计算机网络英语.ppt

UUCP


UUCP 即UNIX间复制协议(Unix to Unix Copy Protocol)的缩写，它同时包括一个电脑程序以及一个协 议，UUCP允许在未连上Internet的UNIX主机间远程执 行命令以及传送文件，email或netnews.UUCP包是由 多种程序组成，包括uucp,uuxqt(front ends for remote copy and execution),uucico（通信程 序）,uustat，以及uuname.现在已经很少使用Modem 来进行通信了，但是有时这个协议仍然在TCP/IP上使用。 在广泛使用Internet全球通信之前，电脑间只能组建非 常小型的网络连接或是点对点连接.UUCP允许机器间可以 进行类似Fidonet（Fidonet在DOS系统上非常流行， UUCP完全模仿Fidonet）的消息交换
TCP/IP


TCP Transmission Control Protocol TCP is responsible for verifying the correct delivery of data from client to server. IP Internet Protocol IP is responsible for moving pacekt of data from node to node.
LAN


Definition: a kind of computer network that spans a relatively small area. Feature: topology(拓扑) protocols(协议) media(媒介)
Topology
Bus topology

Transmission of Information
Well-understood basics From physics
Energy Electromagnetic wave propagation
From mathematics
Coding theory
Transmission Media
The following two conditions must be met for the light rays in a fiber to be reflected back into the fiber without any loss due to refraction(折射):
➢ The core of the optical fiber has to have a larger index of refraction (n) than the material that surrounds it. The material that surrounds the core of the fiber is called the cladding.
Digital signal is a sequence of binary voltage pulses (0’s and 1’s).
Digital transmission avoids the noise problem by encoding the analog signal into digital form. The digitized version is then
Single-mode fiber has a much smaller core that only allows light rays to travel along one mode inside the fiber

unicast 英 [释义] 单播
Status n.地位，状态，身份
Serial a.连续的n.序列
Summary n.摘要，总结
Grip v.握紧n.紧握
Multilink 多链路
Dialer n.拨号器
Encapsulate v.压缩
Encapsulation n.封装
Primary adj.基本的
ethernet n.以太网
install n.v.安装
entry n.入口
execute v.执行
controller n.管理者，控制者，控制器
switch n.开关erminal adj.末端的n.终端
interface n.接口
VLAN＝virtual local area network
disabled 英 adj. 残废的，有缺陷的; v. ( disable的过去式和过去分词) 使无效
generation n. 产生; 一代人; 代（约30年），时代;
digest 英 vt.& vi. 消化; 整理;
modified 英 adj. 改良的，改进的，修正的; v. 修饰; ( modify的过去式和过去分词 ) 修改，更改;
mode 英 n. 方式; 状况; 时尚，风尚; 调式
update 英 vt. 更新，使现代化; 校正，修正; n. 现代化; 更新的信息; 更新的行为或事例
updater 英 更新器;
valid 英 adj. 有效的; 有法律效力的; 正当的; 健全的
client 英 n. 顾客; 当事人; 诉讼委托人; [计算机] 客户端
access 英 n. 入口，出口; 接近，进入; 增长; 爆发; vt. 接近，进入; 使用，接近，获取

异步
Users can send and receive emails at different times, providing flexibility in communication.
附件 support
Emails can include attachments of various file types, allowing users to send documents, images, and other files.
The structure of the Internet is decentralized, with no single authority or centralized control. Instead, it relies on a peer-to-peer model, where each node on the network has equal status and can communicate directly with other nodes. This structure allows for greater scalability and resilience, as well as faster information dissemination.
The definition of the Internet
The origins of the Internet can be traced back to the 1960s, when the US Defense Advanced Research Projects Agency (ARPA) developed the ARPANET, a network of computers used for research and communication.

介绍编程语言的种类和分类，如面向过程、面向对象、函数式、脚本等。
2 常见的编程语言介绍
介绍常见的编程语言，如C、Java、Python等的特点和应用场景。
3 编程语言的发展趋势
介绍编程语言的发展趋势，如人工智能、云计算、大数据等领域的编程语言需求。
软件工程
软件工程的定义和目标
介绍软件工程的定义、目标和 方法，如需求分析、设计、编 码、测试、维护等阶段。
操作系统的层级结构
介绍操作系统的层级结构，如内核、文件系统、进程管理等，并阐述它们之间的关系。
计算机网络
计算机网络的概念和分 类
介绍计算机网络的概念、分 类、组成和作用。
计算机网络的拓扑结构
介绍计算机网络的拓扑结构， 如星型、环型、总线型等， 并分析它们的优缺点。
网络协议和标准
介绍网络协议和标准，如 TCP/IP、HTTP、FTP等， 并重点讲解他们的实现机制 和应用场景。
分析未来计算机专业面临的挑战和机遇，展望 未来计算机技术的发展趋势。
介绍内存、硬盘等存储器的种类 和使用方法。
输入设备和输出设备的分类
介绍键盘、鼠标、打印机等输入 输出设备的分类、特点，以及各 种接口。
操作系统
操作系统的概念和作用
介绍操作系统的定义、作用以及各种操作系统的特点与应用场景。
常见的操作系统介绍
介绍常见的操作系统，如Windows、Linux、iOS等的特点与应用场景。
软件开发的过程和方法
介绍软件开发的过程，如瀑布 模型、敏捷开发、DevOps等， 并重点讲解它们的优缺点和应 用场景。
软件测试和维护
介绍软件测试和维护的方法和 工具，如黑盒测试、白盒测试、 自动化测试、代码重构等信息安全的定义、作用和意义，以及信息安全的保障措施与体系。

Chapter 2 The Physical Layer
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2.5.3 The Local Loop: Modems, ADSL, and Wireless
Figure 2-23. The use of both analog and digital transmission for a computer to computer call. Conversion is done by the modems and codecs.
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Chapter 2 The Physical Layer
DTE
DCE
传输介质 DCE
DTE
用户环境
通信系统
Chapter 2 The Physical Layer
用户环境
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Chapter 2 The Physical Layer
DTE: Equipment that hopes to connect the network. Such as computer, terminal, etc.
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Chapter 2 The Physical Layer
The definition of physical layer:
the interface between DTE(Data
Terminal Equipment) and
DCE(Data Communications
Equipment)
Chapter 2 The Physical Layer
Chapter 2 The Physical Layer
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2.5.1 Structure of the Telephone System
(a) Fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy.

Development of computer network
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HOST
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HOST

TTT
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HOST CCP
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CCP
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HOST
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CCP
C CommunicaCt
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HOST
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ion subnet
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Resource subnet
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computer network vs. distributed system
Wide Area Networks(2)
❖A stream of packets from sender to receiver. ❖Store-and-forward (packet-switched): a packet
is stored in an intermediate router in its entirety, stored there until the required output line is free, and then forwarded.
❖ Software: This is what actually makes computer networks–not the hardware!
➢ Protocols: describe how two communicating parties exchange
information.
➢ Services: describe what a network offers to parties that want

To line—Here is where you type the e-mail address of the person to whom you are sending the e-mail. You can put multiple addresses on this line, allowing you to send your message to many people. cc and bcc lines—They are used to copy the message to people who are not the primary readers, like your supervisors or others who might be interested in your conversation. The cc line shows your message's recipient that others are receiving copies of the message too. The bcc line("blind cc") allows you to copy your messages to others without anyone else knowing.
Yes Can you receive and send messages? Can you forward documents to others? Can you receive and send attached documents? Do you sort your e-mail message into folders? Can you send one e-mail message to multiple peoples? Have you created and used a signature file? Are you on any mailing lists (listservs)? Do you know what flaming is? Do you know what spam is? Do you know what netiquette (network etiquette) is?

What is
the Computer Network Technically, Network is defined as "If at least one process in one computer is able to send/receive data to/from at least one process residing in a remote computer, then the two computers are said to be in network".
The Applications(应用 应用) 应用
A usenet newsgroup（新闻组） is
a repository usually within the Usenet system, for messages posted from many users in different locations. The term may be confusing to some, because it is usually a discussion group. Newsgroups are technically distinct from, but functionally similar to, discussion forums on the World Wide Web. News reader software is used to read newsgroups.
The Applications(应用 应用) 应用
---Video conferencing
The Applications(应用 应用) 应用
Voice over IP (VoIP网络电话) is a family of

wired links wireless links LANs

layer-2 packet is a frame, encapsulates datagram
data-link layer has responsibility of transferring datagrams from one node to adjacent node over a link

compute checksum of received segment check if computed checksum equals checksum field value:

NO - error detected YES - no error detected. But maybe errors nonetheless? More later ….

instantiation and implementation of various link layer technologies

Ethernet：broadcast channel PPP：point to point channel
chapter5-2
Link Layer Roadmap
chapter5-7

Full-duplex, Half-duplex, Simplex

Adapters Communicating
datagram sending node frame adapter link layer protocol frame adapter rcving node

link layer implemented in “adapter” (aka NIC)

Computer Networks -1-Part 2
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The Data Link Layer
• Data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer
Add a checksum (cyclic redundancy check) that should match the bits before it
Also: Provide the mechanisms so that fast senders don’t overwhelm slow receivers (flow control)
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Computer Networks -1-Part 2
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Data Link Layer
• Observation: We also need to specify how a number of computers can share a common channel (e.g. wire), that is medium access control sublayer (MAC):
– How many nanoseconds a bit lasts
– whether transmission may proceed simultaneously in both directions
– how the initial connection is established
– how it is torn down when both sides are finished

You Will Learn (continued)
Internets and Internetworking
Motivation and concept Internet Protocol (IP) datagram format and
addressing Internet routers and routing Address binding (ARP) Internet control messages (ICMP) User Datagram Protocol (UDP) Transmission Control Protocol (TCP) Protocol ports and demultiplexing
You Will Learn
Introduction
Fundamental concepts Basic definitions
Communication basics
Media and signals Asynchronous and synchronous
communication Relationships among bandwidth, throughput,
and noise Frequency-division and time-division
multiplexing
You Will Learn (continued)
Networking and network technologies
Packet switching Framing, parity and error detection Local and wide area technologies Network addressing Connection and extension (repeaters, bridges,

● What’s the problem: if you’re sharing a channel,
then two stations may decide to start frame
transmission at the same time => frame collision
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2020/9/26
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Chapter 4. The Medium Access Control Sublayer
Reading guidance:
4.2 MULTIPLE ACCESS PROTOCOLS A 4.2.2 Carrier Sense Multiple Access Protocols
2. Employ a round-robin technique: each station in turn is allowed to use the channel. Applied in token-based systems – the station that has the token may use the channel.
● A large class of networks is built on top of broadcast channels: a number of stations share the same “wire.” If one station sends, all the others get to hear it.
1. Exercise no control at all: simply let a station try to use the channel, and do something when a collision happens. Applied in contention（竞争） systems.

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Example: (n is the number of harmonics we take into account)
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Computer Networks - 02 -1
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2.1.2 Bandwidth-Limited Signals
• Example: 01100010, 8 bit for ASCII “b”
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Computer Networks - 02 -1
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Computer Networks - 02 -1
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• To understand what’s going on, we need Fourier Analysis.
• A periodic function with period T (and frequency f = 1/T ), g(t) can be written as:
the fact that the line supports only two signal values.
bps T(msec) First harmonic (Hz) # harmonics sent
300 26.67
37.5
80
600 13.33
75.0
40
1200 6.67
150.0
20
2400 3.33
2H samples. No more, no less. Consequence: Maximum transmission rate = 2H log2V bps
(where V is the number of signal values) This is for noiseless channels, say the maxim data rate of a 3-kHz noiseless channel is no more than 6000 bps, for binary transmission.

• To computer scientists, (digital) bandwidth is the maximum data rate of a channel, a quantity measured in bits/sec.
Amplitude Amplitude
••• Time
f
3f
9f
Frequency
b. Frequency-domain decomposition of the composite signal
Computer Networks, Chapter 2 The Physical Layer
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Time and frequency domain of a nonperiodic composite signal
Computer Networks, Chapter 2 The Physical Layer
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Units of period and frequency
Computer Networks, Chapter 2 The Physical Layer
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Simplex, half-duplex, or full-duTransmission
• The timing of a signal is unimportant. • Information is received and translated by agreed upon patterns.
Computer Networks, Chapter 2 The Physical Layer
Computer Networks, Chapter 2 The Physical Layer
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Type of Data