Definition of computer network: Use communication devices to interconnect computer systems with different geographical locations to realize data exchange.

Definition of protocol: rules or conventions that need to be followed between communication entities in the network.

Functions of computer networks: hardware resource sharing, software resource sharing, and information resource sharing.

Classification of computer networks: According to coverage, it is divided into individual area networks, local area networks, metropolitan area networks, and wide area networks; according to topological structure, it is divided into star, bus type, ring, mesh, tree, and hybrid topological structures.

Network edge: Connect to all end systems on the network (host, smartphone, etc.).

Access network: A network that realizes the connection between the end system and the network core, such as telephone dialing, ADSL, HFC, LAN, and mobile access network.

Network core: consists of packet switching devices (routers, switches) and is responsible for data relay and forwarding.

Circuit switching: Establish a dedicated circuit for data transmission, suitable for voice communication.

Message exchange: The entire message is transmitted in storage-forwarding mode, suitable for burst data communication.

Packet switching: Split packets into packets and transmit them independently, suitable for computer networks.

Rate and bandwidth: Rate refers to the amount of data transmitted per unit time, and bandwidth refers to the maximum data rate of the link.

Delay: The transmission time of data from the source node to the destination node, including processing delay, queuing delay, transmission delay, and propagation delay.

Delay bandwidth product: the product of the propagation delay of the link and the bandwidth.

Packet loss rate: the proportion of packet loss caused by network congestion.

Throughput: The amount of data actually delivered within a unit time.

OSI reference model: seven-layer model (physical layer, data link layer, network layer, transmission layer, session layer, presentation layer, application layer).

TCP/IP reference model: four-layer model (network interface layer, network interconnection layer, transport layer, application layer).

Five-layer reference model: five-layer model (physical layer, data link layer, network layer, transport layer, application layer) combining OSI and TCP/IP models.

ARPAnet: The first packet switching network, laying the foundation for the Internet.

TCP/IP protocol cluster: the core protocol of the Internet, including TCP, UDP, IP, etc.

World Wide Web (WWW): An information retrieval system based on the HTTP protocol has promoted the popularization of the Internet.

Client/server (C/S) structure: The server provides centralized services, and the client requests services.

Pure P2P structure: direct peer communication, no central server.

Hybrid structure: Combining the characteristics of C/S and P2P, there is a central server and peer-to-peer communication.

Client/server communication: The client requests actively, and the server responds passively.

Application layer protocol: defines communication rules, such as HTTP, SMTP, FTP, etc.

Hierarchical domain name space: Domain names are composed of top-level domain names, second-level domain names, etc.

Domain name server: Responsible for domain name resolution, divided into root domain name server, top-level domain name server, etc.

Domain name resolution process: recursive resolution and iterative resolution.

Web server and browser: communicate based on the HTTP protocol.

HTTP protocol: defines request and response formats, supports persistent and non-persistent connections.

Cookie mechanism: used for user tracking and session management.

Email system: including mail server, SMTP, POP3/IMAP and other protocols.

SMTP protocol: used for mail transmission, based on TCP connection.

MIME extension: Supports the transmission of non-ASCII characters and multimedia content.

File transfer protocol: used to transfer files on the network, based on TCP connection.

Control connection and data connection: Control connection is used for command transmission, and data connection is used for file transmission.

Features of P2P technology: decentralization, high availability, load balancing.

Typical applications: BitTorrent, Gnutella, etc.

Socket types: Streaming Sockets (TCP), Datagram Sockets (UDP), Raw Sockets (RAW).

Socket API functions: create sockets, bind, listen, accept, send and receive data.

Transport layer functions: multiplexing and decomposition, flow control, congestion control.

Port number: Identifies the process of the transport layer.

Connectionless multiplexing and demultiplexing: UDP protocol.

Connection-oriented multiplexing and demultiplexing: TCP protocol.

Reliable data transmission: Ensure the correctness of data through confirmation and retransmission.

Stop-Waiting Protocol: Only one packet can be sent at a time, and wait for confirmation before sending the next one.

Sliding window protocol: allows multiple packets to be sent to improve channel utilization.

UDP datagram structure: source port, destination port, length, checksum and other fields.

UDP checksum: Simple verification, does not guarantee the correctness of the data.

TCP segment structure: source port, destination port, serial number, confirmation number and other fields.

TCP Connection Management: Three handshakes and four handshakes.

TCP reliable data transmission: serial number, confirmation number, and retransmission mechanism.

TCP flow control: sliding window mechanism.

TCP congestion control: Congestion avoidance and rapid retransmission based on AIMD algorithm.

Network layer addressing: IP addresses are used to identify devices in the network.

Forwarding and routing: Select the appropriate path to forward packets according to the destination address.

Datagram network: Each packet selects a path independently, such as an IP network.

Virtual circuit network: establish a virtual connection, such as the X.25 network.

Heterogeneous network interconnection: interconnection of different networks through routers.

Router functions: routing, data forwarding, isolated broadcast domain.

Traffic-aware routing: select paths based on link load.

Access control: Limit traffic entering the network.

Traffic regulation: Controls the speed at which data is injected into the network.

Load shedding: Discard overloaded packets to relieve network burden.

IPV4 protocol: Internet protocol with version 4, which stipulates IP address allocation and management.

ICMP protocol: used for network diagnosis and error reporting.

ARP protocol: convert IP address to MAC address.

RARP protocol: convert MAC address to IP address.

NAT protocol: network address translation to alleviate the problem of IP address shortage.

IPV6 protocol: Internet protocol with version 6, supports larger address space and automatic configuration.

Distance vector routing algorithm: such as RIP, routing is calculated based on distance vector.

Link state routing algorithm: such as OSPF, routing is calculated based on link state.

Hierarchical routing: manage routing information layered to improve scalability.

BGP protocol: Border gateway protocol, used for routing between Internet autonomous systems.

Data link layer functions: frame synchronization, error control, and flow control.

Framing: encapsulate data into frames for transmission.

Basic methods of error control: parity check, cyclic redundancy check (CRC), etc.

Error detection and error correction capabilities of error encoding: The error detection and error correction capabilities of different encoding methods are different.

Channel division MAC protocols: such as TDMA, FDMA, and WDMA, multiple access is achieved by allocating different channels.

Random access MAC protocol: such as CSMA/CD, access the channel through competition.

Controlled access MAC protocol: such as CSMA/CA, access the channel through appointment.

Features of LAN: high transmission rate, low bit error rate, short-distance transmission.

Ethernet: the most commonly used LAN technology, based on the CSMA/CD protocol.

The working principle of the switch: learn MAC address and realize the rapid forwarding of data frames.

Virtual Local Area Network (VLAN): Logically divides LANs to improve security and management flexibility.

PPP protocol: point-to-point link protocol, supporting multiple network layer protocols.

HDLC protocol: Advanced data link control protocol, commonly used for wide area network connections.

Basic concepts of data communication: signal encoding, transmission medium, transmission mode.

Data communication system model: sending end, transmission medium, and receiver.

Twisted pair: a commonly used transmission medium, low cost, suitable for short-distance transmission.

Coaxial cable: Good transmission performance, suitable for cable TV and broadband networks.

Fiber Optical: Large transmission capacity, suitable for long-distance high-speed transmission.

Wireless media: such as microwave, infrared, Bluetooth, etc., suitable for mobile devices and special environments.

Channel classification and model: wired channels and wireless channels, bandwidth limits channel capacity.

Channel transmission characteristics: attenuation, noise, interference, etc. affect the transmission quality.

Channel capacity: Shannon formula calculates the theoretical maximum transmission rate.

Basic concept of baseband transmission: direct transmission of baseband signals, suitable for digital signals.

Digital baseband transmission encoding: such as Manchester code, differential Manchester code, etc., used for clock recovery and error control.

Basic concept of frequency band transmission: modulate high-frequency carrier transmission signals, suitable for frequency band transmission of analog signals and digital signals.

There are three modulation methods in frequency band transmission: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM).

Physical layer interface overview: Define connection and communication rules for physical devices.

Physical layer interface characteristics: mechanical characteristics, electrical characteristics, functional characteristics, and procedural characteristics.

Basic structure of wireless network: base station, mobile terminal, access point, etc.

Wireless links and wireless network features: limited bandwidth, susceptible to interference, and complex mobility management.

Basic principles of mobile networks: cellular structure, frequency multiplexing, call processing.

Addressing and routing: Dynamic address allocation and routing algorithms adapt to mobility.

IEEE802.11 architecture: infrastructure model and peer model.

MAC Protocol (CSMA/CA): Random Access Protocol to Avoid Collision.

Frame structure: contains fields such as MAC header, payload and CRC check.

Cellular network architecture: composed of base station, mobile switching center, home location register, etc.

Mobility management: location update, call forwarding, roaming and other management functions.

Features of 2G/3G/4G/5G network: Continuously improve transmission rate and service quality.

Agent Discovery and Registration: The mobile node obtains the forwarding address through the agent and registers it with the hometown agent.

Tunneling technology: realizes data encapsulation and transmission across network segments.

WiMax: Broadband wireless access technology based on IEEE802.16 standard.

Bluetooth: Short-range low-power wireless communication technology, suitable for data exchange between devices.

ZigBee: Low-power, low-speed wireless sensor network standard.

Basic concepts: Protect the confidentiality, integrity and availability of network data.

Cybersecurity threats: eavesdropping, tampering, denial of service attacks, etc.

Traditional encryption methods: symmetric key encryption and asymmetric key encryption.

Symmetric key encryption algorithms: DES, AES, etc., with fast encryption speed but difficult key management.

Asymmetric key encryption algorithm: RSA, ECC, etc., with high security but complex calculations.

Message integrity detection method: digest algorithm (MD5, SHA) and hash function.

Digital signature: used to verify source and integrity, preventing forgery and tampering.

Identity authentication based on shared symmetric keys: Both parties pre-share the key and authenticate through the pre-share key.

Public key-based identity authentication: Digital certificates and public key infrastructure (PKI).

The role of one-time random numbers: increase the unpredictability and security of authentication.

The role of KDC: safely distribute keys and prevent key leakage.

The role of CA: issuance and management of digital certificates and establish trust mechanisms.

KDC or CA-based certification process: Simplify the certification process and improve security.

Basic concepts of firewalls: control traffic in and out of the network and protect internal network security.

Firewall classification: Packet filtering firewall, status detection firewall, application layer firewall.

Intrusion Detection System (IDS): Monitor and analyze network traffic, discover and alert intrusion behavior.

Secure Email Protocol (S/MIME): Encrypt and signed emails to ensure safe transmission.

Secure Sockets Layer Protocol (SSL) and Transport Layer Security Protocol (TLS): Provides encryption and authentication services for web communication.

Virtual Private Network (VPN) and IP Security Protocol (IPSec): Remote secure communication through encrypted channels.