As those who have been following the Insights blog for a while are likely aware, I’ve been covering the various parts of the AV signal chain and detailing how they affect overall application design. So far, I’ve looked at design considerations for both live and playback sources, covered audio and video processing, and looked at processing for LED video systems. In today’s post, we’re addressing the backbone of the AV signal chain: distribution.
AV distribution is essentially the method you use to get the audio and video signals from source to destination. You may have processing stops in-between, but the road you take to “get it there” is distribution. Many times, we’ll refer to this as the AV infrastructure. Like a country’s transportation infrastructure, the AV infrastructure is the complex set of pathways you use to connect everything together. Those pathways can merge, split off and even offer multiple ways of getting to the same place. And, much like the transportation infrastructure, determining the best method for AV signals to get there is a highly political topic—everyone seems to have an opinion on the issue.
Broadly speaking, there are three main ways you can distribute AV signals: proprietary AV hardware, an isolated local-area network (LAN) and the existing enterprise network. Before I start, I should point out that these methods are not mutually exclusive. You will rarely pick a single method of distribution for your entire AV infrastructure any more than you would pick a single method for your entire country’s transportation infrastructure. A single long-distance trip could potentially include a car, plane, train, bus and boat, and the same is true for AV distribution—you may traverse multiple distribution methods before you get there. That said, understanding the three main methods for getting your audio and video signals where they need to go will help you determine the best method for designing your own AV infrastructure.
The first method for distribution is what we call the traditional method: using proprietary AV hardware. The traditional method has its roots in analog AV distribution, where signals were sent over wire (usually copper) from source to destination. If you needed to connect multiple sources to multiple destinations, the solution required a matrix switch of some kind—a device with multiple inputs and multiple outputs that switches between them. This approach has carried over in the digital realm, with digital signals and standard category and fiber cabling entering the solution.
However, many of the rules are the same, and they still require a purpose-built AV device. For video (and some integrated audio solutions), this means a digital media switcher, like the AMX Enova DGX series. For some other integrated audio solutions, this functionality might be combined with processing within a digital signal processor (DSP), like the BSS Soundweb London series. If you have more input signals than outputs, you might instead opt for using the local input and output ports on an audio mixer or soundboard. Either way, the distribution method in all of these cases is using AV technology rather than standard network technology (as our other two methods use).
The second method is IP-based distribution over an isolated, independent network. Although, with digital signals, the lines are somewhat blurred (to the point that we could argue about the point at which a digital switch becomes a “network”), the method I’m referring to here specifically involves using standard IP networking equipment. With dedicated IP solutions, there is no need for a purpose-built AV device. Instead, you can use off-the-shelf network switches, routers, etc. to create the AV infrastructure.
The way these solutions work from a topology perspective varies, depending on the networked AV technology. In some cases, the distribution must be entirely “home run,” meaning the distribution must only be done over a single switch with all AV devices connecting to that switch. In other cases, they can traverse multiple switches in any standard network topology. With HARMAN’s proprietary BLU link protocol, audio is distributed in a ring topology, without any switches or routers involved at all.
The way the distribution is implemented in the hardware also varies. Sometimes, network distribution is built into another AV device, with a designated networked AV port on the device (HARMAN’s networked DSPs and amplifiers distribute audio this way). In other cases, a device may be specifically designed to put AV signals on the network (such as AMX SVSI encoders) or take them off the network (decoders).
However, in these applications, the infrastructure is still a separate network from any existing IT network that might be used for Internet access, etc. This might be done for any number of reasons. In some cases, the requirement is a technical need. For example, Martin LED video solutions use Martin’s proprietary P3 protocol. P3 protocol leverages standard gigabit Ethernet equipment, but uses a proprietary layer 2 protocol that allows for fast video distribution over standardized equipment. To achieve this without encountering traffic issues, the protocol is not compatible with existing enterprise networks.
Another reason a solution might require a separate network is due to issues with the existing network. These include limitations to the available bandwidth or other issues with the existing equipment. It could also simply be discomfort on the part of the IT department (or it might be a bit of both). Different AV distribution technologies have different requirements and limitations, and in some cases, you might choose to set up a separate network from the existing IT network (using either existing or new category cabling, depending on the installation).
You may also choose to use our third distribution method: the existing IT network. In some installations, it is possible to distribute audio and video signals over a network that is already in place. This provides maximum reach for AV distribution, because not only is there an infrastructure already in place to send the signal anywhere you want today, there is also already connectivity in place for where you might want to send an audio or video signal tomorrow.
Of course, for distribution over the existing network to be possible, the network requirements must be addressed. Bandwidth can be particularly problematic, especially for video distribution. When you are using an existing network—even when running a virtual LAN (VLAN) to isolate the network signals—you must be sure the network switch can handle the overall bandwidth from both AV distribution and normal network traffic. Simply being sure the video signal’s bandwidth accounts for less than the maximum bandwidth of a gigabit switch is not sufficient. You must take into account all video streams on the switch as well as the normal traffic. Network technologies, like multicast and IGMP snooping, can help prevent the entire network from being flooded, but you must also consider the normal IT traffic. That’s why it is important to get feedback and buy-in from your IT department in order to have a successful and manageable deployment. If you are looking for more information on this subject, we have a whitepaper entitled Workbook to Planning for Video Streaming you might find useful.
The AV distribution method you use depends largely on the specific application. Going back to our transportation infrastructure analogy, it wouldn’t really be physically possible to have a roadway from Los Angeles to Tokyo. Instead, you would need to get a plane or a boat. Even then, which one you use depends on what you’re sending and when it needs to get there. The same is true for AV signals. Physical, environmental and even managerial limitations affect which method you choose.
For example, you might have a conference room solution that connects local AV sources to a nearby display. Since there isn’t a large distance consideration involved, you might choose to use an AV switcher (that is, traditional distribution). While there are technologies that allow you to use traditional distribution over long distances, it is particularly cost-effective when the sources and outputs are nearby. You could also choose to use IP-based distribution, using a separate IT network. The option you choose depends on the features you want. Dedicated AV switchers, like the AMX N7142, offer integrated DSP, amplifier and control capabilities that may be desirable.
For this illustration, we’ve chosen to use traditional switching for our in-room AV distribution. However, imagine that you also want to display digital signage on the screen when the space is not in use. Networked AV is a common choice for digital signage distribution, as it has the advantage of being able to endlessly scale the solution (as long as the network can handle the traffic). If you use networked AV for your digital signage, you can easily add a decoder to the conference room solution to bring in digital signage over the existing IT network.
We now have a hybrid system. The digital signage video is sent over the existing IT network to the decoder. The decoder is connected to the AV switcher, and it uses traditional AV distribution to get from the decoder to the display. In this case, you are using multiple methods of distribution in the application, leveraging the benefits of each solution for the appropriate part of the overall application.
We could certainly extend this scenario and include a number of other parameters that might cause the audio and video to connect in different ways. Public address capabilities, all hands meetings, overflow rooms, hearing assistance systems and more can contribute to the complexity of a system. Even though the layout can get complex, having a good understanding of the basics—including the three main options for distribution—goes a long way in helping simplify the options and making the task less intimidating.
Do you have experience designing complex AV distribution infrastructures? Share your insights in the comments.