AVB: Audio Video Bridging
At present we have these de facto "standards" for streaming data from a laser show controller to the laser projector:
- Analog data, point to point connection via ILDA DB25 cable
- Digital streaming via Ethernet using current network equipment with proprietary protocols like IDN or from different vendors
Another solution that does not fall into this category but uses the advantage of Ethernet is the distributed controllers for example Lasergraph DSP controller built into the laser projector.
The advantage of analog streaming is its easiness to understand and to configure: Plug in the cable and you are done!
The disadvantage is also clear: Since only point-to-point connections are possible, many, possibly long multi-wire cables are necessary.
Digital streaming via legacy Ethernet tries to overcome the analog streaming technology, however has some severe disadvantages:
- There is no concept of “time” in a legacy network and no means to help synchronization.
- Delays are unpredictable because there is no limitation defined in the network, in a legacy network the importance of reliable delivery of data is higher than the time in which data are delivered.
- The network itself does not prevent network congestion, if too many devices are present and the bandwidth becomes too low. Higher level protocols like TCP/IP try to avoid the congestion by throttling transmission and retransmitting dropped packets; leading to possible delays. Possible conflicts of IP-addresses require basic IT-knowledge.
The typical way to handle the problems is buffering, … the more the better … but excessive buffering can cause unwanted or unacceptable delays. Some solutions try to "manage" the network at a higher layer or to impose strictly defined, inflexible proprietary solutions.
What is AVB?
AVB stands for Audio Video Bridging and is a protocol for the transport of time sensitive data via Ethernet for example streaming of audio and video data.
AVB was developed by the IEEE 802.1 AVB task group. IEEE is the organization behind Ethernet that defines all standards and protocols for Ethernet.
The task group started it’s work in 2007 releasing the AVB standard in 2011.
First devices based on AVB became available in 2014/2015.
AVB is promoted and supported by the AVnu alliance with members including Cisco, Meyer sound and many more.
To facilitate communicating about AVB networks the following terminology is used:
- Stream – a "pipe" that contains one or more channels of audio and or video data in a AVB cloud (network). Laser data are considered and treated as multi channel audio data.
- Talker - an entity in the AVB cloud that can send a stream
- Listener - an entity in the AVB cloud that can receive a stream
- Controller - an entity on the network which configures and connects Talkers and Listeners in an AVB cloud
- Entity - a device or a piece of software
Talker: This can be a microphone, a digital audio/video player a Motu 24Ai 24 channel analog input device or a LaserAnimation ILDA 2 AVB adapter.
Listener: This can be a loudspeaker, a digital audio/video recorder, a "sound card" like a Motu 24Ao 24 channel analog output device, a LaserAnimation AVB 2 ILDA adapter or a PHAENON Accurate laser projector (other PHAENON’s coming soon).
Controller: A piece of software that easily connects Talkers to Listeners without any
knowledge of IT. The controller might be stand-alone software or embedded in an AVB device.
What are the benefits of AVB?
AVB is a protocol for the transport of time sensitive data via Ethernet (for example streaming of audio, video, laser). It is based on four IEEE 802.1 standards about bandwidth reservation, configuration, traffic shaping and time synchronization.
AVB was crated with lip synchronicity (i.e. Audio in sync with video) in mind.
All AVB devices are synchronized to a common general master clock. Streams can include a presentation time i.e. the time when a tone, a video frame or a laser images shall be presented. This also works if the different streams (for example Audio, Laser and Video) travel on different paths with different sample rates!
If two devices output the same stream they are precisely locked in their playback even if the streams travel different distances across a different number of switches.
The resulting jitter is below 1 us.
- Reliability with no infrastructure configuration
A professional A/V network especially when transmitting laser frame data needs reliable transmission with no defects like pops or clicks or video- or laser- dropouts or other artifacts.
AVB has an expert IT-guy built into its protocol: "He" manages, checks and reserves the requested bandwidth for each stream, before a stream starts. If bandwidth is available it is blocked for this stream along the entire path until explicitly released when no longer in use; "he" also ensures the timely delivery of streaming data thru the network.
Regular legacy non-streaming traffic (for example TCP/IP) cannot interfere with AVB streams and can be used as usual for example to communicate with a laser projector with LAToolbox.
About 75% of the bandwidth is reserved for collision free streaming AVB traffic, leaving 25% for legacy traffic.
In contrast to legacy networks with unpredictable delay times, AVB guaranties a maximum delay of 2 ms over seven switch hops (switches) in a 100 Mbit network, so only a very small buffer is needed at the end node (listener). With modern gigabit Ethernet solutions the latency can almost be neglected.
- Public Standard
IEEE 802.1 AVB is a public standard; it is free of royalties and open for use by anyone.
How does AVB help with laser display installations?
- AVB can reduce cabling dramatically and can make it much more versatile: for example can laser show controllers be switched to different sets of laser projectors without any rewiring hardware switches or the like.
- AVB is a new technology that for sure will become THE standard in Audio/Video networks in any scale or environment: so laser will perfectly integrate into these networks.
Once AVB networks become common, laser data and all other media data can travel thru the same network with identical properties.
- In fixed installations where always the same shows are running, a digital software based multichannel player is all what is needed. Shows can easily be produced in a standard format since all site depending adjustments (size, offset, color, geometric correction) are done by and stored in the laser projector.
- The AVB cloud is easily manageable, it tells immediately if a device (for example a laser projector) is missing and a replacement device can easily be installed without special configuration.
- AVB is an absolutely professional solution at affordable to low cost.
- AVB is under further development by IEEE now by the group renamed to IEEE TSN (Time Sensitive Network), which shows the importance of this new technology beyond the scope of A/V media streams.
What is the topology of an AVB cloud?
- AVB streams may occur between point-to point (one Lasergraph DSP to one projector) or point-to-multi-point (one Lasergraph DSP to some projectors).
If AVB devices are equipped with dual LAN interfaces they can be daisy chained without the need of a switch
Normal AVB topology is formed by star shaped sub-nets with a special AVB switch at ever node.
AVB clouds are designed for networks covering by size the entire range from car nets over small home nets to large stadium or theme park sized networks.
The AVB cloud can be a part of a larger legacy network, however AVB features are available within the AVB cloud only.
- Devices are referred by their unique MAC address.
LaserAnimation owns a subgroup of MAC addresses, so devices manufactured by LaserAnimation are easily identified by name.
What kind of network hardware is necessary?
AVB used the same data cables as legacy Ethernet (CAT 5, CAT 6, Fiber) with the same cable length restrictions (100m for wire based connections between devices and switches).
AVB requires special AVB switches which are readily available (for example from Motu). These switches do not cost more than other switches of good quality and prices will drop.
In case of a laser show controller with analog ILDA output like a regular Lasergraph DSP you will need an ILDA 2 AVB adapter.
In case of a laser projector with analog ILDA input like a regular PHAENON projector you will need a LaserAnimation AVB 2 ILDA adapter; additionally to DA conversion this adapter gives you advanced features like geometric correction and more.
To connect a Mac you can use AVB directly because Apple already supports AVB in the operating system. You may also use LaserAnimation USB 2 AVB connector which acts as a gateway to multiple projectors.
To connect a PC running Windows you need a LaserAnimation USB 2 AVB connector, because Windows is late as usual and has no support for AVB built into the operating system yet.
What kind of data are used?
LaserAnimation uses the multi-channel AIFF Audio - file format to store the laser display related data i.e. X, Y, Color (where Color can be anything from a single color to R Y G C B color data).
AIFF files can simply be recorded from any ILDA analog signal in perfect quality or converted from ILDA frame files. No special care must be taken about future use of the recorded data in terms of size or color: all these parameters together with for example geometric correction can be changed and set in the laser projector (by LA Toolbox software) in which the data will be presented.
LaserAnimation uses the IEEE 1722 Media transport protocol for the stream of laser display data.
A laser projector is referenced as a sound card or some channels of a sound card so laser display data can also be generated by software used for sound creation and manipulation i.e. Ableton live , Cubase, Max MSP, VVVV or similar.
What is the sample rate and accuracy?
AVB audio streams use 48kHz, 96kHz, 192 kHz and higher sample rates which is sufficient for all laser display requirements even for doted lines and the like (however we currently limit to 192 kHz because of the ADC/DAC used).
Data precision for recoding and play back is up to 32 bit defined by the IEEE 1722 media transport protocol however limited to 24 bit due to the ADC/DACs used.
How many laser projectors can be used in a AVB cloud?
A substandard 100 Mbit network can support 9 independent streams of stereo audio data i.e. 18 channels. Because of less overhead it can support a stream of 45 channels which could serve for example 9 XYRGB laser projectors. Single color laser projectors need fewer channels and do not waste any of the bandwidth available. Now imagine a regular 1 Gbit network or one of the upcoming 100 Gbit networks!