100BASE-T is a 100 Mbps Ethernet physical-layer standard that sends data over two of the four twisted-pair wire pairs in a UTP cable. Its connections use pins 1–2 and 3–6, with one pair carrying traffic in each direction. section 3.3.2
Practical points for cabling:
- Use a straight-through cable for unlike device types, such as a PC and switch; their transmit and receive pin pairs are complementary. section 3.3.2
- Use a crossover cable when equivalent devices transmit on the same pin pair, unless Auto MDI-X adjusts the connection automatically. section 3.3.2
- Keep the UTP connection within the 100-meter maximum supported by 100BASE-T. section 3.5
PC connected to a switch
A straight-through UTP cable connects PC pins 1–2 and 3–6 to the switch's corresponding pins. The PC transmits on 1–2 while the switch receives there; their other pair handles the reverse direction. section 3.3.2
