioritise one over the other.
Yes, we have done those parameters as well but they will improve only RNL failures not MME failures.
Huawei has 2 global witches about this.
Like explained above.
MME failures is when UE drops on a cell and initiate a call on a new cell, then the S1 of initial call will be terminated with MME failure.
It is well expamined here LTE Call Drop Rate - Our Technology Planet at chapter 2 MME induced drops.
Consider a UE that experienced RLF due to maximum number of uplink RLC retransmission.
Such a UE will initiate a RRC ReEstablishment procedure to regain its radio link.
Now this RRC ReEstablishment can be to the serving cell and in that case, it is usually successful since the serving cell already has the UE’s context.
However, this RRC ReEstablishment can also be sent to another cell from eNB2 that does not belong to the source eNB (eNB1).
In this case, if eNB2 is a neighbor of the eNB1 so it will try to fetch the context for this UE from eNB1 and based on that it will accept the RRC ReEstablishment.
However, if the eNB2 is not a neighbor then it will reject the RRC ReEstablishment.
From the UE’s perspective this will be considered a call drop but at the eNB1, the eNB still does not know that this UE has experienced RLF.
Now, the UE will initiate a new RRC Connection at the eNB2 and based on that the eNB2 will forward S1 Initial UE Message to the MME.
MME will check the UE and it will find out that this UE’s context already exists on the eNB1 so it will send a UE Context Release to the eNB1 and then it will send S1 Initial Context Setup Request to the eNB2.
The eNB1 will consider this a MME induced drop since the eNB1 still holds the UE’s context and a release from MME is considered abnormal.
However, in reality, such a release is caused by a failure over the radio interface but the eNB1 does not have this knowledge.
Thanks, but our discussion was on eRAB Establishment phase not after establishment phase.
Currently UeInactiveTimerForQci is on 10 for QCI6/9, we are planning to change it to 6 from10
Huawei experts, any practical negative points seen?
Practically any draw back seen?
Increase in signalling messages is one thing.