Communications in the Internet Real Time Services

Telemedicina e e-Saúde 2010/2011 Communications in the Internet Real Time Services Telemedicina e e-Saúde 2010/11 Pedro Brandão References  These s...
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Telemedicina e e-Saúde 2010/2011

Communications in the Internet Real Time Services Telemedicina e e-Saúde 2010/11 Pedro Brandão

References  These slides are the companions of

“Computer Networking: A Top Down Approach 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009”  They are based in a selection from Prof Rui Prior for Telemedicina e e-Saúde 2008/09

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Application needs Losses  Some applications (eg.: audio) can cope with losses  Others (e.g. file transfer) demand 100% reliabitility Delays  Some applications (e.g., VOIP, network gaming) demand slow demand slow delays Rate  Some applications (e.g. multimedia) demand a minimum rate  Others (“elastic” applications) use what is available

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Application requirements (e.g.) Application

Losses

Delay Sensitive

File transfer

Not Acceptable

No

Elastic

Email

Not Acceptable

No

Elastic

Web

Not Acceptable

No

Elastic

Audio/Video real time

Acceptable

Yes, hundreds of ms

audio: 5kbps-1Mbps vídeo:10kbps-5Mbps

Audio/Video stored

Acceptable

Yes, some seconds

audio: 5kbps-1Mbps vídeo:10kbps-5Mbps

Interactive games

Acceptable

Yes, hundreds of ms

Starting at some kbps

Instant Messaging

Not possible

Partially

Elastic

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Multimedia and Quality of Service: What is it? multimedia applications: network audio and video (“continuous media”)

QoS network provides application with level of performance needed for application to function. Telemed 10/11 - Real Time Services - pbrandao

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MM Networking Applications Classes of MM applications: Fundamental characteristics:  typically delay sensitive 1. stored streaming o end-to-end delay 2. live streaming o delay jitter 3. interactive, real-time  loss tolerant: infrequent

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

losses cause minor glitches  antithesis of data, which are loss intolerant but delay tolerant.

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What are the QoS Parameters?  Delay o Transmission o Propagation o Queues o Node processing o Apps processing  Jitter o Access to medium o Traffic Aggregation o Congestion o Route changes

 Reliability o Losses o Duplicates o Out of order  Rate o Path o Congestion o Temporal Variations • Fast • Slow

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Streaming Stored Multimedia

Stored streaming:  media stored at source  transmitted to client  streaming: client play out begins before all data has arrived  timing constraint for still-to-be transmitted data: in time for play out Telemed 10/11 - Real Time Services - pbrandao

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Streaming Stored Multimedia: What is it?

1. video recorded

2. video sent network delay

3. video received, played out at client

time

streaming: at this time, client playing out early part of video, while server still sending later part of video Telemed 10/11 - Real Time Services - pbrandao

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Streaming Stored Multimedia: Interactivity

 VCR-like functionality: client

can pause, rewind, FF, push slider bar o 10 sec initial delay OK o 1-2 sec until command effect OK  timing constraint for still-to-be transmitted data:

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Streaming Live Multimedia Examples:  Internet radio talk show  live sporting event Streaming (as with streaming stored multimedia)  playback buffer  playback can lag tens of seconds after transmission  still have timing constraint Interactivity  fast forward impossible  rewind, pause possible! Telemed 10/11 - Real 7-12 Time Services - pbrandao

Real-Time Interactive Multimedia

 applications: IP telephony,

video conference, distributed interactive worlds  end-end delay requirements: o audio: < 150 msec good, < 400 msec OK • includes application-level (packetization) and network delays • higher delays noticeable, impair interactivity

 session initialization o how does callee advertise its IP address, port number, encoding algorithms? Telemed 10/11 - Real Time Services - pbrandao

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Multimedia Over Today’s Internet TCP/UDP/IP: “best-effort service”  no guarantees on delay, loss ? ? ? ? ?

?

?

? But you said multimedia apps require QoS and level of performance to be ? effective! ? ?

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How should the Internet evolve to better support multimedia? Integrated services philosophy: Differentiated services philosophy:  fundamental changes in  fewer changes to Internet Internet so that apps can infrastructure, yet provide 1st reserve end-to-end bandwidth and 2nd class service  requires new, complex software in hosts & routers Laissez-faire  no major changes  more bandwidth when needed  content distribution, application-layer multicast o application layer

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Remember Quantization?

Sampling

Images from Wikipedia

Quantization at the sampling times Telemed 10/11 - Real 7-16 Time Services - pbrandao

Remember compression  Sampling  Quantization, i.e., rounded  Bit representation  receiver converts bits back o some quality reduction

 Pixel represented by

bits  Redundancies

Example rates for audio  CD: 1.411 Mbps  MP3: 96, 128, 160 kbps  Internet telephony: 5.3 kbps and up Examples rates for video:  MPEG 1 (CD-ROM) 1.5 Mbps  MPEG2 (DVD) 3-6 Mbps  MPEG4 (often used in Internet, < 1 Mbps)

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