Ia note 1

HCIA： Huawei certified junior network engineer

HCIP： Huawei certified senior network engineer

HCIE： Huawei Certified Expert Network Engineer

What is the Internet ？

1、 Information （ resources ） share , Information collection and release , Data storage and processing , Applications on Computer Networks （ WeChat ,qq）, Packet exchange , Data consists of packets , It is constantly transmitted at each network node , Finally achieve the goal .

Cloud technology

          ----- Cloud storage ： Operators provide servers , For example, baidu online disk , Yunlei network disk, etc .

The difference between server and computer , The memory of the server can reach 256GB, The maximum memory of the computer is 64GB, The performance of the server will also be better , The server directly runs linux operating system , Servers can focus on one thing, such as storage .

          ------ Cloud computing ----- Distributed computing , The so-called distributed computing is to deal with huge data , One computer processing is not awesome, you can put more than one computer processing . Computer cluster .

Computer technology ：（ The computer recognizes the electrical signal ）

Abstract language ------- code ： application layer

code -------- Binary system ： The presentation layer

Binary system ------ Electrical signals ： medium （ Hardware ） Access control layer （ Network card counts ）cpu Process electrical signals

Process electrical signals ： The physical layer

Transmission medium

RJ-45 Twisted pair

8 Copper wire （ Good conductivity , cheap , Good ductility ）, It is divided into 4 Group , Entangle two . The purpose is to counteract electromagnetic interference . Conductivity ： silver > copper > aluminum , Therefore, most twisted pair cables sold on the market are impure , It is mixed with aluminum .

Twisted pair classification ： Shielded twisted pair ： It can shield interference ; Unshielded twisted pair ： cheap . At present, the most commonly used is super 5 Quasilinear . The distance is too long , The signal will weaken .

The transmission of network cable is bit/s, File download rate 1byte/s,1 byte =8 The bit , So the transmission rate calculation ：1000M/8×0.85（0.85 Refers to all kinds of offsetting things ）

Optical fiber

fragile , Most of them are buried under the ground . The transmission medium is optical fiber （ Fiberglass ） It transmits optical signals .

The optical fiber is divided into single-mode optical fiber ： Injection laser diode ------ Small signal distortion .

                Dual mode fiber

Electrical signals ------ optical signal ： Light-emitting diode 、 Injection laser diode

optical signal ------ Electrical signals ： Generator diode

How to guarantee the communication quality , Expand the network ？

Increase the number of network nodes , Extend the transmission distance , At this time, there is still a problem in the expansion of the network , Network latency and security issues .

Increase the number of network nodes

1、 Linear topology

2、 Ring topology

3、 Star topology ： Best value for money

4、 Mesh topology

5、 Hybrid topology （ Multi ring topology ）

6、 Tree topology

Extend the transmission distance

Repeaters are generally used , It's a physical layer device , Repeater is the transmission of electrical signals .（ Single layer equipment , Electrical signals cannot be stored , Current can be stored ）

The hub is used to extend the transmission distance , It's a physical layer device , Hub conflicts 、 Security 、 Address problems and delays .

terms of settlement ：

1、 Conflict --------CSMA/CD（ Carrier sense multiple access control technology / Collision detection ）

Carrier sense ： Just line up      Collision detection ： Add a timer

It can solve the conflict problem, but it has low efficiency and large delay .

2、 Address problem

The only global , use the same pattern .  Mac Address （ Media access control layer ）, When all chips leave the factory , Serial number burned by the manufacturer , The only global , from 48 Bit binary structure , front 24 Manufacturer identification , after 24 Serial number assigned by the manufacturer , Used to distinguish different chips . Open mode ：ipconfig /all

If we want to achieve the current global network , With new requirements 1、 Extend the transmission distance wirelessly 2、 There is no conflict at all ------ All nodes can send data at the same time 3、 Realize unicast ----- One to one correspondence 4、 How to provide port density ？

Realize unicast ----- One to one correspondence ： Switch is needed .（ Second floor equipment ） Electrical signals are converted into binary

The media access control layer needs to add two addresses when converting binary into electrical signals , One is SMac（ Source Mac Address ）, The other is DMac（ Destination address ） The switch realizes unicast , There will be one in the switch Mac Address table , Open up your own memory space in the switch , Storage address . If at first Mac I don't know which address to send in the address table , Will flood . Repeated flooding is bad , Computer network may crash .Mac The address table will have an aging time ,Mac Address 300s After the update . Due to flooding mechanism , We cannot expand the network , A switch can connect hundreds of computers at most （ Each network implemented by the switch is an island , Cannot connect with each other ）. If we want to connect into a global network , We need to connect these islands , We need a router .

Router

Join the router , The original 4 The layer model is not enough , So use the following model

application layer

The presentation layer

The network layer IP----- Internet Protocol （IPV4,32 Bit binary ,43 More than 100 million , Not enough use .IPV6,128 Bit binary ---- Based on this, it is proposed that all things are interconnected , There is the major of Internet of things ）

Media access control layer

The physical layer

The function of router is 1、 Isolate the flood area ------ An interface to a router （ gateway ）, It is a flood range

                          2、 Forward messages , connected 2 A network of switches