NSA accessibility is the LTE anchor chain (RRC/S1/E-RAB — see the LTE page) plus the NR-leg addition. The NR leg is one procedure with a preparation half (network side, over X2/E1/F1) and an execution half (over the air, NR PSCell). Samsung counts all three points in Family 5103 SGNB_ADD_PER_GNB:

On a B1 measurement report (NR neighbour better than threshold) the master eNB fires an X2AP SgNB Addition Request. The gNB admits and replies Addition Request Acknowledge (preparation done); the eNB reconfigures the UE, which performs random access on the NR PSCell; the UE returns Reconfiguration Complete and the eNB signals SgNB Reconfiguration Complete (execution done).

Every SgNB-Addition failure counter is named EndcAdd[Prep]Fail_<domain>. The suffix pins the failure to one interface/element — so the counter tells you which team owns the fix before you open a log.

Preparation is the network handshake: the MeNB’s SgNB Addition Request (attempt) to the gNB’s Addition Request Acknowledge (prep success), spanning the E1 (CU-UP), F1 (DU) and CU-CP internals.

CpFail is a bucket, not a diagnosis. SVR25B breaks it into named sub-counters — each one is a different team's problem. Rule of thumb: CallAlloc* = capacity/license · CpOverload = CU-CP load · SpCellSel* = "no usable NR cell for THIS UE" (capability, coverage, DU state) · UpSelectionFail = no CU-UP · ErabConfigurationFail = bearer config. The execution-phase twin EndcAddFail_CpFail means the E1/F1 modification failed after the UE was already told — same buckets, later timestamps.

Execution is the over-the-air half: after preparation, the eNB reconfigures the UE, which does random access on the NR PSCell. End-to-end success pegs EndcAddSucc; anything that stops the UE reaching the NR cell pegs an EndcAddFail_*.

Once EN-DC is up, the NR leg can still fail. Family 5085 SCG_FAIL_OPER classifies every SCG failure by exact cause and by the operation it triggered (Count / Suspend / Resume) — the retainability companion to the accessibility KPI.

Enter the Family-5103 counters for a cell; the studio computes the three success rates, grades them, finds whether the loss is in preparation or execution, and prints the domain-specific fix from the largest failure counter. All levers are real Samsung MOs / features.

Every SgNB-Addition failure counter is one wire from its domain (which element/interface owns the fault) to the phase where it pegs. Click a domain to light its counters across both phases, a phase to see everything that fails there, or click any counter chip for its full optimization card.

The NR leg is added through four gates — trigger → prep transport → SgNB Addition → keep the leg. Each node is a real Samsung FGR feature; click any node to open its card: what it is, benefit, how it works, the recommended optimization parameters (MO · default · recommended), the optimization technique and the counters it moves.

The B1 threshold decides where the NR leg is added. Both failure directions are counted by the same families — drag the slider and watch which real counters a mis-set threshold feeds. Directional physics only: the counters and consequences are Samsung-exact; your network's exact RSRP number comes from the NR cell-edge survey.

Preparation rides X2AP between MeNB and gNB. Family 5123 X2AP_MSG_UE_PER_GNB counts each message — the raw evidence behind the SgNB-Addition KPI.

Sources: Samsung 5G NR Counter Description — Family 5103 SGNB_ADD_PER_GNB, 5085 SCG_FAIL_OPER, 5123 X2AP_MSG_UE_PER_GNB (counter names & verbatim descriptions, via the operator KPI workbook & SVR25A CU/DU Counter Descriptions) · 5G RAN Feature Description SVR25B (SgNB Addition procedure, Tdcoverall, t310/t312 fast-rlf-recovery, FGR-BC1202 SCG Failure Handling) · live operator KPI report (SgNb addition Success Rate). EN-DC procedure per 3GPP TS 37.340. Targets are typical operator values; counters, families and mechanics are vendor-exact.