1. CISCO NETWORKING ACADEMY Chabot College ELEC 99.05 Application Layer Puzzles

2. CISCO NETWORKING ACADEMY Puzzle When I run a network application, I see results on my screen. Where are those events happening?

3. CISCO NETWORKING ACADEMY Application Layer Host relationships: –Client typically a user PC the source of a transaction –Server a shared host on the network the destination of the transaction Network applications usually are “client-server”

4. CISCO NETWORKING ACADEMY Application Layer Connection types –Make-Break –Session

5. CISCO NETWORKING ACADEMY Make-Break Connections Typically involve a single file transfer. Examples –HTTP HyperText Transfer Protocol web file TCP port 80 –SMTP Simple Mail Transfer Protocol E-mail file TCP port 25

6. CISCO NETWORKING ACADEMY Session Connections Maintained until “session” is closed. Examples –telnet terminal emulation passes keystrokes from client to server TCP port 23 –FTP File Tranfer Protocol manages transfer of many files TCP port 21

7. CISCO NETWORKING ACADEMY telnet Examples telnet://library.uark.edu telnet://locis.loc.gov

8. CISCO NETWORKING ACADEMY Running telnet (DOS) At the DOS Prompt, type > telnet hostname or > telnet Ipaddress Try it! Demo Telnet to library.uark.eduDemo Be sure to choose “Q” to logoff when done.

9. CISCO NETWORKING ACADEMY Running telnet (Windows) Start | Programs | Accessories | Communications | Hyperterminal Double-click Hypertrm.exe Enter a name for this connection At the bottom of the next dialog box, for “Connect Using”, select TCP/IP (winsock) Add the destination host name or IP address (Notice the port number in this dialog) Try it! Demo Telnet to library.uark.edu Demo Be sure to choose “Q” to logoff when done. When asked if you wish to save the session, say “No”

10. CISCO NETWORKING ACADEMY Running telnet (browser) Browsers use helper applications to provide certain functions. By default, Internet Explorer launches Hyperterm when it encounters a URL that specifies the telnet protocol Try it! Demo Demo Point your browser at telnet://library.uark.edu Be sure to choose “Q” to logoff when done. When asked if you wish to save the session, say “No”

11. CISCO NETWORKING ACADEMY telnet In Semester 2, you will use telnet extensively to connect your PC to routers.

12. CISCO NETWORKING ACADEMY DNS Puzzler In the following URL, what does “WWW” refer to? http://www.clpccd.cc.ca.us Answer: It is the hostname (computer name) portion of a “fully qualified domain name” It does not specify the protocol HTTP (web)! This computer just happens to be named “ www ”.

13. CISCO NETWORKING ACADEMY Fully Qualified Domain Name www.clpccd.cc.ca.us Host nameDomain nameTop-Level Domain name

14. CISCO NETWORKING ACADEMY Let’s try it! Point your browser at: http://209.129.156.3 http://www.clpccd.cc.ca.us http://www http://porter.clpccd.cc.ca.us http://porter

15. CISCO NETWORKING ACADEMY Let’s try it! For the host at 209.129.156.3, Chabot’s DNS servers list porter as the host name www as a name alias (a canonical name) We will study the structure of DNS tables in Semester 2.

16. CISCO NETWORKING ACADEMY DNS Puzzler Why is Chabot-Las Positas assigned a domain name of clpccd.cc.ca.us ? Why aren’t we clpccd.edu ? Answer: RFC 14801480 A recent change permits community colleges to move to the.edu top-level domain.

17. CISCO NETWORKING ACADEMY Browser URL Universal Resource Locator Example: http://www.cisco.com Browser uses the text before :// to select protocol and port number. protocolhostnamedomaintop-level domain

18. CISCO NETWORKING ACADEMY Let’s try it! Point your browser at: telnet://library.uark.edu http://library.uark.edu

19. CISCO NETWORKING ACADEMY Browser URL Universal Resource Locator Example: http://www.cisco.com If protocol:// is omitted, then the protocol is not specified. In that case, the browser tries to “guess” the protocol from the hostname: –hostname www defaults to http (port 80) –hostname ftp defaults to ftp (port 21)

20. CISCO NETWORKING ACADEMY HTTP Puzzler When you view a web page, where is it? Answer: On your PC! Let’s look at the contents of C:\windows\temporary internet files demodemo Note that one web page may be made up of many files of various types. Note that one web page may contain files loaded from several servers!

21. CISCO NETWORKING ACADEMY E-mail Puzzler When you view your E-mail, where is it stored? Answer It depends on the protocol! –Post Office Protocol (POP) –Web mail (e.g. yahoo mail)

22. CISCO NETWORKING ACADEMY E-mail Clients POP Clients –E-mail is transferred from the mail server to your PC –Port 110 –Client examples” Eudora, Outlook Express, Netscape –Most ISPs offer POP E-mail Web mail clients –E-mail remains on the server for viewing by any browser in the world. –Port 80 –Browser is the client. –Offered by Yahoo, Hotmail, GroupWise Web Access

23. CISCO NETWORKING ACADEMY POP E-mail E-mail is delivered to client PC. Once delivered, it can only be accessed at that PC. E-mail passes through the post office server but does not remain there.

24. CISCO NETWORKING ACADEMY Web E-mail E-mail is delivered to the Web mail server and remains there. Web E-mail can be viewed from any web browser.