Most 5G engineers know the software.
Very few can explain what’s
physically sitting on that tower.
Here’s every hardware component
of a 5G gNodeB — decoded. 
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THE 4-LEVEL TOWER ARCHITECTURE:
LEVEL 1 — Tower Top
AAU (Active Antenna Unit)
→ 192 antenna elements
→ 64T64R Massive MIMO
→ Integrated RRU + Antenna
→ Beamforming chipset inside
→ Bands: n77/n78/n79
→ Connected via eCPRI fronthaul
LEVEL 2 — Tower Base
DU (Distributed Unit)
→ Real-time L1/L2 processing
→ FPGA + DSP chipset
→ RLC / MAC / PHY layers
→ Latency requirement: <1ms
→ Connected to CU via F1
LEVEL 3 — Edge Data Center
CU (Centralized Unit)
→ CU-CP: RRC + PDCP-C
→ CU-UP: SDAP + PDCP-U
→ E1 interface between CP/UP
→ Non-real-time processing
→ Connects to 5GC via NG (N2/N3)
LEVEL 4 — Core Network
5GC: AMF | SMF | UPF
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PROTOCOL STACK → HARDWARE MAP:
SDAP + PDCP ──→ CU (cloud)
RLC + MAC + High-PHY → DU (tower base)
Low-PHY + RF ──→ RU/AAU (tower top)
3 hardware units.
7 protocol layers.
Perfectly distributed. 
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3 DEPLOYMENT TYPES:
Macro gNodeB
→ 64T64R AAU, 30-90m tower
→ Coverage: 1-5km
→ Band: n78 primary
Small Cell gNodeB
→ 8T8R, 5-10m pole
→ Coverage: 100-500m
→ Urban densification
mmWave gNodeB
→ 256T256R
→ Coverage: 50-300m only
→ Stadiums/venues/indoor
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TRADITIONAL vs O-RAN gNB:
Traditional:
Vendor BBU (CU+DU combined)
Proprietary CPRI
Single vendor lock-in
O-RAN:
O-CU + O-DU + O-RU separated
Open eCPRI fronthaul
Multi-vendor flexibility
RIC intelligence layer
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Cheat codes:
CU = non-real-time (RRC/PDCP)
DU = real-time (MAC/RLC/PHY)
RU = RF only (Low-PHY+antenna)
AAU = RU + Antenna integrated
BBU = CU+DU legacy combined
eCPRI = fronthaul protocol
F1 = DU↔CU interface
E1 = CU-CP↔CU-UP interface
NG = gNB↔5GC interface
3GPP ref: TS 38.401
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Quick poll:
Which gNodeB component do you
work with most?
AAU/RU (RF/antenna)
DU (real-time baseband)
CU (core-facing)
Full stack
Drop role + vendor below
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