Advanced Multimedia

University of PalestineUniversity of Palestine Eng. Wisam ZaqootEng. Wisam Zaqoot October 2010October 2010

Ref: Computer Networking: A Top Down Approach, 4th ed., Kurose & Ross

Multimedia Multimedia Networking Networking ApplicationsApplications

Multimedia Networking Multimedia Networking ApplicationsApplications

The last few years have witnessed an The last few years have witnessed an explosive growth in Multimedia explosive growth in Multimedia Networking Applications.Networking Applications. Entertainment videoEntertainment video IP telephonyIP telephony Internet radioInternet radio Multimedia WWW sitesMultimedia WWW sites TeleconferencingTeleconferencing Interactive gamesInteractive games Virtual worldsVirtual worlds Distance learningDistance learning Etc.Etc.

Multimedia Networking Multimedia Networking ApplicationsApplications

MN applicationsMN applications differ significantly differ significantly from those of from those of traditional data-traditional data-oriented applicationsoriented applications such as web such as web text/image, e-mail, FTP and DNS text/image, e-mail, FTP and DNS applications.applications.

In contrast to In contrast to data-oriented data-oriented applicationsapplications, MN applications are , MN applications are highly sensitive to end-to-end delay and highly sensitive to end-to-end delay and delay variation (jitter), but can tolerate delay variation (jitter), but can tolerate occasional loss of data.occasional loss of data.

Multimedia Networking Multimedia Networking ApplicationsApplications

MN applications characteristics: MN applications characteristics: typically typically delaydelay sensitivesensitive

end-to-end delay (from few hundred milliseconds in end-to-end delay (from few hundred milliseconds in Internet telephony to few seconds in streaming Internet telephony to few seconds in streaming MM)MM)

delay jitter *delay jitter * loss tolerantloss tolerant: infrequent losses cause minor : infrequent losses cause minor

glitches in audio and videoglitches in audio and video In contrast to data, which are loss In contrast to data, which are loss

intolerantintolerant but delay but delay toleranttolerant. Delays here . Delays here are annoying but not harmful. The most are annoying but not harmful. The most important thing here is to keep the data important thing here is to keep the data integrity.integrity.

* Jitter is the variability of packet delays within the same packet stream

network provides application with level of performance needed for application to function.

QoS

Delays and Jitter Delays and Jitter ChallengesChallenges

Delay constraint: Delay constraint: Data not received before their playout time are considered lost.

Jitter: variable delays in the received data. Data transmitted periodically typically will not arrive periodically. This network-induced jitter must not be apparent in the multimedia playout at the receiver.

Delays and Jitter Delays and Jitter ChallengesChallenges

One technique to decrease the amount of late-arriving data and to accommodate jitter is to delay the beginning of playout, essentially pushing the playout deadlines further into the future. (pieces of arriving data are placed in a playout buffer. After some delay, playout begins and data are removed from the buffer).

The playout buffer not only decreases late-arrival loss, but also masks the jitter*.

* Imagine ten packets of data in the playout buffer, it is irrelevant whether those ten packetsarrived smoothly over time (with no jitter) or arrived with wildly different delays (high jitter).

Classes of MM applications:Classes of MM applications:

1) Streaming stored multimedia1) Streaming stored multimedia

2) Streaming live multimedia2) Streaming live multimedia

3) Real-time interactive multimedia3) Real-time interactive multimedia

4) Stored multimedia file (a file 4) Stored multimedia file (a file downloaded in its entirety and downloaded in its entirety and then played out, we will ignore then played out, we will ignore this class)this class)

Classes of MM applications:Classes of MM applications:

In all MM classes, multimedia data has both content (bytes that make up an audio sample or a video frame) and timing attributes.

For example, the timing attribute might be the video frame temporal location during a particular interval of time within the video.

Classes of MM applications:Classes of MM applications: Data must be received from the server in time

for its playout at the client. Data not received before their playout time are considered lost.

Stored applications have the flexibility to transmit data as fast as the network path will allow, since all of the multimedia is stored and always available for transmission.

Live applications do not have this flexibility.

Interactive human-to-human communication (for example, a teleconference or an audio call) requires low end-to-end latencies, typically less than 400 msec in order for such interaction communication to feel “natural” for the participants.

1) Streaming Stored 1) Streaming Stored MultimediaMultimedia

Stored streaming: Stored streaming: media stored at sourcemedia stored at source transmitted to clienttransmitted to client

streaming:streaming: client playout begins client playout begins beforebefore all data has arrived all data has arrived timing constraint for still-to-be timing constraint for still-to-be

transmitted data: in time for playouttransmitted data: in time for playout The most famous applications here The most famous applications here

are offered by Microsoft and Real are offered by Microsoft and Real Networks.Networks.

1) Streaming Stored Multimedia

1. videorecorded

2. videosentCum

ula

tive

data

streaming: at this time, client playing out early part of video, while server still sending laterpart of video

networkdelay

time

3. video received,played out at client

1) Streaming Stored 1) Streaming Stored Multimedia:Multimedia:

Interactivity:Interactivity: VCR-like functionality:VCR-like functionality: client can client can

pause, rewind, FF, push slider barpause, rewind, FF, push slider bar 10 sec initial delay OK10 sec initial delay OK 1-2 sec until command effect OK1-2 sec until command effect OK

Timing constraint for still-to-be Timing constraint for still-to-be transmitted data: in time for playouttransmitted data: in time for playout

2) Streaming Live 2) Streaming Live MultimediaMultimedia

Examples:Examples: Internet radio talk showInternet radio talk show AlJazeera TV channel live streamingAlJazeera TV channel live streaming

StreamingStreaming (as with streaming (as with streaming storedstored multimedia)multimedia)

playback bufferplayback buffer playback can lag tens of seconds after playback can lag tens of seconds after

transmissiontransmission still have timing constraintstill have timing constraint

Interactivity:Interactivity: fast forward impossiblefast forward impossible rewind, pause could be possible!rewind, pause could be possible!

3) Real-Time Interactive 3) Real-Time Interactive Multimedia Multimedia

Applications:Applications: IP telephony, video IP telephony, video conference, virtual class rooms, distributed conference, virtual class rooms, distributed interactive worlds, etc.interactive worlds, etc.

end-end delay requirements:end-end delay requirements: audio: < 150 msec good, < 400 msec OKaudio: < 150 msec good, < 400 msec OK

includes application-level (packetization) and includes application-level (packetization) and network delaysnetwork delays

higher delays noticeable, impair interactivityhigher delays noticeable, impair interactivity What Real-Time Interactive MM What Real-Time Interactive MM

applications you know?applications you know?

Multimedia Over Today’s Multimedia Over Today’s InternetInternet

TCP/UDP/IP:TCP/UDP/IP: “best-effort service” “best-effort service” nono guarantees on delay, loss guarantees on delay, loss

Today’s Internet multimedia applications use application-level techniques to mitigate

(as best possible) effects of delay, loss

But you said multimedia apps requireQoS and level of performance to be

effective!

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?

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How should the Internet evolve How should the Internet evolve to better support multimedia?to better support multimedia?

Integrated services Integrated services philosophy:philosophy:

fundamental changes in fundamental changes in Internet so that apps can Internet so that apps can reserve end-to-end reserve end-to-end bandwidthbandwidth

requires new, complex requires new, complex software in hosts & routerssoftware in hosts & routers

Laissez-faireLaissez-faire no major changesno major changes more bandwidth when more bandwidth when

neededneeded content distribution, content distribution,

application-layer multicastapplication-layer multicast application layerapplication layer

Differentiated services Differentiated services philosophy:philosophy:

fewer changes to Internet fewer changes to Internet infrastructure, yet provide infrastructure, yet provide 1st and 2nd class service1st and 2nd class service

What’s your opinion?

Forward error correction (FEC)

There are a number of reliable data transfer protocols that retransmit lost or damaged packets. An alternative approach toward achieving reliability is to use forward error correction (FEC) techniques.

With FEC, enough redundant information is added to the original data so that even if some of the transmitted data (original data plus redundant data) is lost, the receiver can still recover the original data. The simple two-dimensional parity technique for detection and correction of single bit errors is a simple example of FEC.

FEC techniques can be particularly valuable when an application cannot wait for a round-trip time to recover lost data via a timeout-and-transmit mechanism.