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Media Scaling of IP-Multicast Streams in Heterogeneous Networks Peter Parnes LTU-CDT/Marratech

Media Scaling of IP-Multicast Streams in Heterogeneous Networks Peter Parnes LTU-CDT/Marratech Roxy Workshop 980921-23. Overview. Background Current Problem Proposed Solutions mStar Current Status in the Internet Summary. Background.

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Media Scaling of IP-Multicast Streams in Heterogeneous Networks Peter Parnes LTU-CDT/Marratech

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  1. Media Scaling of IP-Multicast Streams in Heterogeneous Networks Peter Parnes LTU-CDT/Marratech Roxy Workshop 980921-23

  2. Overview • Background • Current Problem • Proposed Solutions • mStar • Current Status in the Internet • Summary

  3. Background • “Broadcasts” of real-time media on the Internet is becoming more and more important. • It is very central to the Roxy project. • If the used system shall scale, IP-multicast HAS to be used!

  4. Requirements and Restrictions • Best-effort delivery • Reliability not required • Applications have to be adaptive, i.e. have to adapt to network congestion and be able to handle different configurations.

  5. Sender Local Receiver Internet Receiver ISDN Receiver 100Mbps 100Mbps 500Kbps 128Kbps Internet • Which bandwidth should be used when transmitting a real-time media stream over heterogeneous networks?

  6. Proposed solutions • Max/Min client bandwidth • Simulcast • Network transcoders • Receiver driven Layered Multicast - RLM • Bandwidth Guessing - TCP friendly • Active Networks • Active Services

  7. Max/Min client bandwidth • Just ignore some set of receivers • Send the stream with high bandwidth • Ignore low bandwidth receivers • Send the stream with low bandwidth • Force high bandwidth receivers to use low quality • Does not take congestion into account

  8. Simulcast • Send the same stream with different encodings from the sender and let the receivers choose what they want to receive. • Can be very expensive CPU wise • Wastes bandwidth on shared links • Does not take congestion into account in the way it is being used today. • Used in mStar (more later)

  9. Network Transcoders • A common approach is to deploy transcoders on the boundaries between different networks. • Transcoding, mixing, downscaling • E.g. transcode MJPEG to H.261 when the traffic leaves a campus (high bandwidth network). • E.g. mStar mTunnel can transcode when tunnelling mcast data (more later).

  10. Receiver driven Layered Multicast - RLM • Divide the stream into a hierarchy of exclusive additive layers • Each layer is multicasted to a different group loop: if no_congestion then join next group to get higher layer else leave group to drop highest layer

  11. RLM Problems • How to detect congestion caused by my tests or by others • Shared learning proposed • Does it scale? • Today long timeout in mcast forwarding trees • Might lead to false interpretation of the current situation • Is not “nice” to TCP

  12. Bandwidth Guessing • In early 97 a proposal called “TCP-Friendly” was distributed. • Describes a way of estimating the bandwidth between a sender and a receiver based on RTT and current packet drop. • Takes TCP into account and will be a “nice” participant in the network

  13. BW Guessing Problems • Hard to calculate RTT accurately • Works only for “broadcast” situations • Not very tested yet

  14. Active Networks • The latest “buzzword” network research topic (since ATM is practically dead) • Basic idea: • Allow injection of small programs into network nodes • Network nodes perform computations on user data

  15. Active Networks... • Two Different Approaches • Code and control is handled out-of-band • Each packet carries miniature programs (capsules) • Allows networks to be modified “on-demand” • Opens a completely new area for real-time media scaling

  16. Active Networks... • Issues: • Safety, fairness, appropriate architecture, common programming model, robustness • Status: • At the very beginning • A very “political” problem “I dare You to run code in my router!” Steve Deering - Cisco (currently :-)

  17. Active Services • Deploy user controllable programs-pads in the network. • Users can deploy their own transcoding programs and can easily up-grade these when needed • A system for this is currently being deployed and tested on Berkeley Campus

  18. mStar • mTunnel contains support for media-aware rescaling, transcoding, mixing and switching of audio and video. • Could be easily be extended for general transcoding between different mcast groups. • Simulcast is currently being used in mStar Pro for the electronic corridor. • BW Guessing and RLM based approaches should be further investigated.

  19. Status in Internet • Almost all traffic is still sent using Unicast - transcoding at the server • Network transcoders probably most common • Simulcast less common than one could imagine (lack of good support in today’s applications).

  20. Summary • A number of more or less proposed solutions: • Max/Min client bandwidth • Simulcast • Network transcoders • Receiver driven Layered Multicast - RLM • Bandwidth Guessing - TCP friendly • Active Networks • Active Services • Still a lot of research needed

  21. Questions? peppar@cdt.luth.se http://www.cdt.luth.se/~peppar/ http://www.cdt.luth.se/mStar/ http://www.marratech.com/

  22. Multicast vs. Unicast

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