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18.3 Internet Services

18.3 Internet Services. World Wide Web (WWW) Electronic mail (e-mail) File Transfer Protocol (FTP) Remote logon Online chat Discussion forums Newsgroups. 18.3.1 World Wide Web. Most widely used Internet service Information Online shopping Applying for jobs Online entertainment

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18.3 Internet Services

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  1. 18.3 Internet Services • World Wide Web (WWW) • Electronic mail (e-mail) • File Transfer Protocol (FTP) • Remote logon • Online chat • Discussion forums • Newsgroups

  2. 18.3.1 World Wide Web • Most widely used Internet service • Information • Online shopping • Applying for jobs • Online entertainment • Booking tickets • Web server • Collection of web pages and linked files • Hypertext Transfer Protocol (HTTP) • Web browser (i.e. Firefox, Chrome, Explorer) sends requests to the web server

  3. Request URL or hyperlink Web browser Web server HTTP User Response Browser or relevant application

  4. Multimedia • Graphics; bitmaps or vector graphics • File formats of bitmap • BMP (Bitmap) – not commonly used • JPG/JPEG (Joint Photographic Experts Group) • GIF (Graphics Interchange Format) • PNG (Portable Network Graphics) • File formats of vector graphics • SWF (Adobe Flash) • WMF (Windows Mediafile) • EPS (Encapulated PostScript)

  5. SWF – most widely used • Vector-based animation graphics for web pages • Adobe Flash • WMF – used in Windows based application software • Cannot be edited extensively • Allow rescaling only • EPS – used in desktop publishing software • Allow rescaling only

  6. Audio • Audio data stored on the Internet should be compressed in order to transmit smoothly • Delay can be further minimized by using file formats which support streaming

  7. Video • Streaming video file format is widely used to reduce the waiting time for watching videos • WMV (Windows Media Video), RM (RealMedia) and MOV (QuickTime Movie) all support streaming • It is possible to compress WMV and RM by specifying frame size, frame rate and audio properties

  8. Techniques for reducing file sizes • Increasing compressing ratio: smaller file size but worse quality • Reducing frame size: by reducing the dimensions by half, the file will be only 25% of the original • Reducing frame rate: will reduce number of frames and therefore file size • Lowering audio quality: minor effect on file size

  9. Media players & Plug-ins • Though web browsers support a few audio file formats, they don’t support video; a media player is needed • Each media player doesn’t support all formats • The web browser itself only displays basic multimedia elements; plug-ins make it possible to play other content • Plug-ins are integrated into the browser • Examples: Flash Player (.flv), Shockwave Player .swf), QuickTime (.mov), Acrobat Reader (.pdf), RealPlayer (.rv and .ra)

  10. 18.3.2 File Transfer Protocol • Polular way of transferring files on the Internet • FTP transfer goes between server (using FTP server software) and client • We can use an FTP client software or web browser to connect to the FTP server • Requires username and password (user authentification) • Anonymous FTP allow users to log in without having their own log-in accounts • Two modes: ASCII (plain text) and binary (transmitting file bit by bit – receiver computer reassembles the bit stream back to single file) • Allows users to use commands like ”put” and ”get”, and it is possible to manage file transfers in batch

  11. 18.3.3 E-mails • Transmission from one computer to another via mail servers on a computer network • Must be adressed to correct e-mail adress (user@domain.com) • An e-mail program/client is needed to handle e-mails • E-mails are transmitted through an e-mail system, then stored on the user’s mail server and forwarded to the mailbox on the computer

  12. Sender’s computer Receiver’s computer Internet POP or IMAP POP or IMAP SMTP SMTP E-mail server (sender side) E-mail server (receiver side)

  13. Simple Mail Transfer Protocol (SMTP) • Communication between two mail servers • ’Push’ mail server; sender’s mail server transmits to receiver’s, but receiver’s can’t request from sender’s • Developed in the early 1980’s • Drawbacks: • Unable to authenticate senders, therefore spam mails and viruses can be spread • Originally designed for ASCII (text-based), and is less efficient concerning binary file attachments • Post Office Protocol (POP) • Allows users to download e-mails from server to mailbox • POP3 is currently most widely used for large organizations and mobile e-mail communication devices • Internet Manage Access Protocol (IMAP) • More advanced that POP • Stores all e-mail in the mail box on the mail server, allowing more users to access at the same time • Mail boxes can be accessed from any computer via web browser or e-mail program • Supports partial fetchings of e-mails

  14. Webmail • Provided by a website • Accounts are accessed through a web browser • i.e. Hotmail, Yahoo!, Gmail • Usually free and no additional software necessary • No offline access, lower access speed and higher security risk

  15. 18.3.4 Newsgroups • Electronic public message board • Users use a web browser or newsreader to log in, then read and post text massages onto a newsgroup • Categorized into hierarchical structure, allowing users to search for particular topics easily • Provided by Internet Service Provider or an organization • No longer popular

  16. 18.3.5 Discussion Forums • Web site similar to newsgroup • Messages can contain text, graphics and hyperlinks 18.3.6 Online Chat • One-to-one or one-to-many discussions • Voice, text and graphics • Nowadays many programs allow voice and video chat

  17. 18.3.7 Remote Logon • Establishment of a connection between a computer and a server via LAN, the Internet or a public communication media (i.e. telephone line) • Allows a server to be operated remotely • Telnet, the first network protocol for remote access of server services, was developed in the late 1960’s • Telnet client completes the login procedure after network connection is made • Telnet has been replaced by Secure Shell (SSH), which has much higher security control

  18. 18.4 Streaming Technology on the Internet • Streaming allows you to watch the video/listen to the audio while it is being downloaded • The media file is parted into many small portions, and as soon as one portion is downloaded, it can be played while the next parts are downloading • Plug-ins or media players are needed to play these files • Widely used in webcasting, voice mail, video conferencing and some peer-to-peer video phone services

  19. 18.4.1 Webcasting • Broadcasting of multimedia contents over the Internet • Used for entertainment, e-learning, commercial promotions etc. • Many major broadcasters, television companies, movie companies and radio stations use webcasting • Many video sharing websites (i.e. YouTube) – legal issues (SOPA, ACTA)

  20. 18.4.2 Voice Mail • Many instant messaging clients support offline messaging and voice mails • Works similar to e-mail 18.4.3 Video conferencing • Virtual meeting with real-time video and sound • Requires microphone, webcam and video conferencing software • Video and audio signals are compressed in order to reduce data size • The qualities of video and audio depend on the bandwidth and network traffic • Examples of usages of video conferencing: • Lectures for students living in remote areas • Telemedicine and telenursing (esp. for patients in rural areas • Business meetings

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