Distributed Multimedia Systems Tarek Elshaarani Vahid Rafiei

Distributed Distributed Multimedia SystemsMultimedia Systems

Tarek ElshaaraniTarek Elshaarani

Vahid RafieiVahid Rafiei

Info

rmat

ions

tekn

olog

i

Institutionen för informationsteknologi | www.it.uu.se

Examples of DMMS

And more!

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


Factors that affect a system

Server bandwidth Cache space Number of copies The number of clients

Info

rmat

ions

tekn

olog

i


Basic Schema

Wide area gateway Videoserver

DigitalTV/radioserver

Video cameraand mike

Local network Local network

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


Info

rmat

ions

tekn

olog

i


Different Designs and Architectures

Database Proxy/information servers Clients Wired or wireless networks

Info

rmat

ions

tekn

olog

i


Approaches

Proxy-based approach Parallel or clustered servers approach

Varies based on clip duration, number of clients, bandwidth available, etc

Caching

Info

rmat

ions

tekn

olog

i


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)

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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.

Info

rmat

ions

tekn

olog

i


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.

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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.

Info

rmat

ions

tekn

olog

i


Traffic Shaping

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


Voddler

Video on Demand and Pay Per View Long movies Requires high bandwidth Hybrid P2P distribution network

Info

rmat

ions

tekn

olog

i


Voddler

http://en.wikipedia.org/wiki/File:P2ptv.PNG

Info

rmat

ions

tekn

olog

i


YouTube, Platform

Apache Python Linux MySQL Psyco lighttpd for video instead of Apache,

because of overheads

Info

rmat

ions

tekn

olog

i


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

Info

rmat

ions

tekn

olog

i


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.

Info

rmat

ions

tekn

olog

i


Questions?Questions?

Documents

Distributed Multimedia Systems Tarek Elshaarani Vahid Rafiei