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Ethernet applications for the Industrial Internet of Things

Ethernet applications for the Industrial Internet of Things

Technology News |
By Julien Happich



This change is due to two main reasons: firstly, people want access to data from anywhere in the factory, country or world. Secondly, the bandwidth required for machinery has increased, for example larger and higher resolution printers, higher resolution video and cameras, and more test data required, such as for more complex semiconductors.

There are low bandwidth Ethernet solutions, running at less than 100Mbits/sec, which can be deployed as drop in replacements for RS232. But for most applications, higher bandwidth connections such as Gigabit Ethernet are being increasingly used in embedded and industrial networking.

Typical applications include visual inspection, testing, motion control, 3D printing, video surveillance, and remote monitoring for maintenance, as well as new use cases such as augmented reality for remote maintenance.

The Industrial Internet of Things (IIoT) is also driving adoption of higher bandwidth networking. IIoT, also known as Industry 4.0, can be defined as using well-established technologies in sensor data, machine to machine communication and automation, and then adding new approaches such as machine learning and big data. This aims to improve efficiencies in manufacturing and other industries, but does require a step up in networking technology for many companies.


Ethernet challenges

Ethernet provides a relatively low-cost, well-understood networking solution, with the bandwidth needed. It provides topological flexibility for network installation, and its status as an IEEE standard can guarantee successful interconnection and operation of compliant products from different manufacturers.

But there remains a significant design and deployment issue: the high CPU overhead of running a full TCP/IP stack, and high latency when compared to other industrial networking solutions. As bandwidths increase, the processor spends more of its time handling network frames rather than running user algorithms.

Let’s look at some of the possible approaches to implementing Ethernet in embedded systems that can be taken by OEMs, and review their advantages and disadvantages.

A common solution is to use an embedded CPU. One approach is creating an optimised software stack, but this can be difficult to integrate, and requires a high level of CPU processing time, as well as having a high system cost. Instead, using an operating system such as Linux can bring down system costs, but still requires a high level of expertise and can be difficult to interface to peripherals – as well as needing a fast and expensive CPU to achieve high bandwidths.

Instead of a CPU, OEMs can use a collection of IP cores with libraries running on a soft processor in an FPGA programmed by the OEM user. This requires a high level of involvement and expertise by the OEM, and integrating the FPGA logic and software can be difficult, particularly when trying to achieve high bandwidths. Overall, system cost can be very high.

Another FPGA-based approach is to use a basic User Datagram Protocol (UDP) core. While simpler than TCP, requiring fewer resources and so bringing down system costs, it remains difficult and time-consuming to integrate. UDP is an unreliable protocol that does not guarantee data delivery, and means that the OEM will be unable to use any higher level protocol that requires TCP, such as SMB or HTTP.


The TCP/IP offload engine (TOE)

Each of the approaches to implementing TCP/IP in software causes bottlenecks and performance degradation, as well as increases in BOM cost and system size. Instead, offloading the TCP/IP stack into dedicated hardware can achieve big improvements in transmission bandwidth, and can minimise latency.

Developers that are looking to introduce or optimize Gigabit Ethernet can defeat the TCP/IP overhead through such an offload, and accommodate the many different Ethernet standards (such as Industrial Ethernet and GigE Vision) on a single, low cost universal platform. As an associated benefit, the use of hardware acceleration of TCP also makes hacking more difficult.

The hardware device is called a TCP/IP offload engine (TOE). For example, Orange Tree offers a range of Gigabit Ethernet interface modules, with the TOE provided on-board, the GigExpedite chip (“GigEx” – see Figure 1).

Fig. 1: GigExpedite integrated hardware UDP & TCP/IP offload engine (TOE) block diagram.

Unlike software based TCP/IP stacks that are implemented in a CPU, the GigEx device offloads the TCP/IP protocols into its dedicated silicon. This frees the companion CPU or FPGA to run applications, rather than handle network traffic.

With a TOE, implementation of the user’s application is much easier, and only basic FPGA or software programming skills are required. Control is via simple registers and streaming interfaces, and it is straightforward to achieve higher bandwidths up to and beyond 100MBytes/sec.


To benchmark this approach, we have compared the performance achieved by our GigEx TOE with figures reported by other vendors. Compared to a system containing a typical low end embedded CPU (96MHz ARM Cortex-M3), the GigEx TOE achieves 20 times the bandwidth over TCP/IP (using figures from ARM). In order to achieve bandwidth approaching that of the GigEx TOE, a much more powerful and expensive platform is required, such as a 1GHz ARM combined with dedicated FPGA logic to offload checksums (comparison based on benchmarks from Xilinx).

 

Minimising latency and improving bandwidth

TCP achieves its robustness by forcing the receiver to acknowledge receipt of data. If either the data or the acknowledgement is lost in the network then the sender will detect this and re-transmit the data. In a naive implementation, this means the sender is idle while waiting for acknowledgement from the receiver (see Figure 2). Actually, TCP allows the sender to send further data (represented by dotted lines in Figure 2) before receiving an acknowledgement, but the amount it can send is limited.

Fig. 2: TCP receipt and acknowledgement of data.

Minimizing the round-trip time between sender and receiver is critical for improving the bandwidth. Since the delay through the network is outside the device’s control, this comes down to minimising the delay between a receiver receiving data and sending an acknowledgement, and the delay between a sender receiving an acknowledgement and sending the next piece of data. It is this delay that limits the bandwidth achieved by embedded CPUs.

However, by offloading these parts of the TCP stack into dedicated hardware, it is possible to saturate the bandwidth of a gigabit network and minimize the delay, or latency, between the receipt and acknowledgement of data. The TOE can also contain a standard processor to handle the irregular parts of the TCP algorithm that are not good candidates for hardware acceleration. This means that the remaining system does not need high levels of intelligence or processing power to be able to connect to the network.


Conclusions

With higher bandwidth networking becoming more widespread, Ethernet is providing a suitable solution for use cases including visual inspection, testing, motion control, 3D printing, video surveillance, and remote monitoring for maintenance.  

New applications are also opening up: for example, being able to transmit good quality video opens up augmented reality as a technology for remote maintenance. A worker can wear glasses that superimpose images on real objects, making it easier to guide someone on a repair job.

Whatever the application, a hardware solution using a TOE can deliver a data rate of more than 100MBytes/s (in each direction), with low latency, and can simplify interfacing between Gigabit Ethernet and an embedded device. As TOEs become more mature they can be integrated into easy-to-use, compact form factor modules to deliver more functionality to the developer.

Fig. 3: ZestETM1 module, including GigExpedite TOE.

As Ethernet enters new markets, designers without detailed networking knowledge and experience face the challenge of implementation. A flexible, easy to use interface closely coupled with TOE technology will help Ethernet adoption in industrial applications, and ease the transition to Industry 4.0.

 

About the author:

 

Charles Sweeney is Hardware Director at Orange Tree Technologies – www.orangetreetech.com

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