Telephony and Multimedia CS2033 PDF

Telephony and Multimedia Sunimal Rathnayake CS2033 Slides by Prof. Gihan Dias 2021  Telecommunications ⚫ Voice – Telephony − Point-to-Point (2-party) − Conferencin...

Telephony and Multimedia Sunimal Rathnayake CS2033 Slides by Prof. Gihan Dias 2021  Telecommunications ⚫ Voice – Telephony − Point-to-Point (2-party) − Conferencing (multi-party) − Radio Broadcast ⚫ Video − Video calls (2 and multi-party) − Television, streaming media, etc. ⚫ Data  Telephony ⚫ The Telephone Network ⚫ Enhanced Services ⚫ IP Telephony  The Telephone Network ⚫ The Telephone Network ⚫ The Access Network ⚫ Switching and Signalling ⚫ Transmission The Telephone Network Access Signalling  The Access Network Provides the subscriber’s connection to the Local Exchange (Central Office, CO) The biggest investment in a telecommunication network The biggest bottleneck in a telecommunication network  Access Technologies ⚫ Local Loop (wired) ⚫ Copper wire pairs optimized to carry voice in analog form ⚫ Wireless Local Loops (WLL) ⚫ Replaces the local loop with wireless connection ⚫ Digital Subscriber Loops (DSL) ⚫ Modified to carry data and voice within certain constraints on copper local loops ⚫ Fiber to the x (FTTx) ⚫ Optical fiber local loop (x=curb, business, home)  Switching ⚫ Connects subscribers to each other on demand ⚫ Manual operators ⚫ Automatic Switches – Electromechanical switches – Software-controlled switches  Transmission ⚫ Transportation of signals between subscribers of networks ⚫ High capacity copper cables, microwave (radio) links, optical fibers ⚫ Carries thousands of multiplexed calls between exchanges  Signalling ⚫ Functions ⚫ Call connection ⚫ Call disconnection ⚫ Billing ⚫ Subscriber loop signalling ⚫ e.g., dial tone, dial-digits, ringing signals ⚫ Inter-exchange signalling ⚫ Control of interconnection between exchanges for the routing of calls  Telephone Numbering System Country Code (94) Area Code (11) Operator Code (2) Telephone No. (650301) Extension (3100) Enhanced Services  Short Message Service (SMS) Sending and Receiving of short messages of up to 160 characters Part of Integrated Digital Subscriber Line (ISDN) Available on Mobile and CDMA networks Store and Forward Service by SMS Centre Receiver does not have to be on-line when message sent  Calling Line ID (CLI) Provides the calling number to the receiver Part of ISDN Also available on analog lines May be enhanced by looking up number in directory May be disabled to protect caller's privacy  Other Services Conference Calls Call Forwarding Voice Mail Follow Me Free calls Short Code numbers (e.g. 1919)  Location Based Services Providing different services based on location of subscriber – e.g. emergency services (119) – delivery services For Fixed lines, location is known For mobiles, location may be identified using – cell ID – GPS – Triangulation  Voice over IP (Internet Telephony)  What is Voice over IP (VoIP)? Using packet-switched data networks for interactive voice communications – Ethernet – WiFi – 3G/4G – any IP-based network – WAN or LAN Also known as Internet Telephony  Why VoIP? Data and multimedia more volume than voice Companies and individuals already have data networks – Ethernet, WiFi, ADSL, 3G, etc. No need to have additional network for voice Cheaper – internally – locally – internationally  How VoIP works User speaks into microphone or handset Voice is converted to a digital form by an encoder (codec) – encoder may be in USB phone, telephone card or by software in a computer Digitised voice is converted into packets for sending over the network Receiving PC/gateway converts packets into electrical signal using a decoder and plays it on speaker, headset or handset  Advantages of VoIP Use existing network Integrate with computer applications Support for advanced features – video – follow me – conferencing – etc.  Disadvantages of VoIP Higher latency (delay) Packet losses Lower (or maybe higher) voice quality Multimedia  What is Multimedia? ⚫ Multimedia is an integration of text, graphics, still and moving images, animation, sounds, or any others ⚫ Characteristics of multimedia ⚫ Digital – key concept ⚫ Integration of multiple media types, usually including video or/and audio ⚫ May be interactive or non-interactive  Media Types ⚫ Text, Graphics, image, video, animation, sound, etc. ⚫ Captured media (natural) : information captured from the real world. e.g.: still image, video, audio ⚫ Synthesized media (artificial) : information synthesized by the computer. e.g.: text, graphics, animation ⚫ Discrete media: has no time component ⚫ Continuous media: time-based Classification of Media Type Sound Video Animation Continuous Continuous Image Text Graphics Discrete Discrete Captured Synthesized From real world By computer  Text ⚫ Plain text ⚫ Unformatted ⚫ ASCII code, Unicode ⚫ All characters have the same style and font ⚫ Rich text ⚫ Formatted ⚫ Characters of various size, shape and style, e.g. bold, colourful ⚫ HyperText Markup Language (HTML)  Graphics ⚫ Revisable document that retains structural information ⚫ Consists of objects such as lines, curves, circles, etc ⚫ Usually generated by software  Images ⚫ 2D matrix consisting of pixels ⚫ Pixel—smallest element of resolution of the image ⚫ One pixel is represented by a number of bits ⚫ Pixel depth– the number of bits per pixel ⚫ Have no structural information ⚫ Two categories: scanned vs. synthesized still image Examples of images Binary image – pixel depth 1 Gray-scale – pixel depth 8 Color image – pixel depth 24  Video and Animation ⚫ Both images and graphics can be displayed as a succession of views which create an impression of movement ⚫ Video – moving images or moving pictures ⚫ Captured or Synthesized ⚫ Consists of a series of bitmap images ⚫ Each image is called a frame ⚫ Frame rate: the speed to playback the video (frame per second) ⚫ Animation – moving graphics ⚫ Generated by computer program (animation authoring tools) ⚫ Consists of a set of objects ⚫ Object may move and change over time  Sound 1-D time-based signal 0. 2 0. 15 0. 1 0. 05 0 -0. 05 -0. 1 -0. 15 -0. 2 0 100 200 300 400 500 600 700 800 900 1000 Speech – supports spoken language Non-speech – various sounds ⚫ Natural sound – Recorded/generated sound wave represented as digital signal ⚫ Example: Audio in CD, WAV files ⚫ Structured sound – Synthesize sound in a symbolic way ⚫ Example: MIDI file Multimedia Networking Classes of Multimedia Applications ⚫ Streaming stored audio and video ⚫ Streaming live audio and video ⚫ Real-time interactive audio and video  Streaming Stored Multimedia  E.G. YouTube  Client can pause, rewind, FF, push slider ba  timing constraint for still-to-be transmitted data: in time for playout  Streaming Live Multimedia Examples:  Internet radio talk show  Live sporting event Streaming  playback buffer  playback can lag tens of seconds after transmission  still have timing constraint Interactivity  fast forward impossible  rewind, pause possible!  Interactive, Real-Time Multimedia ⚫ applications: IP telephony, video conference, distributed interactive worlds ⚫ e.g. Zoom, Viber call ⚫ end-end delay requirements: ⚫ audio: < 150 msec good, < 400 msec OK ⚫ higher delays noticeable, impair interactivity  Summary Telephony The Telephone Network Enhanced Services Voice over IP (VoIP) Multimedia Multimedia Networking