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Internet Telephony

Internet Telephony 3
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Dr.NeerajMittal,India,Teacher
Published Date:19-07-2017
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Internet Telephony Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1Overview  Telephony: history and evolution  IP Telephony: Why ? Adding interactive multimedia to the web Being able to do basic telephony on IP with a variety of devices  Basic IP telephony model  Protocols: SIP, H.323, RTP, Coding schemes, MGCP, RTSP  Future: Invisible IP telephony and control of appliances Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2Public Telephony (PSTN) History  1876 invention of telephone  1915 first transcontinental telephone (NY–SF)  1920’s first automatic switches  1956 TAT-1 transatlantic cable (35 lines)  1962 digital transmission (T1)  1965 1ESS analog switch  1974 Internet packet voice  1977 4ESS digital switch  1980s Signaling System 7 (out-of-band)  1990s Advanced Intelligent Network (AIN) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3Telephone Service in the US AT&T Divestiture Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4Telephone System Overview  Analog narrowband circuits: home- central office  64 kb/s continuous transmission, with compression across oceans -law: 12-bit linear range - 8-bit bytes  Everything clocked a multiple of 125 s Clock synchronization framing errors  AT&T: 136 “toll”switches in U.S. Interconnected by T1, T3 lines & SONET rings  Call establishment “out-of-band” using packet- switched signaling system (SS7) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5Telephony: Multiplexing  Telephone Trunks between central offices carry hundreds of conversations: Can’t run thick bundles  Send many calls on the same wire: multiplexing  Analog multiplexing  bandlimit call to 3.4 KHz and frequency shift onto higher bandwidth trunk  Digital multiplexing: convert voice to samples  8000 samples/sec = call = 64 Kbps Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6Trends: Price of Phone Calls: NY - London AT&T Divestiture Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7Trends: Data vs Voice Traffic Since we are building future networks for data, can we slowly junk the voice infrastructure and move over to IP? Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8Trends: Phone vs Data Revenues Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9Private Branch Exchange (PBX) Post-divestiture phenomenon... 7040 212-8538080 External line 7041 Telephone Corporate/Campus Private Branch Another switch Exchange switch 7042 7043 Corporate/Campus LAN Internet Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10IP Telephony: PBX Replacement Another campus Corporate/Campus 7040 8151 External line 8152 7041 PBX PBX 8153 7042 8154 7043 Internet LAN LAN Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11Voice over Packet Market Forecast – North America Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12Invisible Internet Telephony VoIP technology will appear in . . .  Internet appliances  home security cameras, web cams  3G mobile terminals  fire alarms  chat/IM tools  interactive multiplayer games Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13IPtel for appliances: “Presence” Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14Taxonomy of Speech Coders Speech Coders Waveform Coders Source Coders Time Domain: Frequency Domain: Linear Vocoder PCM, ADPCM e.g. Sub-band coder, Predictive Adaptive transform Coder coder  Waveform coders: attempts to preserve the signal waveform not speech specific (I.e. general A-to-D conv)  PCM 64 kbps, ADPCM 32 kpbs, CVSDM 32 kbps Vocoders:  Analyse speech, extract and transmit model parameters  Use model parameters to synthesize speech  LPC-10: 2.4 kbps Hybrids: Combine best of both… Eg: CELP (used in GSM) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15Speech Quality of Various Coders Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16Applications of Speech Coding  Telephony, PBX  Wireless/Cellular Telephony  Internet Telephony  Speech Storage (Automated call-centers)  High-Fidelity recordings/voice  Speech Analysis/Synthesis  Text-to-speech (machine generated speech) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17Pulse Amplitude Modulation (PAM) Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18Pulse Code Modulation (PCM) PCM = PAM + quantization Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19Quantization Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20