Get the latest updates on the Coronavirus impact on engineers.Click Here
Ethernet

Five key ways an industrial Ethernet protocol can use TSN

Time-sensitive networking (TSN) is a practical option to meet the needs of time-critical applications, create flexibility in network design and plan for the future brought about by Industry 4.0 and IIoT. See five benefits of its use in industrial Ethernet networks.

By Steve Fales April 29, 2020
Courtesy: ODVA

Time-sensitive networking (TSN) in the industrial space will be made up of a subset of IEEE 802.1 standards, known as the IEC/IEEE 60802 TSN Profile for Industrial Automation, which are in the later stages of being selected and approved. The significant amounts of diagnostic and prognostic data, on top of existing control traffic, that will be added by information technology/operations technology (IT/OT) convergence, is a key driver of the set of the standards for transmission of time-sensitive data over industrial Ethernet networks known as TSN.  

TSN will be a practical option to meet the needs of time critical applications, create flexibility in network design and plan for the future brought about by Industry 4.0 and IIoT. Furthermore, TSN will enable greater industrial communication interoperability and can work with existing IEEE 1588 timesynchronization methods such as ODVA’s CIP Motion and CIP Sync. ODVA recognizes the importance of TSN and is engaged in work through its member companies to adapt EtherNet/IP for TSN. 

Figure 1: TSN time standard relationship diagrams show how TSN can meet the needs of time critical applications. Courtesy: ODVA

Figure 1: TSN time standard relationship diagrams show how TSN can meet the needs of time critical applications. Courtesy: ODVA

1. Meet the needs of time-critical applications 

TSN prioritization of data, to ensure motion data isn’t slowed down by routine diagnostics as an example, can take place within Ethernet bridges in different ways based on user commissioning. The IEEE 802.1Qbv Queuing Structure graphic below shows an example of TSN prioritization using some of the following key prioritization mechanisms: 

  • Shapers –Such as strict priority quality of service (QoS) and the credit-based shaper. These algorithms give precedence to high priority traffic and ensure fairness on the wire. While these mechanisms are not new, the shared language to configure them is. 
  • Preemption –Pauses an existing packet transmission to allow higher priority data through. 
  • Scheduled traffic – The ability to control transmission of traffic based on enabling and disabling switch queues on a configured time-based schedule. 

These key TSN prioritization mechanisms also have companion techniques to help provide a solution set, including: 

  • Ingress policing – Knowledge and policing of expected ingress traffic on a port to decrease the probability of a malicious or misbehaving device from affecting overall network determinism. 
  • Frame replication and elimination for reliability – Layer 2 redundancy that uses multiple virtual paths on physically separate infrastructure in a meshed network with active topology control. 
Figure 2: IEEE 802.1Qbv queuing structure is designed to create flexibility in network design. Courtesy: ODVA

Figure 2: IEEE 802.1Qbv queuing structure is designed to create flexibility in network design. Courtesy: ODVA

2. Create flexible network designs 

TSN opens up the possibility for industrial networks to have new technologies on the factory floor, such as cameras that feed image recognition algorithms for quality control, alongside traditional motors, valves, and sensors, and even existing motion control applications using variable frequency drives and ODVA’s CIP Motion.  

Keep in mind fundamental principles of segmented network design and architecture for reliability and security are still a recommended best practice for optimal performance. The clock is a key time consideration to enable flexibility in network design with TSN as master time needs to be kept by speciallydesignated devices known as grandmaster clocks while other devices will need to be capable of synchronizing with the master time clock, in much the same way time is kept with IEEE 1588 Precision Time Protocol 

Devices that do not support TSN can be used on the same network, but may only be end station or engineering tool devices. TSN uses IEEE 802.1AS which implements a peer-to-peer time delay mechanism and is a profile of the IEEE 1588 Precision Time Protocol. CIP Sync uses an end-to-end time delay mechanism and is the default profile in the IEEE 1588 Precision Time Protocol.  

CIP Sync has the advantage of not requiring all devices in the path from grandmaster to the ordinary clock consuming time needing to be time aware as shown in in the clock systems graphic below. CIP Sync and TSN time profiles are sufficiently precise to meet the needs of industrial automation now and in the future and can be converted to each-other via a dedicated device. 

Figure 3: Peer-to-peer and end-to-end clock systems in TSN help enable Industry 4.0 and IIoT. Courtesy: ODVA

Figure 3: Peer-to-peer and end-to-end clock systems in TSN help enable Industry 4.0 and IIoT. Courtesy: ODVA

3. Enable Industry 4.0, IIoT 

Networks are now facing the impending addition of large amounts of data from the factory floor to edge devices and/or the cloud and back for system analysis and prognostic purposes due to Industry 4.0 and Industrial Internet of Things (IIoT). Increased bandwidth as a result of technologies such as WiFi 6 and Gigabit Ethernet will help to mitigate potential data packet delays, deviation in data transmittal relative to the time clock, or packet loss.  

However, keep in mind it is hard to foresee all of the new ways that will be created to produce and consume industrial data in the future. Who could have foreseen the creation of programmable logic controllers (PLCs) that can handle safety and standard control when all that existed were safety relays? Physical and digital roads are no sooner built than they are clogged with traffic, which can benefit from prioritization.  

4. Enable greater interoperability  

The goal is creating one overarching set of TSN standards at the data link layer that allows for increased network interoperability across the application layer. This means EtherNet/IP (ODVA)Profinet (PI North America), and OPC-UA (OPC Foundation) traffic can all co-exist on one network and respect the same quality of service (QoS) considerations, with the addition of common time and common prioritization.  

Data packets with common headers and standardized priority levels will make this possible. Once finalized, TSN will enable prioritization of time critical data on industrial networks based on specific rules and methodologies that will be applied by TSNcapable network switches and bridging devices. 

5. Work with existing time synchronization methods 

Ever increasing demands on manufacturing efficiency and output led to the development of industrial Ethernet networks like EtherNet/IP, which offers greater speed and bandwidth, higher node counts, as well as improved diagnostics and easier vertical integration compared to traditional fieldbus. Network extensions like ODVA’s CIP Motion and CIP Sync were then created to address specific applications such as the use of proportional motion control in positioning conveyors that required a higher level of determinism. CIP Motion and CIP Sync will continue to be supported even with the advent of TSN. A time gateway function also is anticipated to allow CIP Motion and CIP Sync devices to interoperate across TSN networks.  

Figure 4: Illustrating the fifth point, EtherNet/IP network architectures for CIP Motion and CIP Sync will work with TSN Capabilities. Courtesy: ODVA

Figure 4: Illustrating the fifth point, EtherNet/IP network architectures for CIP Motion and CIP Sync will work with TSN Capabilities. Courtesy: ODVA

Along with existing network extensions such as CIP Motion and CIP Sync, the TSN standards for sending time critical data via industrial Ethernet are an option to meet the needs of high determinism applications, add network design options and plan for the significant future increases in data traffic brought about by IT and OT convergence.  

A new level of interoperability will also be possible as other communication network implementations can coexist on Ethernet with TSN. EtherNet/IP’s advantages of being a welladopted, object-oriented, and multi-vendor interoperable network will remain with the additional support of TSN.  

The high level of standardization, leveraging of TCP/IP, and usage of commercial off the shelf hardware will also stay consistent. EtherNet/IP will continue meeting critical industrial communication and control needs today and tomorrow, including interoperability and a performance guarantee for highly-engineered applications with TSN. 

Steve Fales is director of marketing, ODVA. Edited by Mark T. Hoske, content manager, Control Engineering, CFE Media, mhoske@cfemedia.com. 

KEYWORDS: Industrial Ethernet, TSN 

Time-critical, flexible network design 

Enable Industry 4.0 and IIoT. 

Allow greater interoperability. 

CONSIDER THIS 

How can more deterministic industrial networking offered TSN help your time-critical applications? 

ONLINE EXTRA 

What is ODVAODVA is an international standards development and trade organization with members from the world’s leading automation suppliers. ODVA’s mission is to advance open, interoperable information and communication technologies for industrial automation. Its standards include the Common Industrial Protocol or “CIP,” ODVA’s media independent network protocol – and industrial communication technologies including EtherNet/IP, DeviceNet and others.

For interoperability of production systems and their integration with other systems, ODVA embraces the adoption of commercial-off-the-shelf, standard Internet and Ethernet technologies as a guiding principle. CIP, CIP Motion, CIP Sync, and EtherNet/IP are trademarks of ODVA, Inc. Other trademarks are property of their respective owners. www.odva.org 


Steve Fales
Author Bio: Steve Fales is director of marketing, ODVA.