add oci model layer 1

cspell_dict_bash.txt

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 mysqldump
 
 ret
-mutex
+mutex
+
+baseband

docs/source/reference/network/osi-model-1.md

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+# OSI Model Layer 1
+
+## First Layer
+
+The physical layer that is responsible for binary transmission.
+
+Define how transmission is achieved.
+
+## Layer 1 Equipments
+
+Use cables to connect.
+
+Different network uses some medium to communicate.
+
+* Network interface controller (NIC)
+* Repeater
+* Ethernet hub
+* Modem
+* Fiber media converter
+
+### Network Interface Controller (NIC)
+
+For layer 1
+
+Some network interface controllers might also support functionalities
+of layer 2 and layer 3.
+
+### Ethernet Media
+
+This link might be helpful: https://www.electronics-notes.com/articles/connectivity/ethernet-ieee-802-3/cables-types-pinout-cat-5-5e-6.php
+
+Example:
+
+`10 BASE T`
+
+It means, the speed is 100 M, uses baseband transmission, and twisted-pair cable.
+
+Tx: twisted-air
+Fx: fiber
+Lx: long
+
+### Twisted-Pair Cable
+
+There are 8 wires, 4 pairs, and an outer jacket for a Twisted-Pair cable.
+
+2 types of twisted-pair cables:
+
+* Unshielded Twisted-Pair Cable (UTP)
+  * more common
+* Shielded Twisted-Pair Cable (STP)
+  * more expensive
+  * harder to connect
+
+### RJ-45 Connector
+
+The register jet
+
+Has 8 pins.
+
+### RJ-45 Jack
+
+A slot to plug in connector
+
+### Wiring
+
+* 568A
+* 568B
+
+### Straight-Through and Crossover
+
+Straight-Through
+
+* Same wiring on both ends
+
+Crossover
+
+* Different wiring on both ends
+* 1326
+
+Use crossover for devices with same type
+
+Use Straight-Through for devices with different order.
+
+So that both sending and receiving can be done in the same time.