Distributed Multimedia Systems Tarek Elshaarani Vahid Rafiei

Informationsteknologi Institutionen för informationsteknologi | Examples of DMMS And more!

Informationsteknologi Institutionen för informationsteknologi | 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."

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | Factors that affect a system  Server bandwidth  Cache space  Number of copies  The number of clients

Informationsteknologi Institutionen för informationsteknologi | Basic Schema

Informationsteknologi Institutionen för informationsteknologi | Typical infrastructure components for multimedia applications

Informationsteknologi Institutionen för informationsteknologi |

Informationsteknologi Institutionen för informationsteknologi | Different Designs and Architectures  Database  Proxy/information servers  Clients  Wired or wireless networks

Informationsteknologi Institutionen för informationsteknologi | Approaches  Proxy-based approach  Parallel or clustered servers approach  Varies based on clip duration, number of clients, bandwidth available, etc  Caching

Informationsteknologi Institutionen för informationsteknologi | 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)

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | 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.

Informationsteknologi Institutionen för informationsteknologi | 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.

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | 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.

Informationsteknologi Institutionen för informationsteknologi | Traffic Shaping

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | Voddler  Video on Demand and Pay Per View  Long movies  Requires high bandwidth  Hybrid P2P distribution network

Informationsteknologi Institutionen för informationsteknologi | Voddler

Informationsteknologi Institutionen för informationsteknologi | YouTube, Platform  Apache  Python  Linux  MySQL  Psyco  lighttpd for video instead of Apache, because of overheads

Informationsteknologi Institutionen för informationsteknologi | 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

Informationsteknologi Institutionen för informationsteknologi | 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.

Informationsteknologi Institutionen för informationsteknologi | Questions?