Network Engineering
Multicast on JANET
IP Multicast has been supported on JANET since 1991 using an overlay of IP tunnels forming a multicast backbone (MBONE) carrying encapsulated multicast data packets and multicast routing information (Distance Vector Multicast Routing Protocol - DVMRP).
This approach has long been acknowledged to be very difficult to manage and hard to debug, particularly as the number of tunnels increases, so there is a trend to move to a more modern form of multicast service where the multicast packets are transported directly between the routers without the need for tunnels or encapsulation and a different routing protocol is used (Protocol Independent Multicast Sparse Mode - PIM-SM).
This form of the service is known as native multicast. During 2000 the old JANET MBONE was dismantled and mostly replaced with a new native multicast service. DVMRP tunnels are no longer supported. This service was withdrawn as of 31 October 2002 .
