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

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)

2. 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
3. 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
4. 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)
5. 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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