IN.1 Internet Technology

• Basic facts about Internet• Terminology of Internet• Servers on the Internet• Internet access

Basic facts about InternetA. Development of Internet

– In 1969, the US Defense Department built a network called the ARPANET• Tied together computers of military and

universities1. Allow geographically separated computers to

share data2. Allow communication via e-mails3. Designed to withstand damage

– Data could bypass the damaged part of the network

4. Allow various types of computers to run on it

Basic facts about Internet

– Initially, ARPANET consisted of four main computers

– In 1986, US NSF connected its network of supercomputers to ARPANET

Civilian network– NSF allowed anyone to join the network– ARPANET is renamed as “Internet”

Basic facts about InternetB. Development of WWW

– The popularity of the Internet is due to the World Wide Web (WWW), or the Web

• Internet’s fast growing portion

– The Web was invented by Dr. Tim Berners-Lee in 1991

• A researcher in CERN

– In 1993, Mosaic was developed • The first widely distributed Web browser by Marc

Andreessen

– Mosaic is the ancestor of today’s Web browsers • e.g. Netscape, Internet Explorer and FireFox

Terminology1. WWW

2. TCP/IP

3. IP Address / Web site address

4. Domain Name

5. ISP

6. URL

7. VPN

2. WWW

World Wide Web (WWW)– Created in 1989.– The collection of hyperlinked documents

accessible on the Internet– With a web browser, a user views

webpages that may contain text, images, videos, and other multimedia.

2. TCP/IP (1)

Transmission Control Protocol (TCP) and Internet Protocol (IP)– Set of rules used in data transmission on the

Internet – Data is broken up into small packets by the

sender– Each packet is directed by a series of routers

• So, different packets use different routes

– Finally, recombined by the receiver.

2. TCP/IP (2)

Advantages of TCP/IP:1.The load of transmission lines is evenly distributed

2.Unaffected by the failure of any path• More than one path, the packets would be routed round

the problem

3.Entire message is guaranteed to be transmitted• If packet is not received properly, request re-transmission

4.Different Computers can communicate • for all OS that support TCP/IP

3. IP Address Web site address

– On the Internet, computers have unique IP address• each can be uniquely identified

– A series of four numbers separated by a period • Each number between 0 and 255• e.g. 202.148.153.59

– Combination of IP addresses is • 256 x 256 x 256 x 256.

– Large organisations: permanent– Home users: temporary– Each packet carries IP addresses of sender and

receiver• Similar to the addresses on an envelope

4. Domain Name (1)

IP address– Used by computers

• difficult for people to remember

– May change if it is shared

Domain – A group of computers under the same organization

Domain name • Text version of IP address • of a server of the organisation• using words separated by periods, e.g.• “Radian.com.hk” • More meaningful and easy-to-remember

4. Domain Name (2)

Top level domains– can be

1.Generic top level domains • e.g. .com, .org, etc.

2.Country-code top level domains • e.g. .hk, .cn, .au, etc.

Second-level domains – under .hk

• .com.hk, .org.hk, .net.hk• .edu.hk, .gov.hk, .idv.hk

5. Internet Service Providers (1)

Internet – Global collection of networks– Collaborative:

• Each member network provides – servers– communication devices and – connecting lines etc.

• Directs traffic

– The Internet is not run by a single organisation – Large organisations provide Backbones

• e.g. UUNET and NASAR• High-speed channels that link the networks

5. Internet Service Providers (2)

Internet service providers (ISP)– Offer Internet access to

• individuals, companies and organisations.

– Have permanent connection to the Internet backbone

– Service may be• charged at an hourly rate • fixed monthly amount for unlimited access

– means that there is no limit for duration of connection

6. URL

Uniform Resource Locator (URL)– Address of a Web page

• e.g. http://www.stmc.edu.hk/main/namelist2001/3b.htm

– Defining the route to a file on the Web, including• Protocol prefix e.g. http://, ftp://, news://• Type of host server e.g. www, mail, ftp• Domain name e.g. stmc.edu.hk, gov.hk • Path name e.g. main, namelist2001• Filename. For example, e.g. 3b.htm, abc.txt, xyz.doc

7. VPN

Virtual Private Network (VPN) 虛擬私人網路– Communications network tunneled thru’

another network and dedicated for a specific network.

– Makes WANs like LANs– Establishes a secure tunnelling channel

thru’ public network.– Data will be encrypted 加密 before sending

out to the tunnel.

Definition

Domain Name Server (DNS)

DNS – Translate domain name into IP address– Maintain a table with

• Domain names of organisations and their corresponding IP addresses

– For each domain name, e.g. e-mail address or URL

• DNS server translates into IP address

– Kept by major ISP • the table is updated regularly

Web Server

Web Server – Stores collection of Web pages– Accepts HTTP requests form clients

• i.e. web browsers

– Serves HTTP responses along with optional data contents

Proxy Server

Proxy Server – Sits between a client application, such as a web

browser, and a real server– Serve the request without contacting the specified

server.– If one or more Internet sites are frequently

requested, they will be stored in the proxy’s cache– passes all requests and replies unmodified is

usually called a gateway or sometimes tunneling proxy

Internet Access

Countries by number of internet users

Internet AccessConnection method Speed Hardware needed

Dial-up access 56Kbps Modem, Tel. line

ISDN 128Kbps ISDN modem, Tel. line

ADSL Upload: up to 512Kbps

Download: up to 10MbpsASDL modem, Tel. Line, LAN card

Cable internet access 2-50Mbps

(shared by users)Cable modem, Cable TV network

Fibre-2-building

Fibre-2-home

10-1000Mbps

(shared by users)Network card, Gigabit Ethernet Network

Wi-Fi 11-54Mbps Wireless network card, Access point

Internet Access for Home Users

1. Dial-up Access– Using regular modem and telephone line– Temporary link to the Internet– Modem is connected to the serial port

• Network interface card (NIC) is not necessary

– Inexpensive but slow• 56 kbps• In Hong Kong, need to pay for PNETS

– Public Non-Exclusive Telecommunications Service

– charging per minute use telephone line

• Connection may not be successful due to busy phone line

Internet Access for Home Users

2. Broadband Access(1) Asymmetric Digital Subscriber Line (ADSL) or (2) Cable TV network.– Hardware needed:

• NIC and • Special modem

– Applying advanced technology over telephone line • very high transfer rate up to 1.5 M to 10 Mbps

– Connection is fast and easy because • dial-up is not necessary

– Installed by trained technicians

Internet Access by Mobile Users

Wireless Service Provider (WSP)– a type of ISP – that uses radio waves

• rather than cable

– to provide Internet access to users of wireless devices

• e.g. handheld computers and mobile phones

Internet Access for Network Users

Hardware– Router

• to connect a LAN to the Internet• Wireless access point, wireless NIC

– more convenient

Access to ISP via1.broadband with telephone line/optical fibre2.ISDN with dedicated phone line3.T1 with a digital line4.Wireless technology with radio waves/satellites

– Unlimited access• Fixed monthly payment.