lecture 17 – march 21, 2002

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Lecture 17 – March 21, 2002

Content-delivery services.

Multimedia services

Reminder next week individual meetings and project status report are due.

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EdgeRouter

EdgeRouter

EdgeRouter

EdgeRouter

EdgeRouter

EdgeRouter

Local ISP Local ISP

Local ISP

Local ISPLocal ISP

Local ISP

ContentProvider

ContentDelivery

ContentDelivery

ContentDelivery

ContentDelivery

ContentDelivery

Content-delivery services

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Multimedia Services

Voice over IP

Still images

Audio broadcast

Video broadcast

Video on demand

Teleconferencing

Videoconferencing

Remote instrumentation

Telemedicine

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Analog and Digital Information

Sampling – Nyquist theoremQuantization – quantization noiseExamples:

voice – sampling rate 8,000 samples/sec 8 bits/sample-256 quantization levels music – sampling rate 48,000 samples/sec 16 bits/sample color video – 10,000,000 samples/sec 24 bits/sample

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Timing requirements for data streaming

Interactive service – voice over IP, teleconferencing delay and jitter sensitive but loss tolerant

Video streaming rate sensitive and to some extent loss tolerant. 25 frames/sec

Telemedicine and remote instrument control delay and loss sensitive

Stored media applications – video on demand less strict/demanding

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Delay and JitterPlay-out delay

End-to-end delay Delay at the sender Data transmission and propagation delay Delay at the receiver

Jitter – variability of end to end delay

For a normal conversation – play out delay < 100 msec not noticeable < 400 msec acceptable > 400 msec not acceptable

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Delay and Jitter

agt

ast b

gtapt

art

generationtime

receptiontime

playbacktime

bst

sending time

packets

b

a

brt

bpt

time

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Removing the Jitter in Voice over IP

Fixed play-out delay

Adaptive play-out delay takes advantage of silent periods between talk spurts

Fill in a buffer at a variable rate and drain it at a constant rate.

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Data Streaming

Data stream – sequence of bytes flowing out or into a process.

Media server

Media player

Often they require a Web browser to connect to the server and download a metafile describing the media player.

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WebBrowser

MediaPlayer

Http server

Multimedia database

HTTP request

HTTP response - metadata

Commands - TCP connection

Data stream - UDP

Client

ServerThread

ServerCache

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Error Recovery Schemes

Forward error correction – sender adds redundant information.Packet (i) contains the original information and

a low-quality version of packet (i-1)

Interleaving the stream is scrambled. Packet (i) does not contain samples adjacent

to each other.

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Real-time Protocol (RTP)

RTP – application layer protocol

Uses UDP; TCP congestion control and error control prevent delay or rate guarantees.

RTP supports several audio formats including PCM, GSM, G.722,

MPEG audio – MP3video formats – JPEG, MPEG 1, and MPEG 2.

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RTP

One may have multiple RTP connections; one for audio and one for video

RTP supports unicast and multicast

RTP packet: Header + PayloadHeader

Payload typeMagic number to identify the audio or video formatSequence number of the packetTime stampRandom number associated with the RTP session

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RTCP – RTP control protocol

Senders – periodic source reportsRTP session identifierApplication generating the streamAddress of source

Receivers periodic reciver reportsNumber of packets lostJitterNumber of packets Received

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RTCP

An application may use may use the data provided by RTCP toModify transmission ratesSynchronize multiple streamsDiagnostics

For multicast RTCP limits the frequency of receiver reports.

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Real-time Streaming Protocol (RTSP)

Supports interactive applications

Out-of-band channel

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100-Mbps Ethernet

100-Mbps Ethernet

Variable fill rate x(t)Buffer

Constant drain rate d

Stored Media Server

UncompressRemove Jitter

Forward Error CorrectionGUI

Multimedia Client

Multimedia Player

MultimediaDatabase

ServerThread(one per

clientprocess

)

DatabaseAccess

DataStreaming

RTSP

Multimedia Server Process

Setup PlayMedia Stream Pause Teardown

Out-of-Band Client-Server Interactions UsingRTSP

In-BandCommunication

Using RTP

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Data compression

Sender

CompressionInformation

Source

Receiver

Uncompression Player

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Data compression

Text compression

Still image compression

Audio and Video compression

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Loseless compression

Differential encoding – amplitudes of consecutive samples differ only slightly.

Entropy encoding – removes the redundancy based upon the entropyRun Length EncodingStatistical Encoding

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Text Compression

Huffman EncodingProduces optimal results only if the probability of

occurrence of individual characters is a power of ½.

Static Huffman EncodingAdaptive Huffman Encoding

Lemplel-Ziv

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A (0.5)B (0.25)C (0.125)D (0.0625)E (0.0156)F (0.0156)G (0.0156) 1H (0.0156) 0

A (0.5)B (0.25)C (0.125)D (0.0625) (0.0312)E (0.0156) 1F (0.0156) 0

A (0.5)B (0.25)C (0.125)D (0.0625) (0.0312) 1 (0.0312) 0

A (0.5)B (0.25)C (0.125)D (0.0625) 1 (0.0625) 0

L8 L7

L6

L5

A (0.5)B (0.25)C (0.125) 1 (0.125) 0

L3

A (0.5)B (0.25) 1 (0.25) 0 L4

A (0.5) 1 (0.5) 0

L2

ABCDEFGH

1010010001000001000000000011000010

0 1

1.0

0.5 A 0.5

B 0.250.25

0 1

0 1

C 0.1250.125

D 0.061250.06125

0

0

1

1

0.030625

H 0.01565 G 0.01565

0.030625

1100

E 0.01565F 0.01565

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0Ef 0

Ef 0

0 1

a 1

send a

1

11

0

0a 1

Ef 0 l 1

send l

Ef 0 ; a 1

Ef 0; l 1; 1; a 1

l

a

e0

0

0

Ef 0 e 1

l 1

a 11

1

11

2

send e

Ef 0; e 1; 1; l 1; 2; a 1

Ef 0; e 1; 1; l 1; a 1; 2

sort list by count

Ef 0 e 1

11

1

12a 1

0

0

0l 1

a send " "

a 2 2

Ef 0 e 1

1

1

1

1l 1

0

0

0

Ef 0; e 1; 1; l 1; a 2; 2

j

Ef 0

e 1

j 1

0

0

0

01

1

1

1

13a 2

l 12

send j

Ef 0; j 1; 1; e 1; 2; l 1; a 2; 3

Ef 0; j 1; 1; e 1; l 1; 2; a 2; 3

sort list by count

Ef 0 j 1

1

3a 2

l 1 2

1 e 1

1

1

1

0

0

0

0

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Lempel-Ziv

Construct a dictionary consisting of all the substrings in the input string

Instead of transmitting a substring we transmit the index of the substring in the dictionary.

Lempel-Ziv-Welsh the dictionary is constructed dynamically.

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Compression factor for LZ

N # of characters in the text

n bits/character

L average length of a substring

D # of entries in the dictionary D=2d

compression = (N x n) / (N/L x d) = ( n x L) / d

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Still image compression

GIF – Graphics Interchange FormatReduces the number of colors in the image from

224 to 28

Selects the 256 colors that match best the colors in the picture and builds a local color table

Instead of sending 24- bit pixels we send 8-bit pixels that are indexes in the local color table

JPEG – Joint Photographic Experts Group

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JPEG

SourceImage

CompressedImage

Entropy Encoding

Vectoring

RLE

DiffEncoding

HuffmanEncoding

BlockPreparation

DCT Quantization