Newsletter: AV Pro Tricks

April, 2023

By Tony Torres, Technical Support Engineer III

Making AVoIP Work with Cisco Switches

This month, our own Technical Support Engineer III Tony Torres, will share how he found the key to success in working with Cisco switches in the AVoIP ecosystem. 

We’ve often heard that Cisco switches pose a challenge for those setting up AVoIP systems. Here I summarize how I figured out how to make it all work seamlessly.

Cisco switches use a device called a “querier” to interface with the internet group management (IGMP) protocol on which ZeeVee ZyPer4K and ZyPerUHD encoders operate. As a result, Cisco switches routes every single packet of content through the querier before it is directed to the desired decoder. There can be only one querier per network.

This is not a problem for general IT applications and normal multicast applications. However, this is not the case within an AVoIP ecosystem where packets of video content can be as large as 400 megabytes. For example, a single gigabyte switch can only handle a maximum of two and a half video packets of this size at one time—which is not only extremely limiting, but most likely a deal-breaker.

So here we have the catch-22 for integrators: A querier is required for the network to work, but the querier “breaks” the network if you have more than two switches.

After a few weeks of experimentation, I was able to solve this issue. For instance, in a scenario where we have two Cisco switches with 10 devices connected to each, I created a “bubble” for each switch by giving them their own VLAN and querier. Now both switch A and B can talk amongst the10 devices they are connected to, but not to the devices connected to the other switch.

To get all devices on both switches speaking with each other, with control across the entire system, I employed PIM multicasting, a super underutilized methodology in the networking world. Not only are a limited number of pro AV and IT professionals familiar with PIM multicasting, you will find precious little information on it if you Google it—and practically none of what you find will pertain to AVoIP applications.

Using this methodology, I “hypersegregated” the system by establishing a VLAN on the wire that connects the two switches. Based on the three-layer OSI model—where layer one is the physical wire, layer two is the network and level three is the Internet—I was able to connect all components to interface with each other.

The next step was to create a routing mechanism, which is required for PIM multicasting’s layer-three operating protocol. I did this by using the Open Shortest Path First  (OSPF) routing protocol that allows a network packet to elevate out of layer-two into layer-three so that it can travel freely between both Cisco switches and all connected AVoIP encoders and decoders.

Once these steps are completed, you should find that your Cisco switch-driven AVoIP system is working reliably. Simple once you figure it out!

Questions? You can reach me at