Chapter 6 Computer Networks. Understand the rationale for the existence of networks. Distinguish between the three types of networks: LANs, MANs, and.

Chapter 6

ComputerNetworks

Understand the rationale for the existence of networks.Understand the rationale for the existence of networks.

Distinguish between the three types of networks: Distinguish between the three types of networks: LANsLANs, , MANsMANs,,and and WANsWANs..

After reading this chapter, the reader should After reading this chapter, the reader should be able to:be able to:

OOBJECTIVESBJECTIVES

List different connecting devices and the OSI layers in whichList different connecting devices and the OSI layers in whicheach device operates.each device operates.

Understand Understand client-server modelsclient-server models. .

Understand the Understand the OSI modelOSI model and and TCP/IPTCP/IP..

NETWORKS, NETWORKS, LARGE AND SMALLLARGE AND SMALL

NETWORKS, NETWORKS, LARGE AND SMALLLARGE AND SMALL

6.16.1

Network Computer network –

A combination of computers connected through transmission media.LAN (Local Area Network)MAN (Metropolitan Area Network)WAN (Wide Area Network)

Internetwork – (e.g. Internet)Networks can be connected using connecting device.

Model and Protocol

Model –the specification set by a standards organization as a guideline for designing networks.

Protocol –a set of rules that controls the interaction of different devices in a network/internetwork.

OSI MODELOSI MODELOSI MODELOSI MODEL

6.26.2

The The OSI OSI (Open Systems Interconnection)(Open Systems Interconnection) modelmodelis a is a theoreticaltheoretical model model that that shows shows how any two different systems how any two different systems can communicate with each can communicate with each other.other.

Note:Note:

OSI Model –is a framework of 7 layers that gives network designers an idea of the functionality of each separate but related layer.

Figure 6-1 The OSI model

Figure 6-2

control information is added to the data in the form of headers or trailers.

the header or trailer is dropped in each layer.

Flow of data in the OSI model

Functions of the Layers1. Physical

• transmit a bit stream over a physical medium.

2. Data-Link• Organizes bits into logical units called frames.• Node-to-node delivery

3. Network• Source-to-destination delivery of a packet.

4. Transport• Source-to-destination delivery of the entire message.

5. Session• Establishes, maintains, and synchronizes

the dialog between communicating systems.

6. Presentation• Deals with the fact that different systems use

different coding methods.

7. Application• Enables the user to access the network.

OSI Layers 實例：7

Application Layer

產品行銷：策略、合同、邀訪、樣品

6Presentation

Layer秘書：將型錄、報價單、合約翻譯成各國語言的文件格式

5Session

Layer一筆生意：寄型錄、寄報價單、寄合約、…

4Transport

Layer資料打包寄送：將資料拆開、分裝、編號成幾個信封﹐再進行郵寄

3Network

Layer快遞公司：決定使用那個機場、經由哪條路徑傳遞

2Data Link

Layer機場管理局：班次﹑泊位﹑進場 /出場時間間隔﹑收發貨物

1Physical

Layer 飛機：運送包裹

CATEGORIES CATEGORIES OFOF

NETWORKSNETWORKS

CATEGORIES CATEGORIES OFOF

NETWORKSNETWORKS

6.36.3

Figure 6-3Categories of networks

LAN (Local Area Network)

Allow resource sharing between computers.ComputersPeripheral devicesTransmission medium (e.g. cable)

3 types of topology Bus topologyStar topologyRing topology

Figure 6-4LANs

Hub – a device that facilitates connection LAN acts logically like a bus.

Star –the dominant topology today.

Figure 6-5MAN

MAN (Metropolitan Area Network) Uses services provided by a network service

provider. (Tel. Company) Individual users’ computers Organizations’ LANs

Many Tel. Company provide a popular MAN service called SMDS (Switched Multimegabit Data Services)

Prior to SMDS's arrival in 1995, the only way to connect LANs was through a dedicated private line.

Figure 6-6WAN

WAN (Wide Area Network)

The connection of individual computers or LANs over a large area (country, world).

User using a telephone line to connect to an ISP (Internet Service Provider) is using a WAN. Negotiates fee

ISP Tel. company

CONNECTINGCONNECTINGDEVICESDEVICES

CONNECTINGCONNECTINGDEVICESDEVICES

6.46.4

Figure 6-7

Connecting devices

Figure 6-8Repeater (L1)

Regenerates the signal. Extends the physical length of a network.

Repeaters operate at the first Repeaters operate at the first layer of the OSI model.layer of the OSI model.

Note:Note:

Bridge/Switch Bridge

A traffic controller Divide a long bus into smaller segments

so that each segment is independent trafficwise. Regenerate data

Switch A sophisticated bridge with multiple interfaces. A station that needs to send a frame sends it directly to

the switch.

Figure 6-9Bridge (L1-L2)

Bridges operate at the first Bridges operate at the first two layers of the OSI model. two layers of the OSI model.

Note:Note:

Figure 6-10

Switch

Router Connect LANs, MANs, and WANs. Routes a packet based on the logical address

(network layer) of the packet. Connect two independent networks: LAN-WAN,

LAN-MAN, WAN-WAN…

V.S. Bridge

filters a frame based on the physical address (data-link layer) of the frame.

Connect two segments of a LAN or two LANs belonging to the same organization.

Figure 6-11Routers (L1-L3) in an internet

Routers operate at the first Routers operate at the first three layers of the OSI model. three layers of the OSI model.

Note:Note:

Gateway (L1-L7)

A protocol converter. Understands the protocols used by each

connected network and is able to translate from one to another.

Figure 6-12 Connecting devices and the OSI model

frame

packetIP address

Mac address

internetworking

networking

ISP (Internet Service Provider)a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web, and send and receive e-mail.

ICP （ Internet Content Provider ）網際網路內容提供者。指的是在網際網路上提供各種服務內容的廠商。如 Yahoo 雅虎、 AOL 美國線上等，都是屬於 ICP 的一種。任何人只要有網路的空間放置網頁，都可以成為 ICP 。而 ICP 的收入大都來自廣告收入。

Web portalA Web site or service that offers a broad array of resources and services, such as e-mail, forums, search engines, and on-line shopping malls.

ASP (Application Service Provider)ASP 業者向軟體公司購買應用程式，然後將此程式放在 ASP 業者的機房內，然後供企業或個人以存取網路的方式連接到機房來使用應用程式，並依據使用方式與規定向客戶收取費用。

THE INTERNETTHE INTERNETANDAND

TCP/IPTCP/IP

THE INTERNETTHE INTERNETANDAND

TCP/IPTCP/IP

6.56.5

Internet

internetwork (internet)A network of networksConnect individual LANs, MANs, and WANs.

Internet – the most famous one

TCP/IP and OSI model

TCP/IP Transmission Control Protocol/Internet Protocol

A suite of protocols that officially control the Internet.

Physical and data-link layers: Does not define any specific protocol.

Network layer: Supports the Internet Protocol (IP)

Transport layer: Defines Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

Application layer: Equivalent to the combined session, presentation, and application layers

Figure 6-14 IP addresses in dotted-decimal notation

Supports the Internet Protocol (IP) Every computer connected to the Internet is identified

by a unique international address – IP address. (32bits)

TCP/IP Network layer

TCP/IP Transport layer

Defines Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)

TCP is a reliable transport protocol. It divides a message into a sequence of segments that are numbered sequentially. If one segment is lost, it is sent again. If a segment is received out of order, it is ordered with

the help of the sequence numbering mechanism.

TCP/IP Application layer

Equivalent to the combined session, presentation, and application layers of OSI model.

Communication on the Internet uses the client-server model.Client – an AP running on a local machine.Server – an AP running on a remote machine.

Client-server model

FTP File Transfer Protocol The standard protocol on the Internet for

transferring a file from one machine to another.

SMTP(Simple Mail Transfer Protocol) A user machine that is turned off will not receive email. POP(Post Office protocol) UA(user Agent)- a user interface to facilitates these

transactions

Email address

Local part – user mailbox Domain name – the computer that serves as the SMTP server

TELNET TErminaL NETwork A general client-server program on the Internet allows

remote login. Enables the establishment of a connection from a local

system to a remote system in such a way that the local terminal appears to be a terminal at the remote system.

HTTP

HyperText Transfer Protocol the underlying protocol used by the

World Wide Web. use a special kind of addressing called

URL(Uniform Resource Locator).

URL

Method – the client-server program used for transferring the documents.

Host – the computer where the information is located.

Port – the port number of server. Path – the path of the file where the

information is located.

WWW

World Wide Web Hypertext –

a document containing special text, words, and phrases that can create a link to other documents.

Page – a document of hypertext available on the web.

Home page

BrowserCoordinates all activities.

A client AP that retrieves the document.

Display the document.

Categories of Web documents

Document types: Static documents

Have fixed contents HTML

Dynamic documents Programs residing at the server site. Use CGI(Common Gateway Interface) technology

includes Perl and HTML to handle the document creation and interpretation.

Active documents The browser requests the transfer of the program.

After transfer, it is run at the browser site. Java

台灣網路資訊中心（ TWNIC ）國家級財團法人機構，以非營利為目的，是由交通部電信總局及中華民國電腦學會共同捐助設立，宗旨是以超然中立及互助共享網路資源之精神，提供 IP address分配、網域名稱(Domain Name)註冊等服務。

網路蟑螂 1999 年底，登記使用 business.com 的權利，以 75

0 萬美金的天價在拍賣網站電子海灣 (eBay.com) 賣出。

china.com 、 ibm.com apple.com whitehouse.com

即時傳訊 (Instant Messenger) 它支援在 Internet 上聊天、發送消息和文件等，另更有語

音聊天、網路攝影機等功能

1. ICQ全球最早出現的即時傳訊軟體，在 1998 年 6 月被 AOL 以 2.87 億美元所收購

2. AIM AOL Instant Messenger﹙ ﹚由 AOL 所開發出來、類似 ICQ 的即時傳訊軟體

3. QQ中國騰訊公司產品，佔中國 95% 使用人口（ 1 億 500 萬）

4. MSN 即時通由微軟所開發出來的即時傳訊軟體

5. Yahoo! 奇摩即時通由全球入口網站領導品牌 Yahoo! 所開發的即時傳訊軟體

6. YamQQ蕃薯藤 +QQ