Chapter 2 Networking and Internet 國立聯合大學電子工程學系蕭裕弘.

Chapter 2 Networking and Internet

國立聯合大學　電子工程學系蕭裕弘

國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘 Chapter 2: / 55

Chapter Goals

說明資料通訊的基本觀念與電腦網路的主要特性與用途

說明電腦網路的主要種類與特性介紹三種常見的電腦網路圖形結構介紹常見的通訊傳輸介質與其特性介紹通訊協定的重要性與常見的網路通訊

協定介紹網際網路的組成與相關觀念介紹網際網路的連線方式介紹數種常見的網際網路服務說明網際網路所帶來的問題


1. Introduction

Today computer is available in many offices and homes and therefore there is a need to share data and programs among various computers with the advancement of data communication facilities.

The communication between computers has increased and thus it has extended the power of computer beyond the computer room.

Now a user sitting at one place can communicate computers of any remote sites through communication channel.


Data Communication

We all are acquainted with some sorts of communication in

our day to day life.

For communication of information and messages we use

telephone and postal communication systems.

Similarly data and information from one computer system can

be transmitted to other systems across geographical areas.

Thus data transmission is the movement of information using

some standard methods.

These methods include electrical signals carried along a

conductor, optical signals along an optical fibers and

electromagnetic areas.

The modern form of communication like e-mail and WWW is

possible only because of computer networking.


Basic Elements of a Communication System

The following are the basic requirements for working of a communication system. A sender (source) which creates the message to be

transmitted. A medium that carries the message. A receiver (sink) which receives the message.


Communications Protocols

You may be wondering how do the computers send and receive data across communication links. The answer is data communication software. The data communication software instructs computer systems and devices

as to how exactly data is to be transferred from one place to another. The procedure of data transformation in the form of software is commonly

called protocol. A communications protocol or network protocol is the specification of a set

of rules for a particular type of communication.

How are you?

你好嗎？


Data Transmission Modes

There are three ways for transmitting data from one point to another: Simplex Half-duplex Full-duplex


2. Computer Network

Definition: A computer network is a system for

communication among two or more computers.

A computer network is an interconnection of various computer systems located at different places.

In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources.

The computer that provides resources to other computers on a network is known as server.

In the network the individual computers, which access shared network resources, are known as workstations or nodes.


Types of Computer Network

Computer networks may be categorized with respect to range: Personal area network (PAN)

Wireless PAN Local area network (LAN)

Wireless LAN Metropolitan area network (MAN) Wide area network (WAN)


Personal Area Network

A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person.

The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intra

personal communication), or for connecting to a higher level network and the Internet (an uplink).

Personal area networks may be

wired with computer buses

such as USB and Firewire. Wireless PANs can also be

made possible with network

technologies such as IrDA

and Bluetooth.


Local Area Network

A local area network or LAN is a computer network covering a local are

a, such as an office or a home.

Standardization efforts by the IEEE have resulted in the IEEE 802 series

of standards.

The most common wiring technology for a LAN is Ethernet (IEEE 802.

3).

Ethernet: 10 Mbps

Fast Ethernet: 100 Mbps (bits per second)

Gigabit Ethernet: 1 Gbps

10 Gigabit Ethernet: 10 Gbps

Data transfer rate: the speed with which data is moved from one place on a network to another.


Metropolitan Area Network

Metropolitan area networks or MANs are large computer

networks usually spanning a campus or a city.

For instance a university or college may have a MAN that

joins together many of their local area networks (LANs) si

tuated around site of a fraction of a square kilometer. The

n from their MAN they could have several wide area netw

ork (WAN) links to other universities or the Internet.


Wide Area Network

A wide area network or WAN is a computer network covering a wide geographical area.

The best example of a WAN is the Internet.

WANs are used to connect local area networks together, so that users and computers in one location can communicate with users and computers in other locations. TANet: Taiwan Academy Network


3. Network Topologies

A network may be represented as a collection of nodes, some of which are connected by links. A given node may have links to many

others (see diagrams below).

Network topology is determined only by the configuration of connections between nodes. Distances between nodes, physical

interconnections, transmission rates, and/or signal types are not a matter of network topology, although they may be affected by it in an actual physical network.

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Network Topologies – Star Networks

In a Star network all the client computers are connected to a central server or hub. Information between computers travels first to the Hub, which then passes it on to

the other computers on the network. This is one of the most popular forms of network used in workgroup and

departmental networks. The advantages of a star topology are:

The failure of a single computer or cable

doesn't bring down the entire network. The centralized networking equipment can

reduce costs in the long run by making

network management much easier. Disadvantages include:

Failure of the central hub causes

the whole network failure. It is slightly more expensive than

using bus topology.


Network Topologies – Bus Networks

A bus network is a network architecture in which a set of clients are connected via a shared communications line, called a bus.

Advantages of the bus are: This is the cheapest type of network to connect The Bus is easy to use and understand It is easy to extend a network by adding cable

with a repeater that boosts the signal and allows

it to travel a longer distance.

Disadvantages include: A bus topology becomes slower as network traffic increases and more

computers are added to the network. A single break in the cabling or a loose connector can bring down the whole

network.


Network Topologies – Ring Networks

Ring networks are similar to bus networks with the exception that the network is joined back to itself, so does not need a terminating computer.

In this configuration, information is exchanged via a ”token” which passes around the ring until the requesting computer(s) have received the data.

The advantages are: One computer cannot monopolize the network. It continue to function after capacity is

exceeded but the speed will be slow.

Disadvantages are: Failure of one computer can affect

the whole network. It is difficult to troubleshoot. Adding and removing computers disrupts the network.


Network Topologies – Hybrid Networks


4. Transmission Media

Transmission media are the media through which information usually moves from one network device to another.

There are several types of transmission media which are commonly used with LANs.

In some cases, a network will utilize only one type of transmission media , other networks will use a variety of transmission media types.

The type of transmission media chosen for a network is related to the network's topology, protocol, and size.

Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network.

Wired

Wired

Wire

less

Wire

less


Wired Transmission Media – UTP

Twisted pair cabling comes in two varieties: shielded and unshielded.

Unshielded twisted pair (UTP) is the most popular and is generally the best

option for school networks.

The cable has four pairs of wires inside the jacket.

Each pair is twisted with a different number of twists per inch to help

eliminate interference from adjacent pairs and other electrical devices.

The tighter the twisting, the higher the supported transmission rate and the

greater the cost per foot.


Wired Transmission Media – Coaxial Cable

Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable.

The two types of coaxial cabling are thick coaxial and thin coaxial.


Wired Transmission Media – Fiber-Optic

Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials.

It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large

amount of electrical interference. It has also made it the standard for connecting networks between

buildings, due to its immunity to the effects of moisture and lighting.


Wireless Transmission Media

Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs.

Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected.

Advantages: For longer distance, wireless communications can also take place through cellular

telephone technology, microwave transmission, or by satellite. Wireless networks are great for allowing laptop computers or remote computers to

connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or

impossible to install cables. Disadvantages:

They provide poor security. They are susceptible to interference from lights and electronic devices. They are also slower than LANs using cabling.


Examples of Wireless Transmission Media

Radio technology

Infrared

Cellular

Microwave and Satellite

公眾交換電話網路


5. Communication Protocols

Definitions:

In networking, a communication protocol or network protocol is the

specification of a set of rules for a particular type of communication.

A communication protocol is a collection of rules and procedures for

establishing, maintaining, and terminating transmissions between devices.

Protocols specify

How devices physically connect to a network

How data is packaged for transmission

How receiving devices acknowledge signals

from sender devices

How errors are handles

...


Ethernet

Ethernet has become the most widespread LAN technology in use during the 1990s to the present.

A scheme known as carrier sense multiple access with collision detection (CSMA/CD) governs the way the computers share the communication media.

CS

MA

CD


常見的乙太網路佈線方式 – 有線

集線器 (Hub)

UTP

UTP網路卡

UTP


常見的乙太網路佈線方式 – 無線

集線器 (Hub)

UTP

Access Point

USB 無線網卡

802.11b – 11 Mbps802.11g – 54 Mbps


電子系館區域網路系統

Switching Hub

Switching HubSwitching Hub

Switching Hub

校園網路

Teacher’s PCs PCs in Lab.

PCs in Lab.

DHCPServer


6. Internet

The Internet is the publicly available internationally interconnected system of computers (plus the information and services they provide to their users) that uses the TCP/IP suite of packet switching communications protocols.

The Internet is composed of many interconnected computer networks. Each network may link tens, hundreds, or even thousands of computers, enabling them to share information with one another and to share computational resources such as powerful supercomputers and databases of information.

The Internet has made it possible for people all over the world to communicate with one another effectively and inexpensively.


Packet Switching

Packet switching is a communications paradigm in which packets are individually routed between nodes, with no previously established communication path.

A packet is a block of user data together with necessary address and administration information attached, to allow the network to deliver the data to the correct destination.

One data connection will usually carry a stream of packets of data that will not necessarily be all routed the same way over the physical network.


Internet Connections

MAN

R

LAN

R

LAN

R

R

RR

RR

RR

A router consists of a computer networking device that determines the next network point to which to forward a data packet toward its destination, a process known as routing.

R : Router


Internet Protocol Suite

Application layer FTP SMTP HTTP IRC …

Transport layer TCP UDP SCTP ICMP …

Network layer IP IPv6 ARP DHCP …

Data link layer EthernetToken

RingFDDI

802.11 Wi-Fi

…


Internet Protocol (IP)

The Internet Protocol (IP) is a data-oriented protocol used by source and destination hosts for communicating data across a packet-switched internetwork.

Data in an IP internetwork are sent in blocks referred to as packets or datagrams (the terms are basically synonymous in IP).

In particular, in IP no setup is needed before a host tries to send packets to a host it has previously not communicated with.

The Internet Protocol provides an unreliable datagram service, i.e., it makes almost no guarantees about the packet. The packet may arrive damaged, it may be out of order (compared to other

packets sent between the same hosts), it may be duplicated, or it may be dropped entirely.

If the application needs reliability, this is added by the transport layer.


Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP) is a connection-oriented, reliable delivery byte-stream transport layer protocol.

TCP connections contain three phases: connection establishment data transfer connection termination


IP Addressing

An IP Address is a unique number, akin to a mail address, used by machines (usually computers) to refer to each other when sending information through the Internet.

In IPv4, the current standard protocol for the Internet, IP addresses consist of 32 bits.

IPv4 addresses are commonly expressed as a dotted quad, four octets (8 bits) separated by periods.

203.64.185.201

Class A 0Network (7 bits)

Local Address (24 bits)

Class B 10 Network (14 bits) Local Address (16 bits)

Class C 110 Network (21 bits) Local (8 bits)

Class D 1110 Multicast Address (28 bits)

32 bits


Domain Name System

The Domain Name System (DNS) is

the method by which Internet addres

ses in mnemonic form such as www.

dee.nuu.edu.tw are converted into th

e equivalent numeric IP address such

as 203.64.185.201.

To the user and application process t

his translation is a service provided e

ither by the local host or from a remo

te host via the Internet.

The DNS server (or resolver) may co

mmunicate with other Internet DNS

servers if it cannot translate the addr

ess itself.

.

edu com net org tw …

edu com net org

nuu nctu ntu

dee mis

www (203.64.185.201) DNS Tree


7. Internet Access

Common methods of home access include: Dial-up

A form of internet access in which the client uses a modem to dial the ISP's node.

Broadband The typical broadband connection to date, whether cable or xDSL, is config

ured by the ISP to run at bit rates from 350-500 kbit/s. The full rate connection for a typical cable plant might be as high as 10 Mb

it/s and with ADSL it might be 2 to 6 Mbit/s. Satellite

Satellite Internet services are used in locations where terrestrial Internet is not available and in locations which move frequently.

Internet Service Provider: a company that provides other companies or individuals with access to the Internet.


Internet Access: Dial-Up

MODEM

MODEM: Modulator-DEModulator


Internet Access: Broadband - ADSL

ADSL MODEM

ADSL: Asymmetric Digital Subscriber Line


Internet Access: Broadband – Cable


Internet Access: Satellite


8. Some Popular Internet Services

E-mail The World Wide Web (WWW) TELNET FTP Instant messaging Usenet newsgroups …

IRC


E-mail

E-mail, or email, is short for "electronic mail" and is a method of composing, sending, and receiving messages over electronic communication systems.

Most e-mail systems today use the Internet, and e-mail is one of the most popular uses of the Internet.

An e-mail address identifies a location to which e-mail can be delivered. A modern Internet e-mail address is a string of the form:

Username @ Email server’s DNS

yhshiau @ nuu.edu.tw


E-mail System

Computer for x Computer for y

Mail Server for x Mail Server for y

SMTP

SMTP

POP3

SMTP: Simple Mail Transfer ProtocolPOP3: Post Office Protocol version 3

To: y@ms_bFrom: x@ms_a.........

Internet


WWW

The World Wide Web (the "Web" or "WWW" for short) is a hypertext system that operates over the Internet.

Hypertext is browsed using a program called a web browser which retrieves pieces of information (called "documents" or "web pages") from web servers (or "web sites") and displays them on your screen.

You can then follow hyperlinks on each page to other documents or even send information back to the server to interact with it.


Three Standards for WWW

The Uniform Resource Locator (URL) specifies how each page of information is given a unique "address"

at which it can be found.

HyperText Transfer Protocol (HTTP) specifies how the browser and server send the information to each ot

her.

HyperText Markup Language (HTML) a method of encoding the information so it can be displayed on a var

iety of devices.

URLHTTP

HTML


Uniform Resource Locator

A Uniform Resource Locator, URL, or web address, is a standardized

address for some resource, such as a document or image, on the Internet.

The URL combines into one simple address the four basic items of

information necessary to find a document anywhere on the Internet:

The protocol to use to communicate with that machine

The machine or domain name to go to

An open network port on the target machine connected to some service

The path or file name on that machine

A typical simple URL can look like:

http://203.64.185.201:80/~yhshiau/index.html


Uniform Resource Identifier (URI)

URI is an Internet protocol element.

A URI is a short string of characters that confor

m to a certain syntax. The string indicates a nam

e or address that can be used to refer to an abstra

ct or physical resource.

Example URI: http://203.64.185.208/~yhshiau

mailto:[email protected]

telnet://melvyl.ucop.edu/

ftp://ftp.is.co.za/rfc/rfc1808.txt


HyperText Transfer Protocol

HTTP is the primary method used to communicate information on the World Wide Web.

HTTP is a request/response protocol between clients and servers.

Client Web server

Request

The browser sends a URL.

The server sends back a web page.

Response

HTTP


HyperText Markup Language

HyperText Markup Language (HTML) is a markup language designed for creating web pages, that is, information presented on the World Wide Web.

<HTML>

<HEAD>

<TITLE>蕭裕弘的網頁 </TITLE>

</HEAD>

<BODY>

<font size=7>蕭裕弘的網頁 </font>

</BODY>

</HTML>


Functions of Browsers

open desired HTML documents follow links to other Web documents follow links to other Internet information systems such as gopher and ftp open local documents save retrieved documents print the current document maintain a history of visited URLs move back and forward between URLs visited in the current session trigger programs on the server side and review the results view the source (the HTML) of the current document keep a note of URLs required for future reference search for a term in the current document handle forms view images (GIF, JPEG, PNG formats) inline follow links from imagemaps maintain a store (cache) of visited pages for re-use where appropriate


常見的網頁設計程式語言

HTML C/C++ Perl PHP Java JavaScript

LinuxApacheMySQLPHP


常見的網際網路應用 Co-operation

The practice of people or greater entities working in common with commonly agreed-upon goals and possibly methods, instead of working separately in competition.

Electronic commerce Electronic commerce or e-commerce

consists of the buying, selling, marketing, and servicing of products or services over computer networks.

On-line publishing Internet publishing, web publishing,

electronic publishing ......


網際網路的法律與道德問題

There is public concern about the Intern

et stemming from some of the controver

sial material it contains. Copyright infringement 版權侵犯的問題 Pornography 色情的問題 Identity theft 個人資料的盜取 Hate speech 仇恨的語言與製造問題 Social problem 社會問題 ......

Chapter 2 Networking and Internet 國立聯合大學電子工程學系蕭裕弘.

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Transcript of Chapter 2 Networking and Internet 國立聯合大學電子工程學系蕭裕弘.

Chapter 2 Networking and Internet 國立聯合大學 電子工程學系 蕭裕弘.

Documents

Transcript of Chapter 2 Networking and Internet 國立聯合大學 電子工程學系 蕭裕弘.

Chapter 2 Networking and Internet 國立聯合大學電子工程學系蕭裕弘.

Transcript of Chapter 2 Networking and Internet 國立聯合大學電子工程學系蕭裕弘.