Introduction to communication

מידע מידע מערכות מערכות

צוילינג – מוטי העברית האוניברסיטה

מבוא לתקשורת מבוא לתקשורת מחשביםמחשביםואינטרנטואינטרנט

9.3

Course Outline

• Internet• Unix• Word processing• HTML• Spreadsheets• Presentations• Graphics• Peripherals

The Internet: technology and services

9.5

Internet Technologies

9.6

The UNIX Connection

• The Internet has grown out of UNIX Operating System

• Some Internet terms (email address) and services (FTP) become more clear after we cover UNIX

9.7

The Internet: A Network of Networks

The Internet is an interconnected network of thousands of networks linking academic, research, government, and commercial institutions.

9.8

WAN(Wide Area Network)

LAN(Local Area Network)

Networks Near and Far

• There are two general types of computer networks:

9.9

LAN (Local Area Network)

• A LAN is a network in which the computers are physically close to each other– LAN networks are usually set up to share

peripherals, such as printers and network servers

– Each computer andshared peripheral isa node on the LAN

9.10

• A WAN is a network in which the computers are a great distance from one another– Connections are made

via telephone lines, satellites, and/ormicrowave relay towers

– Each network site is anode

WAN (Wide Area Network)

9.11

WAN (Wide Area Network)

• WANs are often made up of LANs

9.12

• A modem is needed to connect a computer to a phone line

• The computercommunicateswith digital signals

• The telephone systemwas designed to transmit voice signals which are analog

Communication with Modem

9.13

Client/Server Model

9.14

Internet Protocols

TCP/IP (Transmission Control Protocol/Internet Protocol) is the protocol at the heart of the Internet.

9.15

Internet Protocols

• TCP/IP translates into:– TCP (transmission control protocol) breaks

messages into packets.– IP (Internet protocol) is the addressing for

the packets.– computer in the Internet (host) is identified

by IP address (e.g. 128.214.9.225)– IP addresses run out

9.16

Internet Addresses

An Internet address is made up of two parts separated by the @ symbol:

• the person’s user name

• the host name

The host is named using DNS (domain name system), which translates IP addresses into a string of names.

9.17

Internet Addresses

An Internet address includes: username@hostname.sub.domusername is the person’s “mailbox”

hostname is the name of the host computer and is followed by one or more domains separated by periods:

• host.subdomain.domain• host.domain• www.cs.helsinki.fi• gurtov@cs.helsinki.fi (Andrei.Gurtov@Helsinki.FI alias)

9.18

Internet Addresses

Top level domains include:

– .edu - educational sites

– .com - commercial sites

– .gov - government sites

– .mil - military sites

– .net - network administration sites

– .org - nonprofit organizations

9.19

Intranets

• Intranets – internal closed networks of organizations that are designed using the same technology as the Internet.

• Firewalls - used to prevent unauthorized communication and secure sensitive internal data.

• Virtual Private Networking (VPN) -- a way to access intranets from public Internet

9.20

Internet Services

9.21

The World Wide Web:Browsing the Web

WWW is a distributed browsing and searching systems developed by CERN.

Use hypertext links and navigational aids to explore information on the Internet.

9.22

Web Addresses

URL (Uniform Resource Locator): addresses for the World Wide Web.

http (hypertext transfer protocol): the protocol of the WWW

9.23

Searching the Web

• A directory (also an index) is a hierarchical catalog of Web sites compiled by researchers.

9.24

Searching the Web

• A search engine offers a more complete database of what is one the WWW. A software robot or spider retrieves the entries according to key word queries.

9.25

Email on the Internet

• Email (one-on-one communication).

• Pine - UNIX-based mail program.

• MIME - Multipurpose Internet Mail Exchange - allows you exchange files through email.

Outlook express and Netscape provide more advanced mail readers

9.26

Disadvantages of Email

• Works only if the recipient responds

• Authentication is not ensured

• Email is not private

• Can be overwhelming (SPAM)

• Both filter out manyhuman componentsof communication

9.27

Mailing Lists and Newsgroups

• Email is a valuable tool for one-to-one communication

• Mailing lists allow you to participate in email discussion groups on special-interest topics.

• Usenet Newsgroups are virtual bulletin boards that you access with a news reader

9.28

Other email features

• Attachments (one MB files are ok)

• Filters

• Ignore sender

• Group by conversation

• Work offline

• Encryption and signature

9.29

Remote Access and File Transfer

The most popular use of the Internet is information discovery and retrieval. Because the Internet is unorganized, you can use the following tools:Telnet: for remote login to other computers.

FTP: file transfer protocol; transfer files from remote computers.

SSH: secure remote login and file transfer

9.30

Paging and chatting

Talk is a UNIX program that allows you to carry on a split-screen communication

Internet relay chat (IRC) allows several users to type simultaneously

ICQ (I seek you): user-friendly messaging system– Microsoft Messenger is a similar tool

9.31

Streaming

• Listen to music from live radio stations

• Using RealPlayer or Microsoft Media Player

• E.g. www.yle.fi provides links to several life stations

• You can even find live air traffic control – Pilots talking to a dispatcher

9.32

File sharing

• Search and download files like latest hits (mp3), blockbuster movies (mpeg), latest software packages (zip),pictures...

• Make your own files available to others• Tools like Gnutella or Napster• Difficult for authorities to snap these

systems to their distributed nature

9.33

Real-Time Communication

Video telephony (see, hear, and type to another person).

• MBONE - Multicast Backbone – centralized distribution

• NetMeeting – works over ”off-the-shelf” Internet

9.34

• Users connect (usually for a fee) to a variety of on-line databases

• On-line databases include:– current stock market status– digital libraries– banking– shopping

E-Commerce

9.35

Online banking

• Provided in Finland by all major banks• E.g. in Leonia costs less than any other

service package• You get a customer number and a PIN code

to log-in at their web site• You get a challenge-response table of codes• All connections are encrypted • Within the same bank money are moved

instantly, otherwise it takes a couple of days

9.36

Rules of Thumb: On-line Survival Tips

• Protect your privacy

• Cross-check on-lineinformation sources

• Netiquette

• Avoid informationoverload