About Multicast

From UW Center for Collaborative Technologies Wiki
Jump to: navigation, search

For background information about Multicast please read: http://en.wikipedia.org/wiki/Multicast

Multicast has been around for a very long time, but it still suffers from interoperability problems and general lack of use. A chicken and egg problem exists: networks don’t bother to enable multicast at their borders because so few applications will take advantage of it and applications don’t take advantage of the improved scalability of multicast because most networks don’t enable it. Although modern routers fully support multicast, they do take some configuration by network administrators, and it’s easy to configure them incorrectly. For example, if no one ever used TCP/IP, network administrators wouldn’t perform simple tests like “ping” or “open my favorite Web site” after each configuration change or firmware upgrade. Eventually, silently, some configuration setting would change or some firmware bug would be introduced that prevented TCP/IP for working and no one would notice. This is the state of multicast today.

While the Internet2 backbone fully supports multicast, it’s been our experience that at almost every university we’ve worked with, multicast isn’t properly working on the routers that connect the university to Internet2. We face a lack of knowledge in network administrators who have never configured multicast before. Even after we get multicast working, it’s all too frequent that a few weeks or months later after some firmware update or configuration change, multicast breaks.

While ConferenceXP is designed around the use of Multicast, it has provisions to enable it to be used in situations where multicast is not fully functional, or is not available:

  • The ConferenceXP Reflector Service exists to allow multicast-enabled and non-multicast-enabled participants to work together.
  • The ConferenceXP point-to-point unicast mode provides a simple way for two nodes to connect over unicast.

ConferenceXP also includes features aimed at informing the user about multicast issues, and aiding in diagnosis:

  • The ConferenceXP Diagnostic Service is designed to aggregate client receiver and sender reports, and to disseminate the information back to clients by means of a webservice. This enables the client to show more accurately where multicast and other network problems exist in a multi-site conference.
  • The ConferenceXP test signal provides a simple local client multicast connectivity check. If the signal is received, the client will show a green light on the lower-right of the main ConferenceXP window. The green light gives an indication that the node may be able to work with other sites using multicast, however this is not foolproof.