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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 • 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 • 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
Request URL or hyperlink Web browser Web server HTTP User Response Browser or relevant application
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)
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
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
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
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
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)
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
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
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)
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
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
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
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
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
18.4 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
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)
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