AVB – Multicast Streams

AVB – Multicast Streams

The Audio Video Bridging (AVB) supports unicast, as well as multicast AV streams. Without going too much into the obvious benefits of multicasting, the AVB uses MAAP (MAC Address Acquisition Protocol) or configured multicast MACs for these types of AV streams. Each multicast stream goes to a unique MCast address.

Furthermore, the AVB multicast is selective in the sense that the streams will be delivered to only those ports where the listeners have requested them and are ready to receive them. On top of this, the MSRP ensures that each node has enough resources to participate in the delivery over the Multicast tree. If no multicast listeners have requested, the talker itself will stay silent.

Multicasting

An AVB Multicast is a Layer-2 (Ethernet based) Multicast, not a Layer-3 (IP based multicast). While it is possible that Multicast IP gets mapped to a Multicast Destination MAC Address, however, the underlying data-flow (for the Audio Video streams) is going to use the Ethernet Muitlcast Destination MAC address to replicate the traffic to the individual ports of an AVB enabled bridge/switch.

Information Flow

The Talkers and Listeners discover and enumerate with the help of AVDECC protocol, while the MAC addresses are assigned by configuration or use MAAP to allocate. Furthermore, the AVTP is used to transfer the AV data payload from the multicast talkers to the listeners. This happens only after the MSRP has ascertained the availability of resources like bandwidth, memory etc for loss-less and low-latency delivery of the AV essence.

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