Transcript 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
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
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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.
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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.
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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.
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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?
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
你好嗎？
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Data Transmission Modes
 There are three ways for transmitting data from one
point to another:



Simplex
Half-duplex
Full-duplex
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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.
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Types of Computer Network
 Computer networks may be categorized with respect
to range:

Personal area network (PAN)
 Wireless

Local area network (LAN)
 Wireless


PAN
LAN
Metropolitan area network (MAN)
Wide area network (WAN)
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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
(intrapersonal 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.
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Local Area Network
 A local area network or LAN is a computer network covering a local area,
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.
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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)
situated around site of a fraction of a square kilometer.
Then from their MAN they could have several wide area
network (WAN) links to other universities or the Internet.
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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
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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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?
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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.
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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.
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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.
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Network Topologies – Hybrid Networks
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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.
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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.
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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.
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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.
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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.
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Examples of Wireless Transmission Media
Radio technology
Cellular
Microwave and Satellite
Infrared
公眾交換
電話網路
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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

...
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Ethernet
 Ethernet has become the
most widespread LAN
technology in use during
the 1990s to the present.
CS
 A scheme known as carrier
sense multiple access with
collision detection
(CSMA/CD) governs the
way the computers share
the communication media.
MA
CD
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常見的乙太網路佈線方式 – 有線
集線器 (Hub)
UTP
UTP
網路卡
UTP
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常見的乙太網路佈線方式 – 無線
集線器 (Hub)
USB 無線網卡
UTP
Access Point
802.11b – 11 Mbps
802.11g – 54 Mbps
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電子系館區域網路系統
校園網路
Switching Hub
DHCP
Server
Switching Hub
Switching Hub
Switching Hub
Teacher’s PCs
PCs in Lab.
PCs in Lab.
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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.
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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.
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Internet Connections
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
R
R
R
R
R
R
R
LAN
R
MAN
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R
LAN
R : Router
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Internet Protocol Suite
Application layer
FTP
SMTP
HTTP
IRC
…
Transport layer
TCP
UDP
SCTP
ICMP
…
Network layer
IP
IPv6
ARP
DHCP
…
Ethernet
Token
Ring
FDDI
802.11
Wi-Fi
…
Data link layer
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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.
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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
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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
32 bits
Network
(7 bits)
Class A
0
Class B
10
Class C
110
Class D
1110
Local Address (24 bits)
Network (14 bits)
Local Address (16 bits)
Network (21 bits)
Local (8 bits)
Multicast Address (28 bits)
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Domain Name System
 The Domain Name System (DNS) is
the method by which Internet
addresses in mnemonic form such as
www.dee.nuu.edu.tw are converted
into the equivalent numeric IP
edu
address such as 203.64.185.201.
.
com
net
org
tw
edu
com
net
nctu
ntu
…
 To the user and application process
this translation is a service provided
either by the local host or from a
remote host via the Internet.
nuu
org
 The DNS server (or resolver) may
communicate with other Internet
DNS servers if it cannot translate the
address itself.
dee
mis
www (203.64.185.201)
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DNS Tree
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7. Internet Access
 Common methods of home access include:

Dial-up


Broadband



A form of internet access in which the client uses a modem to dial the ISP's
node.
The typical broadband connection to date, whether cable or xDSL, is
configured 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
Mbit/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.
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Internet Access: Dial-Up
MODEM: Modulator-DEModulator
MODEM
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Internet Access: Broadband - ADSL
ADSL: Asymmetric Digital Subscriber Line
ADSL MODEM
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Internet Access: Broadband – Cable
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Internet Access: Satellite
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8. Some Popular Internet Services
 E-mail
 The World Wide Web (WWW)
 TELNET
 FTP
 Instant messaging
 Usenet newsgroups
…
IRC
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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 email is one of the most popular uses of the Internet.
 An e-mail address identifies a location to which email can be delivered. A modern Internet e-mail
address is a string of the form:
Username @ Email server’s DNS
yhshiau @ nuu.edu.tw
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E-mail System
Internet
To: y@ms_b
From: x@ms_a
.........
Mail Server for x
Mail Server for y
SMTP
SMTP
Computer for x
POP3
SMTP: Simple Mail Transfer Protocol
POP3: Post Office Protocol version 3
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Computer for y
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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.
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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
other.
 HyperText Markup Language (HTML)

a method of encoding the information so it can be displayed on a
variety of devices.
URL
HTTP
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HTML
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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
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Uniform Resource Identifier (URI)
 URI is an Internet protocol element.
 A URI is a short string of characters that
conform to a certain syntax. The string indicates
a name or address that can be used to refer to an
abstract 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
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
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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.
The browser sends a URL.
Request
Response
The server sends back a web page.
Client
HTTP
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
Web server
Chapter 2: Page 50 / 55
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>
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
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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
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
Chapter 2: Page 52 / 55
常見的網頁設計程式語言
 HTML
 C/C++
 Perl
 PHP
 Java
 JavaScript
Linux
Apache
MySQL
PHP
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
Chapter 2: Page 53 / 55
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
 ......
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
Chapter 2: Page 54 / 55
網際網路的法律與道德問題
 There is public concern about the
Internet stemming from some of the
controversial 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

......
國立聯合大學電子工程學系 – 計算機概論 – 蕭裕弘
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