Multicast

Multicast delivery offers the best features from both unicast and broadcast. It delivers traffic efficiently both when data must be sent from a single source to multiple users (one-to-many) and from multiple sources to multiple users (many-to-many), by sending traffic only to those interested parties that have requested the data.

Unicast is a one-to-one data transfer, so for N users the source must generate N flows of traffic to the intended recipients. This is resource-intensive on both the source of the data and bandwidth.

Broadcast provides delivery to all hosts on a specific subnet whether they want to receive the data or not. This is less demanding on the source of the data but also means the end network bears the burden of the delivery of the traffic to all of its hosts. The forwarding of traffic to broadcast prefixes also has negative security implications.

Routers in multicast-enabled networks build distribution trees, thus making the network responsible for replicating the data where necessary.

The multicast service that was piloted on GÉANT is also available on GÉANT2. The technology that has been used to do so is still under development, but it is considered stable enough to provide a production service. Multicast allows users to provide videoconferencing facilities and distance learning facilities, using the standard IP service with a multicast extension.

Multicast IPv6 was successfully piloted on GÉANT from February 2005, and is being adopted on GÉANT2. Many NREN and interconnection networks are natively connected to the multicast IPv6 core and making use of it.

GÉANT2 offers a transit multicast service to subscribing NRENs, allowing them to:

• Advertise and transit traffic relating to a specific multicast group to other NRENs
  
  
• Join multicast groups advertised by other NRENs
  
  
• Advertise and transit traffic relating to a specific multicast group to other research entities such as Abilene.
  
  
• Join multicast groups advertised by other research entities such as Abilene

The GÉANT2 multicast service additionally allows those NRENs who are also customers of DANTE World Service to:

• Advertise and transit traffic relating to a specific multicast group to the global Internet
  
  
• Join multicast groups advertised by DWS peers
  
  
• Take advantage of GÉANT2’s multicast-enabled peerings with Level 3 and TeliaSonera.

GÉANT2 also provides transit for multicast traffic to the Abilene, CANARIE, ESnet and SINET research networks.

Any network that wishes to transit multicast traffic with GÉANT2, but currently peers with GÉANT2 via unicast only, should contact DANTE.

More information on the technical implementation of multicast in GEANT2, and on GÉANT2's multicast IPv6 service, is available from the links in the left-hand menu.