End Systems Multicast


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Frequently Asked Questions


If you are having trouble watching the broadcast, please take a look at our troubleshooting page.

About the Broadcast

  • What are the encoding formats of the audio and video streams?
  • How do I read your on-line tree?

  • About the Broadcast Application

  • How did you put your system together?
  • What happens when I run your software on a machine slower than 400 MHz?
  • Do you support operating systems other than Windows and Linux?
  • Why does your Linux installation require installing crossover?
  • Can your software rebroadcast content using IP Multicast on the local LAN?
  • Do you support machines that are behind firewalls or NATs?
  • Do you support other media players, such as Real or Windows Media?

  • About the End System Multicast Architecture

  • What is End System Multicast?
  • If I want to broadcast content, why should I use End System Multicast? Why not use IP Multicast, a broadcast server, or a content delivery network (CDN)?



  • The Answers


    What are the encoding formats of the audio and video streams?

    For audio, we use Qualcomm Pure Voice as the compression algorithm. The resulting data rate is 13Kbps. For video, we use Sorenson Video 3 as the compression algorithm. To deal with receiver heterogeneity, we encode the video using two rates at 100Kbps (5 frames/second) and 300Kbps (15 frames/second). Our ESM software dynamically determines the proper data rate for each receiver.


    How do I read your on-line tree?

    The bandwidth values on each link are the bandwidth the child is getting from its parent. Links that are in use are colored in black. If a node leaves the end system multicast group, the link that existed between that node and its parent is colored in red. We update the figure once every minute. If you try to reload more often, you may not see any changes. Also, if the new figure changes drastically from the previous figure, this does not neccessarily mean that the multicast tree has gone through a huge change. We use dot, a graph visualization tool, to draw the tree, and dot is not optimized for incremental changes.

    You may also notice that the reported bandwidth received by a parent node may be less than the bandwidth received by a child. This is because the bandwidth estimation at each receiver is not synchronized, and the source rate is varying over time.


    How did you put the system together?

    Please check out our posters we made on past ocassions.


    What happens when I run your software on a machine slower than 400 MHz?

    There are two pieces of software that run on your machine: QuickTime and our ESM code. In our experience, the ESM code consumes 10-20% of CPU cycles compared to QuickTime. QuickTime consumes a lot of CPU cycles when displayed in 640x480 frame size and 300Kbps data rate. If your machine is slower than 400MHz, QuickTime takes up full CPU, and the perceived audio/video quality goes down.


    Do you support operating systems other than Windows and Linux?

    Although the ESM code works on most Unix-based systems, we are currently only supporting Linux systems. This is because we have chosen to use the Apple QuickTime player, which is not available in most Unix platforms.

    We are currently explorting porting ESM code to MacOS.


    Why does your Linux installation require crossover ?

    We have chosen to use the Apple QuickTime player, which is not available in Unix. We have not found a satisfactory open-source QuickTime player for Unix, and using the Windows version requires crossover support.


    Can your software rebroadcast content using IP Multicast on the local LAN?

    LAN-level multicast support can ensure more efficient utilization of bandwidth in the LAN and result in better scalability of the the End System Multicast architecture. We plan to incorporate support for local LAN Multicast in future versions of the ESM software.


    Do you support machines that are behind firewalls or NATs?

    We now support machines behind firewalls and NATs. Our software currently uses UDP control messages. This will prevent hosts that are behind a firewall blocking UDP from receiving data.


    Do you support other media players, such as Real or Windows Media?

    QuickTime uses the standardized Real-Time Transport Protocol Suite (RTP/RTCP), which Real and Windows Media use proprietary protocols. It is unlikely that we will support Real or Windows Media in the near future.


    What is End System Multicast?

    End System Multicast implements all multicast related functionality on the end systems (hosts) instead of on the IP routers between them. Read more about ESM here.


    If I want to broadcast content, why should I use End System Multicast? Why not use IP Multicast or a content deliver network (CDN)?

    End System Multicast does not rely on dedicated infrastructure support. While support from infrastructure can be exploited when available to provide better performance, such support is not essential for normal operation. Further, no changes are required at the IP or routing layer.

    IP Multicast requires changes to the IP layer, and support from routers. Deployment of this architecture has proved to be very difficult. Content delivery networks require dedicated, provisioned infrastructure support that may not make economical sense to all users.


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