ce80n introduction to networks & the internet

CE80NCE80NIntroduction to NetworksIntroduction to Networks

&&The InternetThe Internet

Dr. Chane L. Fullmer

UCSC

Winter 2002

March 5, 2002 CE80N -- Lecture #17 2

Class InformationClass Information Web page tutorial available on-line Web page submission:

– Email to [email protected]• Subject: cmpe080n-assgn4

– Must be emailed on or before March 15• No extensions can be granted – don’t be late

Final Exam – Last class session

• March 14, 2002– Similar to midterm – open notes/open book

mailto:[email protected]


Personal Web Page of the DayPersonal Web Page of the Day

A few brave souls….Presenting:

– http://members.cox.net/fumanstan/

http://members.cox.net/fumanstan/






Facsimile (AKA as FAX)Facsimile (AKA as FAX)

The first facsimile transmission:– 1843 by Alexander Bain’s “Recording Telegraph”

Early fax machines were expensive and proprietary – no interoperation between brands– Used by weather and news services (wire photos)

1984 – Standardized by the CCITT (The International Telegraph and Telephone Consultative Committee)– Uses basic telephone for interconnections– Today, millions sold annually…– Works globally – where ever there’s a phone.


Sending A FaxSending A Fax The Internet can be used to send a fax.

– A document, image, etc. is converted to a file in facsimile format that can be transmitted via a fax modem to the destination fax machine.

– A facsimile received via the fax modem from a fax machine is stored as a file that can later be viewed or printed.

– C.L. Fullmer, et al “A TCP/IP Network Facsimile System built from publicly available software”, ACM 20th Computer Science Conference, March 1992, Kansas City, Mo.

Why bother?– Automated document retrieval/report generation– Saves money – no long distance/toll charges– Transmits faster than conventional fax

• Bandwidth in the Internet connection is often higher than the fixed voice circuit (64kbps)


The Internet Used To Copy FilesThe Internet Used To Copy Files

E-mail or fax can be used to send short notes.

Download should be used to send large volumes of data.– Large documents/images – Audio – CDs– Video clips– Software (ie, Free BSD)


Data Stored In FilesData Stored In Files

Disks hold large volumes of data.– Stores data in files– Collects files together in

folders (aka directories)


Copying A FileCopying A File

The network can transfer a file from one computer disk to another.– Uses software developed early in ARPANET called

file transfer– Uses a protocol called File Transfer Protocol (FTP)– Today, the application software itself is also called

ftp.


FTP Is InteractiveFTP Is Interactive

A user invokes the FTP application.– Presents the user with a prompt– Waits for the user to enter a command


Example FTP CommandsExample FTP Commands

Many FTP commands are available.You only need three simple

commands to get a file from a remote machine:


A User Can Store Or A User Can Store Or Retrieve A FileRetrieve A File

FTP can retrieve (get) a copy of a file.– Contacts a remote computer– Obtains a copy of a file

FTP can store (put) a copy of a file.– Contacts a remote computer– Sends a copy of a file

• (Uses the put command, instead of get)


Commands For Binary And Text Commands For Binary And Text File FormatFile Format

There are two FTP file formats:– Using text

• Text files are not always obvious

– Using binary• Non text files may include:

– Graphics– Audio– Video– Compressed data


Choosing ASCII or Choosing ASCII or Binary TransferBinary Transfer

FTP does not understand the format or contents of a file.– Using the incorrect transfer type results

in a malformed copy– Using binary to transfer a file is safer if

in doubt


Commands For Authorization And Commands For Authorization And Anonymous FTPAnonymous FTP

A remote FTP service asks users for authorization by:– Prompting for a login identifier– Prompting for a password

Anonymous FTP allows anyone to access public files by:– Entering login of anonymous– Entering password of guest

• Sometimes email address is used for password


FTP Live DemonstrationFTP Live Demonstration


A Browser Can Use FTPA Browser Can Use FTP

The URL specifies to the browser to use FTP.– ftp://www.soe.ucsc.edu/classes/cmpe080n/Winter02/lec1.pdf

– ftp://ftp.cs.purdue.edu/pub/comer/example All the details are handled by the

browser.– Uses anonymous FTP

ftp://www.soe.ucsc.edu/classes/cmpe080n/Winter02/lec1.pdf








ftp://ftp.cs.purdue.edu/pub/comer/example








How FTP WorksHow FTP Works

FTP uses the client-server approach.– Uses TCP/IP for data transfer– Acting as the client

• FTP application software• User’s browser

– Acting as the server • Remote computer

FTP Client-Server exampleFTP Client-Server example


Impact and Impact and Significance Of FTPSignificance Of FTP

FTP data transfer caused more traffic on the early Internet than any other application.– Replaced by Web traffic in 1995


Fax/FTP SummaryFax/FTP Summary

Faxes can be converted to files and transported over the Internet

FTP – File Transfer Protocol– Client-Server architecture– FTP is interactive– “Anonymous” FTP for public access to files

Web browsers can use FTP


GlossaryGlossary

Anonymous FTP– Use of the special login anonymous to

obtain access to public files through the FTP service.

Binary file– Term is used to refer to nontext files.


GlossaryGlossary

Directory– A collection of files and other directories.

Some computer systems use the term folder.

File Transfer Protocol– (FTP) The Internet service used to transfer

a copy of a file from one computer to another.


GlossaryGlossary

Folder– A synonym for directory.

Internet FAX– A fax sent across the Internet instead of a

conventional telephone connection. Login

– The process of entering an account identifier and password to obtain access to a timesharing computer.


GlossaryGlossary

Password– The secret code a user enters to gain access to a

timesharing system or to gain authorization for the FTP service.

Public files– Files that are available to any Internet user.

Text file– Any file that consists of textual characters

separated into lines.


Early Computers Used Textual Early Computers Used Textual InterfacesInterfacesWhen the Internet was being

invented, computers consisted of timesharing systems.– Allowed many users to access the

system simultaneously– Appeared to operate the same as a

personal computer


A Timesharing System Requires A Timesharing System Requires User IdentificationUser Identification

Because multiple users can interact with a timesharing computer, the system requires each user to identify themselves when they begin.– Requires:

• a login identifier • a password


Remote Login Resembles Remote Login Resembles Conventional LoginConventional Login

Remote login service allows a user to access a remote timesharing computer system.– To use the service, a user:

• Invokes an application program• Specifies the name of a remote computer• Provides a login identification• Specifies a password


How Remote Login WorksHow Remote Login Works

Remote login follows the client-server paradigm.

The client:– Is the application that uses TCP/IP to connect

The server:– Allows the user to interact with the remote

computer– Sends output to the client

Remote Login ExampleRemote Login Example

Figure 28.1 Remote login across the Internet uses two programs. The user invokes an application on the local computer. The local application connects the user’s keyboard and display to the remote timesharing system.


Escaping From Remote LoginEscaping From Remote Login

Client software provides a way for a user to escape and communicate with the local client.– Provides a key on the keyboard to abort a running

program– Why do we need it?

• An application runs on the remote computer

• The remote login client is running on the local computer

• If one, or both applications freeze (fail in some way) we have a way to regain control of the local computer system.


Displays And WindowsDisplays And Windows

On a computer system using windows, remote login operates as if the window is a small terminal screen.


The Internet Remote Login The Internet Remote Login Service Is TELNETService Is TELNETThe Internet standard for remote

login service is found in a protocol known as TELNET.– Specifies how a remote client and a

remote login server interacts– Uses a character oriented interface


TELNET Live DemonstrationTELNET Live Demonstration


Remote Access Can Display A Remote Access Can Display A DesktopDesktop

Software can be placed on two computers that displays an exact copy of one computer’s screen on another computer.

Remote Desktop ExampleRemote Desktop Example

Figure 28.2 Illustration of a remote desktop service. Software permits the display on a user’s computer to show the screen image from a remoter computer.


How Remote Desktops OperateHow Remote Desktops Operate

A remote desktop service operates similar to a remote login service.– Invokes an application– Specifies a remote computer– Takes over the screen, keyboard, and

mouse– See:

• www.uk.research.att.com/vnc/


Assessment Of Remote Login Assessment Of Remote Login and Desktopsand Desktops

Internet remote access services are significant for three reasons.– Makes it possible to have computation

remote from user– Is significant because of its generality– Is significant because many people use it


Generality Makes Remote Login Generality Makes Remote Login And Desktops PowerfulAnd Desktops Powerful

The power of remote login arises because it provides general access to the program on a computer without requiring program modification.


Remote Access Accommodates Remote Access Accommodates Multiple Types Of ComputersMultiple Types Of Computers

Remote login service permits arbitrary brands of computers to communicate.


Unexpected Results From Unexpected Results From Remote AccessRemote Access

The user must remember that the application is running on a remote computer.– Cannot print a file using a local printer– Cannot save a file to the local computer

• (email of ftp the file to the local computer)


SummarySummary

TELNET is the Internet remote login application

Remote login resembles conventional login– Login account and password required– Client-server architecture– TCP/IP used for transport of data


GlossaryGlossary

Login – The process of entering an account

identifier and password to obtain access to a timesharing computer.

Remote Desktop – A system that allows a user at one

computer to connect their display, keyboard, and mouse to a remote computer.


GlossaryGlossary

Remote Login – A service that allows a user on one computer to

connect their keyboard and character-oriented display to a remote computer and run programs.


GlossaryGlossary

TELNET – The Internet remote login service. TELNET allows

a user at one site to interact with a remote timesharing system at another site as if the user’s terminal connected directly to the remote machine.

Terminal– A device that enables you to communicate with a

computer. Generally, a terminal is a combination of keyboard and display screen.


GlossaryGlossary

Timesharing Computer – A computer system that permits multiple users to

run programs at the same time. Window

– A rectangular area on a screen devoted to one particular application program.

ce80n introduction to networks & the internet

Documents

ftp file formats

file transferuses

text file formatthere

fax modem

ftp application

destination fax machine

facsimile format

facsimile aka