Computer Network Study Notes (2) --- Physical Layer

I. Basic concepts of Physical Layer

The main task of the physical layer is to determine some features related to the transport media interface.

1. Mechanical Properties

2. Electrical Properties

3. Features

4. procedure features

Ii. Data Communication System Model

Model:

Source System (source point, transmitter)-Transmission System-destination system (receiver, terminal point)

Terms:

1. The purpose of communication is to transmit (messages), (data) is the entity for transporting messages, and (information) is the electrical or electromagnetic manifestation of data.

Signal:

(1) analog signal (continuous signal)

(2) digital signal (discrete signal)

2. (Channel) indicates the media that transmits messages to a certain direction. A communication (Circuit) usually contains a transmission channel and a receiving channel.

Channel:

(1) One-way communication (ticket Communication)

(2) bidirectional alternate communication (Half Duplex Communication)

(3) bidirectional simultaneous communication (Full Duplex Communication)

3,

(1) The signal from the source is called (baseband signal), and The Waveform Transformation of the baseband signal is called (baseband adjustment)

(2) The signal after carrier adjustment is called (band-pass signal), and the carrier modulation is called (band-pass adjustment) (AM, FM, and phase adjustment)

4. Maximum channel capacity

There are two factors that limit the transfer rate of the code element on the channel:

(1) The channel can pass through the frequency range (bandwidth)

(2) signal-to-noise ratio (dB) = 10log10 (S/N) (dB) S: Average Signal Power, N: average noise power

Shannon formula C = Wlog2 (1 + S/N) (B/s) W: channel bandwidth

3. Transmission Media in the Physical Layer

Oriented transmission media:

1. Twisted Pair wires

2. coaxial cable

3. Optical Cable

Non-oriented transmission media:

1. Short-Wave Communication (High-Frequency Communication)

2. Radio and microwave communication

3. Satellite Communication

Iv. Channel multiplexing technology (multiplexing is always used in pairs with the splitter)

1. Frequency Division Multiplexing)

2. time division multiplexing (TDM)

3. Statistical time division multiplexing (STDM)

The short time slot (white) before each time slot on the output line is put into the user's address information, because the time slot in the STDM frame is not fixed to a user's

4. wavelength division multiplexing (WDM)

Optical Frequency Multiplexing

5. Code Division Multiplexing (CDM)

V. Digital Transmission System

1. Pulse Code Modulation PCM System

2. synchronous optical fiber network SONET and Synchronous Digital series SDH

Vi. Broadband Access Technology

1. xDSL: The biggest advantage of ADSL is that it can take advantage of existing user lines in the telephone network.

2. Fiber-Optic coaxial network (HFCs): The biggest advantage of the HFCs is that it has a wide band and can use a cable TV network with a considerable coverage area.

3. FTTx technology: Optical Fiber ......