Computer network

The blog for the personal study of computer network do some notes, the author level is very limited, if there are mistakes and wrong understanding, welcome to point out!! Thank you!!

The textbooks and materials are Computer Networks (7th Edition) and Top-down by Xie Xiren. The course is teacher Han Ligang’s video, forcing the teacher’s video, very good ~

Internet and the Internet

To be honest, I had never heard of the Internet before. I thought it was a mistake on the teacher’s handout. Here’s a common sense concept: “Internet” is not the same as “Internet”.

The Internet

“Internet” is a general term, generally refers to the network connected by multiple computer networks, the specific use of what protocol is not clear. Nodes and links are connected to form a network, and routes are connected to form an interconnection network.

The nodes can be computers, switches, routers, and so on

The Internet

“Internet”, this is what we know as the Internet. Is a TCP/IP protocol family, and global coverage, resource sharing a large interconnection network. My understanding is the Internet

Three stages of Internet development

The first stage

At first there was a single ARPNET network, and then there was a way to connect the various ARPNET networks to form the Internet.

  1. In 1983, the standard protocol on ARPNET was changed to TCP/IP, so computers using TCP/IP could communicate over the Internet
  2. 1983 was also regarded as the birth time of the Internet
  3. In 1990, ARPNET was officially shut down, at which point the testing of the Internet was largely over and the next phase began

The second stage

Then came a three-tier structure of the Internet, forming a backbone – regional network – campus network layout. Since most of the participants were scientific research institutions and schools, more and more enterprises joined in later.

The third stage

Gradually forming a multi-level ISP network (LSP???)

  1. theInternet Service provider ISP(Internet Service Provider)Mobile, telecom (telecom campus network is very poor, small voice BB)
  2. If you pay a fee to an ISP, you can get the right to use the IP address you want and connect to the Internet through the ISP
  3. According to the size of the covered area and all the DIFFERENT IP addresses and numbers, ISPs are divided into different levels: trunk ISP, regional ISP, and local ISP

ISP layering:

IXP

We can see that host A is too troublesome to communicate with host B, which is A big detour. At this time, there is the IXP Internet exchange point, which serves as the intermediate line.

other

There are also some large companies that connect directly to backbone isPs or regional ISPs to increase their network capacity

Bandwidth speed

Do you think what you think 100M is what you think?

100M is actually the speed to your local ISP, but what about your ISP elsewhere? This depends on the ISP with the lowest speed

The world wide web

The World Wide Web is an application on the Internet, and this application also promotes the development of the Internet

Internet Society ISOC

ISOC has an Internet Architecture Research Committee, IAB, which has two divisions:

  1. Internet Research Department IRTF, under which there is an Internet Research Steering Group IRSG to manage each group RG(Research Group)
  2. The Internet Engineering Division (IESG), under which the Internet Engineering Steering Group (IESG) manages the different working Groups in various areas

The stages of becoming an official standard on the Internet

All Internet standards should be published online in the form of RFC

In the past

  1. Start by forming an Internet Draft, which has a six-month validity period and is not yet an RFC document
  2. The Proposed Standard is then reached, and from this stage it becomes an RFC document
  3. Finally reach the Internet Standard (Internet Standard), become an official Standard, can be assigned to a number STD XXXX, a Standard can be associated with multiple RFC documents

now

Now there are two phases, proposed standards and Internet standards

Among them, in addition to recommended standards and Internet standards have RFC documents, there are:

  1. Experiment with RFC, success becomes the recommended standard, failure becomes history RFC.
  2. An RFC that provides information, here is an RFC that provides guidance
  3. Historical RFC(this is what was scrapped)

The Composition of the Internet

Edge part:

It consists of all hosts connected to the Internet, including smart devices and so on. This part is directly used by users for communication and resource sharing.

  1. The edge part of the host is also calledEnd system(End system), the end system may be quite different in function:
    1. Small: a computer is also available, a mobile phone is also available, a smart networked watch, a networked STM32 small alarm clock is also available
    2. Large: an extremely expensive computer
    3. The owner of an end system can be an individual, an enterprise, a school, a government, or an LSP

Core part:

This is made up of a large number of networks and routers, with the core providing services to the edge (providing connectivity and switching)

The meaning of communication between end systems

The communication between host A and host B is actually the communication between A program on A and A program on B.

Communication between end systems:

  1. The client-server mode (C/S mode) is also called the Client/Server mode, or C/S mode for short
  2. Peer-to-peer mode

How the customer service side works

Features of client software:

  1. Run after being invoked by the user to actively initiate communication to the remote server (request service) when intended to communicate. Therefore, the customer service software must guide the address of the server program.
  2. It doesn’t require special hardware or a very complex operating system

Server software features:

  1. A program that specializes in providing a service (for example, Web, DNS, FTP, SMTP, etc.) that can process requests from multiple remote or local customers simultaneously
  2. After the system is started, it is automatically called and has been running, passively waiting and accepting communication requests from customers from all over the world. Therefore, the server program does not need to know the address of the client program.
  3. It generally requires powerful hardware and an advanced operating system

After the communication relationship between client and server is established (three handshakes and four waves??) Communication can be two-way and both can send and receive data.

Packet switching

To understand packet switching, learn circuit switching

Circuit switching

Our traditional telephone communication is a typical example of circuit switching. The whole process is as follows: establish a connection (occupy communication resources)-> call (always occupy communication resources)-> release the connection (return communication resources). From the perspective of communication resource allocation, switching is the dynamic allocation of transmission line resources in some way. From the beginning of the call to the end of the call, much of the time during which line resources are wasted.

Packet switching

Packet switching adopts the store-and-forward technology (in essence, it adopts the policy of intermittently (or dynamically) allocating transmission bandwidth in the process of data communication). It divides a message into several packets and then transmits them. The message is the whole piece of data to be sent. Before sending a packet, the long packet is divided into smaller equal length data segments. A packet is formed by adding some headers composed of necessary control information before each data segment. ** Multiple packets constitute a packet. ** The header of the packet contains important control information such as destination address and source address, so that each packet can independently select the transmission path in the Internet and be correctly delivered to the end of the packet transmission.

Thus, an efficiency problem in circuit switching is solved to a large extent:

  1. Circuit switching is a sprint race, on the same track, used by only one racer during each race.
  2. Group switching is a marathon race, on the same track, everyone’s speed is different, you can follow very closely, most people pressing on the first track is also allowed

The host at the edge of the network and the router at the core of the network are both computers, but they do very different things.

  • Hosts process information for users and exchange information with other hosts over the network.
  • A router is dedicated to packet switching. After receiving a packet, the router stores it temporarily, checks its header, searches for the forwarding table, and forwards the packet to the appropriate interface according to the destination address in the header. Routers must exchange routing information frequently to create and dynamically maintain forwarding tables in routers that can be updated as the entire network topology changes.