Network Considerations for AV over IP

An expert commentary by Digital Signage Magazine's Jeff Greenberg
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To complete the transformation from AV infrastructure to IP infrastructure, you must ensure that the IP network satisfies the requirements of the AV traffic. A big issue here is bandwidth, so let’s compare the needs of the AV traffic and the capabilities of the IP network.

A raw 1080P 60 fps stream with 24 bits of color requires 1920x1080x60x24 = ~ 3 gigabits per second. 4K with the same parameters needs ~12 gigabits per second. However, most applications only transport raw video offline for post-production editing. When used for real-time content delivery, the streams are almost always compressed. Netflix states that they need 5 Megabits per second for 1080P content and 25 Megabits per second for 4K content, although they don’t specify what frame rate or color depth they actually deliver. If you find Netflix quality to be unacceptable, you can configure a system with alternate compression, subsampling, frame rate and color depth to provide the desired balance between quality and bandwidth.

A single stream with reasonable compression and subsampling can be easily conveyed by an ordinary gigabit switch. Multiple streams can be simultaneously delivered from multiple sources to multiple displays through a single switch if the switch is a properly equipped and configured managed layer 2 or 3 SMB gigabit switch. The switch must be non-blocking, which means it can run each port simultaneously at full speed in both the input and output directions. That means a non-blocking 24 port switch is capable of passing 48 gigabits per second without blocking any of the signals. The streams might be delivered via TCP/IP unicast or UDP/IP multicast. If the latter is used, then the IGMP functions of the switch must be properly configured. If IGMP is not configured properly, then each stream might end up being delivered to all ports, resulting in a flooded network that will be unable to properly deliver the streams.

If the network consists of multiple switches, then you must ensure that the links between the switches are sufficient to carry the sum of all bandwidth needs. For example, if you have 16 sources of 150Mbps each connected to one switch and you want to deliver them to 16 players connected to another switch, then you must have bandwidth of 16x150 = 2.4 Gbps between the switches. This can typically be provided with a 10Gbps fiber or copper link between the switches, remembering that if there is any other traffic traversing the link, it will reduce the bandwidth that is available for the video streams.

This expert commentary was first published in our sister publication, AV Network

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