[Computer Network] More than 10,000 words to clearly explain the "Internet Overview", the definition and classification of computer networks, network performance indicators

1. Internet overview

1. The difference between the World Wide Web, the Internet and the Internet

• What is the Internet (internet pay attention to lowercase i)?

Any network composed of devices that can communicate with each other is called the Internet. It can be seen that the scope of the Internet is very wide here.

• What is the Internet (note that the Internet is capitalized)?

It is a huge network that is connected between the network and the network. These networks are connected by a set of standard network TCP/IP protocol suites.

• What is the World Wide Web?

The World Wide Web is a collection of files, pictures, multimedia, and other resources. Resources are connected to each other through hyperlinks to form a network, and are identified by a uniform resource identifier (URL). HTTP is the main access protocol for the World Wide Web.

In fact, according to the explanation on Wikipedia, the browser you usually use can be called: World Wide Web browser software, such as chrome, firefox

At present, due to the widespread use of the Internet, the Internet sometimes directly refers to the Internet, but we can see the difference from the English name, Internet: internet, Internet: Internet. The Internet in a broad sense is very large. A network composed of two computers can also be called the Internet, but it cannot be called the Internet.

The World Wide Web, also known as the Web, is a service (web service) in the Internet. In addition to the World Wide Web, the Internet also includes many other services, such as email services, FTP, Telnet, and so on.

2. Three stages of Internet development

The development of the Internet can be roughly divided into three stages.

• The first stage: the development from a single network APPANET to the Internet; the initial formation of the TCP/IP protocol;

• The second stage: the establishment of a three-level structure of the Internet; divided into backbone network, regional network and campus network;

• The third stage: the formation of the Internet with a multi-level ISP structure; ISP appeared for the first time.

3. Standardization of the Internet

Internet standardization

4. The composition of the Internet

In terms of how the Internet works, it can be divided into two parts:

(1) The edge part is composed of all the hosts connected to the Internet. This part is directly used by users for communication (transmission of data, audio or video) and resource sharing.

(2) The core part is composed of a large number of networks and routers connecting these networks. This part is to provide services for the edge part (providing connectivity and exchange).

Two, three exchange methods

1. Circuit switching

• advantage:
  • Small communication delay: The communication circuit is dedicated to both users of the communication, and the data is direct (conducive to continuous transmission of large amounts of data)
  • Orderly transmission: There is only a dedicated communication line for one day between the communication parties, and the data is only transmitted in one line, and there is no timing problem
  • No conflict: different communication parties have different channels, and there will be no problems of competing for physical channels
  • Wide range of applications: it is suitable for both analog signal transmission and digital signal transmission
  • Strong real-time: because the communication delay is small
  • Simple control: circuit-switched node switches and their control are relatively simple
• Disadvantages:
  • Long connection establishment time: The average establishment time of a circuit connection is too long for computer communication
  • Line exclusive: low efficiency. Once the circuit switching is connected, the physical path is exclusively occupied by both parties of communication. Even if the communication line is idle, it cannot be used by other users, so the channel utilization is very low.
  • Poor flexibility: As long as there is a failure at any point in the physical path established by the connection, you must redial to establish a new connection (not conducive to emergency and important communications)
  • Difficult to standardize: In circuit switching, data is directly delivered, and terminals of different types and specifications are difficult to communicate with each other, and it is also difficult to perform error control in the communication process

2. Message exchange

• advantage:
  • No need to establish a connection: There is no need to establish a dedicated communication line for the communication parties, there is no delay in establishing a connection, and the user can send messages at any time
  • Dynamic allocation of lines: The node switch first stores the entire message, and then selects a suitable idle line to send the message
  • Improve line reliability: If a transmission path fails to send, it will re-select another path to transmit data
  • Improve line utilization: The communication parties do not occupy a communication line fixedly, but partly occupy the physical line at different time segments, thus greatly improving the utilization rate of the communication line
  • Provide multi-target services: a message can be sent to multiple destination addresses at the same time (compared to circuit switching)
• Disadvantages:
  • Caused forwarding delay: the message has to go through the store and forward process on the node switch
  • Requires larger storage and buffer space: There is no limit to the size of the message for message exchange
  • Need to transmit additional amount of information (compared to circuit switching): The message needs to carry information such as destination address, source address, etc.

3. Packet switching

• Advantages:
  • No need to establish a connection: There is no need to establish a dedicated communication line for the communication parties, there is no delay in establishing a connection, and the user can send messages at any time (same as message exchange)
  • Improve the utilization rate of the line: The communication parties do not occupy a fixed communication line, but occupy the physical line at different time segments, thus greatly improving the utilization rate of the communication line (same as message exchange)
  • Simplified storage management (compared to message exchange): Because the length of the packet is fixed, the size of the corresponding buffer is also fixed, and it is relatively easy to manage
  • Accelerated transmission (compared to message exchange): Since the packets are transmitted one by one, this allows the storage operation of the next packet and the forwarding operation of the previous packet to be performed at the same time
  • Reduce the probability of error and the amount of retransmitted data (compared to message exchange): Because the packet is smaller than the message, the error rate is lower; even if the packet is wrong, only the part of the packet that is wrong needs to be retransmitted, which is more than retransmitting the whole The data volume of the message is much smaller, so the reliability is improved and the transmission delay is reduced.
• Disadvantages:
  • Caused forwarding delay: the message has to go through the store and forward process on the node switch
  • Need to transmit additional information (compared to circuit switching, message switching): each message needs to carry information such as destination address, source address, etc.
  • For datagram services, there may be problems with out-of-sequence, loss or regrouping: When the packets arrive at the destination node, they need to be restored to the original message, which is more troublesome; for virtual circuit services, although there is no packet out-of-sequence problem, there are also calls. Three processes of establishment, data transmission, and virtual circuit release

Third, the definition and classification of computer networks

4. Computer network performance indicators

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1. Rate

2. Bandwidth

3. Throughput

4. Delay

5. Delay bandwidth product

6. Round trip time

The source host sends to the target host, and then sends from the target host to the source host

Round-Trip Time(RTT)

7. Utilization rate

8. Packet loss rate