Routing and switching technology (H3C) ① - Computer network basics

Table of Contents of Series Articles

①——Computer network basics

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Textbook: "Detailed Explanation and Practice of Routing and Switching Technology" edited by H3N University, Tsinghua University Press

An overview of computer networks

1.1 Computer Network

Computer Network : A computer network is a collection of autonomous computers interconnected.
Autonomy means that each computer has autonomy and is not controlled by others; interconnection means using communication media to connect computers and achieve the purpose of mutual communication.

In layman's terms, a computer network is a network system that connects independent computers and specialized external devices distributed in different geographical areas using communication lines to form a large-scale and powerful network system, so that many computers can easily transfer information to each other and share information. resource.

1.2 Basic functions of computer networks

• Resource Sharing
• Distributed processing and load balancing
• Comprehensive information services

1.2.1 Resource sharing

• Resources are divided into software resources and hardware resources
• Software resources include data in various forms: digital information, messages, sounds, images, etc.;
• Hardware resources include various devices, such as printers, FAX (fax), Modem (modem, ie modem), etc.

The emergence of the Internet enables both parties to communicate across time and space barriers, transmit information and share resources anytime and anywhere.

1.2.2 Distributed processing and load balancing

Distributed Processing and Load Balancing : Through computer networks, massive processing tasks can be distributed to computers scattered around the world.

For example: a large ICP (Internet Content Provider) has a large amount of network traffic. In order to support more users to access its website, it has deployed WWW (World Wide Web) servers with the same content in multiple places around the world. ;Use certain technologies to enable users in different regions to see the same page placed on the server closest to them. This can achieve load balancing on each server and shorten the communication distance.

1.2.3 Comprehensive information services

Integrated information services : providing integrated information services on a set of systems.

Under the trend of diversified development, new forms of network applications are constantly emerging, such as email (E-mail), IP telephony, video on demand (VOD), online transactions (E-marketing), and video conferencing (Video Conferencing). wait.
Currently widely used IP phones use IP as a transmission protocol to integrate voice into the IP network through network technology, enabling voice communication on IP-based networks, which greatly saves long-distance phone costs and enriches the types of voice services. Similarly, video information can also be integrated into the IP network for transmission, enabling applications such as video telephony and video conferencing.

2. The evolution of computer networks

• In 1837, Samuel FB Morse of the United States and Charles Wheatstone and William Cooke of the United Kingdom took the lead in inventing the telegraph. Each letter is defined as an electrical pulse signal with different lengths.
• In 1876, Alexander Graham Bell further realized the function of transmitting sound through wires and successfully constructed the first telephone system.
• In 1945, the world's first electronic computer, ENIAC (Electronic Digital Computer), was born
• 1946. John Bardecn, Walter Brattain, and William Shockley of Bell Labs replaced vacuum tubes with transistors
• In order to handle more calculations and process tasks in batches, people began to consider using traditional telephone lines to remotely access computers using terminals (such as teletypewriters, transceivers, etc.), thus developing the prototype of the computer network - the host computer . Interconnection form.

2.1 Host interconnection period

1. Host interconnection emerged in the early 1960s and was the initial prototype of computer networks.
2. An online system based on low-speed serial connections between hosts .
3. The terminal uses a telephone line to access the computer. Since the computer sends/receives digital signals , the telephone line transmits analog signals . This requires a modem to be added between the terminal and the host to perform digital/analog conversion.

4. Its main task is to provide functions such as application execution, remote printing and data services through the connection between the remote terminal and the computer.
5. In order to reduce the connection cost of telephone communication, people realize port reuse by adding a concentrator (Concentrator) between the terminal and the modem , and the host reduces the number of telephone network connection lines that directly occupy it.
6. Example: IBM's SNA (Systems Network Architecture). The SNA gateway in the network provides end-to-end access to mainframe computers. Currently, many bank networks in my country use the SNA structure.
7. Disadvantages: Telephone communication networks are not suitable for transmitting data from computers or terminals.

First of all, the communication line fees paid by users are calculated based on the time the line is occupied, and during the entire billing time, computer data appears on the transmission line in bursts and intermittently; secondly,
due to the computer and various The transmission rates of terminals are very different, and it is difficult for terminals of different types, specifications, and rates to communicate with each other.

Measures : The data is temporarily stored in some buffers and processed before being sent or received; computer communication needs to adopt effective error control technology and find new technologies suitable for computer communication.

2.2 LAN era

1. In the 1970s, the complexity of business computing required resource sharing and collaborative operation of a large number of terminal devices, which led to the need for networked connections of a large number of local computer devices, and the Local Area Network (LAN) was born.
2. The primary LAN technology used in today's networks is Ethernet.
   In 1973, Xeroxthe company's Dr. Robert Metcalfe (the father of Ethernet) proposed and implemented the original Ethernet.
   DEC, Inteland Xeroxcooperated to develop a product standard, which was originally named DIX Ethernet after the initials of the three companies' names . Other popular LAN technologies include IBM's brand ring technology .
3. The emergence of LAN has greatly reduced the high costs for business users.
   

2.3 Internet era

A single local area network cannot meet the requirements for network diversity. In the late 1970s, wide area network technology gradually developed to connect local area networks distributed in different regions to each other. In 1983, ARPANET adopted TCP (Transmission Control Protocol) and IP (Internet Protocol) protocols as its main protocol clusters, making large-scale network interconnection possible. Separate local area networks were connected to form the Internet,'

2.4 Internet era

The 1980s and 1990s were a period of development of network interconnection. During this period, the scale of the ARPANET network continued to expand, including countless companies, campuses, ISPs (Internet Service Providers) and individual users around the world, and eventually evolved into today's Internet that extends to every corner of the world, as shown in the figure As shown in 1-5. In 1990, ARPANET was officially replaced by the Internet and withdrew from the stage of history. More and more institutions and individuals are participating in the Internet, causing the Internet to develop rapidly.

Three types of computer networks

3.1 Classification according to regional situation

Computer networks can be divided into

• Local Area Network (LAN)
• Metropolitan Area Network (MAN )
• Wide Area Network (WAN).

3.1.1 Local Area Network (LAN)

1. A local area network usually refers to a collection of communication devices (computers, printers, Odems or other devices ) that can be interconnected through a certain medium within a range of several kilometers (institutions, campuses, factories).
2. It is a network built by users themselves and using private addresses.
3. Classification: From the perspective of media access control method, it can be divided into shared LAN ¹ and switched LAN ² ; from the perspective of media, it can be divided into wired and wireless
4. Features: high data transmission rate (10Mbps ~ 100Gbps), small transmission delay (tens of microseconds), low bit error rate.
5. Advantages: Due to the extremely small distribution range of the LAN, ① easy to manage and configure ② easy to form a simple and regular topology ③ small network delay (generally less than tens of microseconds) ④ high data transmission rate ⑤ reliable transmission ⑥ flexible topology makes it
   possible Widely used, it has become a typical and effective way to realize information exchange and sharing within a limited area.
6. Application: Usually owned by an organization, often used to connect personal computers and workstations within a corporate office or enterprise to share resources (such as printers, databases, etc.) and exchange information.

3.1.2 Metropolitan Area Network (MAN)

1. City area network, referred to as metropolitan area network , refers to the computer communication network established within a city.
2. Scale: Medium scale, between LAN and WAN, usually a network connection within a city (about tens of kilometers).
3. Technology: At present, IP technology and ATM technology are mainly used.
   The metropolitan area network is divided into the metropolitan area network part and the metropolitan area network access part .
   The metropolitan area network part is the operator's network, which is planned and constructed by the operator.
   The access part of the metropolitan area network can be constructed by operators, enterprises, builders and property management departments to provide access functions and provide local services to users.

3.1.3 Wide Area Network (WAN)

1. Wide area network also known as remote network
2. Scope: tens of kilometers to thousands of kilometers, covering several countries, regions, and continents
3. Features: slow data transmission (typical rate is 56Kbps~155Mbps), relatively large delay (a few milliseconds), and inflexible topology
4. Technology: The communication subnet of the WAN can interconnect other systems using public packet switching networks , satellite communication networks , and wireless packet switching networks .
   Due to the slow speed and large delay, the website access site is only responsible for sending and receiving data. Rely on complex interconnection devices (such as switches, routers) to handle network management.
5. Topology: It is difficult to classify, and mesh structures are generally used.

3.2 Network topology

3.2.1 Total display (Bus) topology

3.2.2 Star topology

3.2.3 Ring topology

3.2.4 Mesh topology

3.3 Data exchange (data transmission technology)

3.3.1 Circuit switching

3.3.2 Packet switching

Four main indicators for measuring computer networks

4.1 Bandwidth

4.2 Delay

Five Network Standardization Organization

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1. Shared LANs are typically used in small office environments or home networks. In a shared LAN, all devices are connected through a hub, and the shared LAN broadcasts data packets to all devices through the hub↩︎

2. Switched LANs are suitable for large office environments or applications requiring high bandwidth. Use a switch to replace a hub. Switched LANs forward packets directly to target devices on demand through switches. This architecture provides higher network performance, better security, and better network management capabilities, but is also more complex and expensive. ↩︎