1. Internet Applications Module G Copyright 2001 Prentice Hall

2. 2 File Transfer Protocol (FTP) F FTP host stores files F Client logs into host F Client program sends command to get a file F FTP host downloads the file with error correction FTP Host 2. FTP Get Command 3. Download 1. Login

3. 3 File Transfer Protocol (FTP) F User can also upload a file to the FTP Server –WWW cannot do this FTP Host 2. FTP Upload 1. Login

4. 4 File Transfer Protocol (FTP) F Must Log into FTP Host Before Transfers F Traditional FTP –You log into a specific account with a password –You can transfer to and from directories accessible to that account F 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

5. 5 FTP File Format Standards F 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

6. 6 FTP Archiving F 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

7. 7 FTP Archiving F Receiver must dearchive the files to read them F 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

8. 8 FTP Archiving F Receiver must dearchive the files to read them F 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

9. 9 LISTSERV F 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 Posting via E-Mail Delivery via E-mail LISTSERV host

10. 10 There is a LISTSERV host computer with a host name (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 Host puka.org LISTSERV Program GLOBAL-L Conference CRIME-L Conference

11. 11 Subscribing to a LISTSERV Conference To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko 1. Subscription message is sent to the list management program, LISTSERV, not to a specific conference

12. 12 Subscribing to a LISTSERV Conference To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko 2. Subject field can be left blank; You can have a subject if you like, but it will be ignored

13. 13 Subscribing to a LISTSERV Conference To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko 3. Body must read as follows: subscribe conferencename yourname Not “subscribe to” No period at end

14. 14 Subscribing to a LISTSERV Conference To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko To: LISTSERV@puka.org Subject: ---------------------------------- subscribe GLOBAL-L Ray Panko Nothing else may be in the body In particular, you must NOT have a signature

15. 15 Common Errors F 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 F Not typing “subscribe conferencename yourname” (without the quotes) exactly F Adding a signature or any additional text in the body

16. 16 Posting a LISTSERV Message To: GLOBAL-L@puka.org Subject: Gigaplexe? ------------------- Is anyone using one of the new Gigaplexe LANs in Europe? To: GLOBAL-L@puka.org Subject: Gigaplexe? ------------------- Is anyone using one of the new Gigaplexe LANs in Europe? 1. Post the message to the conferencename at the host, not to the LISTSERV manager program, LISTSERV

17. 17 Posting a Content Message to a Group To: GLOBAL-L@puka.org Subject: Gigaplexe? ------------------- Is anyone using one of the new Gigaplexe LANs in Europe? To: GLOBAL-L@puka.org Subject: Gigaplexe? ------------------- Is anyone using one of the new Gigaplexe LANs in Europe? 2. Always add a descriptive Subject field 3. Put whatever you like in the Body

18. 18 Unsubscribing from a LISTSERV Conference F 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 F Body must read (exactly) –unsubscribe conferencename F Nothing else must be in the body –In particular, the message may not have a signature

19. 19 Recap F Subscribing (Supervisory Message) –Send message to LISTSERV manager –Not to the conference name! –Body: “subscribe conferencename yourname” –No signature or anything else F Posting (Content Message) –Send postings to conferencename F Unsubscribing (Supervisory Message) –Must unsubscribe to stop getting mail –Send message to LISTSERV manager –Nothing in body except “unsubscribe conferencename”

20. 20 USENET F Conceptually like reading magazines F USENET hosts –Like bookstores F Each host has many Newsgroups on specific topics F You can read postings to these Newsgroups F Anyone can post new messages to these Newsgroups Usenet Host with Multiple Newsgroups

21. 21 USENET F 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 Host with Multiple Newsgroups Client Host Connect, choose Newsgroup Read Postings

22. 22 USENET F 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

23. 23 USENET Newgroups F Organized Hierarchically to help users find relevant newsgroups Root (all groups) Comp Alt Comp.risksComp.dcom Comp.dcom.cabling Comp.dcom.servers

24. 24 Reading Newsgroups Menu Bar Subscribed Newsgroups Comp.dcom.cabling... Comp.dcom.Cabling Question on cabling Re: Question on... Subject: Re: Question on cabling From: Pat Lee <Pat.Lee@Busad.Waikiki.edu ----------- Bill, we ran into the same problem. Use duct tape.

25. 25 Threads F 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: Re: Question Regarding Cabling Enhanced Category 5? Thread

26. 26 LISTSERVs vs. USENET F 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 F USENET –Will not clog your mailbox with “junk mail” –Log into almost any USENET host to find a particular Newsgroup

27. 27 Moderated Conferences F Moderated Conference –Moderator reads postings that arrive –Posts to conference only if relevant, polite F Unmoderated Conferences –No moderator –All postings are made available as soon as they arrive

28. 28 Telnet F 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 Host Terminal or PC Emulating a Terminal Phone Line

29. 29 Telnet F Uses Internet to Connect to Host –Can access host from anywhere on the Internet F Telnet Software on Client Host –Manages login, use, and disconnections Telnet

30. 30 Telnet F 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 u Often have complex syntax

31. 31 Why Not POP and IMAP? F Not all mail hosts support POP and IMAP F With most mail readers, you have to store contact information within some preferences file –Inconvenient in school labs or Internet cafes F Telnet is not limited to e-mail –Can be used with other applications