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OSI Physical Layer · Layer 1 · Bit Encoding

BIT TRANSMISSION

// CONVERTING BINARY DATA INTO PHYSICAL SIGNALS & TRANSMITTING OVER THE MEDIUM
// SELECT A MEDIUM · EDIT THE BIT STREAM · WATCH THE SIGNAL TRAVEL

INPUT BITS:
BIT ENCODER NRZ-L SCHEME CURRENT BIT 1 +5.0V → HIGH BITS SENT: 0 TX ACTIVE +5V 0V -5V COPPER WIRE — NRZ-L ENCODING SINGLE-MODE OPTICAL FIBRE — OOK ENCODING CLAD CORE CLAD FREE SPACE — ASK/AM MODULATION BIT DECODER PHOTODETECTOR RECEIVED BIT — AWAITING SIGNAL RECEIVED: ──────── BITS RX: 0 RX ACTIVE SOURCE DEST LASER DETECTOR BITS TRANSMITTED: 0 SIGNAL SPEED: — ENCODING: NRZ-L BIT RATE: — ELECTRICAL
SPEED:1×
⬤ CH1 SIGNAL WAVEFORM TIME/DIV: 1 BIT-PERIOD +A 0 −A
TRANSMITTING: ACTIVE
BIT RATE: —
SIGNAL TYPE: ELECTRICAL
MEDIUM: COPPER WIRE
ENCODING: NRZ-L
HOW IT WORKS
Electrical Signal Transmission

Binary bits are converted to voltage levels by the encoder. Using NRZ-L (Non-Return-to-Zero Level) encoding: a binary 1 maps to +5V (HIGH) and a binary 0 maps to 0V (LOW). These voltage changes propagate as an electromagnetic wave along the copper conductor at roughly ⅔ the speed of light (~2×10⁸ m/s).

ENCODING SCHEMES
NRZ-L Non-Return-to-Zero Level: 1=High voltage, 0=Low voltage. Simple, but causes DC component buildup in long runs.
Manchester Mid-bit transition: 1=High→Low, 0=Low→High. Self-clocking; used in 10BASE-T Ethernet.
4B/5B Maps 4 data bits → 5 code bits to eliminate long runs. Used in Fast Ethernet (100BASE-TX).
TECHNICAL PARAMETERS
Signal TypeElectrical (Voltage)
Propagation~2×10⁸ m/s (⅔c)
Voltage Levels0V (LOW) / +5V (HIGH)
Max Bit RateUp to 10 Gbps (Cat 6A)
Max Distance100m (UTP Cat 5e/6)
Attenuation~0.2 dB/m at 100 MHz
REAL-WORLD EXAMPLES
🖥️Ethernet LANCat 5e/6 twisted pair, up to 10 Gbps
📞ADSL / DSLTelephone copper, DMT modulation
🔌USB 3.xDifferential signalling, 20 Gbps
💾SATA / PCIeSerial internal bus, 8B/10B encoding