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Multimedia

Multimedia. Quality of Service (QoS). Contents. Why Quality of Service (QoS)? Introduction Streaming Multimedia on the Internet Is Internet Real-time? Internet QoS Models. Why Quality of Service (QoS)?. Definition : QoS is the concept for specifying how “good” the offered services are.

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Multimedia

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  1. Multimedia Quality of Service (QoS) T.Sharon-A.Frank

  2. Contents • Why Quality of Service (QoS)? • Introduction • Streaming • Multimedia on the Internet • Is Internet Real-time? • Internet QoS Models T.Sharon-A.Frank

  3. Why Quality of Service (QoS)? • Definition: QoS is the concept for specifying how “good” the offered services are. • Concept: • Quality of service is a concept based on the statement that not all applications need the same performance from the system/network over which they run. • Thus, applications may indicate their specific requirements to the network, including cost, before they actually start transmitting data. T.Sharon-A.Frank

  4. Introduction • QoS Parameters • Why is QoS Hard? • QoS Layering and Mapping T.Sharon-A.Frank

  5. Major Parameters Defining QoS • Throughput – the total amount of work completed during a specific time interval. • Delay – the elapsed time from when a request is first submitted to when the desired result is produced. • Jitter – the delays that occur during playback of a stream. • Reliability – how errors are handled during transmission and processing of continuous media. T.Sharon-A.Frank

  6. Packets experience delay on end-to-end path four sources of delay at each hop: nodal processing: check bit errors determine output link queuing time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing Delay in packet-switched networks (1) T.Sharon-A.Frank

  7. Transmission delay: R = link bandwidth (bps) L = packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s transmission A propagation B nodal processing queueing Delay in packet-switched networks (2) Note: s and R are very different quantities! T.Sharon-A.Frank

  8. Communication QoS Parameters • Average Throughput (bit rate, bandwidth) • Burstiness (average to peak ratio) • Minimum/Maximum transit (delay) • Important for response time and RT perception • Maximum Jitter (delay variance), • Important for synchronization • Reliability • Acceptable bit error rate • Acceptable packet error rate T.Sharon-A.Frank

  9. Example:VC QoS Throughput Loss Jitter Measured QoS Parameters T.Sharon-A.Frank

  10. Application QoS Parameters • Synchronization • Orchestration • Multicast Delivery • Protection/Security T.Sharon-A.Frank

  11. Why is QoS Hard? (1) 1. End-to-End vs. Local Node (control) T.Sharon-A.Frank

  12. Possible Network Bottlenecks T.Sharon-A.Frank

  13. Why is QoS Hard? (2) 1. End-to-End vs. Local Node (control) 2. Global vs. Specific QoS (application) T.Sharon-A.Frank

  14. Global/Standard Channel Types T.Sharon-A.Frank

  15. Why is QoS Hard? (3) 1. End-to-End vs. Local Node (control) 2. Global vs. Specific QoS (application) 3. Uniform vs. Distance Dependant 02 03 02 T.Sharon-A.Frank

  16. Why is QoS Hard? (4) 1. End-to-End vs. Local Node (control) 2. Global vs. Specific QoS (application) 3. Uniform vs. Distance Dependant 4. Higher-Level vs. Lower-Level (user/application/OS/network/device) T.Sharon-A.Frank

  17. QoS Layering Users Application System (OS) Devices Network Disk, MM devices T.Sharon-A.Frank

  18. QoS Mapping Example Interface Specification TYPE VideoSource = INTERFACE BEGIN GetVideo : OPERATION = [ ] RETURNS [ VideoFrame ] WITH QOS “StandardVideo”; END. Orchestration Delivery rate: 25 frames/sec Permissible jitter: 10 ms Synch interval: 1 second Transport Burst size: 100 Kbps Burst rate: 100 per sec Delay: 1 sec Jitter: 20 ms Priority: 10 Error profile: FEC Error rate: 2% T.Sharon-A.Frank

  19. QoS for Networked Applications T.Sharon-A.Frank

  20. QoS Traffic Topics (1) • Routing • Unicast (multi-hop network) • Multicast • Congestion Control • Traffic Topics • Admission Control (on-line): • Systems often use an admission control algorithm that admits a request for a service only if the server has sufficient resources to satisfy the request. T.Sharon-A.Frank

  21. QoS Traffic Topics (2) • Traffic Classes (varied) – priorities • Traffic Control (nodal) • packet classification/scheduling • Traffic Shaping (per session) • Traffic Monitoring • Traffic Policing T.Sharon-A.Frank

  22. Streaming and QoS • With text data, the effect that time has on correctness is of little consequence. • However, audio and video are time-dependent data streams – if the timing is off, the resulting “output” from the system will be incorrect. • Time-dependent information – known as “continuous media” communications: • Example: voice: PCM: 1/44100 sec intervals on playback. • Example: video: 30 frames per second (30-40ms per image). • KEY MESSAGE: Timing is crucial! T.Sharon-A.Frank

  23. Transmission Modes • Asynchronous transmission mode – the data stream is transmitted in order, but there’s no timing constraints placed on the actual delivery (e.g., File Transfer). • Synchronous transmission mode – the maximum end-to-end delay is defined (but data can travel faster). • Isochronous transmission mode – data transferred “on time” – there’s a maximum and minimum end-to-end delay (known as “bounded jitter”). • Known as “streams” – isochronous transmission mode is very useful for multimedia systems. T.Sharon-A.Frank

  24. Two Types of Streams • Simple Streams – one single sequence of data, for example: voice. • Complex Streams – several sequences of data (sub-streams) that are “related” by time. Think of a lip-synchronized movie, with sound and pictures, together with sub-titles … • This leads to data synchronization problems … not at all easy to deal with. T.Sharon-A.Frank

  25. Components of a Stream Two parts: a “source” and a “sink”. The source and/or the sink may be a networked process (a) or an actual end-device (b). T.Sharon-A.Frank

  26. End-device to End-device Streams Setting up a stream directly between two devices – i.e., no inter-networked processes. 2-35.2 T.Sharon-A.Frank

  27. Multi-party Data Streams An example of multicasting a stream to several receivers. This is “multiparty communications” – different delivery transfer rates may be required by different end-devices. T.Sharon-A.Frank

  28. Stream Synchronization • A key question is: • “Where does the synchronization occur?” • On the sending side? • On the receiving side? • Think about the advantages/disadvantages of each … T.Sharon-A.Frank

  29. Synchronization Mechanisms (1) The principle of explicit synchronization on the level data units T.Sharon-A.Frank

  30. Synchronization Mechanisms (2) The principle of synchronization as supported by high-level interfaces T.Sharon-A.Frank

  31. Streams and QoS (1) • Definition: “ensuring that the temporal relationships in the stream can be preserved”. • QoS is all about three things: • Timeliness • Volume • Reliability • But, how is QoS actually specified? • Unfortunately, most technologies do their own thing. T.Sharon-A.Frank

  32. Data Stream A general architecture for streaming stored multimedia data over a network. T.Sharon-A.Frank

  33. Streams and QoS (2) • Properties for Quality of Service (QoS): • The required bit rate at which data should be transported. • The maximum delay until a session has been set up. • The maximum end-to-end delay. • The maximum delay variance, or jitter. • The maximum round-trip delay. T.Sharon-A.Frank

  34. Enforcing QoS (1) Using a buffer to reduce jitter T.Sharon-A.Frank

  35. Enforcing QoS (2) The effect of packet loss in (a) non interleaved transmission and (b) interleaved transmission T.Sharon-A.Frank

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