UE can not attach to NR leg

Hi all,

I’m deploying DSS (NSA) and I have a question related to NR leg setup.
The picture below, UE sent Measurement report to the network, but UE was still not attach to NR leg.
I don’t know why was that, does anyone have any suggestions/ideas for this case?
Thank you in advance!

Which vendor?

Assuming this MR contains NR measurements, since you are seeing no RRC Reconfiguration trying to add the PSCELL, there is something wrong on the eNB/gNB side. Things like, missing or wrong gNB neighbor relationship, or even other parameters related to the NSA configuration. Verify your baseline.

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Thank you for your help! I will do double check that!

maybe due to our relation 4G/5G

This is also common case when UE is 5G capable, but not DSS capable. Check UE capability information for rat-Type: nr and eutra-nr to see if device is DSS capable.

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Try to search in MR message the B1 event like this:

…nr-rsrp-r15 — 0x15 (51)

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Below is sample decoding of “RRC connection reconfiguration” for measurement configuration and DRB configuration:

measObjectId 2,
measObject measObjectNR-r15 :
carrierFreq-r15 643333,
periodicityAndOffset-r15 sf20-r15 : 18,
ssb-Duration-r15 sf5
subcarrierSpacingSSB-r15 kHz30
quantityConfigSet-r15 1,
bandNR-r15 setup : 78
reportConfigId 3,
reportConfig reportConfigInterRAT :
triggerType event :
eventId eventB1-NR-r15 :
b1-ThresholdNR-r15 nr-RSRP-r15 : 46,
reportOnLeave-r15 FALSE
hysteresis 2,
timeToTrigger ms80
maxReportCells 4,
reportInterval ms120,
reportAmount infinity,
ss-rsrp TRUE,
ss-rsrq TRUE,
ss-sinr FALSE

In theory, if it is not capable, no B1 should be configured… but that`s theory… eNB/gNB SW is not 100% yet, especially for DSS, so I agree with you, no harm on checking if the UE is in fact DSS capable :slight_smile:


Thank you everyone, I have some ideas to do now!!! :blush:

From traces, does the eNB send SgNB addition request to the gNB or not?

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Sorry Ibrahim, I did not get the traces :frowning_face: :frowning_face:

If UE sets DCNR bit in the UE Network Capability during the LTE attach and MME sends UE Security Capability for that UE in the Initial Context Setup Request message, you’re good to go for B1-NR measurement configuration for dual connectivity. This doesn’t mean UE has to support DSS, UE Capability Info message should be checked for this.

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The problem here is after sending MR report, UE did not receive RRC conn recfg to obtain infornation about 5G cell. This failure happened at enb or gnb side in 5G SCG ADD procedure, so to analysis detail, it’s better to have X2 trace log.
I think the problem may be due to some of below cause:
1, enb not send sgnb add request
1.1, enb not configure corectly neighboring 5G cell
1.2, enb configure gnb not support NSA
1.3, X2 link between enb-gnb have problems
1.4, enb’s x2 links reach maximum as vendor specific, so enb not send req to target 5g site
1.5 X2-u ping failed

2, enb already send add req but gnb not response or reject
2.1, transmission network failure between gnb and sgw, such as gnb ping to sgw failure
2.2, some parameters in add request not supported by gnb
2.3 dedicated preambles failure by 5G gnb

Many thanks for your support!!!