2. © Chinese University, CSE Dept. Distributed Systems / 11 - 1 Distributed Systems Topic 11: Distributed Multimedia Systems Dr. Michael R. Lyu Computer Science & Engineering Department The Chinese University of Hong Kong

3. © Chinese University, CSE Dept. Distributed Systems / 11 - 2 1 Outline 1.Introduction 2.Characters of multimedia data 3.Quality of service management 4.Resource management 5.Stream adaptation 6.Summary

4. © Chinese University, CSE Dept. Distributed Systems / 11 - 3 1 Introduction  Media: –The term media refers to the storage, transmission, interchange, presentation, representation and perception of different information types, such as text, graphics, voice, audio and video.  Multimedia –The term multimedia is to denote the property of handling a variety of media representation in an integrated manner.

5. © Chinese University, CSE Dept. Distributed Systems / 11 - 4 1 Introduction  Most multimedia is inherently time-based – the arrival time and arrival order of data packets is important  The Internet guarantees neither when transmitting data  We don’t just want interactive multimedia over our networks… we want it to be reliable and high-quality  A distributed multimedia system can come to the rescue

6. © Chinese University, CSE Dept. Distributed Systems / 11 - 5 1 A Distributed Multimedia System

7. © Chinese University, CSE Dept. Distributed Systems / 11 - 6 1.1 Multimedia in A Mobile Environment *

8. © Chinese University, CSE Dept. Distributed Systems / 11 - 7 1.1 History  60s-70s: Distributed computing research with earliest networks  80s: Compact disc, personal computer explosion  80s-90s: Distributed multimedia system research (video conferencing, et al)  90s: Current prevalent paradigm (quality of service management)

9. © Chinese University, CSE Dept. Distributed Systems / 11 - 8 1.1 Multimedia Application Samples  Web-based multimedia: It provides best-effort access to streams of audio and video data published via web.  Network phone and audio conferencing: It has relatively low bandwidth requirements, especially when efficient compression techniques are used  Video-on-demand services: These supply video information in digital form, retrieving the data from large online storage systems and delivering them to the end-user’s display

10. © Chinese University, CSE Dept. Distributed Systems / 11 - 9 1.2 The Window of Scarcity  When dealing with large audio and video streams, many systems are constrained in the quantity and quality of streams they can support.  This situation has need depicted as the window of scarcity. The window of scarcity for computing and communication resources

11. © Chinese University, CSE Dept. Distributed Systems / 11 - 10 2 Characteristics of Multimedia Applications  Large quantities of continuous data  Timely and smooth delivery is critical  Interactive multimedia applications require low round- trip delays  Need to co-exist with other applications  Reconfiguration is a common occurrence  Resources required: –Processor cycles in workstations and servers –Network bandwidth (+ latency) –Dedicated memory –Disk bandwidth (for stored media)

12. © Chinese University, CSE Dept. Distributed Systems / 11 - 11 2 Characteristics of Multimedia Streams Data rate (approximate) Sample or frame frequency size Telephone speech64 kbps8 bits8000/sec CD-quality sound1.4 Mbps16 bits44,000/sec Standard TV video (uncompressed) 120 Mbpsup to 640x 480 pixelsx 16 bits 24/sec Standard TV video (MPEG-1 compressed) 1.5 Mbpsvariable24/sec HDTV video (uncompressed) 1000–3000 Mbpsup to 1920x 1080 pixelsx 24 bits 24–60/sec HDTV video MPEG-2 compressed) 10–30 Mbpsvariable24–60/sec

13. © Chinese University, CSE Dept. Distributed Systems / 11 - 12 3 Quality of Service (QoS) Management  Simplicity in and of itself: We want and need high quality, reliable, interactive multimedia  The general Internet structure is not sufficient to accomplish this  A distributed multimedia system will add protocols and architectures on top of the Internet (or LAN) to guarantee quality levels, thereby satisfying our need

14. © Chinese University, CSE Dept. Distributed Systems / 11 - 13 3 Infrastructure Components for Multimedia Applications

15. © Chinese University, CSE Dept. Distributed Systems / 11 - 14 3 QoS Specifications for Application Components ComponentBandwidthLatencyLoss rateResources required Camera Out:10 frames/sec, raw video 640x480x16 bits Zero ACodecIn: Out: 10 frames/sec, raw video MPEG-1 stream InteractiveLow10 ms CPU each 100 ms; 10 Mbytes RAM BMixerIn: Out: 2 44 kbps audio 1 44 kbps audio InteractiveVery low1 ms CPU each 100 ms; 1 Mbytes RAM HWindow system In: Out: various 50 frame/sec framebuffer InteractiveLow5 ms CPU each 100 ms; 5 Mbytes RAM KNetwork connection In/Out:MPEG-1 stream, approx. 1.5 Mbps InteractiveLow1.5 Mbps, low-loss stream protocol LNetwork connection In/Out:Audio 44 kbpsInteractiveVery low44 kbps, very low-loss stream protocol

16. © Chinese University, CSE Dept. Distributed Systems / 11 - 15 3 The QoS Manager ’ s Task

17. © Chinese University, CSE Dept. Distributed Systems / 11 - 16 3.1 Quality of Services Negotiation  Bandwidth: data rate through a component  Latency: time needed for a packet to travel end to end  Jitter: the rate of change of latency  Loss rate: acceptable drop-frame ratio  Quality of service management: negotiation and allocation of computing resources

18. © Chinese University, CSE Dept. Distributed Systems / 11 - 17 3.1.1 Specifying QoS Parameters  The values of QoS parameters can be stated explicitly or implicitly  Bandwidth: Most video compression techniques produce a stream of frames of different sizes.  Latency: Some timing requirements in multimedia result from the stream itself.  Loss rate: Loss rate is the most difficult QoS parameter to specify.

19. © Chinese University, CSE Dept. Distributed Systems / 11 - 18 3.1.2 Traffic Shaping Algorithms  Traffic shaping: using buffers at source and destination to smooth data flow Token generator (a) Leaky bucket(b) Token bucket

20. © Chinese University, CSE Dept. Distributed Systems / 11 - 19 3.1.3 Flow Specification  Flow specification: explicit representation of required resources Protocol version Maximum transmission unit Token bucket rate Token bucket size Maximum transmission rate Minimum delay noticed Maximum delay variation Loss sensitivity Burst loss sensitivity Loss interval Quality of guarantee Bandwidth: Delay: Loss: The RFC 1363 Flow Spec

21. © Chinese University, CSE Dept. Distributed Systems / 11 - 20 3.2 Admission Control  Admission control: allowing or denying client requests based on available resources –Bandwidth reservation »A common way to ensure QoS level for multimedia stream is to reserve some portion of resource bandwidth for its exclusive use. –Statistical multiplexing »It is based on the hypothesis that for large number of streams the required aggregate bandwidth remains nearly constant regardless of the bandwidth of individual streams. »Multimedia traffic may not obey this hypothesis.

22. © Chinese University, CSE Dept. Distributed Systems / 11 - 21 3.3 Overall Structure 1: Resources provide flow spec to main QoS manager through local QoS managers 2: Main QoS ready to reserve resources 3: Client send request to main QoS 4: Main QoS decides if client can be served based on available resources 5: If so, main QoS tells local QoS to allocate resources (if not, client is rejected) 6: Service begins 7: Main QoS and local QoS monitor resource usage / quality, adjust allocated resources if necessary 8: Return to step 4 if new client connects 9: Service ends, resources are freed Controller Client Resource QoS Main QoS Network Transmission Line Client

23. © Chinese University, CSE Dept. Distributed Systems / 11 - 22 3.4 QoS Summary  Serving multimedia requires strict resource control to maintain quality  Resources consist of bandwidth, latency, and loss rate, among others  Resource components declare the resources they need in flow specifications  Quality of service managers negotiate and reserve resources to guarantee quality  Resource + flow spec + QoS manager + transmission lines = distributed multimedia system

24. © Chinese University, CSE Dept. Distributed Systems / 11 - 23 4 Resource Management System  Provide the means to offer QoS to multimedia applications  Addressing issues –QoS Calculation »To check whether the QoS demands of an application can be satisfied –Resource Reservation »To reserve an amount of resources according to the given QoS guarantee –Resource Scheduling »To enforce that the given QoS guarantees are satisfied by appropriate scheduling of resource access

25. © Chinese University, CSE Dept. Distributed Systems / 11 - 24 4.1 Resources  Resources –All the entities which participate in the overall task of the application –Classification (active vs. passive; exclusive vs. shared; single vs. multiple) –Scheduled, Assigned for QoS  Resource Capacity –Availability for application when needed –Be at least as large as the requirements for QoS –Depending on the mechanisms for QoS calculation, resource reservation and scheduling

26. © Chinese University, CSE Dept. Distributed Systems / 11 - 25 4.2 Reservation Policies  Pessimistic approach –The resource capacities are reserved for the worst case –Advantage: avoid conflicts, offer deterministic guarantees –Disadvantage: high cost, underutilization of resources  Optimistic approach –Resources are reserved on average workload –Advantage : cheaper –Disadvantage : temporal resource conflicts  Resource Reservation Protocol (RSVP) –To exchange and negotiate QoS requirements –Receiver-oriented approach. Receivers are responsible for initiating and keeping the reservation active.

27. © Chinese University, CSE Dept. Distributed Systems / 11 - 26 4.3 Resource Scheduling  Scheduling of resources to meet QoS requirements  Fair scheduling: allow all processes some portion of the resources based on fairness  Real-time scheduling: all to meet real-time requirements (with deadlines) –Regular continuous multimedia streams –Bursty real-time traffic

28. © Chinese University, CSE Dept. Distributed Systems / 11 - 27 4.4 Resource Management Phase –Phase 1: the set-up or QoS negotiation phase »Applications specify their QoS requirements to be used for the admission test and the QoS calculation –Phase 2: the transmission or QoS enforcement phase »Resources are scheduled with respect to the given QoS guarantees. »Schedulers handle time-critical multimedia streams prior to time-independent data l Resource Monitoring l Adaptation –Phase 3 »After the transmission has finished, the allocated resources must be released.

29. © Chinese University, CSE Dept. Distributed Systems / 11 - 28 4.5 Resource Management System Structure  Contain components used in the enforcement phase  Consist of System Resource Manager and Resource Managers –System Resource Manager »Control the single ‘Resource Managers’ –Resource Manager »Contain algorithms for admission control and policy control »Keep information about the characteristics of the resource and its reservations »CPU resource manager, Memory resource manager and so on  Resource management schemes: static vs. dynamic

30. © Chinese University, CSE Dept. Distributed Systems / 11 - 29 4.6 Static Resource Management Scheme  Perform QoS calculation and resource reservation during the setup time  Schedule the resource in such a way that processing deadlines are met  Advantage –Offer strong guarantees for the application’s performance –Provide reliable QoS  Drawback –Difficult to determine the amount of resource needed in advance –Not easily cope with a change in the set of running applications during the run-time of an application –Rely on total knowledge of the set of available resources

31. © Chinese University, CSE Dept. Distributed Systems / 11 - 30 4.7 Dynamic Resource Management Scheme  Renegotiate the resource as changes of requirements at run-time  The goal –Support of variable-bit rate streams –Adaptation to changes in the set of applications to be served –Allowing for a dynamic change in the relative priority of applications –Serving more applications concurrently –Handling of changes in resource availability  Consisting components –Resource monitor –System resource manager: responsible for the negotiations

32. © Chinese University, CSE Dept. Distributed Systems / 11 - 31 4.7 Dynamic Resource Management Scheme  Applications –Receive adaptation notifications –Decide how to change their behavior to adapt their resource demands –Monitor the QoS and start a QoS renegotiation  Drawback –Not able to provide guaranteed, constant QoS

33. © Chinese University, CSE Dept. Distributed Systems / 11 - 32 5 Stream Adaptation: Scaling  Scaling reduces flow rate at source –Temporal scaling: skip frames or audio samples –Spatial scaling: reduce frame size or audio sample quality –Frequency scaling: modify image compression algorithm without much loss of quality. –Color-space scaling: reduce the number of entries in color space.

34. © Chinese University, CSE Dept. Distributed Systems / 11 - 33 5 Stream Adaptation: Filtering  Filtering reduces flow at intermediate points –Filtering provides best possible QoS to each target by applying scaling at each relevant node on the path from the source to the target. –RSVP is a QoS negotiation protocol that negotiates the rate at each intermediate node, working from targets to the source.

35. © Chinese University, CSE Dept. Distributed Systems / 11 - 34 5 Stream Adaptation: Filtering Source Targets High bandwidth Medium bandwidth Low bandwidth

36. © Chinese University, CSE Dept. Distributed Systems / 11 - 35 5.1 A Sample Wavelet Video Filtering  Basic Concept:

37. © Chinese University, CSE Dept. Distributed Systems / 11 - 36 5.1 Wavelet Video Filtering  Video frames are encoded into packets with “priority label”  QoS Filter drops the least important packets in case of insufficient bandwidth  This maximizes visual quality with resource constraints

38. © Chinese University, CSE Dept. Distributed Systems / 11 - 37 6 Summary  Multimedia applications and systems require new system mechanisms to handle large volumes of time-dependent data in real time (media streams).  The most important mechanism is QoS management, which includes resource negotiation, admission control, resource reservation and resource management.  Negotiation and admission control ensure that resources are not over-allocated, resource management ensures that admitted tasks receive the resources they were allocated.  Read textbook Chapter 20.