Title Slide

Title Slide

CSS 404/504Internet Concepts

Telecommunications &

Basic Internet

By

Ralph B. Bisland, Jr.

2Internet Concepts: Telecommunications, Copyright Ralph B. Bisland, Jr, 2001

Client/Server Model• Basic model of how the Internet operates

• Client/Server Model: Consists of at least two computer systems:– Client Computer System– Server Computer System


Client Computer System

Runs “locally” (probably on a PC) May have different versions for different

platforms Initiates requests Example client command: Send me

“file-a”


Server Computer SystemRuns on remote computer that is

permanently connected to the InternetTasks Performed:

Authorizes users Stores and manages data Responds to requests from clients

Example server action: Here is the file you requested


Client/Server Architecture

ClientComputer

ServerComputer

Communication Link

Data


Communication

• How computers communicate with each other (telecommunications)

• Can be either analog or digital– Analog: A representation of

communication using an analog device– Digital: A representation of communication using

a digital device


Analog Data

• Any representation of data in which the amount of a substance or signal is proportional to the information represented.

• Examples: – Watches with hour, minute, and second

hands.

– Gasoline flowing through a punp.


Analog Communication: Example• Phonograph-Recording involved cutting

groves into the record analogous to the vibrations that make sounds. Height of the “bumps” was proportional to the loudness of the sound. A needle traveled across the surface of the record and as it ran across the “bumps”, it vibrated a diaphragm, producing vibrations that humans perceive as sounds.


Analog Communication: Example• Early telephones were analog

devices. Speaker caused an electronic current to be generated and transmitted over telephone line. The louder you talked, the more current was sent over the line.


Advantage of Analog

• Easy to understand how it works. The pitch of a human voice is an exact analog of the force a person applies to stretch their vocal cords.


Disadvantages

• Impossible to produce an exact analog of all possible inputs. (All people do not sing the same way.)

• Media wears out. (Each time a record is played, part of the “bumps” are worn away).

• Inaccuracies arise because amplifiers are not perfect.


Disadvantages (ctd)• Analog signals fade and must be

re-amplified. Amplifications causes noise to (called distortion) to creep into the signal. The more times the signal is amplified, the more distortion is added.


Digital Communication

• Information is represented by specific numbers. These numbers are represented in binary.

• Data is transmitted with a series of 0’s and 1’s.

• Because computers are basically digital machines, digital communication works best with them (no conversion to analog is needed).


A To D Converters

• Most telephone lines are analog lines.• Since computers are digital machines,

the digital signal must be converted to an analog for transmission.

• This is done by an A to D converter• Specific device is called a modem

modulate-demodulate.• Process is transparent to end users.


Example Of The Use Of Modems

ComputerA

ComputerBModem 1 Modem 2

Communication Line

Analog DataDigital Data Digital Data


Morse Code

• Early telecommunication: Morse Code• Series of dots and dashes (Min=1, Max=6)Examples of Morse CodeA: .- B: -... C: -.-.0: -----1: .-----2: ..---3: ...--5: .....6: -.....: .-.-.-


Morse Code (ctd)

• Telegraphs were digital - either a dot or a dash

• Experienced telegraphers knew when a “word break” occurred.

• Telegraph operators “translated” message into Morse code. Receiving telegrapher decoded message for receiver


ASCII Codes

• Modern computer systems do not use Morse Code to transmit data over the Internet

• Use ASCII codes (8 binary bits = 1 byte)• Each character has a specific number

associated with itA = 0100 0001 = 65 (base 10)

B = 0100 0010 = 66 (base 10)• Digital representation of data


Advantages/Disadvantages

• Advantage: Do not “wear out”. Since a number represents a value, the number does not “fade”.

• Disadvantage: Since most values are analog, data must be converted into a number by some A to D process.


Telecommunications

• Key to understanding how the Internet works• Understanding telecommunications and the UNIX

operating system• Telecommunications:

– The electronic transmission of data (text, graphics, sound, and video) over any one of different communications channels, such as public telephone lines, private cables, microwave, or satellite.

• Networks connect a set of computer systems to each other.


Types Of Networks

• A network is a series of interconnected computer systems.

• Two types of networks– Local Area Networks (LANs)– Wide Area Networks (WANs)


LANsHardware, software, and communications

equipment that allow computers to be connected within a limited area.

Limited Area: Within a building or a set of buildings in close proximity.

Analogy: An “in house” telephone system - don’t have to use all digits.


WANso Same as a LAN except that the computers

can be anywhere.o Distance is not a problem.o Difference is how the computers are

connected.o Largest WAN is the Internet.o Analogy: A telephone system to call

anywhere.


What Is The Internet?

A series of interconnected LAN’s and WAN’s

LAN#1USM WAN#1

MILNETWAN#2BITNET

LAN#2MSU

LAN#3Ole’ MS


More About LAN’s

• Because of costs, LAN technology differ in speed of transmission, encoding schemes for data.

• Various LAN technologies are incompatible• LAN’s probably do not use modems to

communicate between computers. • LANs just plug a wire connecting one

computer to another


More About LAN’s (ctd)

• Can not just plug two LAN’s together

• Operate over a limited distance

• May have its own specification for electrical signals (voltage and frequency)

• Technology for encoding data may be different


More about WANs

• WANs (or long haul networks) probably do use modems to connect computers together.

• WAN technologies are also incompatible.• WAN and LAN technologies are

incompatible.• WANs use special purpose computers to

resolve incompatibilities between different WANS.


Routers

• A special purpose computer that connects two or more networks and routes data to its final destination.

• Analogy: An intermediate Post Office.• A router forwards datagrams to another

router, etc. until the datagram can be delivered to its final destination

• Routers connect “nodes” on networks


Routers (ctd)

• Since routers are computers, they have a finite amount of storage space in which to store queued messages.

• If the storage space is full (the router has too many messages to store), the messages can not fit in the storage spaces are thrown away.


How To Connect Them All Together

• ARPA (Advanced Research Products Agency) allocated money to research the connectivity problem.

• Came up with a new approach called “internetwork”.

– internet: approach in general

– Internet: experimental prototype


The Solution• ARPANET: A large WAN (called a backbone) that

tied many researcher’s computers together.• Agreed upon a standard for packaging data to

transmit to other computers.• Software consisted of two parts:

– IP: Internet Protocol– TCP: Transmission Control Protocol

• Produced a smooth seamless method of transmitting data.


Example Of A Backbone

Internet

R1 R2

R3

R4R5

R6

N1 N2

N3

N4

N5

N6


Protocols• An agreed upon set of rules on how

something is to be done.

• Examples:

– Red and Green traffic lights

– Answering the telephone

– Transmitting data between computer systems


IP- Internet Protocol• IP: The basic rules of how computers

communicate with each other• Makes Internet appear to be one big network• Data is packaged into fixed size bundles

called packets (general term: datagrams)• The format of the packet follows the IP

protocol• Internet computers must have IP software to

code/decode data


IP Addresses

• Every computer connected to the Internet must have a unique address

• IP Address Syntax: A quadruple set up in “dotted notation”

• Example IP addresses:195.31.115.204 = orca1100 0011 0001 1111 0111 0111 1110 1100195.31.82.42 = ocean

• All computers on the same network have the same prefix


Domain Name System

• Most people can not remember IP address numbers

• Domain Name System (DNS): A distributed database that translates IP address numbers into names

• Example DNS entries:195.31.115.204 = orca.st.usm.edu

195.31.82.42 = ocean.otr.usm.edu

• Synonyms: computer aliases195.31.115.204 = www.cs.usm.edu


How Data Is Transmitted

• Networks usually do not dedicate a single wire for each pair of communicating computers

• Multiple computers share underlying hardware facilities

• Sharing causes delays• Sharing is economical• Sharing is accomplished by taking turns

transmitting data• Accomplished by packet switching


Packet Switching• Computer divides data to be transmitted into

packets• As packets are created, they are are placed

on the network for transmission.• Each packet contains a “header”

– To IP address– From IP address– Sequence Number– Checksum total– Other stuff


Packet Switching (ctd)

• As packets are received, they are placed in order and the computer distributes them to the designated “receiver”.

• All packets are not the same size, but there is a maximum size. Size depends upon the application - may be a large E-mail message or a single keystroke.


TCP/Transmission Control Protocol

• Insures that data is delivered correctly

• Works closely with IP

• Collectively called TCP/IP protocol suite

• TCP is also software to exists on most computers connected to the Internet


How TCP Works

• Sometimes because of network volume, data is lost.

• Sometimes some of the packets are received and some are not.

• Because of network traffic, all packets in a transmission may not travel the same route to the receiver.


How TCP Works (ctd)

• If all packets are received and the checksum is correct an acknowledgment is sent back to the sending computer. If not, a message to retransmit is sent back to the sending computer

• Retransmission can result in duplicate packets being received

• If a duplicate packet is received, it is ignored


Intranets

• Most organizations that are very security “aware”

• Some organizations want the capability of the internet, but only for their employees.

• Solution: An intranet (applications restricted to a local closed LAN)

• A software “firewall” is created on the LAN allowing no packets in or out.


Why Protect Your Computer?• Viruses

• E-mail Viruses

• Worms

• Trojan Horses

• Spyware


Viruses• Virus: A small piece of computer

code that is piggybacked onto a real program.

• It might attach itself to a spreadsheet, etc. Each time the spreadsheet is opened, the virus could spread to other programs.


How Viruses Spread• Early viruses were pieces of code that were

attached to a common program (word processor or computer game).

• When the program started up, the virus loads itself into main memory and looks for other executable programs to attach itself to.

• If the program was copied to a floppy disk and loaded onto another computer, it spread.


How Viruses Spread (ctd)• This technique worked for a while

because the virus could write itself out to floppy disks.

• After a while programs became so sophisticated they could not fit on one floppy disk.

• Larger programs were now loaded onto CDs. CDs can not be written to. This virus spreading technique faded out.


Boot Sector Viruses• To spread, a program that contains the virus

must be started up.• Virus creators needed a program that was

always executed.• The “boot sector” of a floppy disk or hard disk

contains the first part of the operating system. It basically loads the operating system into memory.

• Viruses began infecting the boot sector program which is executed when the computer starts up.


Boot Sector Viruses (ctd)• This was a fool proof method of

infecting a computer.• It was particularly bad on college

campuses as students share computer resources.

• Executable program and boot sector viruses are not very threatening any more as operating systems have built in methods of eliminating this kind of virus.


Origins of Viruses• People create viruses.

• They are a program designed to do something.

• Once written, the virus is “released”.

• The virus may be simply a nuisance (writing a message on your screen) or highly destructive (erasing files on your hard drive).


Why Create A Virus?• The same thing that drives vandals and

arsonists. Just for the thrill of being able to do it.

• The thrill of watching things “blow up”. Some people like to see accidents or wrecks.

• Bragging rights. “Hey I created the XYZ virus and it messed up 10,000 computers.”


E-mail Viruses• E-mail viruses: Same as viruses, but

they get spread via inbound E-mail messages.

• The virus usually attacks the users E-mail address book by sending itself to every address in the address book.


How E-mail Viruses Work• Virus is attached to a down loaded E-mail.

• When the E-mail is opened, the virus is started up.• Once opened, the virus has access to the users

address book to ship the virus to unsuspecting friends of the “victim” – and the return address is “friendly”.

• E-mail viruses can be spread by opening E-mails or attachments to E-mails (actually a Trojan Horse).


Famous E-mail Viruses• Melissa (1999): Infected many Microsoft

Word documents. Took advantage of a programming language built into Microsoft Word – VBA (Visual Basic for Applications) which could start up other programs.

• ILOVEYOU (2000): Came as an attachment sent with E-mail messages.


Worms• Worms: A small piece of software that

uses security holes in a network to replicate itself.

• A copy of the worm scans the network for security holes. When it finds one, it enters, replicates itself, then tries to find other security holes.


Code Red Worm• Found security holes in Microsoft SQL

Server and later in Windows NT and Windows 2000 servers.

• Replicated itself over 250,000 times on July 19, 2003.

• Slowed down network traffic with replications.


Code Red Worm (ctd)• Code Red worm was designed to:

– Replicate itself for the first 20 days of each month

– Replace web pages on infected computers with a page that declares “Infected by Chinese”.

– Launch a concerted attack on the White House web server in attempt to overwhelm it.


Trojan Horses• Trojan Horses: This is simply a

program that “disguises” itself to do one thing, but actually does something else (like erase your hard disk).

• Trojan horses do not replicate them selves.


Spyware• Internet jargon for Advertising Supported Software

(aka adware).• How shareware authors make money.• Large media companies offer spyware to place ads

in their products in exchange for part of the revenue from banner sales.

• You don’t pay for the software and the advertisers get paid.

• You can have the spyware removes but you usually have to pay a price for doing this.


Protection from Intruders• Virus Protection Programs (such as

Norton Anti Virus.)• Scans your computer for viruses, worms,

and Trojan horses and either quarantines or deletes them.

• Scans incoming (and outgoing) E-mail for viruses.

• You must keep virus definitions updated.


Firewalls• A barrier that protects your computer

from the outside world.

• Analogy: One hole that all traffic into and out of your computer travels – there all traffic can be monitored.

• It filters incoming (and outgoing) data.

• Firewalls are customizable.


Customizing Firewalls• IP Addresses: All traffic from certain IP

addresses can be blocked (blacklists) or allowed in (whitelists).

• Domain Names: All traffic from specific domain names (ex. usm.edu) can be blocked or allowed in.

• Protocols: All traffic to do certain this is allowed (get web pages, send and receive E-mail, etc)


Customizing Firewalls (ctd)• Ports: Requests come into computers via

ports. Ex. Port 80 for web pages, port 21 for FTP requests, etc.. The firewall might only allow web requests on a certain computer to come from within the company (i.e., an Intranet).

• Specific word and phrases: The firewall will sniff each packet for certain words or phrases and not allow them into the system.


What Firewalls Protect You From• Remote Login: Someone is allowed to

connect to your computer and use it.• Application Backdoors: Some programs

have special features that allow remote login. Your system has bugs in it that allow the user to do something to your computer.

• SMTP Tracking: Gain access to your address book which allow them to gain addition addresses to send spam to.


What Firewalls Protect You From (ctd)• Operating System Bugs: This may allow

backdoor access to your computer.• E-mail Bombs: This is usually a personal attack

on a person or organization. A hacker sends you many, many E-mails until your system can not accept any more.

• Macros: Some programs (ex. Excel spreadsheets) allow you to store mini programs to perform frequently used tasks. Hackers create their own macros to wreak havoc on your computer.


What Firewalls Protect You From (ctd)

• Denial of Service: A hacker sends a request for service to a server to connect to it. When the server responds with an acknowledgement and tries to establish a connection, it cannot find the system that made the request. By inundating a server with these unanswerable requests, the hacker causes the server to slow down and eventually fail. This is very hard to prevent.


What Firewalls Protect You From (ctd)• Viruses: Enough said.

• Spam: Totally harmless, but annoying stuff. Electronic junk mail. These may contain a “cookie” that allows backdoor access to your computer.

• Redirect Bombs: Hackers can use ICMP (Internet Message Connect Protocol) to change the path information and hence sending replys to a different router. One way to set up denial of service.


What Firewalls Protect You From (ctd)

• Source Routing: In most cases packets are sent from one location to another by routers along the path. However, the source providing the packet can arbitrarily specify the route the packet is to travel. Hackers can use this to make packets appear to come from trusted sources or even inside your network. Most firewalls simply dispose of these packets.


How Most Firewalls Are Configured

• Block all incoming traffic, then only allow in what you need.

• Example: Block all requests for service except E-mail, then heavily filter them.


Proxy Servers• Proxy Servers are often used with firewalls.

• Used to access web pages by other computers.• When a computer requests a web page, it is

retrieved by the proxy server and then sent to the requesting computer.

• The net effect of this action is that the remote computer hosting the Web page never comes into direct contact with anything on your home network, other than the proxy server.


Proxy Servers (ctd)• Proxy servers can monitor access to web

pages.• Proxy servers can also make web access more

efficient.• If you access a web page it is places the code

to create the web page into a special type very fast memory called cashe memory.

• The next time you request the page acess is from cashe memory and not disk.


DMZ• Demilitarized Zone.

• If you want to place stuff for all users to have access to, you can set up a DMZ.

• Things to place in a DMZ:– Web Pages– Online business– FTP site for download and upload

• DMZs are just outside your firewall.• Analogy: The front yard of your house


How Computers Are Physically Connected

• No matter how sophisticated a network is, it must be “physically” connected to the other computers in the network.

• Bandwidth: The amount of data that can travel through a circuit expressed in bits per second. Measure of capacity, not speed.


Methods of Connecting Computers• Telephone Lines

• ISDN (Integrated Services Digital Network)• DSL (Digital Subscribers Line)• Ethernet Lines• Fiber• Radio Waver• Satellites• Cable TV• WAP (Wireless Access Protocol)


Telephone Line• Data is transmitted over copper wire.

• Most used because its everywhere.

• Slow in relation to other methods of data transmission.

• Must use a telephone modem to convert digital data to analog data and then analog data back to digital data.


Telephone Lines (ctd)• Transmission speed is measured in bits per

second (bps). Old terminology: baud rate.• Most common transmission rates are:

– 300 bps– 2400 bps (1)– 9600 bps (4)– 14400 bps (6)– 28800 bps (12)– 57600 bps (aka 56000) (24)


ISDN• Integrated Services Digital Network

• A special type of phone line that can be used for voice or data (or both)

• Good for organizations that need both voice and data lines

• Has both analog and digital transmission of data• Approximately 5 times faster than a 28800

modems


DSL• Digital Subscribers Line

• Replaces ISDN (much faster and cheaper)• The DSL signal is mixed in with your normal

phone signal at the phone companies central office (CO).

• Handles both analog (telephone) and digital (data) transmission without interfering with each other.

• Speed: 1.5 - 2 MB/sec


DSL (ctd)• Inside your home you must have an external

DSL modem which is connected to a “splitter”. The “splitter” device separates the signal.

• Your modem must be connected to your computer via a NIC (Network Interface Card).

• The signal is sent out to your local phone company which acts as your ISP.

• Must be close to the source for fast transmission.


DSL (ctd)

PhoneCompany Splitter

Telephone

DSLModem

ComputerInternet


T1 And T3 Links Used to transmit data between LANs and WANs

Very fast method of transmitting data Use high speed leased telephone lines Relatively expensive method of transferring data T1 Link: Capable of sending information at 1.544

MB/sec Consists of 28 voice channels of 64 Mbps 24 - 8 bit packets are transmitted followed by a

synchronization bit (193 bits) T3 Link: Capable of sending information at 44.54

MB/sec (28 T1 channels)


Ethernet ConnectionDeveloped by Digital Equipment Corporation

(DEC) and Xerox Corporation.Ethernet refers to the wires and the

electronic signals used to transmit dataOnly able to transmit at short distances

before signal fadesAnalogy: Throw a rock into a pond.

Speed: 100 MB/secMostly used on LANsCheap,reliable, and simple.


Ethernet Connection (ctd)• Transmission speed much faster than telephone

lines• Three types of Ethernet lines

– Thick cable - Approximately 1600 feet, 20 mbps– Thin cable - Approximately 600 feet, 10 mbps– Twisted pair - Approximately 300 feet, 4-16 mbps

• An Ethernet modem is needed to connect a computer to an Ethernet line.

• PCMCIA: Personal Computer Memory Card International Association– People Can’t Memorize Computer Industry

Acronyms


Optical Fiber Connections Based on fiber optics technology

Transmits data as pulses of light Digital transmission Requires optical modem Very fast transmission of data

100 MB per second USM campus has fiber cables connecting

some buildings


Cable• Data is transmitted through a TV cable.

• Speed up to 2MB per second.• Useful because it is at least 100 times faster

than telephone lines and almost every home has a cable hookup. Since most telephone modems transmit at 28.8 KB, cable is about 200 times faster.

• Cable needs a modem to separate the video from the data.


WAP• Wireless Access Protocol

• Client computer does not have to be “physically” connected to the network.

• Uses a beacon to transmit data.• Range: About 500 yards• Transmission is done through radio waves.• Speed: 11MB (soon to be 50MB).


ATM• Asynchronous Transfer Mode

• A transfer mode in which information is organized into cells (53 byte packets) and is asynchronous in the sense that recurrence of cells containing information from an individual user is not periodic.

• Used to transmit voice, video, text, pictures.• Smaller cells so video does not flicker when

transmitted.• Transmission of information can start at any time.


Gigabit Ethernet• Since most Internet traffic begins and ends

with some type Ethernet connection, a group of users developed a set of standards that could be used on LAN and WANs.

• Only works on fiber optic cables.

• Can run at 10 gigabits/sec.


Point to Point Protocol

• PPP: Point-To-Point Protocol• Function of PPP: Most modems assume

that a dumb terminal (VDU + keyboard) is used to connect to a host computer systems and provides only limited "services".


Point to Point Protocol (ctd)• PPP allows the host computer to

recognize the "computer" connection. • It allows more functionality.• In order to use some of the Internet

features (i.e. transmitting graphics), you must have PPP protocols.


Post Office Protocol

• Post Office Protocol Version 3 is usually written as PoP2.

• Works like an old time Post Office. People did not get mail delivery at their homes (too expensive). Their mail went to a Post Office and when the people were near the Post Office they went in and picked up their mail.


Post Office Protocol (ctd)• PC usually can not serve as a mail

server – they are not connected to the Internet, they don’t have ginormus memory to store queued up mail, etc.

• The PoP server provided the function of storing messages for the user. When the user logs on to their computer and checks their mail, all of the queued up mail is delivered.


Who Owns The Internet?Nobody - The Internet simply exists!!!!

The Internet exists like a common carrier (i.e. the telephone company)

Some (but not many) Federal Laws exist to police it in the U. S.

Example: Telephone company can not dictate to a organization how to run their business. (You can have a phone if you run your business a particular way.)


Who Owns The Internet? (ctd)Almost no requirements that you

must obey certain rules to connect to the Internet.

Local network administrators are generally responsible for managing it.


Internet SocietyU. S. governing body of the

Internet: Internet Society (well, kind of anyway)

Acts as a clearinghouse and gentle guardian to help maintain cooperation among Net members - particularly on technical standards.


Connecting To The Internet

• Full time IP connection– Computers that reside on a LAN that is

connected to the Internet via a router.– Could be connected to the Internet via a

dedicated telephone line• Dial up access to a computer on the internet

– Connected to the Internet via a terminal emulation package

– Not running TCP/IP - can not run programs directly from a PC


Connecting To The Internet (ctd)• Running Internet protocols over

dial-up– Runs programs from PC via PPP

• Cable• WAP: Through cell phones or

PDAs


Internet Service Providers (ISPs) Your “ramp” onto the Internet

Local Internet Service Providers: USM (Faculty, Students, & Staff) Netdoor Comcast (cable) Cybergate Megagate

Look in your Yellow Pages under ISPs


Typical Connection To The Internet

ClientUser #1

ClientUser #2

ClientUser #3

InternetServiceProvider

TheInternet


Internet2• A consortium of 205 universities working in

partnership with government and industry to develop and deploy advanced network applications and technologies, accelerating the growth of tomorrow’s Internet.

• Internet2 is creating a partnership of academia, industry, and government that fostered the Internet in it’s infancy.


Goals of Internet2• Create a leading edge network

capability for the national research community.

• Enable revolutionary Internet applications.

• Ensure the rapid transfer of new network services and applications to the broader Internet community.


USM’s Connection To The Internet• USM uses Internet 2

– Uses a WAN connection– Trunks to:

• Gulf Coast Research Lab• Gulf Park campus• Marine Education Center• Jackson County campus• Keesler AFB campus• Stennis Space Center• JCJC


USM’s Connection to the Internet• USM uses its state contract for its local

service provider • Aberline is its Internet 2 PVC

(Permanent Virtual Circuit) provider• Cost to USM

– About $50,000 per year– Plus the T! lease line cost per mile (in 2000

it was $7/mile/month – about $700 per month).

• Post Office analogy


How USM Is Connected To The World

• Currently in the process of redesigning it.

• Now an ATM is used.

• Going to a Gigabit network backbone


ATM Design (current)• From orca to a primary router in TEC bldg.

• From there to an Ethernet bridge in TEC bldg.• From there to a core campus ATM Switch in TEC bldg.• From there to a campus ATM router in TEC bldg.• From there to a campus primary ATM router in the FCH bldg.• From there to a campus firewall.• From there to a core campus ATM Switch in the WFS bldg.• From there to a campus core Router in the WFS bldg.• From there through a campus core ATM Switch in WFS out to

PoP link in Jackson.• From there to the outside world.


Gigabit Design (future)• From orca to a 10/100 switch in the TEC bldg.

• From there to one of either the primary or secondary router in either TEC or FCH bldg.

• From ther to a Gigabit switch in the TEC bldg.• From there to a core Gigabit switch in the FCH bldg.• From there to the campus Firewall.• From there to a campus core ATM Switch out to PoP

line in Jackson.• From there to the outside world.


Operating Systems

• A program that allows the hardware of the computer to be used.

• Some functions of an operating system:– Scheduling programs for execution– Memory management– File management– Communications

• Common Operating Systems– Disk Operating System (DOS) -- IBM PC (and clones) based

Microsoft Disk Operating System (MS-DOS)– Windows/Windows 95/Windows NT/MR/XP - IBM PC (and clones)

Based– OS X - Macintosh based– UNIX - Mainframe/Minicomputer based (multiuser systems)– Linux: PC version of UNIX


Using Computers On The Internet• When you wish to use the Internet, you may use

it in two different ways– By using client programs from your PC.

• All the "dirty work" (behind the scenes stuff) is handled by your client program.

• Easy to use.• Limited to what you can do (Only what menus allow)• Inflexible.

– By using a PC to connect to a mainframe and using UNIX commands to access Internet resources.

• Much more powerful and flexible.• Must learn some UNIX commands.• Harder to use.

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