distributed multimedia systems - uni-klu.ac.atlaszlo/courses/distmm_lyon/intro.pdf · lászló...
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László Böszörményi Distributed Multimedia Systems Introduction - 1
Distributed Multimedia Systems
1. Introduction
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László Böszörményi Distributed Multimedia Systems Introduction - 2
What is Distributed?• “A distributed system is a collection of independent
computers that appear to the users of the system as a single computer.” – Tanenbaum & Enslow
• “A distributed system is a system designed to support the development of applications and services which can exploit a physical architecture consisting of multiple, autonomous processing elements that do not share primary memory but cooperate by sending asynchronous messages over a communication network” – Blair & Stefani
• “A distributed system is one that stops you getting any work done when a machine you’ve never even heard of crashes” – Leslie Lamport
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László Böszörményi Distributed Multimedia Systems Introduction - 3
Why Distributed?• Resource and Data Sharing
– Printers, databases, multimedia servers etc.• Availability, Reliability
– The loss of some instances can be hidden• Scalability, Extensibility
– System grows with demands (e.g. extra servers)• Performance
– Huge power (CPU, memory etc.) available• Inherent distribution, communication
– Organizational distribution, e-mail, video conference
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László Böszörményi Distributed Multimedia Systems Introduction - 4
Problems of Distribution• Concurrency, Security
– Clients must not disturb each other• Partial failure
– We often do not know, where is the error (e.g. RPC)• Location, Migration, Replication
– Clients must be able to find their servers• Heterogeneity
– Hardware, platforms, languages, management• Convergence
– Between distributed systems and telecommunication
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László Böszörményi Distributed Multimedia Systems Introduction - 5
Distribution Transparencies• Access
– Mask out different representations• Location• Failure• Migration
– Mask out movements • Relocation
– Mask out movements during an existing interaction• Replication• Persistence• Transactions
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László Böszörményi Distributed Multimedia Systems Introduction - 6
Scalability – example (1)
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László Böszörményi Distributed Multimedia Systems Introduction - 7
Scalability – example (2)
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László Böszörményi Distributed Multimedia Systems Introduction - 8
Openness• Well-defined Interfaces
1. Black box with no public interfaces2. Black box with a well-defined public external interface3. White box with well-defined public internal interfaces
• Interoperability– Components of different origin can communicate
• Portability– Components work on different platforms
• Separation of Concerns• Standards – a necessity
– Should allow competition in non-normative areas
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László Böszörményi Distributed Multimedia Systems Introduction - 9
Most relevant Standards• Reference Model for Open Distributed
Processing (RM-ODP)– ISO / ITU; de jure standard (law maker status)
• CORBA– OMG; de facto standard (market driven acceptance)
• Multimedia System Services (IMA MSS)– International Multimedia Association– Based on CORBA, adopted by ISO (PREMO)
• JPEG (Joint Photographic Experts Group)• MPEG (Moving Pictures Expert Group)
– Both ISO / ITU, de jure standards
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László Böszörményi Distributed Multimedia Systems Introduction - 10
Multimedia• Media
– Storage, transmission, interchange, presentation, representation and perception of different data types:
– Text, graphics, animation, voice, audio and video– Movie: video + audio + …
• Multimedia– Handling of a variety of representation media
• Technology push– Emerging technology to integrate media
• End user pull– Information overload and starvation
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László Böszörményi Distributed Multimedia Systems Introduction - 11
The Challenge• New applications
– Multimedia will be pervasive in 10 years (as graphics)• Storage and Transmission
– E.g. 2 hours uncompressed HDTV movie: 570 GB– Videos are extremely large, even compressed
• Continuous delivery– E.g. 30 frames/s (NTSC), 25 frames/s (PAL) for video– Guaranteed Quality of Service– Admission Control
• Search– Can we look at 100… videos to find the proper one?
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László Böszörményi Distributed Multimedia Systems Introduction - 12
Multimedia System Environment
Media Server
Business Users
Home Users
Business Users
Meta-Database
Proxy Server
Router
“Lastmile“
WAN
LAN
LANLAN
LAN
Streaming video
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László Böszörményi Distributed Multimedia Systems Introduction - 13
Applications – Broadcast and VOD• Broadcast Video
– Store and play back (e.g. on behalf of MTV)– Substitutes a bank of VCRs, without control– Enhanced reliability, availability and maintenance
• Video-on-Demand (VOD)– Users can select from a list of choice, maybe preview– Interaction via set-top box + remote control or via PC– New movies are more popular
• Near Video-on-Demand (NVOD)– Popular videos are broadcasted periodically– VCR control is more difficult
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László Böszörményi Distributed Multimedia Systems Introduction - 14
Applications - Composite Documents • Hypermedia
– Collections of MM documents with explicit links– Search is limited to text based search– Documents and their presentations can defined by
SMIL (Structured Multimedia Interchange Language, defined by the World Wide Web Consortium, W3C)
• Multimedia Databases– Collections of MM documents with implicit links– Automatic or manual annotation– Complex search– Multimedia Query Languages (MOQL, MM-SQL etc.)
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László Böszörményi Distributed Multimedia Systems Introduction - 15
Applications – Collaborative Work • Videoconferencing
– Geographically distributed virtual meetings– Presenters and audience with different facilities– Audio/visual input and output devices– Participants see a seating chart– Presenter can broadcast speech and graphics,
maybe also real-time video– Polling for the audience– Logging facility– Puts hard requirements on the infrastructure– Enterprise solutions are more feasible than internet
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László Böszörményi Distributed Multimedia Systems Introduction - 16
Some Technology Steps• Single-computer multimedia
– DVD, similar to CD, higher density, 5-17 GB– Video editing tools
• Video on demand– Video servers provide a large selection of movies
• Systems with e.g. 1000 disks– Set-top boxes convert the TV set into a computer– Improving network throughput even at the “last mile”
• ADSL: Dedicated, guaranteed, low-bandwidth channel• Cable TV: Shared, high-bandwidth channel
• Interactive, distributed multimedia– E.g. video conferencing
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Some Technology DataMultimedia Source Mbit/s GB/h
Telephone (PCM) 0.064 0.003
MPEG-2 movie 4 1.76
MP3 music 0.14 0.06Audio CD 1.4 0.62MPEG-1 movie 1 - 1.5 0.66
Digital camcorder (720*480) 25 11
Uncompressed TV (640*480) 221 97
Uncompressed HDTV (1280*720)
648 288
Device Mbit/s
Fast Ethernet 100
EIDE disk 133
ATM OC-3 156
SCSI Ultra wide disk
320
IEEE 1394 (FireWire)
400
Gigabit Ethernet 1.000
SCSI Ultra-160 1.280
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László Böszörményi Distributed Multimedia Systems Introduction - 18
Continuous Media• Discrete interaction
• Continuous interaction
Node-A Node-B
time
Node-A Node-B
time< Δ
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László Böszörményi Distributed Multimedia Systems Introduction - 19
Streams• Continuous Data
– Audio, video, animation• Flow
– A single continuous media type – produced and/or consumed• Simple (elementary) stream
– Single flow– E.g. an audio track, or a telephone connection
• Complex stream– Several, related flows– E.g. a movie with
• 1 video track• Several audio tracks in different languages• Several subtitles in different languages• A superposed animation track …
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László Böszörményi Distributed Multimedia Systems Introduction - 20
Movie as a set of elementary streams
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László Böszörményi Distributed Multimedia Systems Introduction - 21
Quality of Service Categories• Timeliness
– Data must be delivered in time• Volume
– The required throughput must be met• Reliability
– A given level of loss of data must not be exceeded• Cost
– May give the basic motivation to be “federative”• Criticality• Quality of Perception
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László Böszörményi Distributed Multimedia Systems Introduction - 22
Quality of Service Dimensions• Timeliness dimensions
– Latency (max. delay between consecutive frames)– Start-up latency (max. delay before starting a
presentation)– Jitter (delay variance)
• Volume dimensions– Throughput in frames/sec or bits/sec or bytes/sec
• Reliability dimensions– MTBF (Mean Time Between Failure) of disks– MTTR (Mean Time To Repair) – Error rates on the telecommunication lines
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László Böszörményi Distributed Multimedia Systems Introduction - 23
Quality of Service Requirements• Deterministic
– Precise values or ranges– E.g. latency must be between 45 and 55 ms
• Probabilistic– Probability of the required QoS– E.g. the latency should be < 50ms for 95% of the
frames• Stochastic distributions
– E.g. frame arrival should follow normal distribution with mean interval-time 40 ms and 5ms variance
• Classes – e.g. guaranteed and best effort
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László Böszörményi Distributed Multimedia Systems Introduction - 24
Typical QoS Requirements
QoS Max. latency (s)
Max. jitter (ms)
Throughput (Mb/s)
Bit error rate
Packet error rate
Voice 0.25 10 0.054 < 10-3 < 10-4
Video (TV) 0.25 100 100 < 10-2 < 10-3
Compressed video
0.25 100 2 - 10 < 10-6 < 10-9
Image 1 - 2 - 10 < 10-4 < 10-9
Data (file tr.) 1 - 2 - 100 0 0
Real-time data
0.001 - 1 - < 10 0 0
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QoS Dependencies, Contracts• QoS of one part depends on that of other parts
– E.g. in a layered system, timeliness adds up• Dependent components make a contract
QoS required
Depends on
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Static QoS Management Functions• Specification
– E.g. deterministic range for timeliness, volume and reliability categories, and dependencies
• Negotiation– The application may accept lower level QoS for lower
cost• Admission control
– If this test is passed, the system has to guarantee the promised QoS
• Resource reservation– Maybe necessary to providing guaranteed QoS
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Dynamic QoS Management Functions• Monitoring
– Notices deviation from QoS level– At a certain level of granularity (e.g. every 100ms)
• Policing– Detect participants not keeping themselves to the
contract– E.g. source sends faster than negotiated (e.g. 25 f/s)
• Maintenance– Sustaining the negotiated QoS– E.g. the system requires more resources
• Renegotiation– Client tries to adapt – maybe can accept lower QoS
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László Böszörményi Distributed Multimedia Systems Introduction - 28
QoS and Viewpoints (RM-ODP)• Enterprise Viewpoint
– E.g. the management declares the application critical• Information Viewpoint
– E.g. applications requires high quality TV (HDTV)• Computational Viewpoint
– Decomposition to components and their related– QoS dimensions as frame/s and error rate etc.
• Engineering Viewpoint– E.g. required scheduling, compression, storage etc.
• Technology Viewpoint– E.g. overall reliability of the used cameras etc.
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Requirements on Client (1)• Playback
– The compressed A/V data must be decompressed at the client side• In hardware or software
– Streaming must be provided either from• The local disk – easy, or from • The network – might be very hard
• Consumer environment (set-top box)– Must be inexpensive (ca. 600$ or less)– Equipment costs ∼ to total number of clients– Server and network load ∼ to number of active clients
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Requirements on Client (2)– Set-top box as simplified workstation
• E.g. IBM offers a set of ASICS, based on PowerPC 403 with real-time operating systems: pSOS and OS/9000
– Set-top box as proprietary equipment• E.g. WebTV• Inexpensive, easy to maintain and to use (remote control)
• Business Environment – good workstations– Multimedia adapters
• E.g. Mwave adapter, (actually a DSP + a real-time OS)• Programmable functions, e.g. modem+audio decompression
– Multimedia processors• E.g. Intel MMX: parallelized instructions on byte data types• Drawback: these instructions use the floating-point registers
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Requirements on the Environment• User Interface
– The client needs to be able to formulate queries– To make selection on MM contents– Special challenge with limited devices, such as
• Set-top box + TV, mobile phones, PDAs …• Multimedia Document Retrieval
– Multiple A/V data may be retrieved and displayed– Sufficient bandwidth is needed in all components
• Server, network and client system• The actual requirement is variable• Reservation for the peak is inefficient
• Server and Network – see later