AVB Network Card

 

 

AVB Overview

The Soundweb London BLU-805 and BLU-325 are capable of sending and receiving Ethernet AVB audio.  AVB, or Audio/Video Bridging, is a common name for a set of IEEE standards that ensure the transmission of high quality streaming audio and video over a standard Ethernet connection.

Note: Soundweb London devices cannot send, receive, or process video data.

As a networked audio transport, AVB is similar to CobraNet in many ways, with a few key differences:

The AVB standards were created through a consortium of industry experts which was then ratified and accepted by the IEEE industry standards body. This means that AVB is not just another proprietary non-standard protocol that floats on top of the Ethernet layers. AVB is the Ethernet. The big difference between AVB and previous solutions for network streamed media (such as CobraNet) is that the IEEE controls the Ethernet standards, which allowed for the specifications of not just the endpoints, but more importantly the switches. This allows an entire network to be designed to accommodate audio and video, with compatibility between AVB devices that are made by different manufacturers.

The standards specify a means to provide time synchronized low latency audio and video over standard CAT5e cable. The majority of the bandwidth across the network is reserved to carry audio and video, and to guarantee the arrival of a signal

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In order to accomplish transporting the large amount of information required by both audio and video across a network, bandwidth is reserved and defended throughout the network by the switches. By default the switch will reserve and defend 75% of network bandwidth to be exclusively used for AVB media, both audio and video. This will guarantee precisely synchronized audio/video without interruption from non-time sensitive data and communication, such as email or control protocol traffic (also known as “Best Effort” traffic). By design, the switch will not allow for the audio or video to become corrupted.

Each audio/video sample is time-stamped with exactly what time to play, and all AVB devices are synchronized to a common clock known as the Grand Master clock. This allows for the synchronization of multiple streams of audio and video to be rendered at the correct time with respect to each other.

An AVB network inherently supports multiple simultaneous sample rates and (sample) clock sources which allow video and audio streams to be synchronized even though they travel on different paths with different sample rates.

Details for the six IEEE audio/video bridging standards (802.1AS, 8021.Qat, 802.1Qav, 802.1BA, 1722, and 1733) are available at IEEE.org and AVnu.org

 

Soundweb London AVB Module

The BLU-805 and BLU-325 devices are fitted with an AVB module. The module offers a Primary and a Secondary AVB port. Under normal operation, only the Primary port transmits and receives data to and from the network. Should the Primary port or connection fail, the AVB module automatically switches to receive from and transmit with the Secondary port. This must be considered in the network design. It may be appropriate to connect the Primary AVB port to a Primary network and the Secondary AVB port to a Secondary, backup network. In this event, it should be noted that the backup network should in some way be bridged to the Primary network in order for the audio data to be present on the Secondary network should the module switch over.

NOTE: The secondary port is not currently enabled.  It will be enabled in a future release of HiQnet London Architect.

 

Network Connections

Devices can only be connected together through switches which support AVB. Examples of such switches are the BSS Audio / NETGEAR GS724T Ethernet Switch or the LABX Titanium 411 Ruggedized AVB Ethernet Bridge Switch. Do not connect the AVB ports to any switch which does not support AVB.

The AVB devices can be wired in London Architect as shown.

 
Note that the standard Ethernet ports (labeled “Control” in London Architect) must also be physically connected to ensure communication between the devices. In the same way that Soundweb London CobraNet ports send and receive audio only (not control data), the Soundweb London AVB ports send and receive audio only.

In 2-device systems, it is possible to connect the AVB ports directly together, as shown

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Cable Requirements

CAT5e or better cable may be used, allowing cable runs of up to 100m per connection. If more distance is required, Gigabit fiber converters—such as the BLU-MC1—can be used. 100Mb (“Fast Ethernet”) fiber converters cannot be used for the Soundweb London AVB ports, because they are Gigabit ports.

AVB Audio Channels per Device

Audio channel rules

Stream rules:

Talker (Transmit)

Example A: 2 streams of 32 channels

Example B: 32 streams of 2 channels

Example C: 29 streams of 2 channels, plus 1 stream of 5 channels plus 1 stream of 1 channel

Example D: 61 streams of 1 channel plus 1 stream of 3 channels

Example E: 64 streams of 1 channel

Listener (Receive)

Example A: 2 streams of 32 channels

Example B: 32 streams of 2 channels

Example C: 29 streams of 2 channels, plus 1 stream of 5 channels plus 1 stream of 1 channel

Example D: 61 streams of 1 channel plus 1 stream of 3 channels

Example E: 62 streams of 1 channel

There are thousands of permutations as long as the total number of channels transmitted is 64 or less. Similarly, the total number of channels received must be 64 or less.

Note: It is advised to configure and use (multi-channel streams) vs. (single channel streams). This is the most efficient transport method for transmitting and/or receiving  AVB audio channels across a network switch.  

Resource Meter

The configuration view of a BLU-805 or BLU-325 contains a second resource meter which displays the AVB resources only. This AVB resource meter shows the % of streams and channels used for a particular configuration as shown below.

In the above example, 32 AVB input channels are enabled, and 32 AVB output channels are enabled. 32x32 is exactly half of the BLU device’s AVB I/O capability. Therefore 50% is displayed in the AVB resource meter (which is the same shade of purple as the AVB input/output objects).  

In a design where, for example, 32 AVB input channels are enabled,  50% will still be displayed even though no output channels have been enabled. As output channels are enabled the resource meter will continue to display 50% until the number of outputs channels enabled exceeds 32.

In a design where, for example, 33 AVB input channels are enabled and no AVB output channels are enabled then 51% will be displayed on the resource meter.  Again as output channels are enabled the resource meter will continue to display 50% until the number of outputs channels enabled exceeds 32.

The above examples also apply to the resource meter where it is the output channels which have been assigned.

Creating Streams

In the configuration window of a BLU-805 and a BLU-325, by default there is one AVB Input processing object (Rx, Listener) and one AVB Output processing object (Tx, Talker).  Initially they have no nodes on them.

            

You can add or remove as many AVB processing objects as you wish inside a BLU-805 and BLU-325 although the number of streams is limited as described.

Streams are defined system-wide. They can be created using the dialog which can be accessed in several ways:

Use the above dialog to view details of, add, delete and edit streams.  

Define AVB Stream

Click on the 'NEW' button to open the 'Define AVB Stream' dialog shown below.

Channel names are displayed on the Stream Tx and Rx objects after the signal name.

Stream Restrictions

Streams are subject to the following restrictions :-

If London Architect detects a problem with a stream the AVB Input and AVB Output objects are drawn in red. In this state a tooltip will show what the error is:-

Example A:

Example B:

Example C:

Control Panel

PTP (Precision Time Protocol)

Media Clock

The following parameters can be accessed from the Design Tree

Transmitter Object (Talker) Properties

Receiver Object (Listener) Properties

Clocking

The device will clock from the AVB under any of the following conditions

See BLU link Mastership for further clocking scenarios where the device is not clocking from the AVB..

AVB vs CobraNet I/O Comparison

Users already familiar with CobraNet will perhaps find it useful to compare the two transports’ I/O capabilities.

Whereas CobraNet-capable BLU devices can simultaneously send and receive up to 32 channels of CobraNet audio (32x32), AVB-capable BLU devices can simultaneously send and receive up to 64 channels of AVB audio (64x64).

Whereas up to 8 channels of audio can be packaged into 1 CobraNet “bundle,” up to 32 channels of audio can be packaged into 1 AVB “stream.”

Whereas CobraNet-capable Soundweb London devices can simultaneously transmit up to 4 CobraNet bundles and receive up to 4 CobraNet bundles (4x4), AVB-capable Soundweb London devices can simultaneously transmit up to 64 streams and receive up to 62 streams (62x64).

PTP (Precision Time Protocol)

Precision Time Protocol is used to synchronise time in the AVB cloud. One device is elected as Grand Master and each device uses PTP to calculate the exact time. Once the devices have agreed on the current time they can then create synchronised audio clocks using Media Clock Negotiation.

MCN (Media Clock Negotiation)

Media Clock Negotiation is used to synchronise audio clocks between devices in a single audio clock domain. AVB allows multiple media clocks on the network with multiple sample rates co-existing. Each talker stream must specify which media clock it is using. There can be 256 different media clocks on an AVB network.

Individual AVB devices will have a number of audio clocks that it uses. Typically, there is one audio clock used by a device and all the audio within the device uses that clock.

Media clocks are propagated throughout the AVB network using streams. These streams may also contain data (audio), but that is not a requirement. For each media clock domain, primary and secondary clock masters are negotiated using the MCN protocol. If the MCM priorities for all devices in a given PTP cloud are the same, the device with the lowest MAC address wins. The primary and secondary clock masters create media clock streams which all devices can listen to. Devices monitor the primary and secondary media clock streams, and if the primary fails the secondary will be promoted to primary and a new secondary media clock master will be negotiated based on the defined priority or lowest MAC address. 

Suitable Switches