The reporting headline is Session PS Drop Rate % (the operator's OMC recommended-KPI set). Underneath sits the deck-verbatim 5G Context Drop Rate — note what it does: adds the radio failures, subtracts MCG-mobility releases (the anchor moving is not a drop), and puts user inactivity in the denominator (a leg that fell asleep is not a drop either).
| KPI | Formula (Samsung counters) | Read it as |
|---|---|---|
| 5G Context Drop Rate [%] (deck, verbatim) | ((CauseInternalT310Expiry + CauseInternalRlcMaxNumRetx + EndcRelBySgnbMr + EndcRelByMenb − EndcRelByMenbMcgMob) ÷ (CauseInternalT310Expiry + CauseInternalRlcMaxNumRetx + EndcRelBySgnbMr + EndcRelByMenb − EndcRelByMenbMcgMob + CauseInternalUserInactivity)) × 100 | abnormal ends ÷ (abnormal + inactivity ends) |
| Session PS Drop Rate [%] (operator OMC) | Nom ÷ Denom per cell from the recommended-KPI report — the NSA twin of "SgNb addition Success Rate" | network-reported session loss |
| SCG failure intensity (derived) | Σ SCGFailOper_*_Count (5085) ÷ SgNB Addition Succ (5103) | failures per added leg — typical target <2% |
| Rescue share (derived) | Σ *_Resume ÷ Σ *_Suspend (5085) | how many suspended legs came back — the NSA rescue rate |
EndcRelByMenbMcgMob (Fam 5113) counts SgNB Release Requests with cause MCG mobility: the LTE anchor is handing over, so the NR leg is released by design and re-added after — Family 5092 even counts the variant with "UE context kept" indicator. Counting those as drops would punish your busiest, best-moving cells. Same logic as LTE's normal-vs-abnormal split, EN-DC edition.The SCG fails on the DL (the UE detects: T310 expiry, RACH problem, RLC max-retx, reconfig/integrity failure) or on the UL (the gNB detects: out-of-sync, UL RLC max-retx). The UE reports via SCGFailureInformationNR — carried over the LTE RRC connection — and the MeNB/SgNB then suspend, resume or release the leg. Every step pegs on both sides of X2.
Three grammars cover all of NSA retainability. Learn them once and every counter self-explains:
| Pattern | Who / what | Meaning | First place to look |
|---|---|---|---|
EndcRelBySgnb_DL_* | UE detected (via SCGFailureInformationNR) | DL-side SCG failure: t310Expiry · randomAccessProblem · rlcMaxNumRetx · syncReconfFailure · scgReconfFailure · srb3IntegrityFailure | NR coverage/beam at the PSCell edge; NR t310/RACH |
EndcRelBySgnb_UL_* | gNB detected | UL-side failure: outOfSync · rlcMaxNumRetx · srb3IntegrityFailure | UL link budget / interference — the en-dc UL-outage levers |
SCGFailOper_<cause>_Count / _Suspend / _Resume (5085) | the rescue machine | Same causes, three checkpoints: reported → leg suspended → leg revived | Resume÷Suspend ratio per cause — FGR-BC1202 health |
EnDc_RelRequest_* (717, LTE) | MeNB asks (X2 SgNB Release Request) | Anchor-driven: ErabRelease · UeContxtRel · UserInactive · VolteConf · DL_RLF_t310Expiry… | Anchor policy & mobility — mostly deliberate |
EnDc_RelRequire_* (717, LTE) | SgNB demands (X2 SgNB Release Required) | NR-side driven: DcOverallTO · BearerNotSupp · UserInactive · UL_RLF_RadioConnection_UeLost | The NR leg's own failures, seen from LTE |
CauseInternal* (5100 CSL) | CU-CP call summary | The per-release cause ledger — T310Expiry, RlcMaxNumRetx, RandomAccessProblem… verbatim: "the UE transmits an SCGFailureInformationNR message following T310 expiry" | KPI numerator — the drop formula reads this family |
RelRequest = the MeNB initiates (anchor decision), RelRequire = the SgNB initiates (NR-side necessity). The same release lands in Family 5105 (MeNB-init) or 5106 (SgNB-init) on the NR side, and in Family 717 on the LTE side. If the two ledgers disagree in trend, you're looking at an X2 signalling problem, not a radio one.The family (verbatim): "statistics for handling SCG failure per SCG failure cause" — 23 counters: for each cause a _Count, and for the recoverable causes a _Suspend and _Resume pair. This triple is the rescue instrumentation: Count says it happened, Suspend says the leg was parked instead of killed, Resume says it came back.
| Cause (5085 triple) | Side | CSL twin (5100) — verbatim meaning |
|---|---|---|
| SCGFailOper_DL_t310Expiry_* | DL · UE | CauseInternalT310Expiry: release because "the UE transmits an SCGFailureInformationNR message following T310 expiry" — KPI numerator |
| SCGFailOper_DL_randomAccessProblem_* | DL · UE | CauseInternalRandomAccessProblem: random access problem indication by SCG MAC |
| SCGFailOper_DL_rlcMaxNumRetx_* | DL · UE | CauseInternalRlcMaxNumRetx: SCG RLC reached max retransmissions — KPI numerator |
| SCGFailOper_DL_syncReconfFailure_* / _scgReconfFailure_* | DL · UE | CauseInternalScgReconfigFailure: reconfiguration failure of the NR RRC Reconfiguration message |
| SCGFailOper_DL_srb3IntegrityFailure_* | DL · UE | CauseInternalSrb3IntegrityFailure: SRB3 IP check failure — security, not radio |
| SCGFailOper_UL_outOfSync_* / _UL_rlcMaxNumRetx_* | UL · gNB | gNB-detected uplink loss — the half the UE cannot report; pairs with the en-dc-ul-radio-link-outage levers |
| SCGFailOper_MrBased_Suspend / _Resume | MR · policy | CauseInternalMeasurementReportBasedRelease: release on an event A2 measurement report — coverage-based suspension, deliberate |
| Dominant cause | Diagnosis | Technique / lever |
|---|---|---|
DL_t310Expiry | PSCell coverage/beam collapse — the NSA analogue of the LTE RLF drop | NR coverage at the PSCell edge (SSB beams, tilt); NR t310/n310 widening for fade-rich cells; B1 threshold hygiene so weak PSCells aren't added at all |
DL_randomAccessProblem | SCG RACH breaks after addition — UL coverage or RACH config on NR | NR RACH levers (preamble-trans-max, power-ramping-step, prach-configuration-index); check per-beam RACH (5243) on the PSCell |
DL/UL_rlcMaxNumRetx | Sustained bad link the ARQ can't bridge | NR RLC depth (gnb/ue-max-retransmission-threshold — deck rec 8), BLER targets (dl-target-bler 8% / ul 10%), MCS caps under congestion |
UL_outOfSync | UL dies first — classic NSA edge (UE TX power split between LTE+NR) | The EN-DC UL-outage machinery: en-dc-ul-radio-link-outage-support enable, …-count-threshold +50%, …-resume-max-tbs-threshold +20% (deck-verbatim moves) |
MrBased_* | A2-based suspends — policy working | If excessive: the A2/B1 thresholds are fighting (add-drop ping-pong) — widen the hysteresis between addition B1 and release A2 |
srb3IntegrityFailure | Security/config, not radio | Key-refresh & SRB3 configuration audit; escalate as SW issue if systematic |
The family (verbatim): "statistics for the SgNB initiated SgNB release for each cell and MeNB" — the NR node giving the leg up, cause-split with the same DL/UL grammar, plus two deliberate causes. EndcRelBySgnbMr (Fam 5111, KPI numerator) counts "SgNB Release Required messages transmitted to the MeNB" on measurement-report grounds.
| Counter | Class | Meaning |
|---|---|---|
| EndcRelBySgnb_DL_t310Expiry / _DL_randomAccessProblem / _DL_rlcMaxNumRetx | radio · DL | The UE-reported SCG failures that ended in release (not resume) |
| EndcRelBySgnb_DL_syncReconfFailure / _DL_scgReconfFailure / _DL_srb3IntegrityFailure | config · security | Reconfiguration / integrity failures — procedure-level causes |
| EndcRelBySgnb_UL_outOfSync / _UL_rlcMaxNumRetx / _UL_srb3IntegrityFailure | radio · UL | gNB-detected uplink loss ending in release |
| EndcRelBySgnb_MrBasedSuspendResume | policy | MR-based suspend/resume flow ending in release |
| EndcRelBySgnb_UserInactivity | normal | Leg released because it fell idle — healthy, keep out of the drop numerator |
_UserInactivity dominant = traffic profile, not a fault — but if the LTE ledger shows EnDc_RelRequire_UserInactive diverging from it, the two inactivity timers (LTE vs NR) are fighting: align them.The anchor's view. Family 5105 (verbatim): "MeNB initiated SgNB release for each cell and MeNB" — including EndcRelByMeNB_radioConnectionWithUeLost: the LTE anchor lost the UE entirely, taking the NR leg with it. On the LTE side, Family 717 splits the same X2 procedure into RelRequest_*/RelRequire_* causes, and Family 788 books the release of the whole EN-DC-capable RRC connection with the full LTE 25-cause grammar.
| Counter | Ledger | Meaning |
|---|---|---|
| EndcRelByMenb (5105) | NR side | SgNB Release Request messages received from the MeNB — the anchor asked |
| EndcRelByMeNB_radioConnectionWithUeLost (5105) | NR side | The anchor lost the UE — an LTE drop cascading into the NR leg; fix the LTE page's problem, not NR |
| EndcRelByMenbMcgMob (5113) | NR side | Cause MCG mobility — the anchor is handing over; subtracted from the drop KPI |
| EndcRelByMenbMcgMobUeCtxInd (5092) | NR side | MCG mobility with UE context kept — the leg survives the anchor HO (SN-terminated bearer kept) |
| EnDc_RelRequest_UserInactive / _VolteConf / _ErabRelease / _UeContxtRel / _InternalResouFail (717) | LTE side | Why the anchor asked: inactivity, VoLTE conflict (voice arrives → NR leg dropped by policy), bearer/context teardown, internal resource fail |
| EnDc_RelRequire_DcOverallTO / _BearerNotSupp / _UL_RLF_RadioConnection_UeLost (717) | LTE side | Why the SgNB demanded: Tdcoverall expiry (the EN-DC guard timer), unsupported bearer, UL RLF with UE lost |
| EnDc_ConnRelease_* (788, 25 causes) | LTE side | The whole EN-DC-capable connection released — LTE grammar (RrcHcTo/UpMacUEInact/S1ap*/CpPreemption/MmeOverload…) |
| SgNB Release due to SCG / MCG Mobility / Re-establishment (707 · 710 · 711) | LTE side | Mobility-caused releases, split by which side moved — plus re-establishment-triggered |
EnDc_RelRequest_VolteConf is unique to NSA: a voice call arriving on the LTE anchor can evict the NR leg (UE capability / power sharing). If it dominates, that's a policy choice — verify the intended behaviour (keep EN-DC during VoLTE vs drop) matches the configuration, and check the UE capability mix before "fixing" it.Sessions are bearers. Family 5120 (NR): "E-RAB Release per gNB" — 12 counters. LTE Family 719 books EN-DC E-RAB releases by initiator (byMme / byEnb / bySgnb) per bearer type — MCG, SCG, or split — and Family 948 covers the split-bearer specifics. Family 5220 (DRB Release and Erase) is the NR DRB-level twin.
endc_bearerType: SCG-bearer releases tracking 5106 = radio story already told; split-bearer releases without SCG failures = the PDCP-split path (X2-U capacity, flow control); bySgnb spikes = NR-side, byMme = core-driven (same treatment as the LTE page's by-MME family). Bearer-type divergence is the fastest NSA triage cut after DL:UL.Pick a failure cause and the recovery policy; watch the flow route through report → suspend → resume/release and read exactly which counters peg on the NR and LTE ledgers. This is the 5085 triple, animated.
Enter the five formula counters plus the rescue pair; the studio computes the deck-verbatim 5G Context Drop Rate, the rescue share, and the healthy-mobility share — then routes you to the dominant cause.
Every EN-DC release counter routed from its root-cause domain to the ledger where it books — NR CU-CP families on top of the LTE-anchor twins. Click a domain, a ledger, a scenario, or any counter chip for its optimization card.
NSA shares the NR radio levers with SA (BLER/HARQ/RLC — full table on the SA page); what's unique to EN-DC is the UL-outage machinery, the guard timer, and the mobility couplings:
| Parameter | Default | Deck recommendation | Why / target scenario |
|---|---|---|---|
| en-dc-ul-radio-link-outage-support | default | Enabled | "Improve mobility robustness for NSA" — arms the UL-outage detection that feeds UL_outOfSync handling |
| en-dc-ul-radio-link-outage-count-threshold | network default | Increase by 50% | "More tolerance for temporary path issues" — fewer premature UL-outage suspends |
| en-dc-ul-radio-link-resume-count-threshold | network default | Decrease by 30% | "Faster path recovery" — resume the leg sooner |
| en-dc-ul-radio-link-resume-max-tbs-threshold | network default | Increase by 20% | "Faster recovery from path issues" |
| Tdcoverall (EN-DC guard) | release default | raise only on EnDc_RelRequire_DcOverallTO evidence | The overall EN-DC procedure guard — its expiries are counted verbatim in Fam 717 |
| handover-margin-nr | 3 dB | 1–2 dB in dense areas | "Less aggressive handovers in dense areas" — steadier PSCell choice |
| time-to-trigger (NR events) | 480 ms | 160 ms high-mobility | "Faster handovers in high mobility scenarios" — before the SCG dies |
| B1 (add) vs A2 (release) thresholds | plan | keep a clear hysteresis gap | Add-release ping-pong manufactures MrBased_* suspends and 5111 releases |
| gnb/ue-max-retransmission-threshold (RLC) | release default | 8 | Deck's RLC retainability set — bridges bad patches before rlcMaxNumRetx fires |
| dl-target-bler / ul-target-bler | ~10% | 8% / 10% | Deck RRC & BLER optimization table — link adaptation headroom |
UL_outOfSync, EnDc_RelRequire_UL_RLF…) at cell edge is often a power-split problem: the LTE anchor is consuming the budget. Check LTE UL health and the power-sharing configuration before touching NR timers.Baseline both ledgers
NR: 5085 + 5106 + 5105/5113 + 5100 causes + 5120. LTE: 717 + 719 + 788. Compute the deck drop formula and the rescue share (Resume÷Suspend).
dual ledger — always both sides of X2 Skip this and an X2 signalling problem masquerades as a radio one.Subtract the healthy releases
MCG-mobility (5113/5092), user inactivity (both sides), VoLTE-conflict policy, MR-based suspends that resumed. What remains is the true drop mass.
the formula's own subtraction, extended If wrong: your busiest cells look like your worst cells.Cut DL vs UL
DL-heavy (t310Expiry, randomAccessProblem, reconf) = PSCell coverage/config — the UE saw it first. UL-heavy (outOfSync, UL rlcMaxNumRetx) = uplink budget/power-split — the gNB saw it first.
the DL:UL ratio of 5106/5085 If wrong: you tilt antennas for an uplink power problem.Check the rescue machine
Per cause: Suspend high + Resume low = the leg parks but never returns — work the resume thresholds (en-dc-ul-…-resume-*) and FGR-BC1202 config before chasing the failure itself.
Resume ÷ Suspend per cause (5085) If wrong: you prevent 10 failures while 100 rescues stay broken.Apply ONE lever
DL radio → PSCell RF + NR t310/RACH. UL → the four en-dc-ul-outage levers (deck moves: +50% / −30% / +20%). Mobility → handover-margin-nr, TTT, B1/A2 gap. Policy → align inactivity timers, verify VolteConf intent.
one change per soak If wrong: unattributable results.Verify on both ledgers + the anchor
The cause must fall on 5085/5106 and its 717 twin; SgNB Addition SR (5103) must hold (don't fix drops by not adding legs); LTE-anchor drop rate must hold (Fam 24 — the other page).
guards: 5103 addition SR · LTE Fam 24 If wrong: the NSA "gain" was bought by breaking LTE.NSA retainability is two ledgers, one leg, and a rescue machine.
Count the SCG failures, subtract the healthy mobility, read DL vs UL, and keep Resume÷Suspend high. Then compare with LTE's three ledgers and SA's clean single-node chain.
Sources: Samsung 5G NR Counter Description (CU-CP ACPF — Families 5085 SCG_FAIL_OPER, 5106/5111/5114 SgNB-initiated release, 5105/5113/5092 MeNB-initiated release, 5100 CUCPCSL_PER_GNB incl. the verbatim CauseInternalT310Expiry/RlcMaxNumRetx/RandomAccessProblem descriptions, 5120 ERAB_REL_PER_GNB, 5220 — via the operator NR KPI workbook) · Samsung LTE eNB Counter Description (EN-DC Families 717/719/788/948, 707/710/711 — via the operator LTE KPI workbook) · 5G NR Retainability Optimization SA deck (5G Context Drop Rate formula verbatim, en-dc-ul-radio-link-outage recommendations, mobility table) · operator OMC recommended-KPI report (Session PS Drop Rate). EN-DC procedures per 3GPP TS 37.340. Targets marked "typical" are operator practice; counters, families and the formula are vendor-exact.