计算机网络概述(翻译版)Overview of Computer Networks

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计算机网络概述(翻译版)Overview of Computer Networks

1、 Overview of Computer Networks
1 Composition of the Internet
Network edge: computers and other devices connected to the Internet at the edge of the Internet, such as desktop computers, mobile computers, servers, and other intelligent terminal devices
Network core: A mesh network composed of packet switching devices and communication links of interconnected systems
For example: packet switching routers, link layer switches, communication links (fiber optic, copper cable, radio, laser links)

  1. Network classification
    Personal Area Network (PAN)
    A network capable of short distance communication between portable consumer appliances and communication devices
    The coverage range is generally within a radius of 10 meters, such as Bluetooth earphones, etc
    Local Area Network (LAN)
    Regional networks formed in local areas, such as corporate networks
    The distribution area is limited and can range from large to small, ranging from building to office networking
    Computer WLAN access, printer sharing, and more
    Metropolitan Area Network (MAN)
    A network covering a city
    Wide Area Network (WAN)
    Covering a large geographical area, even covering regions and countries
  2. Access network
    The purpose of access network
    The purpose of access network is to connect hosts to edge routers
    An edge router is the first router on the path from the host end system to any other remote end system
    Various heterogeneous networks are accessed through edge routers
    Access network classification:
    Fiber to Home FTTH
    Digital User Line DSL
    coaxial cable
    wireless access
    Corporate and Home Networking
  3. The two major functions of the network core
    ① Routing
    Determine the path used for data grouping from the source to the target (global operation)
    ② Forward
    Routers or switches forward received data packets (i.e., move to an output interface of the device) (local operation)
  4. Network layering
    ① OSI 7-layer model
    Insert image description here
    Data Link Layer
    Implement data transmission between adjacent network entities
    Framing: Extracting complete frames from the bitstream of the physical layer
    Error detection and correction: providing possibilities for reliable data communication
    MAC address: 48 bits, theoretically a unique network identifier, burned on the network card, inconvenient to change
    Flow control to avoid “flooding”: When a fast sender encounters a slow receiver, the receiver’s cache overflows
    Access Control (MAC) on Shared Channels: Simultaneously transmitting signals on the same channel. Just like: if the same WiFi hotspot (AP) is connected to multiple wireless users (mobile phones), multiple users need to send data at the same time. How to control the sending order?
    Network Layer
    Send data packets across the network from the source device to the destination device (host to host)
    Routing: Selecting a forwarding path from the source to the destination in the network, often dynamically selecting the best path based on network accessibility, or static routing can be used
    Routing protocol: The protocol specification followed by routers to exchange routing information, enabling a single router to obtain network accessibility and other information
    Quality of Service (QoS) control: handling network congestion, load balancing, admission control, and ensuring latency
    Heterogeneous Network Interconnection: Routing Addressing and Forwarding in Heterogeneous Addressing and Heterogeneous Networks
    Transport Layer
    Send data from the source port to the destination port (process to process)
    The network layer locates a host, and the scope of the transport layer is specific to a process on the host
    The control of the network layer is mainly aimed at operators, while the transport layer provides end-to-end data transmission control for end users
    Two types of modes: reliable transmission mode or unreliable transmission mode
    Reliable transmission: Reliable end-to-end data transmission, suitable for application scenarios that require communication quality, such as file transfer, etc
    Unreliable transmission: Faster and lighter end-to-end data transmission, suitable for application scenarios that do not require high communication quality and high communication response speed, such as voice conversations, video conferences, etc
    Session Layer
    Utilize the services provided by the transport layer to establish and maintain sessions between applications, and enable sessions to be synchronized
    Presentation Layer
    Pay attention to the syntax and semantics of the transmitted information, manage the representation methods of data, and transmit the data structure
    Application Layer
    Provide convenient network service calls for applications through application layer protocols
    ② TCP/IP 4-layer model
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原文链接:https://blog.csdn.net/leah126/article/details/131517101

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