1. T.Sharon-A.Frank 1 Internet Resources Discovery (IRD) Introduction to the Internet/WWW

2. 2 T.Sharon-A.Frank Introduction to the Internet Internet Resources/Services What is the Internet Standards/Protocols

3. 3 T.Sharon-A.Frank Internet Resources/Services Electronic Mail (E-Mail) News (Usenet) File Transfer (FTP) Remote Login (Telnet) Information Browsing (Gopher) Automated Title Search (Archie, Veronica) Automatic Content Search (WAIS) Advanced Browsing (WWW)

4. 4 T.Sharon-A.Frank Internet Resources Discovery (IRD) Resources discovery - locating unfamiliar resources. Resources can be documents, files, users and services, both textual and multimedia. IRD is resource discovery on the internet and in the Web.

5. 5 T.Sharon-A.Frank What is the Internet? Internet is a Multi-Network Architecture Internet = Interconnected Network Internet is based on TCP/IP Protocol Set IP = Internet Protocol TCP = Transmission Control Protocol Based on former ARPANET by DOD

6. 6 T.Sharon-A.Frank What’s the Internet: “nuts and bolts” view millions of connected computing devices: hosts, end-systems –pc’s workstations, servers –PDA’s phones, toasters running network apps communication links –fiber, copper, radio, satellite routers: forward packets (chunks) of data thru network local ISP company network regional ISP router workstation server mobile

7. 7 T.Sharon-A.Frank Internet Infrastructure Router Regional and National Providers (ISP) Corporate Network Campus Ethernet LAN WAN

8. Interconnected Network Local Area Private Dedicated Public Circuit Switched Metropolitan Area Public Packet Switched Local Area Bridge Gateway Router Gateway Router ISDN

9. 9 T.Sharon-A.Frank Who Runs the Internet? “nobody” Standards:Internet Engineering Task Force (later…) Numbers: IANA (Internet Assigned Numbers Authority)IANA Names: Internic (US), RIPE (Europe),…InternicRIPE Network: ISPs (Internet Service Providers), NAPs (Network Access Points),… Fibers: telephone companies (mostly) Content: thousands of companies, universities, individuals,…

10. 10 T.Sharon-A.Frank What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific messages sent … specific actions taken when messages received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

11. 11 T.Sharon-A.Frank What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocol? Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://gaia.cs.umass.edu/index.htm time

12. 12 T.Sharon-A.Frank TCP/IP TCP breaks the message data into pieces Data IP Packet

13. 13 T.Sharon-A.Frank TCP/IP IP TCP Internet IP TCP TCP takes a long message and breaks it up: –Each piece has a sequence number. –Each piece is sent using IP: Destination has enough info to reassemble message. Will request missing piece until all is there.

14. 14 T.Sharon-A.Frank IP Packet Packet Data From: 192.112.36.5 To: 128.174.5.6 Packet Envelope IP Address

15. 15 T.Sharon-A.Frank IP Properties IP will get it there, but… –Message might be lost, or sent out of order. –Message can’t be too long (about 1K max). –For email, web, want reliable transfer of big files. –Still doesn’t say for which process a packet is intended: Message come to a machine, but are handled by a process. Like a house with many people in it. Solution is TCP. Network Delay is Variable

16. 16 T.Sharon-A.Frank Protocols in the TCP/IP Model TELNETFTPSMTPDNS TCPUDP IP ARPANETSATNET Packet radio LAN Application Transport Network Physical+ data link Networks Protocols

17. 17 T.Sharon-A.Frank Internet/WWW Standards Internet –Domain Name System (DNS) WWW –Uniform Resource Locator (URL) –Hypertext Markup Language (HTML) –Hypertext Transfer Protocol (HTTP)

18. 18 T.Sharon-A.Frank Domain Name Service (DNS) Map Domain Name to IP Address Domain Names must be Unique Domain Names have many Parts Suffix of Domain Names Significant cs.biu.ac.il www.netscape.com www.cmu.edu

19. 19 T.Sharon-A.Frank Domain Names il ac biu tau cs.biu.ac.il cs

20. 20 T.Sharon-A.Frank DNS - Domain Name Lookup Search in cache Search in local repository –If the name is in the same domain –If the name was retrieved lately Ask other servers

21. 21 T.Sharon-A.Frank DNS - Domain Name Lookup Domain name server in Israel User’s computer in Israel User’s computer in USA Internet Name IP Address

22. 22 T.Sharon-A.Frank DNS - Domain Name Lookup Domain name server in Israel Domain name server in USA User’s computer in Israel User’s computer in USA Internet Name IP Address

23. 23 T.Sharon-A.Frank Uniform Resource Locator (URL) Protocol: http, ftp, gopher... Domain-Name (or IP-address) Port (for security purposes) Directory File-Name Protocol://domain-name:port/directory/file-name Example: http://www.cs.biu.ac.il:8080/~taly/mm/index.html URL is an address of a Web page in the Internet.