Environment : This article applies to OS version 6.1 and above.
Distributed Dynamic Multicast Optimization (D-DMO) is a feature introduced in ArubaOS 6.1 and is similar to DMO except that the multicast-to-unicast conversion happens at the AP instead of the controller. DMO is for VAPs in tunnel forwarding mode where the multicast-to-unicast conversion happens at the controller. For VAPs operating in decrypt-tunnel forwarding mode, the multicast-to-unicast conversion can be moved to the APs. So the VAPs that are operating in decrypt-tunnel forwarding mode implement D-DMO instead of DMO.
The bandwidth consumption on the link between the controller and APs is lower with D-DMO than DMO. This is because in D-DMO the transmissions between the controller and the APs are still multicast and the actual multicast-to-unicast conversion occurs only on the AP. With D-DMO, the controller sends multicast packets to APs only through the GRE tunnels of decrypt-tunnel mode VAPs that have active subscribers. The number of multicast streams through the GRE tunnel of a decrypt-tunnel VAP on an AP is equal to the number of multicast groups with active subscribers on that VAP. However, in DMO the controller performs the actual multicast-to-unicast conversion. So, the transmissions between the controller and the APs are unicast. For DMO, the number of converted unicast streams through the GRE tunnel of a tunnel mode VAP on an AP is equal to the number of active subscribers per multicast group on that VAP.
For example, if 6 clients join a stream, it is only sent once INSIDE the tunnel, as opposed to 6 times for regular DMO. But if 6 APs on the same switch need the same multicast stream, we are still sending 6 times (1 per tunnel).