CCNA Networking · Quick Reference

Module 4 — Physical Layer Cheat Sheet

CCNA Networking

In one line: OSI Layer 1 — Physical is responsible for transmitting raw bits over a physical medium. It doesn't understand frames or packets — it simply converts binary data into electrical ...

Key Ideas

1The Physical Layer. OSI Layer 1 — Physical is responsible for transmitting raw bits over a physical medium. It doesn't understand frames or packets — it simply converts binary data into e...

2Copper Cabling. Copper is the most common and cheapest network medium. It uses electrical signals to transmit data. The main challenge with copper is susceptibility to EMI (Electromag...

3UTP Categories. Twisting wire pairs reduces crosstalk. The tighter the twist, the better. UTP cables are categorized by the TIA/EIA standards body:

4UTP Cabling Standards and Pinouts. The TIA/EIA-568 standard defines two wiring schemes for UTP — T568A and T568B. The difference is which pairs are assigned to pins 1/2 and 3/6. Both work fine; the impo...

5Fiber-Optic Cabling. Fiber-optic cable transmits data as pulses of light rather than electrical signals. This makes it completely immune to EMI and capable of much higher bandwidths over m...

Code Examples

T568B Wiring (most common in US):
Pin 1: White/Orange  (TX+)
Pin 2: Orange        (TX-)
Pin 3: White/Green   (RX+)
Pin 4: Blue          (unused in 100Mbps)
Pin 5: White/Blue    (unused in 100Mbps)
Pin 6: Green         (RX-)
Pin 7: White/Brown   (unus...