Internet Applications Module G Copyright 2001 Prentice Hall

Internet Applications

Module G

Copyright 2001 Prentice Hall

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File Transfer Protocol (FTP)

FTP host stores files Client logs into host Client program sends command to get a file FTP host downloads the file with error correction

FTP Host

2. FTP Get Command

3. Download

1. Login

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User can also upload a file to the FTP Server

– WWW cannot do this

FTP Host

2. FTP Upload

1. Login

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Must Log into FTP Host Before Transfers

Traditional FTP– You log into a specific account with a password– You can transfer to and from directories accessible to that

account

Anonymous FTP– You log in as “anonymous”– Give your e-mail address as password (usually optional)– Host gives you access to public directories– Usually for downloading only– Not truly anonymous: your internet address is known

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FTP File Format Standards

There are no standards for FTP file formats

– Nothing like HTML

– No limit on generality

– No help in handling after downloads

– You must know the file structure of the file you download

– You must have an application program that can read that file format

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FTP Archiving

Many FTP files are archived

– Two-step process

– First, several files are combined into one archive to avoid having to make multiple downloads

– Second, the combined files are compressed to reduce download times

1.Combine

2.Compress

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FTP Archiving

Receiver must dearchive the files to read them

Unfortunately, many archiving standards– Zip is the most common

– UNIX users tend to use others

– Some dearchiving programs handle only one archiving standards, others several

Dearchive

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FTP Archiving

Receiver must dearchive the files to read them

Self-Dearchiving Files– Usually, you need a dearchiving program to dearchive

– However, some archives have the extension .exe

– Really programs; Dearchive themselves

– Executing the archive file dearchives its files

– These are programs, so be wary of viruses!

Dearchive

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LISTSERV

LISTSERV Host Maintains Lists of E-Mail Addresses

– You subscribe to a specific list

– Messages posted to the list are mailed to you

– You receive them in your ordinary e-mail system

Postingvia E-Mail

Deliveryvia E-mail

LISTSERV host

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There is a LISTSERV host computer with a hostname (puka.org in this example)

A LISTSERV program manages conferences on the host (in this case, the program is named LISTSERV)

The program manages multiple conferences (GLOBAL-L and CRIME-L in this example)

A LISTSERV Conference

LISTSERV Hostpuka.org

LISTSERV Program GLOBAL-L Conference CRIME-L Conference

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Subscribing to a LISTSERV Conference

To: [email protected]:----------------------------------subscribe GLOBAL-L Ray Panko


1.

Subscription message is sent to the list management program, LISTSERV, not to a specific conference

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2.

Subject field can be left blank; You can have a subject if you like, but it will be ignored

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3.

Body must read as follows:

subscribe conferencename yourname

Not “subscribe to”No period at end

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Nothing else may be in the body

In particular, you must NOT have a signature

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Common Errors

Sending the subscription message to a conference name, not to the LISTSERV manager program– It doesn’t work– It goes to everyone in the conference, annoying them

Not typing “subscribe conferencename yourname” (without the quotes) exactly

Adding a signature or any additional text in the body

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Posting a LISTSERV Message

To: [email protected]: Gigaplexe?-------------------Is anyone using one of the newGigaplexe LANs in Europe?


1.

Post the message to the conferencename at the host, not to the LISTSERV manager program, LISTSERV

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Posting a Content Message to a Group



2.

Always add a descriptive Subject field

3.

Put whatever you like in the Body

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Unsubscribing from a LISTSERV Conference

Send an unsubscribe message to the LISTSERV management program– In this case, LISTSERV– NOT to the conference!!!!!!!!!– Be sure to record the name of the management program

when you subscribe so you can unsubscribe later

Body must read (exactly)– unsubscribe conferencename

Nothing else must be in the body– In particular, the message may not have a signature

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Recap Subscribing (Supervisory Message)

– Send message to LISTSERV manager– Not to the conference name!– Body: “subscribe conferencename yourname”– No signature or anything else

Posting (Content Message)– Send postings to conferencename

Unsubscribing (Supervisory Message)– Must unsubscribe to stop getting mail– Send message to LISTSERV manager– Nothing in body except “unsubscribe conferencename”

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USENET

Conceptually like reading magazines

USENET hosts

– Like bookstores

Each host has many Newsgroups on specific topics

You can read postings to these Newsgroups

Anyone can post new messages to these Newsgroups

Usenet Hostwith Multiple Newsgroups

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USENET Browsing Newsgroups

– Host maintains many conferences (Newsgroups)– Connect to any USENET host (there are thousands)– Subscribe to Newsgroups (there are thousands)– Read postings to subscribed newsgroups

Usenet Hostwith Multiple Newsgroups

ClientHost Connect, choose Newsgroup

Read Postings

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USENET

There are many USENET hosts– Postings to one are replicated (copied) to all others– May take time– Not all USENET hosts support all Newsgroups

Posting

Copy

Copy

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USENET Newgroups

Organized Hierarchically to help users find relevant newsgroups

Root (all groups)

Comp Alt

Comp.risks Comp.dcom

Comp.dcom.cabling Comp.dcom.servers

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Reading Newsgroups

Menu Bar

Subscribed NewsgroupsComp.dcom.cabling...

Comp.dcom.CablingQuestion on cabling Re: Question on ...

Subject: Re: Question on cablingFrom: Pat Lee <[email protected], we ran into the same problem. Use duct tape.

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Threads

Replies are grouped under original messages

– Original message plus replies is called a thread

– Easy to follow content

RJ-45 problem

Question Regarding Cabling

Re: Question Regarding Cabling

Re: Question Regarding Cabling

Re: Re: Question Regarding Cabling

Enhanced Category 5?

Thread

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LISTSERVs vs. USENET

LISTSERVs

– No need to check for new postings: delivered via e-mail

– Must remember how to unsubscribe

– Must find the LISTSERV host holding the conference

USENET

– Will not clog your mailbox with “junk mail”

– Log into almost any USENET host to find a particular Newsgroup

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Moderated Conferences

Moderated Conference

– Moderator reads postings that arrive

– Posts to conference only if relevant, polite

Unmoderated Conferences

– No moderator

– All postings are made available as soon as they arrive

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Telnet

Traditional Terminal-Host Communication– Log into host computer– You can run programs there, such as E-mail– Processing is done on the host– Expensive if long-distance connection

HostTerminal orPC Emulatinga Terminal

Phone Line

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Telnet

Uses Internet to Connect to Host

– Can access host from anywhere on the Internet

Telnet Software on Client Host– Manages login, use, and disconnections

Telnet Telnet

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Telnet

Poor User Interface

– Based on dumb VT100 terminal (Module H)

– Text-only display

– Monochrome (One color for text, one for background)

– Have to type command-line commands Often have complex syntax

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Why Not POP and IMAP?

Not all mail hosts support POP and IMAP

With most mail readers, you have to store contact information within some preferences file

– Inconvenient in school labs or Internet cafes

Telnet is not limited to e-mail

– Can be used with other applications

Documents

Internet Applications Module G Copyright 2001 Prentice Hall