计算机导论

packets).
(传输层)：在源站点和目的站点之间整个消息的传输。(消息由一个或多个包构成)
OSI MODEL---Functons of the layers
• Session layer---5
– It controls the dialog between users. It establishes, maintains, and synchronizes the dialog between communicating systems.
(数据链路层)：将位组成叫做帧(frame)的逻辑单元。在两个邻近站点之间进行点对点的帧传输。
OSI MODEL---Functons of the layers
• Network layer---3
– Packet: the data unit handled by the network layer. – It’s responsible for delivery of a packet between the original source
router可以连接两个独立的网络而形成交互式网络(如互 联网)。
• Gateway(网关)：充当协议转换器。允许不同(协议)的网络交 换信息。工作在OSI模型的所有层上。
Repeater
• Repeater---中继器
– It’s an electronic device that regenerates data.
Flow of data in the OSI model
OSI MODEL---Functons of the layers
• Physical layer---1
– Bit: – It’s responsible for transmitting a bit stream over a physical
OBJECTIVES
After reading this chapter, the reader should be able to:
Understand the rationale for the existence of networks.
Distinguish between the three types of networks: LANs, MANs, and WANs. Understand the OSI model and TCP/IP.
(表示层)：该层关心两个系统间所交换的信息的语法（格式）和语义（意义）。在表示层对数据进行压缩(compress)和解 压缩(decompress)、加密(encrypt)和解密(decrypt)。
• Application layer---7
– It’s enables the user, whether human or sofeware, to access the network.
Note:
The OSI model is a theoretical model that shows
how any two different systems can communicate with each other.
OSI
Figure 6-1
The OSI model
Figure 6-2
and final destination, end-to-end delivering one packet. – Addressing information is added to data. Logical address, IP address. – Physical address(layer 2) change from station to station, but the logical
• (应用层)：使用户（人或软件）都可以访问网络。(如通过应用层访问网络、使用邮件服务和目录服务)
6.3 CATEGORIES
OF
NETWORKS
Figure 6-3
Categories of networks
LAN
• LAN(local area network)：
It’s designed to allow resource sharing(hardware,software,and data)between computers. A LAN can be simply defined as a combination of computers and peripheral devices connected through a transmission medium.
address (layer 3) remains unchanged from source to the destination.
(网络层)：在两个源站点和目的站点之间点对点的数据包(packet)传输。
• Transport layer---4
– Message: A message can be made of one or more packets. – It’s responsible for end-to-end delivery of the whole message(many
由标准化组织制定的用于网络设计的规范。
• Protocol(协议) --- a set of rules that controls the interaction of different devices in a network or an internetwork. (TCP/IP)
用于控制网络间不同设备间交互的一套规则。
of their underlying architecture.
开放系统互联模型---由国际标准化组织(ISO)设计的一个模型，理论上允许两个不同系统相互通信而不需 要考虑它们的底层体系结构。
• OSI模型有7层---
– Application (应用层) – Presentation (表示层) – Session (会话层) – Transport (传输层) – Network (网络层) – Data link (数据链路层) – Physical (物理层)
计算机网络：通过不同的传输介质（如电线、电缆等）连接起来的组合。
• Three types of networks
– LAN(local area network)：局域网。 – MAN(metropolitan area network)：城域网。 – WAN(wide area network)：广域网。 • Model(模型) --- the specification set by a standards organization as a guideline for designing networks. (OSI model)
6.4
CONNECTING DEVICES
Figure 6-7
Connecting Devices
Connecting Devices
• Connecting devices：连接设备。
连接设备的类型：中继器(repeater)、网桥(bridge)、路由器 (router)、网关(gateway)。
6.1
NETWORKS, LARGE AND SMALL
NETWORKS, LARGE AND SMALL
• Computer Network---a combination of systems(e.g., a computer)
connected through transmission media(e.g.,a wire,a cable, or air).
– It extends the physical length of a network.
TCP/IP ---the official protocol suite of the Internet.
6.2 OSI MODEL
OSI MODEL
• OSI (Open Systems Interconnection)---
It’s designed by the International Organization for Standardization (ISO). The model theoretically allows any two different systems (e.g., computers) to communicate regardless
medium.
(物理层)：负责在物理介质中传输位流。
• Data-Link layer---2
– Frame: organizes bits into logical units(header+data+trailer) called frames.
– It’s responsible only for node-to-node delivery of the frame. – Addressing information is added to the data. physical
局域网:通过传输介质连接起来的计算机及其外围设备的组合。
– Bus Topology(总线拓扑)：用总线来连接计算机。 (需要电缆终结器cable terminator)
– Star Topology(星形拓扑)：通过集线器(hub)或交 换机(switch)来连接计算机。
– Ring Topology(环形拓扑)：环状连接计算机。 – Mesh Topology(网形拔掉)：网状连接计算机
• Repeater(中继器)：使数据信号再生(regenerate)的设备。运 行在物理层。(从一个网络段接收信号并将其放大，再传送到 另一个网络段。)
• Bridge(网桥)：通信控制器。工作在物理层和数据链路层。 (用来分割信息流segment traffic)
• Router(路由器)：根据数据包的逻辑(网络层)地址为其选择路 由(route)。运行在OSI模型的前3层。
– Synchronization points. – It’s usually included in the application layeห้องสมุดไป่ตู้.
(会话层)：控制用户间的会话。当今大多数网络实现不使用单独的会话层，通常把它们包括在应用层中。
• Presentation layer---6
– It’s concerned with the syntax(format) and semantics(meaning)of the information exchanged between two systems.
address---source address, destination address. – It’s responsible for error handling between two adjacent
stations by adding redundant data to trailer to either correct or detect errors.
List different connecting devices and the OSI layers in which each device operates. Understand client-server models.
Contents
6.1 Networks, Large and Small 6.2 OSI Model 6.3 categories of networks 6.4 Connecting Devices 6.5 The Internet and TCP/IP Summary
Topology of LAN
Figure 6-4
Figure 6-5
MAN
MAN(metropolitan area network)：城域网。通常 使用公用通信公司提供的 服务，如电话公司。覆盖 镇或城市，并向个人用户 或组织提供服务。
Figure 6-6
WAN
WAN(wide area network)：广域 网。覆盖大范围内（州、国家和 世界）的个人计算机或局域网的 连接。由公用通讯公司安装和运 营。