A straight-through cable connects each pin pair to the matching pin pair at the opposite connector. In 10BASE-T and 100BASE-T, pins 1–2 and 3–6 carry the two communication directions. This wiring suits devices whose transmit and receive pin pairs complement each other, such as a PC and switch. section 3.3.2
Use the pin relationships to predict whether a connection will work:
- A PC-to-switch connection works because the PC transmits on pins 1–2 while the switch receives on pins 1–2. section 3.3.2
- A straight-through cable can fail between two routers, PCs, or switches when both devices transmit on the same pin pair; a crossover cable swaps the pairs. section 3.3.2
