How Multicast domain representative discovery works in Targeted Multicast

Multicast Domain Representative (MDR) Discovery in Targeted Multicast

In order to perform Multicast domain discovery the Multicast server must be able to discover subnet representatives.

1. Subnet representative discovery The TMC server (on the core server) continues through the various discovery methods until a subnet/multicast domain representative is found. When a representative is found using UDP broadcast discovery the TMC server does not attempt the Target list discovery step. The check for targets w/file method only works after domain discovery has been accomplished, so it is never used in selecting a representative as part of domain discovery.
2. UDP scanning Because several of the discovery methods use a UDP ping sweeping technique to locate a multicast representative the protocol used is outlined here below: For each machine in the target list, or preferred representative list, for the subnet or multicast domain the TMC server sends a "Can anyone be a subnet Rep?" message to the target. If the target can be a subnet representative, it responds with "I can be subnet Rep". If the TMC server does not receive a response after approximately 20 milliseconds, it moves to the next target. The TMC server uses the first machine responding as being capable of being a multicast representative. If no responses are received the multicast discovery method will fail, and the next method will be tried.

An advantage of UDP scanning over UDP broadcast is that its point-to-point communications allow it to get past routers that are configured not to forward UDP broadcasts.

• Preferred representatives discovery

• Preferred representatives are defined in the "multicast domain representative" alias file. The representative is located using the UDP scanning as outlined above. The TMC server scans through the list of preferred representatives and will use the first representative to respond.
• Cached file discovery
  • when performing a multicast domain discovery the TMC server obtains information about computers that have a portion or the entire file to be multicast. If the TMC server is configured to use domain information in the registry and cached file discovery is enabled, the TMC server performs a cached file discovery. When a cached file discovery is performed the TMC server groups the subnets according to the information in the registry. Then a multicast domain discovery is performed. This does not provide further consolidation of subnets but does discover cached file information. The TMC server uses the information about the machines that have the cached file to determine the multicast representative.
• UDP broadcast discovery
  • The UDP broadcast discovery method can be enabled/disabled through the registry. The TMC server locates a multicast representative using a UDP broadcast as shown in the following diagram.
• Target list discovery
  • the discovery method of last resort. If no other discovery method succeeds in finding a multicast representative this method attempts to locate a multicast representative. This is done by performing UDP scanning on all targets for the multicast domain in the target list.