Computer Networks
Computer-Networks(计算机网络课件)
– TCP, UDP
• network: routing of datagrams from source to destination
– IP, routing protocols
• link: data transfer between neighboring network elements
2021/6/7
8
Application Layer
Our goals
• Conceptual, implementation aspects of network application protocols
• transport-layer service models
• client-server paradigm
Functions: 1. Encapsulation 2. Fragmentation and reassembly 3. Connection control 4. Ordered delivery 5. Flow control 6. Error control 7. Addressing 8. Multiplexing 9. Transmission services
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5
Protocol Functions
• Small set of functions that form basis of all protocols
• Not all protocols have all functions
– May have same type of function in protocols at different levels
ComputerNetworks
These are the physical media (such as cables, fiber optical lines, or wireless signals) that connect the devices on the network
Classification of Computer Networks
03
LAN technology
The basic concepts and characteristics of local area
• Metropolitan Area Network (MAN): A MAN is a larger network that connects multiple LANs within a Metropolitan area
• Internet: The internet is a global network of connected computers that uses the TCP/IP protocol suite to communicate It provides a wide range of services, such as email, web browsing, and file sharing
UDP (User Datagram PA rcoonnteoctcioonlel)ss protocol that
allows applications to send messages to other computers without establishing a formal connection first It does not guarantee reliable delivery of messages
计算机网络概述
计算机网络(COMPUTER NETWORK)概述主机（H, Host) 可以是大型机、中型机、小型机、微型机。
主机是资源子网的主要组成单元，它通过高速通信线路与通信子网的通信控制处理机相连接。
普通用户终端通过主机连人网内。
主机要为本地用户访问网络其他主机设备和资源提供服务，同时为远程服务用户共享本地资源提供服务。
终端(T, Terminal) 是用户访问网络的界面。
终端可以是简单的输入、输出终端，也可以是带有微处理机的智能终端。
终端可以通过主机连人网内，也可以通过终端控制器、报文分组组装与拆卸装置或通信控制处理机连入1.1网络基础知识1.计算机网络是计算机技术与又通信技术紧密相结合的产物。
计算机技术构成了网络的高层建筑，通信技术构成了网络的低层基础。
2.计算机网络是计算机科学发展的一个重要方向。
1.1 计算机网络的发展1.计算机网络在发展过程中经历了四个阶段：联机系统阶段，互联网络阶段，标准化网络阶段，网络互连与高速网络阶段。
（1）联机系统阶段：网络的雏形，终端------通信线路---------计算机的系统（面向终端的计算机通信），实际是一个联机多用户系统。
SAGE(半自动防空系统)设备组成：终端（数据收集），集中器（数据集中处理），调制解调器（数字信号与模拟信号的转换），电话线（传输模拟信号），线路控制器（串行与并串转换与差错控制），前端处理机（FEP）(数据通信控制) （2）计算机互联网络阶段：计算机----------计算机的系统。
（ARPANET）互联网的开始（3）标准化网络阶段：由于网络的发展，采用分层方法解决网络的各种问题，一些公司开发出自己的网络产品：IBM的SNA(系统网络体系), DEC的DNA.在1984年由ISO颁布了”开放系统互连参考模型”（OSI/RM）,制定网络结构由七层组成，又称为”七层模型”,不同公司的网络可以互连。
（4）网络互连与高速网络：90年代以后，更大的网络互连和信息高速公路。
计算机网络技术名词解
计算机网络技术名词解计算机网络技术名词解释计算机网络技术是现代信息技术的重要组成部分，它涉及到大量专业术语和概念。
以下是一些常见的计算机网络技术名词及其解释：1. 计算机网络（Computer Network）：由多台计算机通过通信线路相互连接，实现资源共享和信息传递的系统。
2. 互联网（Internet）：全球最大的计算机网络，由数以百万计的计算机和服务器组成，使用TCP/IP协议进行通信。
3. 局域网（Local Area Network, LAN）：在较小地理范围内（如办公室、学校或家庭）的计算机网络。
4. 广域网（Wide Area Network, WAN）：覆盖较大地理范围的计算机网络，如城市、国家或跨越国界。
5. 无线网络（Wireless Network）：不使用物理电缆连接的网络，通过无线电波传输数据。
6. 以太网（Ethernet）：一种局域网技术，使用电缆连接计算机和网络设备。
7. 路由器（Router）：连接不同网络的设备，负责在网络之间转发数据包。
8. 交换机（Switch）：局域网内的设备，用于连接多台计算机或网络设备，提高数据传输效率。
9. 网关（Gateway）：连接不同类型网络的设备，负责数据格式转换和路由选择。
10. 协议（Protocol）：计算机网络中用于规定数据交换格式和规则的一套标准。
11. TCP/IP（Transmission Control Protocol/Internet Protocol）：互联网的基础协议，负责数据的传输和路由。
12. IP地址（IP Address）：分配给网络中每个设备的唯一标识符。
13. 子网掩码（Subnet Mask）：用于定义IP地址中网络部分和主机部分的位掩码。
14. 域名系统（Domain Name System, DNS）：将域名转换为IP地址的系统。
15. HTTP（HyperText Transfer Protocol）：用于从网络传输超文本到本地浏览器的协议。
Computer network中英文对照简介
Computer network计算机网络A computer network is a group of more computers connected to each electronically. This means that the computers can "talk" to each other and that every computer in the network can send information to the others. Usually, this means that the speed of the connection is fast - faster than a normal connection to the Internet.计算机网络是一组多台计算机连接到每个电子。
这意味着计算机可以“讲”给对方，并且每一个在网络上的计算机可以将信息发送到其他。
通常情况下，这意味着连接速度快 - 速度比正常的连接到互联网。
Some basic types of computer networks include:▪ A local area network (often called a LAN) connects two or more computers, and may be called a corporate network in an office or business setting.▪An "internetwork", sometimes called a Wide Area Network (because of the wide distance between networks) connects two or more smaller networks together. The largest internetwork is called the Internet.计算机网络的一些基本类型包括：局域网络（通常被称为一个LAN）连接两个或更多的计算机，并可能被称为一个企业网络，在办公室或业务设置。
computer networks(Tanenbaum)【第6章 传输层】
第六章 传输层传输层解决一个应用进程与另外一个应用进程之间的数据传输的问题。
对网络进行分类，通常也是以传输层为界限来进行分类的：1、 把网络分为通讯子网和资源子网（传输层分在了上面）通讯子网用于传递数据，它不关心数据的意思，通讯子网只有7层协议中的下面三层；资源子网（网上的所有主机）的设2、 传输服务的使用者和传输服务的提供者（传输层分在了下面）传输层以上是应用进程自己要处理的东西，如：进程要发送什么消息，如何理解消息；传输层以下（包括传输层）为进程之间的通讯提供传输服务。
对于需要进行数据通讯的应用进程来讲，它不管数据传输是如何实现，它只是将要传输的数据交给传输层就行了，因此传输层为高层的用户屏蔽了通讯的细节，同时也提供了一组通讯的接口。
的服务质量很好，则传输层的实现就比较简单，只需要提供通讯进程的标识就可以了；如果通讯子网提供的服务质量不好，则所有的数据传输的可靠都必须由传输层自己来保证。
传输服务一、传输层的功能及在协议层中的作用 1、传输层在OSI 模型中的位置1)介于通讯子网和资源子网之间，对高层用户屏蔽了通讯的细节2)弥补了通讯子网所提供服务的差异和不足，提供端到端之间的无差错保证 3)传输层工作的简繁取决于通讯子网提供服务的类型 2、传输层与上下层之间的关系传输层使高层用户看到的好像就在两个传输层实体之间有一条端到端的、可靠的、全双工的通信通道（即：数字管道） 二、传输层为上层提供的服务1、 面向连接的服务（即：可靠的服务）：通讯可靠，而且是按序传输的，对数据有效验和重发（针对数据包丢失，传输层采用重传机制解决）针对按序传输（发送顺序和接受顺序是一样的），传输层采用缓冲区来解决：当一个数据到达后，在交给应用进程处理前，传输层要看收到的数据的序号，若序号排在该数据前面的数据没有收到，则收到的数据会暂存在缓冲区，等前面序号的数据到达后，再一起交给应用进程。
如：TCP/IP 模型中应用层协议FTP 、Telnet 等 2、 面向非连接的服务（即：不可靠的服务）：提供的是不可靠的传输，对数据无效验和重发，通讯速率高，如：TCP/IP 模型中应用层协议SNMP 、DNS 等 三、传输服务原语1、传输服务原语是应用程序和传输服务之间的接口1)一个典型的面向连接的服务原语（采用C/S 的工作方式提供服务）2、TPDU 的发送过程3、 伯克利套接字（Berkeley Sockets ）在TCP/IP 协议当中，用得最多的传输层服务原语就是伯克利套接字。
Computer Networks
Computer NetworksIntroduction:Computer networks refer to the interconnected system of devices like computers, routers, switches, servers, etc. that facilitate data communication and exchange between different nodes over a shared channel or medium. These interconnected nodes can be located in remote areas and work collaboratively to accomplish the required tasks within a network.The concept of computer networking has revolutionized the way communication is conducted among different entities and is responsible for the birth of the digital era. It lays the foundation for modern-day activities like online shopping, social networking, e-learning, cloud computing, and telecommunication services.In this article, we will discuss the architecture, protocols, and standards of computer networks, along with their advantages and limitations.Architecture of Computer Networks:The architecture of computer networks can vary depending on factors like the size of the network, the geographical area they cover, and the devices used. Some of the widely used network architectures are:1. Local Area Network (LAN):A Local Area Network connects computers within a confinedgeographic area like a building, a campus or an office. LANs can be wired or wireless and utilize technologies like Ethernet, Token Ring, or Wi-Fi.2. Wide Area Network (WAN):Wide Area Networks cover a large geographic area and connect several LANs or other WANs. The internet is an example of a Wide Area Network that connects thousands of computers globally. WANs operate over technologies like leased lines or satellite connectivity.3. Metropolitan Area Network (MAN):Metropolitan Area Networks connect devices within a city or a town and are used for high-speed data exchange. They use optical fibers, microwave, and WiMAX technology to provide connectivity.4. Virtual Private Network (VPN):Virtual Private Networks are used to provide secure communication between remote sites or users over the internet. They use encryption and tunneling protocols to ensure data privacy during communication.Protocols and Standards:Several protocols and standards are followed in computer networks to ensure reliable and secure data exchange. Some of thecommonly used protocols are:1. Transmission Control Protocol (TCP):TCP is a transport layer protocol responsible for establishing, managing, and terminating connections between devices. It ensures reliable data exchange by maintaining packet sequence and acknowledging the successful delivery of packets.2. Internet Protocol (IP):IP is a network layer protocol responsible for addressing, routing, and fragmentation of packets. It takes care of delivering the packets to their destination and ensures that all packets arrive without being lost or duplicated.3. User Datagram Protocol (UDP):UDP is a transport layer protocol that provides connectionless communication between devices. It is used when less reliable but faster communication is required, like in online gaming oraudio/video streaming.4. Simple Mail Transfer Protocol (SMTP):SMTP is a protocol used for sending and receiving emails over the internet. It operates in the application layer and uses TCP to ensure reliable communication.Advantages of Computer Networks:1. Improved Communication:Computer networks enable real-time communication and collaboration in an organization, allowing employees to communicate and share information with each other, regardless of their location.2. Resource Sharing:Computer networks allow resources like printers, scanners, and storage devices to be shared among users, reducing costs and improving efficiency.3. Centralization:Computer networks facilitate centralized storage of data, making it easier for organizations to manage and analyze large amounts of data.4. Cost-Effective:Computer networks provide cost-effective solutions for communication, file sharing, software licensing, and system management.Limitations of Computer Networks:1. Security Threats:Computer networks are prone to security threats like hacking, viruses, and malware, which can cause data breaches and lead to financial losses.2. Technical Expertise:Computer networks require technical expertise to maintain and troubleshoot problems, which can be expensive for small organizations.3. Reliance on Technology:Organizations heavily rely on computer networks, and any downtime of the network can cause a significant loss of productivity and revenue.Conclusion:In conclusion, computer networks are the backbone of the digital era, enabling communication and collaboration among different entities. The architecture, protocols, and standards that are followed ensure reliable and secure data exchange. However, with advantages come limitations, and computer networks are no exception. To mitigate these limitations, organizations should implement best practices like regular backups, using firewalls, and training employees in security practices. With proper implementation and management, computer networks can provide significant gains in productivity and efficiency.5. Scalability: Computer networks can be scaled up or down as per therequirements of an organization. This flexibility allows organizations to expand or shrink their infrastructure based on their needs, making it cost-effective.6. Remote Access:Computer networks allow remote access to resources and applications, enabling employees to work from any location, increasing productivity, and reducing travel costs.7. Enhanced Customer Service:Computer networks enable organizations to provide better customer service, like online support, instant messaging, and video conferencing. This improves customer satisfaction, loyalty, and retention.8. Competitive Advantage:Computer networks provide a competitive advantage to organizations by promoting innovation, enabling faster decision-making, and improving business processes. This helps organizations stay ahead of their competitors.9. Easier Collaboration:Computer networks make it easier for employees to collaborate on projects or documents, increasing productivity and reducing errors. Collaboration platforms like SharePoint and Google Drive enable teams to work together seamlessly and efficiently.10. Disaster Recovery:Computer networks make disaster recovery easier by allowing organizations to backup critical data and applications on a remote server. In case of a disaster, the organization can quickly restore its data and resume operations, minimizing downtime and financial losses.Limitations of Computer Networks:1. Security Threats:As mentioned earlier, computer networks are prone to security threats like hacking, viruses, and malware. These threats not only lead to data breaches and financial losses but also affect an organization's reputation.2. Technical Complexity:Computer networks are complex systems that require technical expertise to manage and troubleshoot issues. Small organizations may not have the resources to hire IT personnel, which means they have to rely on third-party vendors, increasing costs.3. Reliance on Technology:Organizations heavily rely on computer networks, and any downtime can lead to significant financial losses and impact their reputation. Furthermore, organizations may face legal issues if databreaches occur due to negligence or inadequate security measures.4. Compatibility Issues:Organizations may face compatibility issues when integrating different systems or devices into their network. This can make it difficult to share data or resources between different departments.5. Cost:Setting up and maintaining a computer network can be expensive, especially for small organizations. The cost of hardware, software licensing, and IT support can be a significant financial burden.Conclusion:Computer networks have revolutionized the way organizations communicate, collaborate, and conduct their operations. They provide several benefits like improved communication, resource sharing, cost-effectiveness, and scalability. However, they also face limitations like security threats, technical complexity, and compatibility issues. Organizations can mitigate these limitations by implementing best practices and following industry standards.A well-managed and secure computer network can provide significant gains in productivity, efficiency, and competitive advantage.。
有关计算机网络的英文作文
有关计算机网络的英文作文English:Computer networks play a crucial role in our modern society, allowing people to communicate, share resources, and access information seamlessly. The development and advancement of computer networks have transformed the way we live and work, enabling global collaboration, real-time communication, and efficient data sharing. In today's interconnected world, computer networks not only connect devices and systems but also connect people from different parts of the world, breaking down geographical barriers and enabling diverse and inclusive interactions. The evolution of computer networks from simple local area networks to complex and expansive wide area networks has propelled the growth of businesses, education, and innovation, amplifying the potential for information exchange and technological progress. However, with the increasing reliance on computer networks, the issue of cybersecurity has become a prominent concern. The protection of sensitive data, privacy, and infrastructure from cyber threats and attacks has become paramount in ensuring the reliability and security of computer networks. As technology continues to evolve, the future ofcomputer networks holds infinite possibilities, from the integrationof emerging technologies like IoT and 5G to the expansion of virtual and augmented reality experiences, thereby redefining the way we connect, communicate, and interact in the digital age.Translated content:计算机网络在我们现代社会中扮演着至关重要的角色，使人们能够无缝地交流、共享资源和获取信息。
计算机网络简介英语作文
计算机网络简介英语作文English: Computer network, as the backbone of modern communication, plays a crucial role in connecting people, sharing resources, and facilitating communication. It is a system that consists of interconnected computing devices that can communicate and exchange data with each other. Computer networks can be classified into different types, such as local area network (LAN), wide area network (WAN), and the internet. LAN connects computers and devices within a limited area, while WAN covers a larger geographical area and often connects multiple LANs. The internet, on the other hand, is a global network that connects millions of devices all around the world. With the advancement of technology, wireless networks have become increasingly popular, allowing devices to connect without the need for physical cables. Overall, computer networks have revolutionized the way we communicate, work, and access information, making it an indispensable part of our daily lives.中文翻译: 计算机网络作为现代通信的支柱，对于连接人们、共享资源和促进沟通起着至关重要的作用。
计算机网络基础知识
计算机网络基础知识第1章Computer Network (1)1．1 Computer Network的基本概念 (1)1．2 地址和协议的概念 (2)1．2．1地址和协议 (2)1．2．2 TCP/IP协议 (2)1．2．3 IP地址 (3)1．2．4 域名地址 (3)第2章有线网络和无线网络知识 (5)2．1 有线网络的特点 (5)2．1．1 速度可做到更快 (6)2．1．2 投入低廉 (7)2．2 无线网络的特点 (8)2．2．1 更具灵活性 (9)2．2．2 速度只有百兆，但使用更方便 (11)2．2．3 安全性已能保障普通应用 (12)2．2．4 价格虽高于有线，但已可接受 (12)第3章无线局域网的设置 (13)3．1 路由器的设置 (13)3．2 电脑IP地址的设置 (13)3．3 无线网卡设置 (17)第4章无线局域网安全设置 (21)4．1 设置取消SSID广播 (21)4．2 无线数据加密 (23)第1章Computer NetworkComputer Network，是指将地理位置不同的具有独立功能的多台计算机及其外部设备，通过通信线路连接起来，在网络操作系统，网络管理软件及网络通信协议的管理和协调下，实现资源共享和信息传递的计算机系统。
1．1 Computer Network的基本概念Computer Network通俗地讲就是由多台计算机（或其它Computer Network设备）通过传输介质和软件物理（或逻辑）连接在一起组成的。
总的来说Computer Network的组成基本上包括：计算机、网络操作系统、传输介质（可以是有形的，也可以是无形的，如无线网络的传输介质就是空气）以及相应的应用软件四部分。
一个网络可以由两台计算机组成﹐也可以拥有在同一大楼里面的上千台计算机和使用者。
我们通常指这样的网络为局域网(LAN﹐LocalAreaNetwork)。
在局域网中，工作站的数量在几十到两百台次左右，距离可以是几米至10公里以内，一般位于一个建筑物或一个单位内。
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Connection-oriented transport: TCP
segment structure reliable data transfer flow control connection management
Principles of congestion control
TCP congestion control
Transport Layer 3-8
How demultiplexing works
host receives IP datagrams
each datagram has source IP address, destination IP address
each datagram carries 1 transport-layer segment
services not available:
delay guarantees bandwidth guarantees
application transport network data link physical
network data link physical
ห้องสมุดไป่ตู้
network data link physical
host 1
PP11 application P2 transport network link physical
host 2
Computer Networks – Transport Layer
P4 application transport network link physical
host 3
Connectionless demux (cont)
DatagramSocket serverSocket = new DatagramSocket(6428);
P3
P3
PP11
SP: 6428 DP: 9157
SP: 6428 DP: 5775
client IP: A
SP: 9157 DP: 6428
TCP congestion control
/ 天津塔吊租赁 河北塔吊租赁 西安塔吊租赁 塔吊租赁
Computer Networks – Transport Layer
Transport Layer 3-2
Outline
Transport-layer services
Computer Networks – Transport Layer
Transport Layer 3-12
reliable data transfer
flow control
congestion control
learn about transport layer protocols in the Internet:
UDP: connectionless transport
TCP: connection-oriented transport
Connectionless demultiplexing
Create sockets with port numbers:
DatagramSocket mySocket1 = new DatagramSocket(99111);
DatagramSocket mySocket2 = new DatagramSocket(99222);
Transport Layer 3-6
Outline
Transport-layer services
Multiplexing and demultiplexing
Connectionless transport: UDP
Principles of reliable data transfer
each segment has source, destination port number (recall: well-known port numbers for specific applications)
host uses IP addresses & port numbers to direct segment to appropriate socket
rcv side: reassembles segments into messages, passes to app layer
more than one transport protocol available to apps
Internet: TCP and UDP
application transport network data link physical
Computer Networks – Transport Layer
Transport Layer 3-7
Multiplexing/demultiplexing
Demultiplexing at rcv host:
delivering received segments to correct socket
IP datagrams with different source IP addresses and/or source port numbers directed to same socket
Computer Networks – Transport Layer
Transport Layer 3-10
network data link physical
network data link physical
network data link physical
network data link physical
network data link physical
application transport network data link physical
Computer Networks – Transport Layer
Transport Layer 3-4
Transport vs. network layer
network layer: logical
communication between hosts
transport layer: logical
= socket
= process
Multiplexing at send host:
gathering data from multiple sockets, enveloping data with header (later used for demultiplexing)
application P3 transport network link physical
communication between processes
relies on, enhances, network layer services
Household analogy:
12 kids sending letters to 12 kids
processes = kids
app messages = letters in envelopes
between app processes running on different hosts
transport protocols run in end systems
send side: breaks app messages into segments, passes to network layer
each socket identified by its own 4-tuple
Web servers have different sockets for each connecting client
non-persistent HTTP will have different socket for each request
32 bits source port # dest port #
other header fields
application data
(message)
TCP/UDP segment format
Computer Networks – Transport Layer
Transport Layer 3-9
Principles of congestion control
TCP congestion control
Computer Networks – Transport Layer
Transport Layer 3-3
Transport services and protocols
provide logical communication
hosts = houses
transport protocol = Ann and Bill
network-layer protocol = postal service
Computer Networks – Transport Layer
Transport Layer 3-5
Internet transport-layer protocols
source IP address
source port number
dest IP address
dest port number
recv host uses all four values to direct segment to appropriate socket
Server host may support many simultaneous TCP sockets:
Computer Networks