LTE ERAB AbNormal Release Causes Correct _1

8/11/2019 LTE ERAB AbNormal Release Causes Correct _1

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HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential

HUAWEI TECHNOLOGIES CO., LTD.

E-RAB Abnormal Release Causes




Contents

• Counters names & description

• Abnormal Releases causes mapping

• Difference between E-RAB Release & UE Context release Command messages

• Types of Normal Releases.

• Abnormal Releases causes Measurement points

–

MME – Radio

– TNL

– HO failure

– Congestion

• Examples from Nastar for some ERABAbnormal releases

• Queries about ERABAbnormal Release due to load.




Counters names & description and related KPI

The counters measure the number of abnormal E-RAB releases due to different causes in a

cell. An E-RAB is the access layer bearer for carrying service data of users. The E-RAB release

is a process of releasing the access layer bearer resources of users

Total no. of Abnormal release affect on call drop rate KPIs




Abnormal Releases causes mapping

E-RABAbnormal Rel.MME

E-RAB MME/SGW

E-NodB

UE

E-RABAbnormal Rel.Cong.*

E-RABAbnormal Rel.HOfail

E-RABAbnormal Rel.Radio E-RABAbnormal Rel.TNL

• * ERABAbnormal release due to congestion can be mainly due to radio resources congestion but i am not

sure if it doesn't include other entities congestion ( transmission & MME )




Difference between E-RAB Release & UE Context release

• E-RAB RELEASE COMMAND• Only will to release the RAB/s with the mentioned ID/s so in case of a UE having

more than one RAB it will not release all its RABs only the mentioned IDs

• UE Context RELEASE COMMAND• Will release all RABs allocated to this UE and the same if multiple number of

UEs are mentioned in the message

Types of Non-exception E-RAB releases initiated by the MME• Normal Release.

• Detach

• User Inactivity

• CS fallback triggered




E-RABAbnormal Rel.MME’s two triggering msgs.

• UE CONTEXT RELEASE COMMAND As in figure 2 all RABs for the UE/s are released each time the UE context release is initiated by the

MME and the eNodeB receives a UE CONTEXT RELEASE COMMAND message from the MME. The

L.E-RAB.AbnormRel.MME counter is incremented each time the Release Cause information element of

the message is not Normal Release, Detach, User Inactivity, or cs fallback triggered. If the UE

CONTEXT RELEASE COMMAND message requires multiple E-RAB releases at the same time, the

L.E-RAB.AbnormRel.MME counter is incremented according to the number of E-RAB releases.

• E-RAB RELEASE COMMAND As in figure 1 the L.E-RAB.AbnormRel.MME counter is incremented each time the E-RAB release is

initiated by the MME and the eNodeB receives an E-RAB RELEASE COMMAND message from the

MME and the Release Cause information element is not Normal Release, Detach, User Inactivity, or

cs fallback triggered. If the E-RAB RELEASE COMMAND message requires multiple E-RABreleases at the same time, the L.E-RAB.AbnormRel.MME counter is incremented according to the

number of E-RAB releases


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E-RABAbnormal Rel.Radio/TNL/Congestion

As in Figure 3 The eNodeB sends an E-RAB RELEASE INDICATION message to the MME.

The L.E-RAB.AbnormRel.Radio counter is incremented each time the access layer bearer

resources are abnormally released due to faults at the radio network layer.

The L.E-RAB.AbnormRel.TNL counter is incremented each time the resources are abnormally

released due to faults at the transport network layer. The L.E-RAB.AbnormRel.Cong counter is incremented each time the resources are

abnormally released due to network congestion including preemption and resource congestion.

If the E-RAB RELEASE INDICATION message requires multiple E-RAB releases at the same

time, the corresponding counter is incremented according to the number of required E-RAB

releases.

When the MME sends a UE CONTEXT RELEASE COMMAND message back to the eNodeB,

the corresponding counter is not incremented repeatedly

• Suspected reasons.

Radio

• RF conditions

TNL

• Transmission

• NE40

Congestion• Users prioritizing

• Load(RAB bitrate is lower than a specific value) explained

in details in the last slide.



E-RABAbnormal Rel.HO failure

As in figure 4 the L.E-RAB.AbnormRel.HOFailure counter is incremented each time the

resources are abnormally released due to handover failures. When the MME sends a UE

CONTEXT RELEASE COMMAND message back to the eNodeB, the corresponding counter is

not incremented repeatedly. If the UE CONTEXT RELEASE REQUEST message requires

multiple E-RAB releases at the same time, the corresponding counter is incremented according

to the number of required E-RAB releases.



Examples from Nastar



Radio/ Radio connection with UE lost



HO Failure



No Radio resources available



Queries

• Need to confirm how the E-NodB is recognizing between different causes ( Radio, TNL &

congestion) from messages sent from the E-NodB (found in Nastar).

• ( No Radio Resources available ) sent from e-nodb may indicate ERABAbnormal

release.congestion

• ( Radio connection with UE lost ) sent from e-nodb may indicate ERABAbnormalrelease.Radio

• As per document below it may mean that RABs having low bit rate lower than a specific

threshold will be released due to load so

• Is E-RABAbnormal Rel.cong. counter is covering this case.

• What is the threshold value for minimum bit rate for each RAB



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LTE ERAB AbNormal Release Causes Correct _1

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