What may be the different possible reasons mutiple UEs not getting attached ?

Question

UE-1 attached and pumped max peek througput in UL and DL.... when trying to attach UE-2, its not getting attached ...

What are the possible reasons for UE not getting attached ?

Answer 1

Failure can happen at various steps during attach procedure.

1. Due to contention of RACH preamble or RACH response.
2. Radio resources are not enough to accommodate a new UE in the cell.
3. MME is overloaded.
4. Subscription profile not exist in HSS
5. Authentication failure.
6. NAS security failure.
7. Other network nodes such as SGW, PGW responds with failure.
8. ENodeB is unable to establish SRB2 and DRBs due to crunch in radio resources or other reason.
9. UE is unable to impose the configuration that is sent by eNodeB to UE.

This is not complete list of reasons, there could be other reasons also in the system which results attach failure.

Answer 2

Hi sripathi,

Based on your scenario i will list the possible reason,

** You said full throughput on first UE. so main reason is sceduling problem. Other UE may not got the grant to send data.

** Enodeb may not scheduled RAR to second UE because of full throughput.

** May be second UE UL noise will be more, even though he gets some grant but not able to decode at enb.

** Check whether SRB data of second UE is scheduling or not..

** Check whether second UE is havinh more NACK at MAC level or not.

If you tell me the place where it stopped in attach procedure i can tell the exact reason.

Comments

Thanks alot vimal and jaganathan ..... i am able to observe eNB receiving rach request  but RACH response is not sending by eNodeB.

How to resolve this ?

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It is problem of scheduler. scheduler has to prioritize the RAR to send, You have to look into the scheduler implementation and make RAR as high priority, or else make less throughput so that you will have some resource to schedule RAR.