Multimedia Network

1. Multimedia Network Introduction to Multimedia

2. Reference: Guojun Lu, “Communication & Computing for Distributing Multimedia Systems” Read Chapter page 124-150

3. Network Characteristics 1. The network bandwidth should be sufficiently high to support many applications at the same time; 2. Network resources should be shared efficiently among applications so that as many applications as possible are supported given certain resources; 3. The network should provide performance guarantees, if required, to applications; 4. The network should be scalable.

4. 1. Network Speed vs Bandwidth • Sufficient BW for supporting multimedia communications. • Speed vs BW  the time intervals representing each data bit  “high-bandwidth network” instead of “high- speed network” • Network speed is determined by the physical transmission medium used, protocols, distance between intermediate nodes, and switching speed of intermediate nodes.

5. two different points of a network: • user access point  the bandwidth at this point is called user access bandwidth. • network access point,  the same amount of bandwidth should be available for both directions.

6. 2. Efficient Sharing of NW Resources • Each user requires a large amount of bandwidth, • If each user reserves a bandwidth equal to its peak bit rate, some bandwidth is wasted when the output bit rate is not at the highest  solution: bandwidth on demand or statistical multiplexing  discuss: Circuit switching technology? Synchronous time division multiplexing (STDM)? Packet-switching network? Packet size? Retransmission of lost data? • A better approach to reduce the effect of lost packets on playback quality is to use traffic priorities  the most likely source of data loss is buffer shortage in network exchanges.  discard the lower priority data first

7. 3. Performance Guarantee • the network should guarantee that a packet can access the network within a specified time • when the packet is on the network, it should be delivered within a fixed amount of time • when the performance is not guaranteed? • transmission medium access control (MAC) protocols? • the network switches?

8. Some techniques: 1.Characteristics of different types of traffic should be determined in terms of peak data rate, average data rate, bursty intervals, delay, and delay jitter requirements. 2. Network access time should be guaranteed. 3. Network resources (bandwidth and buffer queues) should be managed efficiently so that as many applications as possible are supported with performance guarantees.

9. 4. Network Scalability • Three types of scalability: • Distance ? • Bandwidth ? • The number of users ?

10. 5. Multicasting Capability • There is a common need to distribute a stream to multiple destinations.  For example, in a videoconference • It is slow and wasteful for the source to send a copy of the data to each destination one by one. Why? • Circuit switched or Packet switched ?

11. The suitable network for MM communication • The individual access bandwidth should be at least a few Mbps. The aggregate bandwidth should at least be in the order of 100 Mbps at the local area, and higher for WANs. • The network should be based on packet-switched statistical multiplexing instead of dedicated circuits for efficient sharing of network resources.

12. The suitable network for MM communication • The network should provide throughput, error rate, delay, and delay jitter guarantee to applications. • The network should be scalable in terms of bandwidth, the number of users, and distance covered. • The network should have multicasting capability. It is easier to implement multicasting in packet-switched networks than in circuit switched networks.

13. End-to-End QoS for Multimedia Communication

14. ICE BREAKER….. “When communications networks are fast enough, multimedia communication can be achieved.” Is this statement correct? Why?

15. IntroductionChallenges • Operational Issue • Performance/Bandwidth • Robustness/Stability • Technology Integration • Business Issue • Grow traffic and revenue • Differentiate Services • Respond quickly to customer application and service requirements • Efficiently capture and utilize key information for flexible billing, planning, and monitoring

16. IntroductionServices Issues-1 • Network Providers • Increase utilization • More money for some traffic • Differentiation vs. Competition • Users • Broad spectrum of choices • Services enable applications • Industry • New business area

17. IntroductionService Issue-2 • What new differentiated services can be offered? • How to handle bandwidth hug multimedia applications and mission-critical application at the same time • How to handle congestion? • How to provide scaleable performance for new services? • How to bill new services • How to support new services

18. Internet QoSNew Definition - Good Service • Better than “Best Effort Service” • Service Classes • Enough for “Customer’s Needs” • Bandwidth, Capacity, Usage Pattern • Support for “Various Applications” • Multimedia Applications • Mission-Critical Applications • Secure Transactions ...

19. Internet QoSEffective Use of Networks • Exponential Growth Rate World-Wide • 120 million subscribers today, 350 million in 3 years • Ever increasing dial access numbers & speeds • Increasing leased line access speeds • Backbone bandwidth doubles every 6 months • Increasing bandwidth is only “passive solutions” • Effective use of bandwidth is “active solutions”. • Eliminate “overhead and useless usage”.

20. End-to-End Multimedia System

21. Resource Management

22. Introduction • Why resource management? • Resources in Multimedia Systems • Requirements of a multimedia system • Quality of Service • Layered Model • QoS Parameters • QoS Classes • Operations Introduction to Multimedia

23. Why resource management? • Limited capacity in digital distributed systems despite data compression and utilization of new technologies. • End-to-end nature of multimedia applications • Processing of continuous data requires the cooperation of every hardware and software component along the data path. • Competition for resources exists in an integrated multimedia system. • Resources required at different levels of a distributed multimedia system • Application, system, device, network... Introduction to Multimedia

24. Interactive video insufficient insufficient Sufficient but scarce High-quality audio abundant Network file access 1980 1990 2000 Window of insufficient resources Introduction to Multimedia

25. Application Level CPU Memory System Level (Operating System and Communication System) Network Level Multimedia Device Level Multimedia devices (e.g. video/audio device) Network host interface (bandwidth) Resources in Multimedia Systems Layered Partition of a Multimedia System wrt to required resources and processing/communication services Introduction to Multimedia

26. Resources - Classification • Resource • is a system entity required by tasks for manipulating information. • Types of resources • Active vs. passive resources - • e.g. CPU is an active resource, main memory is a passive resource • Shared vs. exclusive resources • CPU is a shared resource, video board is an exclusive resource • Single vs. multiple resources • In a uniprocessor the CPU is a single resource whereas in a multiprocessor system the CPU is a multiple resource. Introduction to Multimedia

27. Requirements • High level resource management • Resource Reservation/Allocation/Adaptation • Process Management • Real-time processing of continuous data • Communication and Synchronization between processes • Memory Management • Guaranteed timing delay and efficient data manipulation functions • File System Management • Transparent and guaranteed continuous retrieval of audio/video. • Device Management • Integration of audio/video devices Introduction to Multimedia

28. Huge Real-time requirement • Real-time system • Correctness of a computation depends not only on obtaining the right results, but also upon providing the result on time. • Real-time process • is a process which delivers the results of processing in a given time-span. • Real-time applications • Temperature control in a chemical plant • Driven by interrupts from an external device that occur at regular and unpredictable intervals. • Control of a flight simulator • scheduling of commands that execute at periodic intervals. This scheduling is performed by a timer service which the application requests from its OS. Introduction to Multimedia

29. Deadlines • Deadlines represent the latest acceptable time for the presentation of a processing result. • Types of deadlines • Soft Deadline - In some cases the deadlines are missed, but • not too many deadlines missed and • deadlines not missed by much. • E.g. flight arrival/departure • Hard Deadline • deadlines should never be violated since violations imply system failure. • E.g. deadline failures in nuclear power plants, robotic arm failures in process control systems Introduction to Multimedia

30. Requirements for Real-time operating systems • Multi-tasking capabilities • Real time application is divided into multiple tasks. • Helps keep CPU busy and ensures that processing of one event is not blocked because the application is waiting for a different event. • Short interrupt latency • Interrupt latency • is the time interval between a hardware device generating an interrupt and execution of the first instruction of the software interrupt handler. • Interrupt Latency = hardware delay to get interrupt signal to processor + time to complete current instruction + time executing system code in preparation for transferring execution to the device’s interrupt handler. Introduction to Multimedia

31. Real-time operating system requirements • Fast context switch • Context switch time (Dispatch latency) • time between the OS recognizing that the awaited event has arrived and the beginning of execution of the waiting task. • Control of memory management • Virtual Memory vs. Real Memory • A OS with VM support that aims to support real-time programming must provide a way for a task to lock its code and data into real memory so that it can guarantee predictable response to an interrupt. • Proper scheduling • OS must provide a facility to properly schedule time-constrained tasks. Introduction to Multimedia

32. Real-time Operating System requirements • Fine granularity timer services • need access to fine granularity interval times • Millisecond resolution is a bare minimum, microsecond resolution is required in some cases. • Accurate time-of-day services • Rich set of intertask communication mechanisms. • Message queues, shared memory, • Synchronization - semaphores • event flags Introduction to Multimedia

33. Real-time and Multimedia • Audio and Video • represent data streams of periodically changing values. • Semantics of multimedia information is dependant on timely delivery. • Differences b/w real-time requirements for traditional real-time systems and multimedia systems • Fault tolerance and security • soft deadline vs hard deadline • periodic behavior vs. random behavior • bandwidth requirements Introduction to Multimedia

34. Resource Management Resource Management Resource management in networked multimedia systems End-System End-System Application Application System System Network Network Switch Network Resource Manager Introduction to Multimedia

35. Qos Definition-1 “Quality of service represents the set of those quantitative and qualitative characteristics of a distributed multimedia system necessary to achieve the required functionality of an application.”

36. QoS Definition-2 “QOS is a quantitative and qualitative specification of an application’s requirement, which a multimedia system should satisfy in order to achieve desired application quality.”

37. Conceptual Model

38. Sample QoS Parameters

39. Quality of Service • Multimedia systems consist of a set of services • These services may have different requirements • timeliness, delay, jitter, accuracy, performance etc. • These requirements are specified using QoS parameters. • Examples of QoS parameters • Audio service • sample rate of 8000 samples/sec, sample resolution of 8bits/sample • Network service • throughput of 100Mbps, connection setup time of 50ms Introduction to Multimedia

40. QoS concept (continued • QoS originated in the networking service domain • provided a specification of how good the offered network services are (ISO standard definition). • Layered model of QoS • extended QoS concepts to include not only networking services, but also OS services and services for the provision of end-to-end QoS to the human user. • Services may be performed on different objects • media sources, sinks, connections, tasks • QoS specification characterizes the service objects. • Various definitions of QoS parameters • real-time channels, streams, sessions, media... Introduction to Multimedia

41. Layered Model for QoS User (Perceptual QoS) Application (Application QoS) System (Operating and Communication System) (System QoS) (Network QoS) (Device QoS) MM devices Network Introduction to Multimedia

42. Application QoS parameter examples Application Qos Media Relations Media Quality …... Synchronization Skew Integration Communication Conversion Intraframe Interframe Media Characteristics Component Spec Sample Size Sample Rate Compression Name Size Rate Importance Loss Rate Transmission Characteristics End-to-end Delay Sample Loss Rate Importance Cost Introduction to Multimedia

43. System QoS parameter examples System Qos Network Subsystem Application Subsystem Tasks per Medium Spec Tasks per Connection Spec Priority Duration Period Priority Duration Period Task Scheduler Task Scheduler Task Ordering Time Begin Time Deadline Task Ordering Time Begin Time Deadline Space Requirements Space Requirements Introduction to Multimedia

44. Network QoS parameter examples Network Qos for a connection Throughput Spec Performance Spec Traffic Spec Connection ID Packet Loss Rate Ordering Packet Size Intermediate Delay Error Control Throughput Packet End-to-end Delay Fragment/Reassembly Communication Type Burstiness Cost Priority Introduction to Multimedia

45. QoS Classes • QoS Service Classes determine • reliability of offered QoS • utilization of resources • Guaranteed Service Class • QoS guarantees are provided based on deterministic and statistical QoS parameter values. • Predictive Service Class • QoS parameter values are estimated and based on the past behavior of the service • Best-effort Service Class • No guarantees or only partial guarantees provided • No QoS parameters are specified or some minimal bounds are given. Introduction to Multimedia

46. Resource Allocation Tradeoffs in QoS Classes Needs of appl 1 Reserved for appl 1 unused Reserved for appl 2 unused Needs of appl 2 Reserved for appl 1 Needs of appl 1 conflict appl2 Reserved for appl 2 Introduction to Multimedia

47. Deterministic QoS parameter values • Single value • QoS1 - average value (QoS_ave), contractual value, threshold value, target value. • Pair of values • <QoS1,QoS2> - • QoS1 - required value • QoS2 - desired value • <QoS_ave, QoS_peak>,<QoS_min,QoS_max> etc. • Triple of values • <Qos1,Qos2,Qos3> • QoS1 - best value, Qos2 = average value, QoS3 = worst value • e.g. <BW_peak,BW_ave,BW_min>,similarly jitter…. Desired value Required value Acceptable value Increasing quality Introduction to Multimedia

48. Guaranteed QoS • Need to provide • 100% guarantees for QoS values (hard guarantees) or • very close to 100% guarantees (soft guarantees) • Current QoS calculations and resource allocations are based on • hard upper bounds for imposed workloads • worst case assumptions about system behavior • Advantages • QoS guarantees are satisfied even in the worst possible case, hence high reliability • Disadvantages • Over-reservation of resource capacities, hence needless rejection of reservation requests. • Qos values may in reality require softer bounds and significantly less resources than calculated hard bounds. Introduction to Multimedia

49. Predictive QoS parameters • Average • Can utilize QoS values in the past (QoS1,…QoSi) and compute the average from 1 to i values. The desired QoS_bound at step K>I will be • QoS_K = 1/i *  QoS_j • Maximum Value • Can utilize QoS values in the past (QoS1,…QoSi) and take maximum value as the desired QoS bound • QoS_K = max QoS_i • Minimum Value • Can utilize QoS values in the past (QoS1,…QoSi) and take minimum value as the desired QoS bound • QoS_K = min QoS_i i j=1 i=1,..i i=1,..i i=1,..i Introduction to Multimedia

50. Best Effort QoS • No Qos bounds or possible soft QoS bounds • Possible calculation of performance one might get is based on • average case with stochastic description of imposed workload • average case with stochastic assumptions about the system behavior. • Advantages • resource capacities can be statistically multiplexed, hence more processing requests can be granted. • Disadvantages • QoS may be temporarily violated, hence the service guarantees are not reliable. Introduction to Multimedia