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Distributed Distributed Multimedia SystemsMultimedia Systems
Tarek ElshaaraniTarek Elshaarani
Vahid RafieiVahid Rafiei
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Institutionen för informationsteknologi | www.it.uu.se
Examples of DMMS
And more!
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Introduction
Definition: "A distributed multimedia system (DMS) is an integrated communication, computing, and information system that enables the processing, management, delivery, and presentation of synchronized multimedia information with quality-of-service guarantees."
http://encyclopedia.jrank.org/articles/pages/6729/Distributed-Multimedia-Systems.html
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Characteristics
Delivering the streams of multimedia data Audio samples, Video frames
To meet the timing requirements QoS (Quality of Service)
Flexibility (adapting to user needs) Availability Scalability
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Factors that affect a system
Server bandwidth Cache space Number of copies The number of clients
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Basic Schema
Wide area gateway Videoserver
DigitalTV/radioserver
Video cameraand mike
Local network Local network
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Typical infrastructure components for multimedia applications
Microphones
Camera
Screen
Window system
CodecD
BMixer
PC/workstation PC/workstation
CVideostore
Networkconnections
K
L
M
: multimedia stream
CodecA G
Codec
H
Window system
White boxes represent media processing components, many of which are implemented in software, including:codec: coding/decoding filter
mixer: sound-mixing component
Video file system
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Different Designs and Architectures
Database Proxy/information servers Clients Wired or wireless networks
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Approaches
Proxy-based approach Parallel or clustered servers approach
Varies based on clip duration, number of clients, bandwidth available, etc
Caching
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Quality of Service (QoS) DMMS are real-time systems as data
must be delivered on time Not critical – Some flexibility exists Loss is acceptable when resync is
possible. “Acceptable” service is measured by:
Bandwidth (Throughput) Latency (Access time) Data Loss Rate (Acceptable loss ratio)
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QoS Management
“QoS Management” Process of managing resources to meet the
Acceptable service criteria. Resources include:
CPU / processing power Network bandwidth Buffer memory(on both ends) Disk bandwidth Other factors affecting communication
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Why do we need QoS?
As multimedia becomes more widespread, strain on network increases!
Networks provide insufficient QoS for distribution of multimedia. Ethernet (wired or wireless) is best effort Collisions, data loss, congestion, etc.
For some multimedia applications, synchronization is vital.
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QoS Managers
Software that runs on network nodes which have two main functions: QoS negotiation: get requirements from apps
and checks feasibility versus available resources.
Admission control: If negotiation succeeds, provides a "resource contract" that guarantees reservation of resources for a certain time.
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Ways to achieve QoS
Buffering (on both ends) Compression
More load on the nodes, but that is okay Bandwidth Reservation Resource Scheduling Traffic Shaping Flow Specifications Stream Adaptation
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Traffic Shaping Output buffering at the source to keep data
flowing smoothly. Two main algorithms:
Leaky bucket: guarantees that data flows at a constant rate without bursts - completely eliminate bursty traffic.
Token bucket: variation of leaky bucket where tokens are generated to allow for some bursty traffic when bandwidth is unused for a certain period of time.
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Traffic Shaping
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Flow specifications
RFC 1363 defines QoS parameters: Bandwidth Latency and jitter
constraints Data loss limits Token bucket size
Instructor’s Guide for Coulouris, Dollimore and Kindberg Distributed Systems: Concepts and Design Edn. 3 © Pearson Education 2001
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Stream Adaptation Adjust the data flow based on resource availability. Scaling
Scale down content at the source to reduce bandwidth required:
Audio: reduce the rate of audio sampling or dropping channels Video: reduce resolution, number of pixels, change compression
algorithm, color depths, color spaces, and combinations.
Filtering One target asks the source to reduce quality for all the clients, even if
some can handle higher quality. Suitable for more than one simultaneous target and guarantees the
same QoS for all the targets
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Applications of DMMS Digital Libraries Distance learning Teleconferencing Video on Demand (VoD) & Video on Reservation
(VoR) Pay Per View Audio Streaming Video Streaming E-commerce P2PTV
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Voddler
Video on Demand and Pay Per View Long movies Requires high bandwidth Hybrid P2P distribution network
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Voddler
http://en.wikipedia.org/wiki/File:P2ptv.PNG
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YouTube, Platform
Apache Python Linux MySQL Psyco lighttpd for video instead of Apache,
because of overheads
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YouTube, Serving Video
Each video hosted by a mini-cluster. Each video is served by more than one machine.
Most popular content is moved to a CDN (content delivery network)
Less popular content (1-20 views per day) uses YouTube servers in various proper sites
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YouTube, Data Center Strategy Used manage hosting providers at first. Living off
credit cards so it was the only way. Managed hosting can't scale with you. You can't
control hardware or make favorable networking agreements.
So they went to a colocation arrangement. Now they can customize everything and negotiate their own contracts.
Videos come out of any data center. Not closest match or anything. If a video is popular enough it will move into the CDN.
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Questions?Questions?