Essential foundation of programming - Summary of written interview examination sites - computer network (1) overview

explain ： This note is from moke.com @ Dong Dong Qiang teacher Curriculum 《 Fundamentals of programming computer network + operating system + The principle of computer organization 》, Interested friends can learn step by step , Here I just sort out some notes , Knowledge is not very deep , I also hope to communicate with you . If you want to learn more about computer networks , Recommended books ：《 computer network 》. It will be updated in succession ...

One 、 summary

1. computer network

2. Computer network classification

3. The development of computer network

Two 、 Computer network hierarchy

1. Basic principles of hierarchy design

2. OSI Seven layer model

3. TCP/IP Four layer model

3、 ... and 、 Network topology

1. Fringe part

2. The core part of the

Four 、 Performance index of computer network

1. rate

2. Time delay

3. Round trip time RTT

4. Maximum transmission unit MTU

5、 ... and 、 Physical layer overview

1. The role of the physical layer

2. channel

3. Demultiplexing technology

6、 ... and 、 Data link layer Overview

1. Package into frames

2. Transparent transmission

3. Error detection

7、 ... and 、 Detailed explanation of Ethernet protocol

1. MAC Address

2. Ethernet protocol

exercises

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One 、 summary

1. computer network

    The computer network is mainly composed of some general-purpose 、 Programmable hardware interconnection , Through these hardware , Different types of data can be transmitted , And can support a wide range of applications and growing .

2. Computer network classification

Scope of action ：WAN Wide area network ,MAN Metropolitan area network ,LAN LAN

Network users are divided into ： Public network , private network

3. The development of computer network

Single network ARPANET  --- >  Three tier Internet   --- >  multi-level ISP Internet

ISP(Internet Service Provider): Internet service provider ：  China Telecom 、 China Mobile 、 China Unicom, etc

Two 、 Computer network hierarchy

1. Basic principles of hierarchy design

（1） The layers are independent of each other

（2） Each layer should have enough flexibility

（3） The layers are completely decoupled

 

2. OSI Seven layer model

（ application layer ： We will be in direct contact with computers ;

The network layer ： The data transfer , From one place to another , Emphasize the whole process ;

Data link layer ： Emphasize the communication between adjacent nodes ;

The physical layer ： Physical devices ）

 

3. TCP/IP Four layer model

3、 ... and 、 Network topology

1. Fringe part

 

2. The core part of the

client - The server （C/S） Pattern

Peer to peer connection P2P Pattern

Four 、 Performance index of computer network

1. rate

Company ：bps=bit/s

2. Time delay

Include ： transmission delay , Propagation delay , Queuing delay , Processing delay

Queuing delay ： The time a packet is waiting to be processed in a network device

Processing delay ： The time required for a packet to arrive at the device or destination machine to be processed

Total delay = transmission delay + Queuing delay + Propagation delay + Processing delay

3. Round trip time RTT

RTT(Route-Trip Time) It is an important index to evaluate network quality .RTT It refers to the time of data packet back and forth in end-to-end communication

Usually use ping Command view RTT

4. Maximum transmission unit MTU

Maximum transmission unit MTU(Maximum Transmission Unit) ; The data frame of the data link layer is not infinite

Ethernet MTU It's usually 1500

 

byte

5、 ... and 、 Physical layer overview

1. The role of the physical layer

Connect different physical devices ; Transmit bitstreams

Twisted pair , Coaxial cable , Optical fiber , Infrared , wireless , laser

2. channel

A channel is a medium that transmits information in one direction ; A communication circuit comprises a receiving channel and a transmitting channel

 

classification ： Simplex communication channel , Half duplex communication channel , Full duplex communication channel

3. Demultiplexing technology

classification ： Frequency division multiplexing , Time division multiplexing , Wavelength division multiplexing , Code division multiplexing

6、 ... and 、 Data link layer Overview

1. Package into frames

“ frame ” It is the basic unit of data in the data link layer ;

The sending end adds specific marks before and after a piece of data in the network layer to form “ frame ” ; The receiver recognizes according to the specific mark before and after “ frame ”

In the network layer IP Datagrams are forwarded to the data link layer , The data link layer takes it as frame data after receiving it , And add marks before and after the frame data

 

The beginning and end of the frame are specific control characters （ Specific bit streams ）

The first one ： SOH: 00000001

The tail ：  EOT: 00000100

But what if there are these bit streams in the data ？ Never mind , Transparent transmission

2. Transparent transmission

“ Something that actually exists but doesn't seem to exist ” ;“ That is, the control character in the frame data , But treat it as nonexistent ”  Escape character ：ESC

 

3. Error detection

The physical layer only transmits the bitstream , There's no way to control if something goes wrong ; The data link layer is responsible for “ Error monitoring ” The job of

（1） Parity code

limitations ： When the number of error bits is even , Unable to judge

（2） Cyclic redundancy check code CRC

According to data transmitted or preserved Generate fixed digit parity check code Methods

testing Errors that may occur after data transmission or storage ; The generated numbers are calculated and Attach to the data

 

Ideas ：

（1） Select a polynomial to check G(x), And add... At the end of the data r individual 0

（2） Will add r individual 0 Later data , Use model “2” division Divide Bit string of polynomial

（3） Remainder obtained Fill in The original data r individual 0 The location of Get a verifiable bit string

 

  Judge ：  The data received by the receiving end is divided by G(x) Bit string of , Error in judging according to the remainder

CRC The error detection ability and the order of bit string r of ; The data link layer only detects data , Do not correct

7、 ... and 、 Detailed explanation of Ethernet protocol

1. MAC Address

MAC Address （ Physical address 、 Hardware address ） ; Each device has a unique MAC Address

MAC Address in total 48 position , Use hexadecimal to represent

Look at the computer MAC Address ： Use command ipconfig /all

2. Ethernet protocol

Ethernet (Ethernet) It's a widely used LAN technology

Ethernet is a protocol used in data link layer

It can be done with Ethernet Adjacent devices Data frame transmission

 

 

exercises

1. What is the seven layer model of computer network from top to bottom ？ application layer 、 The presentation layer 、 The session layer 、 Transport layer 、 The network layer 、 Data link layer 、 The physical layer .
2.ARP agreement 、RARP Which layer of computer network does the protocol belong to ？ Data link layer
3.IP agreement 、ICMP Which layer of computer network does the protocol belong to ？ The network layer
4. What are the two most important protocols in the transport layer ？. TCP agreement 、UDP agreement
5. Common application layer protocols are HTTP agreement 、FTP Agreements, etc , Can you also list some common application layer protocols ？ HTTP、FTP、SMTP、DNS、POP3、Telnet、TFTP、DHCP etc. .
6. Which layers of computer network does the router work on ？ The physical layer 、 Data link layer 、 The network layer .
7. What are the two modes of interconnection of modern network equipment ？ What are their characteristics ？ Customer - Server mode 、 Peer to peer connection mode . Customer - Server mode: the server provides network services , The client uses the service , It often appears as a server , Connection mode of multiple clients . The peer-to-peer connection mode does not distinguish between client and server , As long as both hosts are running peer-to-peer connection software （P2P Software ) They can have equal 、 Peer to peer communication .
8. Time delay is an important criterion to judge the quality of computer network , What are the components of network delay ？ Network delay can be divided into transmission delay 、 Propagation delay 、 Queuing delay 、 Processing delay several parts .
9. What is the main function of the physical layer ？ The main function of the physical layer is to connect different network devices and transmit bit streams between network devices .
10. Please list the common transmission media in the physical layer . Wired transmission （ Copper wire 、 Optical fiber ）, Wireless transmission .
11. What is channel , What is simplex channel 、 Half duplex channel 、 Full duplex channel ？ A channel is a medium that transmits information in one direction , Simplex channel refers to a channel that can only be sent or received , Half duplex channel refers to a channel where both parties can send and receive information but cannot send or receive information at the same time , Full duplex channel refers to the channel where both parties can freely send and receive information .
12. What are the three important functions of the data link layer ？ Package into frames 、 Transparent transmission 、 Error detection .
13. The physical layer is only responsible for the transmission of bit streams , What are these data called at the data link layer ？ Data frame

14. In order to define and distinguish a single data frame , What does the data link layer usually do ？ Add special bits to the head and tail of the data .
15. Suppose there's data 00100101 Need to transmit , The data received by the target machine is 10100100, Can I use parity check code to detect errors ？ You can't , Because parity bits can only detect errors in a single bit .
16. What is? MAC Address ？ How to view the MAC Address ？MAC What does an address do ？MAC An address is also called a physical address 、 Hardware address , By means of windows Enter command under system ipconfig You can view the of network devices MAC Address ,MAC Address using 48 Bits mark a physical device .
17. Please briefly describe the working process of Ethernet .MAC What role does address play ？ The Ethernet protocol passes MAC The mapping relationship between the address and the hardware interface shows which interface sends the data to the next hop .