This time we are going to update the computer network. What we are watching is the Wangdao postgraduate entrance examination. The notes and supplements made by ourselves do not conflict with our Java. I will update the two at the same time and it will not affect the progress. Please watch carefully
Article directory
A computer network overview
Two computer network functions
Three stages of Internet development
The composition of four computer networks
Five classifications of computer networks
Six computer network performance indicators
seven formula
Eight Summary
foreword
提示：这里可以添加本文要记录的大概内容：
This is my first computer network article. We will probably divide it into six chapters, namely: computer network architecture, physical layer, data link layer, physical layer, transport layer, and application layer. I also refer to the computer network textbook, which is the textbook written by Professor Xie Xiren, and our black book "Computer Network Top-Down Direction".
提示：以下是本篇文章正文内容，下面案例可供参考
A computer network overview
Concept: A computer network is a system that connects decentralized computer network systems with independent functions through communication equipment and lines , and realizes resource sharing and information transmission by software with complete functions . In short, computer networks are some interactive systems. A collection of connected, autonomous computer systems.
Interconnection: Interconnection through communication links
Autonomy: no master-slave relationship
Among them we will talk about:
- concept, composition, function, classification
- Standardization work and related organizations
- Performance
The concept of a network: a net-like thing or a networked system
Two computer network functions
There are many functions of a computer, and many applications today are related to the network. Now we list the following five functions:
- data communication
- Resource sharing can share hardware, software, data
- Distributed processing Multiple computers share different tasks in the same job
- Improve reliability Alternative machine
- Load balancing Balanced distribution to each computer in the computer network
Three stages of Internet development
The development of the Internet is divided into three stages
The first stage: ARPANET------internet----------Internet
Phase Two: The Internet with a Three-Level Structure
For example: backbone network ----- regional network ----- campus network
Backbone: Integrated to provide interconnection
Region: Business Services
Local: Company
The third stage: Internet with multi-level ISP structure
The composition of four computer networks
There are different classifications from different angles, and the following three angles are used to analyze:
1. From the perspective of components:
- Hardware host (end system), communication link (twisted pair, fiber optic)............
- Software Various software to realize resource sharing
- Protocol A collection of rules and conventions
A complete computer must consist of these three parts, none of which can be dispensed with.
2. From the perspective of working methods:
Edge part: The edge part is a combination of hosts directly used by users on all connected Internet for communication and resource sharing
Core part: The core part consists of a large number of networks and routers connecting these networks, which provide connectivity and switching services for the edge parts
3. From the perspective of functional composition (data communication, resource sharing)
Communication subnet: The communication subnet is composed of various transmission media, communication equipment and corresponding network protocols, and it has the functions of data transmission, exchange, control and storage
Resource subnet: A resource subnet is a collection of devices and software that implement resource sharing functions, providing network users with services to share hardware resources, software resources and data resources of other computers
Five classifications of computer networks
There are many classifications of computers, divided by distribution range, by users, by switching technology, by topology, and by switching technology. Let's explain in detail:
1. Classified by scope:
- Wide Area Network (WAN)
- Metropolitan Area Network (MAN)
- local area network (LAN)
- Personal Area Network (PAN)
Its manifestation is different, so its scope is also different, so we should answer the question according to the question.
2. Classification by user:
- public network
- private network
We can understand the scope of their use from these nouns, so they are only divided into public networks and private networks according to user classification.
3. Classified by switching technology:
Exchange technology refers to the data format and the way of exchanging devices collected for exchange and learning between each host, between each communication device or between the host and communication equipment 1, and can be divided into the following categories:
circuit switched network
message switching network
packet switched network
4. Classification by topology: (you can check the conditions and reasons online, and there are also books)
- bus network
- star network
- ring network
- mesh network
5. Classified by transmission technology
1. Broadcast network. All networked computers share a common communication channel. When one computer sends a packet of messages over a shared communication channel, all other computers "listen" to the packet. A computer that receives the packet will check the destination address to decide whether to accept the packet.
The local area network basically adopts broadcast communication technology, and the wireless and satellite communication network in the wide area network also adopts broadcast communication technology.
2) Peer-to-peer network. Each physical line connects a pair of computers. If there is no direct connection between the two communicating hosts, the packet transmission between them will be received, stored and forwarded through the intermediate node until reaching the destination node. Whether to adopt packet storage and forwarding and routing mechanism is an important difference between point-to-point network and broadcast network, and wide area network basically belongs to point-to-point network.
6. Classification by transmission mechanism
Transmission media can be divided into two categories: wired and wireless. Should be divided into wired network, wireless network
Six computer network performance indicators
- Bandwidth: Originally, it means that the communication line is allowed to pass through the signal frequency range, and the unit is hz. In the computer network, the bandwidth means the ability of the network communication line to transmit data, which is the "highest data transmission rate" that can be transmitted by the digital channel.
- Latency: Refers to the time required for data (message/packet/bit stream) to be transmitted from one end of the network (or link) to the other, also called delay or delay, which consists of four parts: transmission delay, propagation delay, processing delay, queuing delay
- Delay-bandwidth product: refers to how many bits the sender has sent when the first bit stream at the sender is about to reach the end, so it is also called the link length in units of bits, namely: delay-bandwidth product = propagation delay * channel bandwidth
- Round-trip delay: refers to the delay from when the sender sends a packet to when the sender receives the confirmation from the receiver, the general manager’s delay, that is, the delay between two round trips. The larger the RTT, the more things can be sent , the more data, the RTT also includes the end processing time, we can read the relevant coordinate system pictures on the Internet.
- Throughput: Indicates the amount of data passing through a network (or channel, interface) per unit time. Throughput is the limit unit of network bandwidth or network rated rate b/s, etc.
- Rate: that is, the rate at which the host computer connected to the computer network transmits data on the digital channel, also known as the data transmission rate, data rate, bit rate, the unit is bit/second and the rate is 10^3
- Utilization: channel utilization and network utilization
seven formula
1. Sending delay = data length / channel bandwidth (sending rate)
2. Propagation delay = channel length / propagation rate of electromagnetic waves on the channel
3. Total delay = sending delay + propagation delay + processing delay + queuing delay
Eight Summary
This is the first part. In the first chapter, there are layered organizations, protocols, interfaces, services, ISO/OSL, TCP/IP models, which can only be placed in the next chapter. I want to finish writing these things and post them. Example questions, and then explain in your own words, I don’t know what everyone’s intentions are, please leave a message in the comment area