Computer network Overview---physical layer

Basic concept of physical layer

The physical layer solves how to transmit the bitstream on the transmission media connected to various computers, rather than the specific transmission media;

The physical layer's main task is described as: determining some of the characteristics of the transport media, namely:

Mechanical properties: Interface shape, interface size, number of interface leads

Electrical characteristics: Specified voltage range ( -5v to 5V)

Features: Specified -5v is low, 5V is 1 high

Process characteristics: Also known as the procedure characteristics, the establishment of the connection when the relevant components of the work steps

Basic knowledge of data communication

Channel: A channel represents a medium that transmits information to a direction;

Simplex communication: Only One Direction of communication, but not the opposite direction of communication;

Half-duplex communication: Communication can not be sent by both parties at the same time;

Full duplex communication: Both sides of the communication can send and receive information at the same time;

Baseband signal (basic band signal): The signal from the source, the computer output represents a variety of text or image file data signal is a baseband signal;

Band-pass signal: After the baseband signal is modulated by the carrier, the frequency range of the signal is moved to a higher band to facilitate transmission in the channel;

The transmission Media channel multiplexing technology under the physical layer broadband access technology for digital transmission system

Computer network Overview---physical layer