Personal Computer Network Learning Notes (a) physical layer
On the computer network of a recent study summarized.
Make a note of the above recording mind FIG.
Physical Layer
Action: transparent transmission bit stream
main tasks: determining relevant interfaces and transmission media.
Four Characteristics
1. Mechanical: and the relevant contact interface.
2. Electrical: voltage range.
3. Functions: a sense of power frequency represents.
4. Regulations: relations procedures and timing.
Thinking : procedures and protocols What is the difference?
----- protocol is a protocol of the physical layer.
Communication data transmission
1. Simplex: a channel is only transmitted.
2. Half: There are two channels for transmission, but not enabled at the same time.
3. Full duplex: both channels are enabled.
The two data transmission
1. The serial transmission: for remote. (Communication line)
2. parallel transmission: for short distances. (Computer)
Coding and modulation
Signal ( can be divided into two categories )
1. Digital signal: a discrete signal (i.e., mutation occurs)
2. Analog signals: a continuous signal
in which a digital signal of the basic waveform is called a symbol , or refers to a signal waveform when a fixed length.
Symbol content
1. rate of
symbol transmission speed (baud rate): How many baud symbol unit B on behalf of the one second transmission
information transfer rate: represents a second transmitted bit number
two relationships: one symbol carries n bit, M symbol information transmission baud rate (M * n) bit / s
Note: 1 'bit representative of binary symbols when using only a single 0 or 1, using a quaternary symbol representative of the use of two 2bit _ _ bit
combinations of 0 and 1.
While: the transmission rate comparison system speed, comparing the information transfer rate.
Distortion factors
. A symbol rate of propagation
. Two signal transmission distance
. Three noise interference
. Four transmission medium (media) mass
channel bandwidth :( highest frequency - the lowest frequency) Hz
Two calculation of the transmission rate limit method
1.nice criterion :( general computing symbol transmission rate)
calculated transmission rate limit is under ideal conditions (limited transmission rate of the symbols, there is no limitation on the information transmission rate)
exceeds the rate limit will produce intersymbol crosstalk
2. Shannon's theorem is calculated :( bit transmission rate)
is not ideal conditions, the presence of noise, there is SNR
information transfer rate does not exceed the rate limit, the transmission can be performed without a difference
3. The baseband signal: a signal from the source, and transmitted in a digital channel, wherein the digital channel for transmission is called baseband transmission
4. wideband signal: The baseband signal is modulated, transmitted in the analog channel, wherein the analog channel of transmission called broadband transmission
Code: also called baseband modulation
Introducing the concept of data: physical transport information.
. Digital data ① -> Digital Signal
1. NRZ: As shown in the book. (P44)
2. Return to Zero: a positive pulse, a negative pulse is zero.
3. Manchester encoding: The transition represents 0 or 1.
4. Differential Manchester encoding: the hop cycle boundary becomes represents 0 or 1. (With 1, iso 0)
. 5 4B | 5B coding: efficiency of only 80% of the
analog data -> digital signal (PVM Modulation)
1. Sampling: mining frequency F> = 2f highest frequency signal
2. quantization
3. coding
Modulation: Modulation is also called a band-pass
Digital data -> analogue signal (P44)
1. FM
2 AM: amplitude of the signal varies with the digital band carrier varies based
3. The phase modulated
analog data -> an analog signal
Physical transmission media layer
1. oriented transport medium :
1. UTP: shielded / unshielded
2. coaxial cable: a baseband / broadband
3. multimode fiber / single-mode single-mode wherein the total reflection is not required, is a straight line.
2. Non-oriented transmission medium
1. The radio wave (non-directional)
2. microwave (with fixed directivity)
3. Infrared (fixed directivity)
Physical layer transmission device
Repeater : digital signal regeneration and reduction
Hub : digital signal regeneration and reduction, but inseparable conflict.
The above picture comes from the beep beep miles miles king PubMed, PubMed thank benevolent knowledge to offer.
