AVB Primer Part 1
AVB was birthed from the realization that Ethernet was not suitable for AV Distribution. The architects of Ethernet understood that the industry would work around the limitations of ethernet unless they went to work and fixed the network’s capability to handle the precision timing AV requires.
AVB is inherently bi-directional in nature, data flows both ways on the network. AVB is quick to install. You’ve got many signals on one wire, which makes for quick termination! And AVB gives you “splits” for free. One source can speak to many listeners.
At it’s simplist, an AVB network needs three componants to operate: A talker, a listener and a bridge.
The talker is a source for audio/video content on the network. The listener is a reciever for audio/video content on the network.
A bridge to the future
The bridge manages the conversations on the network, acting kind of like an old school telephone operator. The Bridge is where the magic happens on AVB. In fact the bridge is the key componant that makes the AVB spec work. Now in the IT world, they call their bridges “switches”, or sometimes routers or hubs. And there Ethernet switches will look a lot like our AVB switches however there is a critical difference that we need to understand.
Ethernet was designed to get data from point A to point B. The architects weren’t really concerned with how long it took to get there, so long as it got there. Ethernet switches default to sending all data recieved at one port to all the other ports. The switches act as a traffic cop to ensure that data from different ports doesn’t step on each other. And yes enterprise switches can be tuned to focus certain types of data onto particular ports…. however…Ethernet switches, even high end enterprise switches were not designed to handle the precision time and bandwidth reservation that audio/video systems need to operate.
AVB Bridges have special hardware that allows content to be performed at a particular time. That buys us consistant low latency, and lip syncing. AVB bridges automatically reserve the appropriate bandwidth for a given stream. They are designed to ensure that every talker on the network will have the needed bandwidth at all times. And they leave 20% of the networks bandwidth for “legacy” communication, i.e. Ethernet, so you can still move some control data around the network.
In addition the bridge handles the “one to many” part of the AVB specification. It will route a talker’s content to any and all listeners who want to hear it. If no one’s listening to a talker, the bridge will tell the talker to standby.
- Talker – As stated before a talker is a source for audio/video content on the network.
- Listener – A listener is a reciever for audio/video content on the network.
- Endpoint – A device on the network. An endpoint can be a talker , listener or both
- Stream – A flow of AV media between a talker and a listener, or many listeners
- Bridge – The device that manages all the talker/listener conversations on the network, otherwise known in the IT world as a switch.
- Cloud – The local AVB network in its entirety. It’s the walled off garden that will be a safe haven for your AV media. ( This cloud has nothing to do with the internet.)