computer network basics
computer network system
Test point 6 Computer network hardware
The main equipment
• called host
• Generally can be divided into central station (also known as server) and workstation (client)
connect device
• network card
• Works at the data link layer
• A network card, also known as a network adapter, is an interface connecting a host computer and a network cable
• Mainly provide a fixed physical address (MAC), the only one in the world
• hub
• Works at the physical layer
• The main function is to amplify and relay
• Repeater
• Works at the physical layer
• Amplify the electrical signal to increase the effective transmission distance of the signal
• Network bridge
• Works at the data link layer
• Extend the maximum transmission distance of the network by connecting independent network segments
• switches
• Works at the data link layer
• It is a network device based on MAC address identification that can complete the function of encapsulating and forwarding data packets
• router
• Works at the network layer, using IP addresses
• With routing function, that is, to send data packets to the destination network according to an optimal path
• It is mainly used to connect LAN and WAN to realize communication between different networks
• Key devices connecting different physical networks
• Gateway
• Works at the transport layer or higher
• Also known as a protocol converter
• Mainly used to connect networks of different systems
Transmission medium
• Performance
• Transmission distance, anti-interference, bandwidth (the larger the bandwidth, the larger the channel capacity, and the higher the transmission rate), attenuation, cost performance
• Wired transmission medium
• Twisted pair, coaxial cable, optical fiber (fast transmission speed, long transmission distance, strong anti-interference, small size, light weight)
• Wireless transmission medium
• Radio frequency communication, infrared communication, microwave communication, satellite communication
Test point 7 Computer network protocol and architecture
Network protocol (protocol)
• Network protocol refers to a set of communication procedures agreed in advance to ensure orderly data exchange between independent computer systems and reasonable resource sharing.
• Composition
• Grammar
• Semantics
• Timing
• Network protocols are layered Open
Systems Interconnection Reference Model (OSI/RM)
• 7 layers
• Physical layer, data link layer, network layer, session layer, presentation layer, application layer
TCP/IP Reference Model
• De facto international standard
• TCP is Transmission Control Protocol
• IP is Internet Protocol, also known as Internet Protocol
•
• Commonly used network protocols: (1) http (Hypertext Transfer Protocol): used to transfer web page files on the World Wide Web (2) FTP (File Transfer Protocol): transfer files (3) SMTP (Simple Mail Transfer Protocol): send e-mails and transit (4) POP3 (Post Office Protocol Version 3): remote login server, get mail, delete mail (5) Telnet (remote login protocol): remote login function in the Internet (6) DNS (Domain Name System): domain name and IP Mutual conversion between addresses (7) RIP (Routing Information Protocol): exchanging routing information between network devices (8) SNMP (Simple Network Management Protocol): used to collect and exchange network management information (9) NFS (Network File System ):
Internet infrastructure for file sharing between different hosts in the network
Test point 8 The development and origin of the Internet
The development of the Internet
• Originated from American ARPANet
The Development of Internet in China
• public computer internet
• ChinaNet
• China Education and Research Network
• CERNet
• China Science and Technology Information Network
• CST
• National public economic information communication network
• (Jinqiao Network) ChinaGBN
Internet development trend
• Bigger
• Faster
• Safer
• Smarter
Scale
• ISP (Internet Service Provider)
• Mainly provide users with dial-up Internet access, www browsing, ftp, sending and receiving e-mail, BBS, Telnet and other services
Test point 9 Internet IP address and domain name system
IP address
• Composed of 32-bit binary numbers, divided into four sections, each 8-bit form a section
• The range of the maximum decimal number that can be represented by each segment does not exceed 255
• Separate paragraphs with dots
• Commonly used ABC three types of IP addresses
• Class A
• 8 digits identify the network number
• 24 digits identify the host number
• the highest digit 0
• Class B
• 16 digits identify the network number
• 16 digits identify the host number
• the highest digit 10
• Class C
• 24 digits identify the network number
• 8 digits Identifies the host number
• The highest digit is 110
•
Subnet mask
• Class A subnet mask
• 255.0.0.0
• Class B subnet mask
• 255.255.0.0
• Class C subnet mask
• 255.255.255.0
• Role
• Determine whether the IP addresses of two computers belong to the same subnet
IPv6
• Using 128-bit address length
Internet Domain Name System
• A user-oriented character host naming mechanism. This is the Domain Name System
• Regulations of the Internet Domain Name System
•
• Domain name regulations of the Chinese Internet
• The highest level is cn
• Second-level domain names (com, edu, gov, net, org)
• There are up to four levels of domain names: host name/network name, organization name, subdomain name, top-level domain name
Test point 10 Internet access methods
PSTN mode (telephone line Internet access) (public switched telephone network)
• computer
• Modem (Modem)
• telephone line
ADSL mode (Asymmetric Digital Subscriber Loop)
• The uplink rate is slow, the downlink rate is block, and the frequency band is relatively wide
LAN mode (local area network)
• No modem and phone line required
• Network card and hub required
Wireless (WLAN)
Test point 11 Internet application
Email service (SMTP, POP3)
• Emails are not interactive
• Delete messages are deleted from the server
• Email can spread viruses
• Format: username@email server name
Search Engines
• A search engine is not a browser
Instant Messaging
Internet Music and Internet Video
• Internet Music (Musical Instrument Digital Interface)
• MP3 (MPEG) Moving Picture Experts Group
• Video on Demand (VOD)
File transfer
• File transfer protocol (FTP) adopts client/server mode of operation
• Anonymous FTP: general account anonymous connects to the host
streaming application
• Streaming media refers to the continuous audio/video data stream transmitted and played in chronological order on the data network
• Three characteristics
• Continuity
• real-time
• Timing
www service
• www: World Wide Web
• HTML: Hypertext Markup Language
• HTTP: Hypertext Transfer Protocol
• URL: Universal Resource Locator
• Composed of protocol name, host name, path, file name
• www system
• www client
• www server
• hypertext transfer protocol
• works as client/server
Overview of computer networks
Test point 1 The emergence and development of computer network
definition
• Computer network refers to a system in which a group of computers with independent functions can share resources, exchange information or work together with the support of communication software through communication equipment and transmission media.
• Computer network is the product of the close combination of computer technology and communication technology
development path
• The first generation of computer network based on data communication
• Second-generation computer network based on resource sharing
• The establishment of the ARPA network marks the second generation of the development of the computer network era and is also the predecessor of the Internet
• System standardized third-generation computer network
• Open Systems Interconnection Reference Model (OSI-RM)
• The fourth-generation computer network with the Internet as the core
development trend
• Triple play
• Communications network
• computer network
• wired TV internet
• Optical communication technology
• IPV6 protocol
• 128-bit address length, theoretically there are 2 to the 128th power addresses
• Broadband access technology and mobile communication technology
Test point 2 Basic knowledge of data communication
basic concept
• Signal
• Analog signal is a continuous signal, which means that the parameters of the message are continuous
• Digital signal is a discrete signal, which means that the parameters of the message are discrete
• Frequency
• Signal bandwidth
• Data communication system
• Bandwidth of the analog channel
• The effective frequency range of transmission allowed by the channel, the difference between the upper and lower limits is in (Hz)
• The bandwidth of the digital channel (channel capacity)
• The maximum transmission rate unit allowed by the channel is bit/second (b/s)
• Baseband and Broadband
data encoding
• Encoding and decoding
• Modulation and demodulation
• Modem (Modem)
• Modulation: digital-to-analog demodulation: analog-to-digital
data communication
• Serial-parallel communication
• Serial communication, slow speed, suitable for long distance
• Simplex, half-duplex, full-duplex communication
• Simplex communication means that data signals are transmitted in only one direction
• Half-duplex communication means that signals can be bidirectional in both directions
• Full-duplex communication means that data can be bidirectionally transmitted in two opposite directions at the same time. Full-duplex communication requires two channels to transmit signals
Performance metrics for computer networks
• rate
• Bits per second (b/s, bps, ie bit per second)
• bandwidth
• Throughput
• Throughput represents the actual amount of data passing through a network per unit of time
• Latency
• BER
• Utilization
• Excessive utilization can cause very large delays. Therefore, the utilization rate is not as high as possible
Test point 3 Composition of computer network
From the physical connection
• computer system
• The task is the collection, storage and processing of information
• network nodes
• Mainly responsible for sending, receiving and forwarding information in the network
• Example: Router
• Communication link
• Can be twisted pair, coaxial cable, optical fiber and other wired media
• repeater
• Amplify digital signals
• modem
• Conversion of digital and analog signals
from logic function
• Communication subnet
• The communication subnet provides the communication function of the computer network and consists of network nodes and communication links
• resource subnet
• The resource subnet provides the ability to access the network and process data, and is composed of hosts, terminal controllers, and terminals. The host is responsible for local or network-wide data processing, providing various software, hardware and network services
Test point 4 Functions of computer network
data communication
Resource sharing (the most important feature)
distributed processing
Improve system reliability
Test point 5 Classification of computer networks
According to the coverage of the network
• Local Area Network (LAN)
• LAN transmission rate is high, reliability is good, applicable to various transmission media, construction cost is low
• Twisted pair, coaxial cable as transmission medium
• Metropolitan Area Network (MAN)
• Wide Area Network (WAN)
• Internet's largest wide area network
According to the topology of the network
• Bus topology
• Messages spread in both directions along the bus and can be received by every host on the bus
• Simple structure, easy wiring, convenient site expansion, high reliability
• Difficult fault detection and isolation, low bus load capacity
• Ring topology
• Single closed loop information travels in the same direction
• Easy to install and monitor, the maximum transmission delay time is fixed, the transmission control mechanism is simple, and the real-time performance is strong
• The failure of any computer in the network will affect the normal operation of the entire network, making it difficult to detect faults and inconvenient to add or delete nodes
• Star topology
• Each node computer is connected to the central node through a transmission line, and information is transmitted from the computer to all computers on the network through the central node. The computers of each node are connected to the central node through transmission lines, and the information is transmitted from the computer to all computers on the network through the central node.
• Transmission speed block, small error, easy expansion, easy management and maintenance, convenient fault detection and isolation
• The central node must have high reliability, once the central node fails, the entire network will be paralyzed
• Tree topology (level-by-level transmission, slow response)
• The tree topology is evolved from the bus topology. In the tree topology, any node sends information to the root node, and then returns to the entire network from the root node
• It has great advantages in expansion and fault tolerance, and it is easy to isolate errors in a small area.
• Mesh topology
• Mesh topology usually exists in optical and network sites. The advantage is that there are many paths between nodes, local failures will not affect the normal operation of the entire network, high reliability, and flexible and simple network expansion and host network access. However, the structure and protocol of this kind of network are relatively complicated, and the cost of network construction is high.
• Highest structural reliability
• Hybrid network
Divided by transmission medium
• wired network
• Wi-Fi
According to the nature of network usage
• public network
• private network