RJ45コネクター
Birds and Bees (Plugs vs. Jacks)

     The EIA/TIA specifies an RJ-45 (ISO 8877) connector for Unshielded
     Twisted Pair (UTP) cable.  The plug is the male component crimped
     on the end of the cable while the jack is the female component in
     a wall plate or patch panel, etc.  Here is the pin numbering to
     answer the question, where is pin one?

  Plug                          Jack
  (Looking at connector          (Looking at cavity
   end with the cable             in the wall)
   running away from you)

      ---------- /                   ----------
     | 87654321 |                   | 12345678 |
     |__      __|/                  |/_      /_|
        |____|                         |/___|