In 5G NR SA the gNB is split into CU (RRC, PDCP) and DU (High-PHY, MAC, RLC). The CDU runs the DU and drives the radios; the CU-CP/CU-UP run on the CU — increasingly virtualized on COTS servers under vRAN 3.0. F1 joins DU↔CU, E1 joins CU-CP↔CU-UP, NG joins the gNB to the 5GC.
| Item | Specification |
|---|---|
| Technology | 5G · LTE · GSM (multi-RAT) |
| Backhaul interface | 1G/10G/25G × 4 ports (GMA1) · × 2 ports (GUC1) |
| Fronthaul interface | 2.5G/5G/10G/25G × 12 (GCB4) · × 9 (GUC1) · 2.5G/5G ×6 (BCA1) |
| Synchronization | GNSS (GPS · GLONASS · Galileo) / IEEE1588v2 PTP |
| Input voltage | −48 V DC (−40 to −57 V DC) |
| Power consumption | Full config (GMA1 + 3× GCB4): Typ 1017 W (25 °C, 50 %) · Max 1210 W |
| Dimensions (W×D×H) | 434 × 385 × 88 mm (2U, excl. ear mount) |
| Weight | 17 kg or less (full config, excl. optic modules) |
| Cooling | Fan cooling (FANM) |
| Operating temperature | 0 °C to +50 °C (to +55 °C at CDU inlet) |
| Operating humidity | 5–95 % RH, non-condensing (≤ 30 g/m³) |
| Altitude | −60 to 1800 m |
| Acoustic noise | ≤ 60 dBA @ 25 °C (1.0 m) |
| Ingress protection | IEC 60529 · IP20 (indoor) |
| Earthquake | Telcordia GR-63-CORE Zone 4 · EN 300 019-1-3 |
The CDU is a UCBS card cage: a UCDB backplane the cards plug into, a PDPM power distribution module fed by −48 V DC, and a FANM fan module (with an air filter) that cools the stack. The Main card and the Channel cards slot into the backplane.
| Card | Class | Weight | Fronthaul | Backhaul | Inter-card / clock |
|---|---|---|---|---|---|
| GMA1 | Main | — | — | 1/10/25G × 4 (BH0–3, QSFP+) | HSI · SYNC · GNSS |
| GCB4 | Channel · NR | 2.8 kg | CPRI 12 ports (L0–L11, SFP+/SFP28) | — | HSI 3 ports (QSFP+) |
| GUC1 | Unified | <3.1 kg | CPRI 9 ports (L0–L8) | 1/10G Eth (BH0/1, SFP+/SFP28) | Clock: GPS |
| LCC2 | Channel · LTE | 2.5 kg | CPRI 12 ports (L0–L11) | — | — |
| BCA1 | Channel · BTS | 2.5 kg | eCPRI 12 ports (L0–L11, SFP+) | — | — |
All cards: 356 × 370 × 21 mm blades, −48 V DC. Fronthaul ports run 2.5G/5G/10G/25G (SFP+/SFP28); backhaul 1/10/25G (QSFP+/SFP28); HSI (high-speed inter-card) uses QSFP+/QSFP28 across the UCDB backplane.
| Card | Full name | Class | Role |
|---|---|---|---|
| GMA1 | gNodeB Main card type A1 | Main | Main processor, network interface, clock generation/distribution, per-board reset, O&M storage |
| GUC1 | gNodeB Unified Card type C1 | Unified | Main + Channel combined (processor + CPRI) on one board |
| GUC2 | gNodeB Unified Card type C2 | Unified | Unified card variant — adds NAVIC GNSS constellation |
| GCB4 | gNodeB Channel card type B4 | Channel | Subscriber channel processing; modulates data → 12× CPRI → RU (NR) |
| LCC2 | LTE Channel card type C2 | Channel | LTE subscriber channel processing; 12× CPRI |
| BCA1 | BTS Channel card type A1 | Channel | 2G/BTS channel processing; 12× eCPRI external interface |
| GCC1 | gNodeB card type C1 | Card | Used in the GUC-based CDU50/CDU51 configuration |
G=gNodeB · L=LTE · B=BTS(2G); M=Main · C=Channel · U=Unified. So GMA1=gNodeB-Main-A1, LCC2=LTE-Channel-C2, GUC1=gNodeB-Unified-C1, BCA1=BTS-Channel-A1.Samsung ships the CDU in two mutually-exclusive builds. The Main-card build above pairs a dedicated Main card (GMA1) with Channel cards. The build documented in the CDU50 and CDU51 Product Specifications (for GUC1, GUC2, GCC1, BCA1) folds the main processing and a channel onto one Unified card (GUC1 / GUC2), then adds pure Channel cards — GCC1 for LTE/NR, BCA1 for GSM. Straight from the spec: “the Main Card and Unified Card cannot be mounted on the same shelf; the Unified Card is mounted at the Main Card position.”
CDU = Cabinet DU · UCBS = Universal platform type C Basic Shelf · UCDB = …Digital Backplane · PDPM = Power Distribution Panel Module · FANM = Fan Module · GUC = gNodeB Unified Card · GCC = gNodeB Channel card · BCA = BTS Channel card · UDA = User-Defined Alarm · UDE = User-Defined Ethernet · USM = Unified System Manager.| Item | CDU50 | CDU51 |
|---|---|---|
| Shelf assembly | UCBS-C4B (with FANM-C4N) | UCBS-C4C (with FANM-C41) |
| Height · card slots | 2U · 4 slots (1 Unified + up to 3 Channel) | 1U · 2 slots (1 Unified + 1 Channel) |
| Dimensions (W×D×H) | 434 × 385 × 88 mm (excl. ear mount) | 436 × 385 × 44 mm (excl. ear mount) |
| Weight | ≤ 17 kg (full, excl. optics) | ≤ 11 kg (full, excl. optics) |
| Example basic config | GUC2 + GCC1 + GCC1 + BCA1 | GUC2 + GCC1 / BCA1 |
| Power — typ / max | GUC1 build 542 / 671 W GUC2 build 593 / 733 W | GUC1+GCC1 335/442 · GUC2+GCC1 385/503 GUC1+BCA1 398/493* · GUC2+BCA1 469/580* W |
| Backhaul | 1G/10G/25G × 2 ports per Unified card (BH0, BH1 · SFP+/SFP28) | |
| Fronthaul → RU | GUC1 9 · GUC2 12 · GCC1 12 (6×2.5–25G + 6×2.5–10G) · BCA1 12 × 10G eCPRI | |
| Technology | 5G · LTE · GSM (multi-RAT) | |
| Synchronization | GNSS — GPS · GLONASS · Galileo · NAVIC (GUC2) — and IEEE1588v2 PTP | |
| Input voltage | −48 V DC (−40 to −57 V DC) | |
| Environmental | 0 to +50 °C (+55 °C at CDU inlet) · 5–95 % RH non-cond. (≤30 g/m³) · −60 to 1800 m · ≤ 60 dBA @ 25 °C · IEC 60529 IP20 | |
| Compliance | Telcordia GR-63-CORE EQ Zone 4 · EN 300 019 (1-3 Cl.3.5 / 1-2 Cl.2.3) · CISPR 22/32 · IEC 62368-1 3rd Ed | |
* CDU51 GUC+BCA1 figures are predicted in the spec. Power values ±5 %, exclude optical modules, include FAN power. Source: Samsung CDU50 / CDU51 Product Specification for GUC1, GUC2, GCC1, BCA1, Ver 1.0.
CDU50 chassis population Figure 2 · 2U · UCBS-C4B
−48 V DC enters the PDPM, is distributed across the UCDB backplane, and each card rectifies it locally. Max power (GUC2 build): 733 W.
CDU51 chassis population Figure 2 · 1U · UCBS-C4C
Half-height 1U shelf — one Unified card + one Channel card. Max power (GUC2 build): 503 W; a compact-site CDU.
Downlink traffic from the BSC/EPC is TDMA/OFDMA-processed in the Modem (channel-card function), converted to a Digital I/Q + C&M optical signal by the built-in E/O device, and driven out over Optic CPRI/eCPRI to the RU. Uplink runs the reverse path through O/E. The Main-card function handles main processing, OAM and clock; the Reference Clock (GNSS / IEEE1588v2) and Power → EMI filter feed the whole card.
Pick any of the seven cards — Main (GMA1), Channel (GCB4 · LCC2 · GCC1 · BCA1) and Unified (GUC1 · GUC2) — to see its real front-panel layout from the Product Specification. Click any port for its exact connector type and function; colour codes the role. This is the "pure connectivity" view — every optical, electrical, sync and management port on the faceplate.
| Connector | Used for | On which cards / ports | Notes |
|---|---|---|---|
SFP+ | 10G optical — backhaul & CPRI fronthaul | GMA1 BH0–BH3 · ETH1 · all L-ports | Small Form-factor Pluggable Plus · ⚠ never look into the optic |
SFP28 | 25G optical — fronthaul & 25G backhaul | GCB4/GUC1/GUC2 L-ports · GUC1/GUC2 BH0/BH1 | same cage as SFP+, higher rate |
QSFP+ / QSFP28 | 40/100G optical — inter-card High-Speed Interface | GMA1 HSI · GCB4 HSI0–HSI2 | Quad SFP — links Channel cards to the Main card |
RJ-45 (8-pin) | electrical Gigabit Ethernet | GMA1/GUC LMT · GMA1 ETH0 | 100/1000 Base-T — Local Maintenance Terminal + in-gNB Eth |
SMA | coaxial RF — timing | SYNC (1 PPS out) · GNSS (antenna in) | screw-on coax; GNSS carries the satellite antenna feed |
Harting (10-pin) | reference-clock SYNC IN / OUT | GMA1 CLK0/CLK1 · GUC CLK | rugged clock daisy-chain between units |
68-pin (UDA) | external dry-contact alarms | all Main/Unified cards | User-Defined Alarm — Rx 18 / Tx 2 ports |
USB (4-pin) | RS-232 CPU/DSP debug | DBG / DBG0 / DBG1 on every card | serial console @115200 for board-level debug |
| Card | Type | Weight | Fronthaul → RU | Backhaul | Feeds |
|---|---|---|---|---|---|
| GUC1 | Unified C1 | < 3.1 kg | 9× CPRI (L0–L8, SFP+/SFP28) | 2× 1/10/25G (BH0/1) + ETH | Clock: GPS |
| GUC2 | Unified C2 | < 3.1 kg | 12× CPRI (L0–L11, SFP+/SFP28) | 2× 1/10/25G (BH0/1) | GNSS+NAVIC · PTP |
| GCC1 | Channel C1 | ≈ 2.5 kg | 12× CPRI (L0–L5 → SFP28, L6–L11 → SFP+) | — | → GUC1/GUC2 (LTE/NR) |
| BCA1 | Channel A1 | ≈ 2.5 kg | 12× eCPRI (L0–L11, SFP+) | — | → BSC via GUC (GSM) |
STS status-LED decoder — the exact states from every card's LED table. This is what you read off the faceplate on a site visit:
The CDU51 is CDU50's half-height sibling: the same brains (GUC1/GUC2 Unified + GCC1/BCA1 Channel cards), the same 5G·LTE·GSM multi-RAT, the same GNSS/PTP sync — packed into a 1U shelf that takes one Unified card + one Channel card. It's the pick for compact sites, low ceiling-height rooms and dense racks where a 2U CDU50 won't fit or isn't needed.
4 card slots · up to 733 W
~⅓ lighter (17 → 11 kg),
half the card slots
2 card slots · up to 580 W
Both are drawn to scale on the vertical axis (88 mm vs 44 mm). Depth (385 mm) and width (~435 mm) are effectively identical — only the height and slot count differ.
| Item | Specification |
|---|---|
| Shelf assembly | UCBS-C4C · 19-inch 1U shelf (backboard + power module + fan + air filter), fan-cooled with FANM-C41 |
| Card slots | 2 slots — 1 Unified (GUC1/GUC2) + 1 Channel (GCC1 for LTE/NR, or BCA1 for GSM) |
| Technology | 5G · LTE · GSM (multi-RAT) |
| Backhaul interface | 1G/10G/25G × 2 ports per Unified card (BH0, BH1 · SFP+/SFP28) |
| Fronthaul interface | GUC1 9 · GUC2 12 (2.5G/5G/10G/25G) · GCC1 12 (6×2.5–25G + 6×2.5–10G) · BCA1 12 × 10G eCPRI |
| Synchronization | GNSS (GPS · GLONASS · Galileo · NAVIC on GUC2) / IEEE1588v2 PTP |
| Input voltage | −48 V DC (−40 to −57 V DC) |
| Power consumption | GUC1+GCC1 Typ 335 / Max 442 W · GUC2+GCC1 Typ 385 / Max 503 W · GUC1+BCA1 398 / 493 W* · GUC2+BCA1 469 / 580 W* |
| Dimensions (W×D×H) | 436 × 385 × 44 mm (1U, excl. ear mount) |
| Weight | 11 kg or less (full config, excl. optic modules) |
| Cooling | Fan cooling (FANM-C41) |
| Operating temperature | 0 °C to +50 °C (to +55 °C at CDU inlet) |
| Operating humidity | 5–95 % RH, non-condensing (≤ 30 g/m³) |
| Altitude | −60 to 1800 m |
| Acoustic noise | ≤ 60 dBA @ 25 °C (1.0 m) |
| Ingress protection | IEC 60529 · IP20 (indoor) |
| Earthquake / vibration | Telcordia GR-63-CORE EQ Zone 4 · EN 300 019 (1-3 Cl.3.5 / 1-2 Cl.2.3) |
| EMC / safety | CISPR 22/32 · IEC 61000 series · IEC 62368-1 3rd Ed |
* GUC1/GUC2 + BCA1 power figures are predicted in the spec (25 °C / 100 % and 50 °C / 100 %). Source: Samsung CDU51 Product Specification for GUC1, GUC2, GCC1, BCA1, Ver 1.0.
CDU51 config & power planner — pick the Unified card and the Channel card that go in the two slots. The planner reads out the verbatim power, fronthaul-port budget, backhaul, clock and RAT support for that exact combination:
The baseband doesn't just carry data — it configures every cell. These are actual managed-object leaves under gnb-du-function / gutran-du-cell from the Samsung Parameter Description — the identity, frequency and SSB config each CDU cell is provisioned with:
| Leaf | Range | Default | What it sets |
|---|---|---|---|
| nr-physical-cell-id | −1 … 1007 | −1 | NR PCI — how UEs distinguish this cell |
| nr-arfcn-dl | 0 … 3279165 | 0 | Downlink carrier centre (NR-ARFCN) |
| subcarrier-spacing-common | 15/60 · 30/120 kHz | 30/120 | SCS of SIB1 / Msg2·4 / broadcast SI |
| ssb-subcarrier-spacing | 15 / 30 kHz | 30 kHz | SSB sub-carrier spacing |
| ssb-periodicity | 20 … 160 ms | 40 ms | SSB burst period (cell lock to change) |
| cell-barred | barred / not-barred | not-barred | Manually bar the cell (access control) |
| tracking-area-code-usage | use / not-use | use | Use the 5GS TAC of the NR cell |
TDD (n78, B40/n40) demands tight phase sync so neighbouring cells don't transmit into each other's receive slots. The CDU takes timing from GNSS — GPS, GLONASS, Galileo and (on GUC2) NAVIC — over the GNSS antenna port, and/or IEEE1588v2 PTP over the backhaul as a backup / GNSS-free option.
| Parameter | Range | Default | What it does |
|---|---|---|---|
switch-mode / quality-level-mode | auto | forced · user-defined | actualql-mode | auto · user-defined | how the clock source is chosen — auto follows quality level |
apts-mode | off | on | off | Assisted Partial Timing Support — PTP helps GNSS through outages (G.8273.4 class) |
ptp-info/log-sync-interval-g8275-1 | −4 (16 msg/s) | −4 | full-timing-support telecom profile (phase) — the TDD baseline |
ptp-info/log-sync-interval-g8275-2 / -g8265-1 | −6 (64 msg/s) | −6 | partial-timing (phase) / frequency-only profiles |
ptp-hybrid-mode | disable | enable | disable | PTP phase + SyncE frequency together (hybrid) — tightest holdover |
ptp-phase-holdover-exceed-threshold | 0m | 5m | 10m | … | holdover-5m | how long phase holdover is trusted before alarm/action |
ptp-frequency-holdover-exceed-threshold | 7d | 30d | holdover-30d | frequency holdover budget — much longer than phase |
synce-info: quality-level-mode / acceptance-QL | enabled · ql-eprtc…ql-ssu | enabled · ql-prc | SyncE input policing — refuse sources below QL-PRC by default |
synce-assisted-holdover-extension-enable | off | on | off | SyncE stretches PTP phase holdover when the PRTC is lost |
holdover-exceed-switchover-enable | off | on | off | auto-switch source when a holdover budget is exceeded |
ucr: expected-holdover-time / gps-position | read-only | — | the unit's own estimate of how long it can free-run — read it during backhaul works |
TDD phase-sync failure chain to remember: GNSS lost → PTP (G.8275.1) carries phase → past holdover-5m the cell is a slot-format interferer. apts-mode + SyncE assistance are the two knobs that stretch that window.
Once the CDU drives a radio, the two questions you ask every busy hour are: how full is the downlink (Tx) and how full — and how clean — is the uplink (Rx). "Utilization" has two layers: the air resource (PRB usage, from the DU counters) and the radio path (Tx power + Rx noise floor, from the AU MOs on the Radios page). Read them together — a PRB number without its RF context lies.
Tx utilization — the downlink
"How much of the cell's downlink am I using?" — two dimensions:
- DL PRB utilization =
TotDLUnicastPrbSche÷TotDLAvailablePrb(NR fam 5041 · LTE fam 55TotPrbDLAvg). The air-capacity gauge — >70 % at busy hour = congestion. - Tx power headroom = actual output vs
dl-max-tx-power(170 = 17 dBm/0.1 step) &tx-attenuation(AU carrier-control-info). Coverage vs the power ceiling. - PDCCH / CCE can cap DL before PRBs do —
UsedCCEperSlot(fam 5012) +RatioSlotwBlockDL(fam 5097).
Rx utilization — the uplink
"How much of the uplink am I using, and is it clean?" — usage AND noise:
- UL PRB utilization =
TotULUsedPrb÷TotULAvailablePrb(NR 5041 · LTE 55TotPrbULAvg). ⚠ interference inflates this — retransmissions burn PRBs. - Rx noise floor = per-path
carrier-rssi+ therssi-high-alarm-threshold−620 (=−62 dBm) /rssi-low-alarm-threshold(AU MO). The interference & dead-path detector. - UL quality = PUSCH SINR (fam 5044) + interference power (fam 5045) + UL BLER (fam 5166). Clean UL = high SINR, low residual BLER.
| Symptom | Open these (in order) | Likely root cause | Action |
|---|---|---|---|
| High DL PRB util (>70 %), thpt falling | DL PRB util → CQI (5018) → active-UE count (5087) | genuine capacity limit, or a few heavy users | activate CA/SCell · load-balance/offload via mobility · add a carrier; if few users → policy/QoS cap |
| High DL PRB but low thpt | CQI (5018) → DL BLER (5165) → 256QAM share | poor DL radio quality — PRBs used inefficiently | fix coverage/interference first (tilt, power); PRBs aren't the problem, quality is |
| DL blocked, PRB not full | CCE util (5012) → RatioSlotwBlockDL (5097) | PDCCH/control-channel congestion, not data PRBs | increase CORESET / aggregation-level tuning; PDCCH capacity, not PDSCH |
| High UL PRB util, poor UL thpt | UL PRB → PUSCH SINR (5044) → UL BLER (5166) | usually UL interference → retransmissions eat PRBs | if SINR low → hunt interference (below); if SINR fine → real UL load, add UL capacity |
| UL SINR low / UL BLER high | per-path carrier-rssi (AU MO) → RSSI alarm (−62 dBm) → interference power (5045) | external interference, PIM, or overshooting neighbour | find the offending band/direction; check PIM (feeder/connectors); coordinate/retilt the neighbour |
| One Rx path RSSI ≫ others | per-path carrier-rssi + temperature + current-amp-state (AU path-control) | path imbalance — feeder/antenna/PIM or a sick PA path | swap/inspect that feeder+antenna; if PA fault → path-switch isolate; not a parameter fix |
| RSSI high-alarm firing (≥ −62 dBm) | RSSI alarm threshold → spectrum sweep → neighbour list | strong external interferer or intermod (PIM) | locate & remove the interferer; PIM test the passive chain; never mask it by raising the threshold |
| Low Tx util but coverage complaints | dl-max-tx-power · tx-attenuation · electrical-tilt · path-energy-saving-state | power capped/attenuated, tilt too high, or ES muted a path off-peak | raise power / cut attenuation / adjust tilt; check ES state (default enable) before blaming coverage |
| Off-peak UL util/SINR shifts | radio-sleep-mode · path-energy-saving-state · carrier switches | energy-saving muted carriers/paths in the low-traffic window | expected behaviour — confirm ES schedule; only intervene if it hurts residual traffic |
The baseband runs the DU — and configures every cell.
Main card thinks and carries transport + timing; Channel cards modulate 12 fronthaul ports each; the UCDB backplane ties them together; GNSS/PTP keeps it in phase — and the DU object tree provisions PCI, ARFCN and SSB for every cell. Next in 1.1: the small cells that extend coverage.