Multicast

Multicast is one of three main types of delivery used on the internet today. The other two are unicast and broadcast.

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.

Multicast provides the best attributes from both unicast and broadcast, with none of the negative aspects. Multicast provides efficient delivery of traffic in both 'one-to-many' and 'many-to-many' scenarios by sending traffic only to those interested parties that have requested the data. Routers in multicast-enabled networks build distribution trees and thus making the network responsible for replicating the data where necessary.

GÉANT 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 GÉANT 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 the GÉANT’s multicast-enabled peerings with Global Crossing and Telia

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

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