What is AVB and How Does it Work?
AVB is the common name for the set of technical standards developed by the IEEE Audio Video Bridging Task Group of the IEEE 802.1 standards committee. This task group was later renamed the Time-Sensitive Networking [TSN] Task Group in November 2012 to reflect the expanded scope of its work. IEEE 802.1 defines a set of standards that provide the means for highly reliable delivery of low-latency, time-synchronized AV streaming services through Layer 2 Ethernet networks, which consist of ensuring proper time synchronization, stream reservation, and queuing.
Time Synchronization
Defined by IEEE 802.1AS, the Generalized Precision Time Protocol (gPTP) provides timing and synchronization for time-sensitive applications on Layer 2 devices. gPTP is a simplified version of the PTP default profile, and it’s purpose is to make sure that all the AVB devices are in synchronization with each other. Like PTP, in AVB domain, one device is selected as the Grand Master, while the other devices stay in sync with that Grand Master (see Image 1).
Image 1. IEEE 802.1AS (gPTP). Best master clock selection algorithm to establish Parent/Member hierarchy.
Stream Reservation
Defined by IEEE 802.1Qat, Stream Reservation Protocol (SRP) and Multiple Stream Reservation Protocol (MSRP), is an end-to-end traffic admission control system that helps ensure the availability of resources, such as bandwidth and latency, that are required to transport AV streams. MSRP has a purpose of making sure that all the various AVB streams are preserved; and to ensure that only AVB streams that have the bandwidth to complete from the talker to listeners are onboarded to the network.
QoS
Defined by IEEE 802.1Qav, Forwarding and Queuing for Time-Sensitive Streams (FQTSS) provides AV traffic scheduling capability for mainstream Ethernet and other network switches. This has the purpose of making sure that AVB streams are prioritized and transmitted correctly across the AVB network. AVB endpoint devices can have pre-defined classes, defined by the device vendors, and the AVB network will honor whatever those classes are.
AVB End-to-End Flow
Now that all components and standards are discussed, what does the end solution look like? With MSRP, the gPTP standard is initiated to mandate time synchronization. Then MSRP initiates QoS policy on the AVB switch ports, and signals to the AVB talker and listeners, and begins to check for resources on the AVB network to ensure that there is enough networking bandwidth and ensure proper latency. Then the QoS shaper dynamically adjusted the stream of data, while also allocating 75% AVB network bandwidth for SR Class A and B devices. Then MSRP adds the layer 2 multicast route, beginning the start of the AV stream flow.
Image 2. AVB Flow.
Configuration, Simplified!
Configuring AVB with the Catalyst 9300/9500 devices is very simple. The network admin just needs to enable AVB on the switch and the VLANs on which the traffic is to flow. And then configure the switch interfaces along the AVB connectivity path as dot1Q trunk ports. Optionally, MVRP (Multiple VLAN Registration Protocol) can be enabled on the switch to enable dynamic VLAN propagation. And PTP priority can be adjusted on the switch level. Image 3 below shows how the WebUI can be used to configure the AVB connectivity on the switches in a simple click and drag/drop manner.
Image 3. AVB configurations via switch WebUI.
Why AVB?
So why do we need AVB? Traditionally for Audio-Video networks, there have been complex requirements where we require point-to-point cabling of end-clients to the source stream with various cables (non-ethernet based). Which introduced a lot of complexity into the infrastructure to maintain an audio-video network. With AVB, we can take the complex requirements of audio-video networks and move them over to an ethernet network. Simply put, we can connect the audio-video endpoints to our ethernet network and build the audio-video streams between the sources and the receivers. In turn, eradicating the point-to-point connections required for audio-video networks, since everything is converged on the ethernet network. This in turn allows for any AVB source on the network to communicate with any receiver on the AVB network. And there are many benefits to this, including: lower capital and operating expenses, improved audio-video experience with less than 2ms of latency, and flexible deployment speeds.
Image 4. AVB Benefits.
Industry Vectors and Use-Cases
The use cases are plenty, and the Catalyst 9000 series of switches are there to provide for the AVB needs of customer networks.
Image 5. Next-generation collaboration converges the AVB-capable endpoints such as microphones and speakers to the existing IP infrastructure.
Digital courtrooms and government newsrooms require precision timestamping across the network infrastructure and AV endpoints for digital record keeping. For example, judicial court rooms where a judge may have one mic while there are multiple speakers in the room that broadcast audio. This is one particular use case where Cisco AVB can ensure proper time syncing of AV endpoints.
Conference rooms and town-halls, where business announcements are carried out, can deliver a high-quality and low-latency AV experience for the audience with the help of Cisco’s AVB solution.
Media and entertainment customers or content creators require high-quality AV streams at variable bandwidths that can be used by different teams to enhance the content production. Sports stadium for example, where there is one audio and video source which is streaming to multiple speakers and televisions.
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