2.3 OSI Model in the CCNA Curriculum.

2.37 Encapsulation

PDU(Protocol Data Unit).

De-Encapsulation.

TCP/IP Model

段（section)，包(Packet)，帧(Frame)，比特(bit)

core labs:2.36 and 2.37

CCNA 1 Model 3: Network Medium.

Atoms and electrons Valtage Resistant

Resistance and Impedance

Current

flow of charges created when electrons move.

Current is measured in Ampers (Amp)

Summary Graphic