In our last post, we explained why A/V requirements should be considered when designing the network infrastructure. A/V has become mission-critical but many networks lack the bandwidth and Quality of Service (QoS) capabilities needed for an optimal user experience. In some instances, there are physical constraints — there aren’t enough IP addresses and Ethernet ports for A/V components. These issues limit an organization’s ability to implement the latest A/V technologies.
Now we’ll take a deeper dive into some of the networking requirements for A/V. A number of these have to do with the IEEE 802.1 Audio Video Bridging (AVB) standard, which was developed to spur the transition from traditional point-to-point link architectures to Ethernet networks. Eliminating legacy A/V cabling in favor of Ethernet simplifies management, reduces costs and enables the integration of A/V applications. AVB provides synchronization, traffic shaping and other functions needed for the reliable delivery of A/V streaming services.
The AVB standard is broken down into four components:
- IEEE 802.1BA: Audio Video Bridging Systems is the umbrella standard that “defines profiles that select features, options, configurations, defaults, protocols and procedures” needed to architect a network that supports time-sensitive A/V streams. Network equipment manufacturers use 802.1BA to develop components that are AVB-compatible.
- IEEE 802.1AS: Timing and Synchronization for Time-Sensitive Applications synchronizes A/V applications on Layer 2 devices so that, for example, related audio and video streams arrive at the same time. It uses the Precision Time Protocol (PTP), which offers the sub-microsecond accuracy needed for time-sensitive A/V. The Network Time Protocol used for most applications is only accurate down to the millisecond.
- IEEE 802.1Qat: Stream Reservation Protocol (SRP) controls traffic so that adequate network resources are available for A/V transmissions. AVB networks have “talkers” (the source of a stream, such as a microphone) and “listeners” (the destination of the stream, such as a speaker). When a talker initiates a stream, SRP reserves the necessary network resources along the path to the listener.
- IEEE 802.1Qav: Forwarding and Queuing for Time-Sensitive Streams schedules A/V traffic for delivery over network switches. It also performs traffic shaping so that A/V streams are distributed evenly and prioritizes A/V traffic for QoS.
For these protocols to function properly, every device in the network domain must be AVB-capable. Therefore, the network switches within the domain must support all of these IEEE standards. In addition, one AVB talker must be designated the grandmaster — the reference clock for synchronization — and all devices must communicate using the 802.11AS protocol. That’s because AVB reserves a portion of the available network bandwidth for A/V traffic and all nodes within the AVB network share a virtual clock.
The network must also be designed in such a way that the devices don’t get out of sync. This can be particularly challenging when circuits are link-aggregated to firewalls without proper configuration. The firewalls may drop sessions if they are unable to sync properly.
None of this is especially difficult. In fact, the AVB standard was designed so that someone without networking expertise can set up an A/V network. But if AVB wasn’t considered when the network was originally implemented, you may be looking at replacing some equipment and making configuration changes. Rahi Systems’ A/V and networking teams can review your existing infrastructure and take steps to ensure that it’s ready for your A/V deployment.