Beginners of Computer Networks-Introduction to Computer Networks

1 The formation and development of computer networks

1.1 The 4 stages of computer network development

1.1.1 The first stage-the initial formation of computer networks

The first stage can be traced back to the 1950s (1940~1950), the characteristics and landmark results of this stage.

1. Data communication technology gradually matures, laying a technical foundation for computer networks
2. The concept of packet switching laid a theoretical foundation for the formation of computer networks
3. The successful operation of ARPANET proves the correctness of the packet switching theory .
4. The wide application of TCP/IP protocol has laid a solid foundation for larger-scale Internet networks

ARPNET, like the Internet, is the iconic network in the formation of computer networks, in addition to NSFNET

ARPANET researchers initially divided network protocols into Transmission Control Protocol (TCP) and Internet Protocol (IP).
TCP: Realize the function of distributed process communication between two hosts.
IP: Realize the routing function of grouping through the communication subnet

1.1.2 The second stage-Internet formation and development

The second stage can be traced back to the 1990s (1980~1990), the characteristics and landmark achievements of this stage.

1. E-mail, FTP, TELNET, DNS and other applications show the broad application background of computer networks.
2. NSFNET allows commercial applications to accelerate the formation of the Internet.
3. The emergence of Web technology promotes the development of e-commerce, e-government and other applications
4. High-speed global information and large-scale participation of users accelerate the development of the Internet

1.1.3 The third stage-the formation and development of mobile Internet

The third stage can be traced back to the 1990s (1980~1990), the characteristics and landmark results of this stage.

1. Mobile IP technology and wireless communication technology
2. The integration of mobile communication network and Internet business
3. Wearable computing devices promote the rapid development of mobile network applications
4. Mobile Internet has become a new growth point of the information industry

1.1.4 The fourth stage-the formation and development of the Internet of Things

The fourth stage started around 2010, the characteristics and landmark results of this stage.

1. The integration of the physical world and the network world promotes the development of the Internet of Things
2. Perception technology The development of smart technology has laid the foundation for the development of the Internet of Things

Computer network develops along the trajectory of Internet-Mobile Internet-Internet of Things

1.2 Basic design ideas of packet switching technology

After vetoing the telephone switching network ( disadvantage one: low utilization of communication lines, disadvantage two: high bit error rate of telephone lines. These two points do not apply to data transmission between computers ) researchers proposed a new data exchange Technology-packet switching

1. Independence , the networked computer independently completes the receiving and forwarding of data
2. Packet , encapsulate the data to be sent into multiple short, fixed format packets
3. Store and forward , if there is no direct path between the sending host and the receiving host, the intermediate node (router) can use the store and forward method to forward the packet
4. Selection algorithm , each router can find the optimal route by selecting the algorithm according to the link state and the destination of the packet .
5. Can be combined . After receiving all the groups, combine all the groups to restore the original text.
   The three most important concepts of packet switching technology: packet, router selection, store and forward.

1.3 ARPANET design ideas

In order to meet the requirements of a "survivable network", the US Department of Defense created
APRANET and adopted the idea of ​​packet switching. The designer divided ARPANET into two parts: communication subnet and resource subnet.

The communication subnet forwarding node is implemented by a small computer called an interface message processor (IMP). The rate between IMPs is 56kbps, and each IMP is associated with multiple IMPs, ensuring the security and safety of the entire communication subnet. reliability.

There may be duplication, loss, or disorder of data.

1.4 Research and development of TCP/IP

In 1972, ARPANET researchers hoped to interconnect different types of networks, and thus proposed a device called a gateway to realize network interconnection. At this time, the gateway is a kind of router in terms of function.

In 1977, ARPANET researchers have proposed transmission control protocol (Transport Control Protocol, TPC) and the Internet network protocol (Internet Protocol, IP)
TCP realize the function of distributed interprocess communication between the source and destination hosts operating system
IP protocol is mainly used Identify the node address and realize the routing function.