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! ? ?
Today’s Internet multimedia applications use application-level techniques to mitigate (as best as possible) effects of delay, loss Telemed 10/11 - Real Time Services - pbrandao
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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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