Conclusion of The Class

Internet History, Technology, and Security

From the birth of computer, to the development of network, to the introduction of network security

History

• Data transmission depends on leased line(拨号上网)
• Store and forward networks（存储和转发网络）——BITNET

cost reduction

• packet switching
• Build a national sharing network
  
  

Layered Architecture(分层架构)

The Link Layer

• Physical transmission media, such as wired, wireless transmission and optical cable, can be regarded as a link.

Ethernet（以太网）
For conflict resolution, Ethernet adopts CSMA/CD. The device will listen to the channel before sending data. When there is no other data being transmitted, the transmission can be carried out. Otherwise, it will continue to listen in a certain period

The Internetwork Layer

（Connection problem of multiple links）

• In the layered network architecture, different layers are invisible to each other. The link layer is only responsible for the work on one link and identifies the MAC address of the device. For the network layer, it is concerned about the whole link. Whether different packets will all reach the target host, which uses the IP address.
• An Internet protocol address (IP address) is assigned to the numeric label computer network connected to each device, which uses the Internet protocol to communicate. IP address has two main functions: host or network interface identification and location addressing.
  

The Transport Layer

• The purpose of the TCP layer is to compensate for possible errors in the IP layer and make full use of available resources. Since the IP layer may lose data, the TCP layer will keep a copy of the data and continuously resend the data packets until the acknowledgement response is received. If the time is too long (too many hops), the TCP layer will resend the data.

The Application Layer

Provide a reliable "pipeline" through the transport layer，The Application Layer can realize some specific Application functions without considering the underlying technical details.

• Ports（to gain the data)

• Protocols(Follow the rules)
  HTTP
  

to be continue...