Overview of the Internet

Transcription

1 Overview of the Internet IVPR 1 Outline Goals and Objectives Topics headlines Introduction Internet and WWW Client/Server Model Diagnostic commands Evolution of Internet Transmission IP Addresses and Domain Names URLs addresses File Protocols File Compression and Decompression Intranets and Extranets Connecting to the Internet Modems Types Internet Tools Summary IVPR 2 1

2 Goals and Objectives Goals Understand and master basic concepts of Internet and WWW use effectively Objectives IVPR 3 Objectives Client/Server Model Data and file transmission IP addresses, Domain Names, URLs addresses File protocols, compression and decompression Intranets and Extranets Internet connections Modems IVPR 4 2

3 Topic Headlines Introduction Internet dubbed as new mode of transportation The Internet and the World Wide Web Web: multimedia section of internet Internet Jargon Learn internet jargon IVPR 5 Client Server Model allows two networked computers to talk to each other Client/Server Diagnostic Commands probe communication with server IVPR 6 3

4 Evolution of internet and World Wide Web since the 1960s Transmission across Internet TCP/IP protocol and its packets central to internet use IP Addresses and Domain Names Computers: IP addresses Humans: Domain Names IVPR 7 URI / URL Addresses extends naming scheme of domain name IVPR 8 4

5 Protocols Formats and rules of exchanging files Compression and Decompression speed up downloads & uploads Intranets and Extranets private networks for security reasons Connecting to the Internet dial-up DSL cable T lines Modems Analog (phone), DSL, cable IVPR 9 Introduction Internet: instant information and communication more users in first five years than telephone did in first thirty years s already outnumbers regular mails IVPR 10 5

6 Internet and World Wide Web Internet: network of networks information superhighway Link servers around world WWW: driving force of internet Multimedia & hyperlinking E.g., text, audio, video, graphics, images IVPR 11 The Internet IVPR 12 6

7 Client/Server Model 2 programs on diff / same computer Client Server Client requests services from server Multiple clients can access server concurrently IVPR 13 2-tier / 3-tier Architecture Client/Server dbs used extensively on web 2-tier architecture most common model. 3-tier model: middle server added between db and client security IVPR 14 7

8 Simple Diagnostic Commands 1. finger: finger <host> // who currently logged in finger // user logged in? 2. ping: client check if server up and running ping <host> 3. tracert: Traces xmission route client server tracert <host> IVPR 15 Evolution of the Internet Early research Network / xmission reliability Under nuclear attack Advanced Research Project Agency (ARPA), 1962 IVPR 16 8

9 Internet development evolution 1960s: ARPANET 1970s-1980s: CSNET USENET ITNET NSFNET Internet IVPR s: World Wide Web 1989, WWW conceived by Berner-Lee Cern (Geneva) Initial goals Local Sharing Collaboration Takes off w/ 1st graphic browser (Mosaic) NCSA, U. Illinois, Urbana-Champaign, : 50 50k servers IVPR 18 9

10 Xmission across Internet Underlying protocols: TCP/IP IP: lower level TCP IVPR 19 Internet Protocol (IP) Numeric addresses Format: 32-bit binary number Dotted Octet : New standard, IPv6: 128 bits (1998) Each node: unique address Organizations assigned groups of IPs IVPR 20 10

11 Xsmission across Internet IP protocol: data packets Sender Bundle Label Sender & receiver IP addresses Send to receiver s IP address Travel different routes No guarantee Delivery Correct order IVPR 21 TCP Sender Also packet sequence numbers Receiver Unpack TCP packets Reconstruct original data Verify packet arrival Request resend if necessary Assemble correct sequence Make available to application program IVPR 22 11

12 IP Addresses and Domain Names IP address Unique Easy for computers Hard for humans Domain names IVPR 23 Domain names Easy for humans to remember [<alias>.]<host> <sub domain>. <TLD> Sub-domains (< 5) 1 st : host name / alias Last: top-level domain (TLD) 2nd level domain excludes host name IVPR 24 12

13 Domain names E.g., weblab.cs.uml.edu Domain name weblab.cs.uml.edu Host name Second level domain names TLD IVPR 25 TLD Type / location, e.g.,.com commercial.edu educational.gov government agency.org nonprofit organization.net network service provider.mil U.S. military.us US.au Australia.uk for England, etc. DNS IVPR 26 13

14 DNS DNS: Domain Name System (Server) Hierarchical Map to IP address IVPR 27 FIGURE 1.1 Domain name conversion IVPR 28 14

15 URI / URL / URN URI: Uniform Resource Identifier Locator / name / both All URIs can be treated as names URL and URN subsets of URI IVPR 29 URL (locator) Identify resource Provide means to Act upon, or Obtain representation of resource Primary access mechanism Network location E.g., Resource (Wikipedia's home page) Representation of resource E.g., current HTML code Get via HTTP protocol IVPR 30 15

16 URN (name) Identify resource by name In some namespace Location / dereferencing info not necessarily implied E.g., urn:isbn: URI like International Standard Book Number (ISBN) Allow to talk about book, but No info Where & how to obtain actual copy IVPR 31 Protocols File formats + exchanging rules server <--> client Most common http: Hyper Text Transfer Protocol https: Secure http smtp: Simple Mail Transfer Protocol pop: Post Office Protocol imap: Internet Message Access Protocol nntp: Network News Transfer Protocol newsgroups ftp: File Transfer Protocol telnet: remote access to a computer file: Display file on client local drive IVPR 32 16

17 URL General form: scheme:object-address Scheme: often communications protocol E.g., http, telnet, ftp, file For http, object-address is: <fully qualified domain name/doc> path For file protocol only <doc> path needed IVPR 33 may include port number lhaim5.cs.uml.edu: is http default port 8080 often used for alternative / experimental URLs cannot include spaces / other special characters (semicolons,...) doc path may be partial / relative Unix-like (~/./../ / etc) Completion by server configuration If doc path ends with / directory IVPR 34 17

18 Addresses Unique address / user Format: <user>@<domainname> <DomainName>: usually 2 nd level (no host) <user> Name selected by user (usually) Can be combination of letters, numbers, certain special characters E.g.,: haim@lhaim.com haim@cs.uml.edu haim@lhaim5.cs.uml.edu not common / not recommended IVPR 35 Compression & Decompression File transfer depends on connection speed, file size and server traffic File size affects transfer time and disk space compression & decompression control file size Compression SW use complex algorithms to encode & decode file E.g., AAAAAAAGGGWZZZZ 7A3G1W4Z Multiple files can be compressed together archives maintain file directory structure IVPR 36 18

19 Intranets and Extranets Same as internet, but diff Geographical domains Level of security Intranet Contained within organization Outside intruders not allowed access Firewalls installed around intranets for security Extranet Organization network Allows access to outside networks Extranet: intermediate between internet and intranet IVPR 37 Intranets and Extranets IVPR 38 19

20 Connecting to the Internet ISPs: access via dial-up, DSL, Cable connection AOL & MSN: access and content Phone & cable companies: access only Finding content: user s task Some ISP selection guidelines: Maximum connection speed Type of connection (dial-up vs. broad band) Available help line Software provided Costs and charges IVPR 39 Modem Types Data line signal data Modem types: Telephone (analog) Cable DSL and ADSL ISDN (digital) B-ISDN Satellite Wireless (cellular) IVPR 40 20

21 Internet Tools Programs Allow effective use of the internet Shareware / freeware / commercial Basic internet tools : Web browsers Virus scan programs File compression and decompression FTP and Telnet Graphics programs IVPR 41 Summary TCP/IP protocols IP addresses vs. Domain Names DNS: Domain Name IP-address conversion Top-level domains: e.g.,.com,.edu,.gov,.org,.net, and.mil addresses <user>@<domain> Intranets and Extranets: private networks IVPR 42 21