Pin Numbering, Colors, and Registered Jacks
Previously, we had already started referring to the pin numbers and also their functions for data transfer and for PoE. Let us complete that discussion.
The familiar socket (or “jack”) in Ethernet is called the RJ-45, and it is actually an evolved form of a previous family of registered (modular) jacks (or RJs), all slightly smaller on the sides than the Ethernet jack. In Fig. 2.5, we see one of the earliest/simplest of all was the RJ-11, or more accurately a 6p2c connector, which stands for six positions, two contacts (two copper wires). Typically, these two contacts only had red and green wires and could serve one analog telephone because there was just one twisted pair. The pin numbering was equally ...

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