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A Need for Speed: Time Sensitive Networking

David Meyer | Apr 20, 2021

 

 

The IP network has become central to virtually all technology subsystems around the home: communications, security, IP control, streaming media, AV-over-IP, etc. The protocols used are predominantly those of wired Ethernet networks (IEEE 802.3) but can of course extend through to wireless networking (IEEE 802.11). Either way, the standards are typically focused on the integrity of data delivery, with no emphasis on time or constraints on latency. That’s because IP networking used to be more about moving files, but the way we use Ethernet networks has changed. Today, media streams and control systems are converging to the IP domain, and they sometimes require synchronization. And for this, time matters! 

The IEEE have a task group and a whole suite of standards under the banner IEEE 802.1, originally known as Audio-Video Bridging (AVB). As the name implies, AV was the primary focus, with bridging across network segments being common in target applications. AVB is a layer 2 extension to Ethernet networks, providing guaranteed quality of service (QoS) with reserved bandwidth and precise sync clock to ensure that streams are delivered with minimal latency. For example, to maintain sync between many channels of audio (think stage and mixing desks), or concurrent audio and video streams to maintain lipsync.  

As the years went on, the potential for applications grew to include things like climate control and assistive technologies, and network bridging gave way to layer 3 control and VLANs. In response to this, the scope of AVB was expanded and renamed Time Sensitive Networking (TSN). TSN remains backwards compatible with AVB. There are many protocols to make TSN work, with interoperability a focus of standards bodies including IEEE and AES. An example of one such protocol is Precision Time Protocol (PTP), wherein PTP packets take priority over other packet types. This keeps latency low and availability high, and is typically multicast. 

Think of AVB/TSN as being like an emergency response vehicle that turns on its siren to be permitted priority through traffic, as time is of the essence. 

The Dante Example

An excellent example of a time sensitive application is Dante technology, by Australian company Audinate. Dante first made a name for itself in the pro audio space, replacing multitudes of hugely cumbersome analog audio cables by packetizing digital audio for sending over standard Ethernet networks using VoIP protocols. This hugely reduced the size and quantity of cabling and reduced noise -- and also mitigated ground loops and impedance mismatches. But what really underpinned Dante’s transformation of that industry was its ability to send hundreds of channels of audio over a single Ethernet (copper or fiber) cable with precise time sensitivity, with longer distances, and with extraordinary interoperability between devices on standard networks — albeit enterprise grade.  

The lure of high performance, simplicity, and interoperability saw the adoption of Dante spill over from pro audio to enter the commercial AV space, too. The latest reports show that adoption of Dante has surpassed 500 manufacturers and 3,000 devices. And now, for these same reasons, its coming to residential for high-performance digital audio distribution. 

What does this mean for integrators? Well, it’s yet another very compelling reason to ensure the Ethernet networks you design, install, and manage are robust and high performance, but also Dante optimized if the technology is to feature in a project. Focusrite, a manufacturer of pro audio gear, provide some simple advice as to what to look for when specifying a network switch for use with Dante; it should be: 

  • Gigabit rated (1000 Mbps) 
  • Managed (layer 3) 
  • Non-blocking (gigabit at every port, with all ports connected) 
  • Quality of Service (QoS) with four queues 
  • Differentiated services (Diffserv) QoS capable with strict priority 
  • Capable of disabling Energy Efficient Ethernet or "EEE" (also called Green Ethernet) 

Of course, there’s far more to the network than the switch. In any case, time sensitive networking will only grow in prevalence, whether it’s for Dante or other low-latency applications. As always, education is key, so watch this space for more along those lines. 

For more on CEDIA's educational offerings on networking, see cedia.net/education.


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