Advanced Computer Networks Lecture 3 Distributed Multimedia Systems

1 Outline Introduction Characters of multimedia data Quality of service management Resource management Stream adaptation Summary

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.

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

1.1 Multimedia in A Mobile Environment * Global System for Mobile Communications

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)

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

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)

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

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

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

3 The QoS Manager ’ s Task

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

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.