Internet Resources Discovery IRD Introduction to the InternetWWW

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

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

Internet Resources/Services • • 3 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) 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. 4 T. Sharon-A. Frank

? What is the Internet • • • 5 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 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 router server regional ISP – fiber, copper, radio, satellite • routers: forward packets (chunks) of data thru network 6 mobile local ISP running network apps • communication links T. Sharon-A. Frank workstation company network

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

Interconnected Network Private Dedicated Public Circuit Switched Router Local Area ISDN Bridge Router Metropolitan Area Local Area Gateway Public Packet Switched T. Sharon-A. Frank

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

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

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

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

TCP/IP • 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. TCP IP 13 TCP Internet T. Sharon-A. Frank IP

IP Packet Data From: 192. 112. 36. 5 To: 128. 174. 5. 6 IP Address 14 Packet Envelope T. Sharon-A. Frank

IP Properties • IP will get it there, but… – – Network Delay is Variable Message might be lost, or sent out of order. Message can’t be too long (about 1 K 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. 15 T. Sharon-A. Frank

Protocols in the TCP/IP Model Protocols Application Transport TELNET FTP TCP IP ARPANET SATNET Networks 16 DNS UDP Network Physical+ data link SMTP T. Sharon-A. Frank Packet radio LAN

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

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

Domain Names cs. biu. ac. il il ac tau biu cs 19 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 20 T. Sharon-A. Frank

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

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

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