directory

  • An overview of the
  • The physical layer
  • Data link layer
  • Network layer (1) Basic knowledge
  • Network layer (2) IP address design and exhaustion
  • Network layer (3) Network layer packet transmission process
  • Network layer (4) Network layer multicast and other applications
  • Transport layer (1) Reliable transport and TCP/UDP
  • Transport layer (2) congestion control and handshake waving
  • Application layer (1) HTTP and the World Wide Web

The network definition

A network connects many computers together, whereas an interconnecting network connects many networks together through routers. Those connected to the network are called hosts. Mutual “linked” network (Internet) refers to the world’s largest, open, by a number of networks linked to each other into a specific Internet, it uses THE TCP/IP protocol family as the rules of communication.

Stage of development

  1. U.S. Department of Defense Switching Network ARPANET
  2. The three-tier Internet, covering universities and research institutes across the United States, is divided into backbone, regional, and campus (or enterprise) networks.
  3. A multi-level ISP(Internet Service Provider) structure for the Internet. Isps apply for many IP addresses from Internet management agencies, and have communication lines and routers to provide paid services. Isps are classified into trunk ISP, regional ISP and local ISP.

Internet standard setting

Developed by the Internet Society (ISOC), all standards are published in the form of RFC documents, the standard development process has 2 stages, suggested standards – Internet standards.

Internet composition

edges

Refers to all hosts connected to the Internet, also known as end systems. This part is used directly by the user. Communication between them refers to communication between computer processes. There are two kinds of communication modes: client-server mode and P2P mode. The client-server approach is the most common, for example when browsing the Web or sending E-mail. Characteristics are defined by a particular requester and server, with the client being the service requester and the server being the service provider. Peer-to-peer connection (P2P) refers to the communication between two hosts without distinguishing which one is the service requester and which is the service provider. As long as two hosts are connected to P2P software, they can be connected to each other equally. You can download each other’s shared data. For example, we use thunderbolt.

The core part of the

It provides connectivity to a large number of hosts on the edge of the network, allowing any host on the edge to communicate. Is the most complex part of the network. The router, which plays a special role, is a special computer, not a host. The main function is to achieve packet switching. The task is to forward the received packet. Previous telephone networks used circuit-switched technology. After the two ends were connected, the line remained occupied as a dedicated physical channel. Communication resources are released only after the call is complete. This method is called circuit switching. When the network resources are insufficient, a busy tone is displayed. But when the computer network transmits data, the transmission efficiency of the line is often very low during the period of communication between the two parties, because the computer transmits data in a burst, such as when the computer processes the received data waiting for return or when editing an online document. So computer networks use packet switching, mainly store-and-forward technology. We call “the whole piece of data to be sent as a message”, and when sending, “dividing into small data segments and adding headers with control information is called packet, or packet”. The router receives a packet, stores it temporarily, checks the header, and looks for the forwarding table according to the destination address in the header. Find an appropriate interface to forward the packet. This step by step operation, delivery of the final target host. The transmission process does not need a dedicated line. When forwarding, appropriate lines are found and forwarded, communication resources are occupied successively (between routers), not the whole line is occupied. And the Internet is a network structure, many-to-many relationship, one broken, can go to other lines.

Common indicators of computer networks

  • Rate: The number of bits propagated per unit of time over the network. It refers to the rated rate rather than the actual rate over the network.
  • Bandwidth: The capacity of channels in a network to carry data. Indicates the maximum data rate that can pass through the network in a unit time. The unit is bit/s. The higher the bandwidth of a line, the higher the maximum data rate that can be transmitted.
  • Throughput: indicates the actual data volume of a network per unit time. Measurements that embody real-world networks.
  • Delay: Indicates the time it takes for data to travel from the network to the destination. It is transmission delay (data is sent by the sender) + transmission delay (information is transmitted by the router) + queuing delay (waiting for processing in the router).
  • Latency bandwidth product: transmission latency ✖️ bandwidth, which indicates the maximum amount of data that a link can hold. It can be imagined that the cross section of a cylinder is the product of bandwidth and propagation delay is the product of height.
  • Round-trip time: Round-trip time of data transmission
  • Utilization: Channel utilization is the percentage of time a channel is utilized. Network utilization is the weighted average of channel utilization of the whole network. Not the higher the better, the higher the utilization, then the delay will be larger (similar to the quadratic function curve). General control in 50%, more than the capacity expansion.