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Class10 - CSCI 233 Class 10 Click to edit Master subtitle style Agenda VoIP Internet telephone service SNMP 22 Voice and Video over IP How can IP

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Click to edit Master subtitle style CSCI 233 Class 10
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22 Agenda VoIP Internet telephone service SNMP
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33 Voice and Video over IP How can IP be used to transfer real-time data such as voice and video? Telephone service is most developed at this time. How can routers guarantee sufficient quality of service for video and audio reproduction?
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44 Audio Encoding Codec—converts audio to digital or vice versa Pulse code modulation (PCM) is standard for telephones, produces 64 Kbps PCM standard is 8-bit sample 8,000 times per second Requires one megabyte for 128 seconds of audio How to reduce the amount of data transmitted: 1. Take fewer samples per second 2. Use fewer bits per sample 3. Compress the data Each method of reducing data has its own costs
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55 Accurate Reproduction Audio, video applications are typically real-time, requiring timely transmission and delivery Phone system is isochronous—entire system delivers output with the same timing as input Both order of data and timing as samples are converted into signals must be the same as org IP is not isochronous, so time stamp (for timing) is needed in addition to packet number (for ordering)
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66 Receiver overcomes jitter with a playback buffer K is called playback point. At start of transmission, system fills to playback point, then starts playing. Choice of K is tradeoff between delay and loss of data. If K is too large, excessive delay is introduced. If K is too small, jitter may occur. What happens when an empty spot is encountered in the buffer? Jitter, Playback Delay
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77 Real-Time Transport Protocol RTP provides time stamp and sequence number No mechanisms for timely delivery
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88 Mixing Mixing is needed to allow for conferences RTP works with multicasting Sources can unicast to mixer, which then mixes and multicasts the result Mixing may involve translating all sources back to analog, mixing the analog, then resampling the mixed signal)
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RTP Encapsulation RTP is formally transport-level, so would be encapsulated in IP datagrams Usually it runs over UDP, so each RTP
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This note was uploaded on 09/03/2010 for the course CS 233 taught by Professor Davidc.roberts during the Fall '10 term at GWU.

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Class10 - CSCI 233 Class 10 Click to edit Master subtitle style Agenda VoIP Internet telephone service SNMP 22 Voice and Video over IP How can IP

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