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Human-Computer Interface

Human-Computer Interface. Human-Computer Interface. Course 5. ISPs and Internet connection. Domain Naming Service (DNS). DNS provides name to IP address mapping Originally one single central huge table. Today – each domain name provides its own DNS servers. Hierarchical structure:

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Human-Computer Interface

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  1. Human-Computer Interface Human-Computer Interface Course 5

  2. ISPs and Internet connection

  3. Domain Naming Service (DNS) • DNS provides name to IP address mapping • Originally one single central huge table. • Today – each domain name provides its own DNS servers. • Hierarchical structure: • Root DNS servers (serving .com .org .net, etc) • Domain serves – serve domain queries.

  4. DNS – How it works ? Connect at www.yahoo.com • Ask Root Server for the DNS server of .com => a.gtld-servers.net • Ask a.gtld-servers.net who is the DNS server for yahoo.com => ns1.yahoo.com • Askns1.yahoo.comwho is www.yahoo.com => is alias for www.yahoo.akadns.net • Ask ns1.yahoo.comwho is www.yahoo.akadns.net =>216.109.118.68

  5. The World Wide Web • HTML Language – to describe Web pages =>RFC1866 and RFC1942 • HTTP protocol – to transmit web pages • The Uniform Resource Locator – to name Web pages • Hypertext – a way of describing documents and data that reference other documents/data.

  6. TCP/IP Peer to peer communication HTTP 63.78.171.45 Port: 80 193.231.20.34 Port: 1563 IPAddress + Port: Identify communicating applications on the source and destination machines

  7. TCP/IP – peer to peer • IP Address – identifies the computer • Port • a communication channel descriptor • 0-65535 possible ports on one machine • 0-1024 – reserved well known ports (ex:80 – Web Servers) • Servers listen on well known ports

  8. Client/Server –architectures • Generally involves two entities • Server – application designed to service specialized requests. • Clients– applications using the services offered by the server. They are calling the server and ask him specific tasks. Example:Calling telephone information to find someone’s phone number

  9. URLs and URIs • URL – described in RFC1738 and RFC1808. • URI – Uniform Resource Identifiers – strings that specify how to access network resources. Ex: URL: http://www.cs.ubbcluj.ro http://www.cs.ubbcluj.ro/math/index.html Download RFCs: http://www.rfc-editor.org/

  10. TCP/IP Client Servers • Server – applications listening/waiting for client requests on a well known port. • Clients – connect to the server and issue requests on the communication channel. Requests are processed by the server and responses are sent back to clients.

  11. URL – Locating resources http://www.FreeSoft.org/Connected/index.html • http – we are using the HTTP protocol to access the resource. • www.Freesoft.org - the DNS name of the web server that has our resource. • /Connected/index.html – the name of the directory where the server stores our document.

  12. HTTP Protocol • Allows exchange of HTML and Web data. • Works on TCP port 80 and is human readable. Ex: Connect to www.cs.ubbcluj.ro GET / HTTP/1.0 > > < HTTP/1.0 200 OK < Date: Wed, 18 Sep 1996 20:18:59 GMT < Server: Apache/1.0.0 < Content-type: text/html < Content-length: 1579 < Last-modified: Mon, 22 Jul 1996 22:23:34 GMT < < HTML document

  13. The File Transfer Protocol-FTP • Provides ability to transfer files between machines heterogeneous env. and Op. Syst • Works on the port 21 using the TCP protocol. Ex: ftp ftp.ubbcluj.ro User: anonymous Password: dadi@cs.ubbcluj.ro ftp> get README

  14. Internet Mail • Mail protocols: SMTP, IMAP, POP3 • SMTP – Simple Mail Transfer Protocol • IMAP, POP3 – mailbox access protocols. • SMTP – works on TCP – port 25. • Each domain name has >=1 mail exchange servers • Human readable text protocol • Best effort mail transfer protocol.

  15. Internet Security • Internet connectivity and access to each computer – opportunity for hackers to access distant machines or intercept communications. • Protection methods: • Firewalls, proxy servers. • Encrypted communications • Digital signatures

  16. Internet Security – Firewalls • Firewall – piece of software or hardware implemented component that blocks IP packets for non-authorized users/machines. • Proxy Server – software component that intermediates connections between web browsers and external web servers.

  17. Encryption, signatures • SSL – Secure Sockets Layer – protocol implementing encrypted communication between two hosts with source and destination authentication. • Digital signatures allow to identify if a piece of data has been tampered during its transport.

  18. Firewalls Internet Computers

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