Fast Track Ethernet Switching augments automation IT performance, Harting says
Consistent use of standard Ethernet IEEE 802.3 networks helps automation IT. Genuine automation performance, such as deterministic data transport, is essential. Standard Ethernet switching technology and standard Ethernet with new Fast Track Switching technology give automation messages priority over other traffic on the same physical layer.
Ethernet for industrial applications
Ethernet euphoria unleashed in 2000 included high hopes for a network that could serve all applications. It quickly became apparent that, although Ethernet was the right technology, it could not meet all automation requirements. What happened?
When applied to automation, Ethernet performance was insufficient to fully replace fieldbus systems. That led to further Ethernet developments and some incompatible industrial Ethernet profiles.
The new profiles have IEEE 802.3 in common but may not interoperate with each other or devices and applications using standard Ethernet. The performance problem was resolved by changing Ethernet on OSI layer 2. Profile performance is generally good. Determinism, speed, topologies, and installation are similar to fieldbus systems, a benchmark that Ethernet needed for wider automation use.
The automation IT approach began in 2006 to counteract deviation from the Ethernet standard and to secure a uniform communication platform for office IT and industrial automation. One Ethernet can serve as a standard communication platform.
Platform for all applications: Automation IT
All industrial applications can interlink via a uniform automation IT Ethernet network. Doing so ensures direct communication among various applications connecting plant floor and business process, such as manufacturing execution systems (MES) and enterprise resource planning (ERP) systems. Unification avoids complex transitions, accelerates processes, and increases efficiency.
Networks based on automation IT deliver multiple customer benefits, such as lower costs, simplified installation, and greater availability.
Ethernet has become the global communication standard for MES, ERP, and other office IT communications using the Ethernet specification, IEEE 802.3.
Starting in 2008, Harting Fast Track Switching network components increased Ethernet to automation-level performance. The technology works with unchanged Ethernet protocols, recognizes automation protocols, and accelerates these deterministically.
Store and forward, cut-through Ethernet switching
The performance of switching technology is greatly enhanced by use of cut-through switching technology rather than store-and-forward technology. (See figure 1.)
Neither will guarantee determinism, however, making both insufficient for many automation applications. Protocol prioritization for IEEE 802.1q also is ineffective because automation protocols compete with other protocols of the same and higher priority. The delays that can result are unacceptable for automation.
Two delay mechanisms are :
– Delays in the input port: If an input port’s queue (memory) is saturated with traffic from other protocols of the same or higher priority than the automation protocols, then the automation messages are delayed. (See figure 2.) This leads to unpredictable delays for automation protocols.
– Bottleneck in the output port: If the switch’s output port is saturated with messages, high priority automation protocols also have to wait for port release. (See figure 3.) A low priority message with a length of 1,500 bytes leaves the output port. The high priority automation message then has to wait up to 125μsec for port release.
If traffic in the network is very low, then only the Ethernet transmission rate, the message length, and switch latency periods determine the message transition delay.
In this example, the minimum message transition delays are approximately 160μsec. An increase in Ethernet network load results in delays in the input ports and also creates bottlenecks in switch output ports. If a very long message leaves an output port on the above route and if a high-priority automation message leaves the switch on the same port, then the automation message has to wait for release of the port.
This effect can be repeated on the route and culminate in several milliseconds of delay. In a line, this can occur at one switch as both messages travel the same route. The automation message always follows the long message and, each time, would have to wait until after the long message leaves the ports. There is no passing lane. Probability of this undesired effect grows with network load.
With just 16 switches, message transition delays of several milliseconds occur.
Deterministic Ethernet with Fast Track Switching
Harting Fast Track Switching resolves this problem. The Fast Track Switch detects automation protocols and passes them on with priority over all other protocols. In this way, it gives automation priority over other Ethernet applications. The Fast Track Switch accelerates all detected automation messages using the integrated cut-through method and prevents delays.
Benefits of automation IT
Automation IT with deterministic Harting Fast-Track Switching:
– Dispenses with unnecessary redundancies (figure 4), operating on all network levels with standard Ethernet technologies;
– Integrates all devices with Ethernet interfaces;
– Increases performance of Ethernet-compatible automation profiles;
– Can serve all applications at field level, from safety to rapid I/O communications;
– Eliminates the negative effects of IT communication and line topologies on automation performance;
– Gives users maximum application freedom; and
– Eliminates dedicated planning of transmission performance and strict rules for segmenting network areas.
Moreover, with Fast Track Switching, automation messages can overtake other messages occupying a required port, eliminating "waiting times." If an IT message is being sent and the port is occupied by an automation message, forwarding of the IT message is terminated in a controlled manner. The cut-through method forwards the automation message without delay. Afterward, the buffered IT message continues. Fast Track Switching guarantees message transition delays at a higher performance than fieldbus systems.
Switching technology comparison
Worldwide, an immense number of devices have Ethernet interfaces linked via the store-and-forward mode. While not all Ethernet-connected devices are relevant for automation, automation innovations can be triggered via new technologies integrated into new devices. Examples include machine vision and radio frequency identification (RFID) – neither derives from classic automation.
Innovative new devices, open to standard Ethernet, may be integrated for industrial use. Fast Track Switching also can be used for automation profiles that support standard Ethernet communication.
Store-and-forward switching only offers high performance in flat office hierarchies. QoS (quality of service) does not ensure that high-priority messages overtake lower priority ones. Network capacity utilization and performance using various line topologies can be improved using Fast Track Switching.
EtherNet/IP and Profinet RT protocols can enhance performance and facilitate device design. Mechanical engineers and other users supporting different automation profiles can use traffic-analyzing components and uniform design to network their devices.
Fast Track Switching combines advantages of IT methods with special processes. Separate automation technology lifecycles can co-exist with the uniform Ethernet lifecycle, offering additional advantages. With Ethernet technologies, automation applications can incorporate new developments more quickly, such as wider bandwidths or security. Fieldbus networks advance less quickly, perhaps in five or 10 years, compared to Ethernet networks.
Andreas Huhmann, in-house consultant strategy, CN, and Stefan Korf product manager, Germany, are part of Germany Harting Technology Group. Reach them at andreas.huhmann@Harting.com and stefan.korf@Harting.com.
Also see a PDF from Harting on Fast Track Switching .
And feature articles from Control Engineering: Plug into Industrial Ethernet Protocols and Ethernet Explained .