Distributed Multimedia Systems - uni-klu.ac.atlaszlo/courses/distmm_lyon/intro.pdf · László Böszörményi Distributed Multimedia Systems Introduction - 11 The Challenge • New

László Böszörményi Distributed Multimedia Systems Introduction - 1

Distributed Multimedia Systems

1. Introduction


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


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


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


Distribution Transparencies• Access

– Mask out different representations• Location• Failure• Migration

– Mask out movements • Relocation

– Mask out movements during an existing interaction• Replication• Persistence• Transactions


Scalability – example (1)


Scalability – example (2)


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


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


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


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?


Multimedia System Environment

Media Server

Business Users

Home Users

Business Users

Meta-Database

Proxy Server

Router

“Lastmile“

WAN

LAN

LANLAN

LAN

Streaming video


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


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.)


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


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


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


Continuous Media• Discrete interaction

• Continuous interaction

Node-A Node-B

time

Node-A Node-B

time< Δ


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 …


Movie as a set of elementary streams


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


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


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


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


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


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


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


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.


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


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


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