10 GigE: high speed for your machine vision task

With a GigE Vision compliant interface, 10 GigE cameras are easy to integrate and are ideal for high-resolution, high-throughput applications.

Image processing systems have become an integral part of machine control and quality assurance. At the same time, they must confront ever more demanding requirements — primarily driven by new sensor features and host systems with high processing power. Where previously VGA resolutions (640 x 480 pixels) were good enough, present-day applications call at least for HD resolutions (1920 x 1080 pixels). Even sensors with up to 50 MP resolution have become standard. The demand for higher resolution goes together with the need for increased machine speed in 100% final inspections, which requires the camera to deliver higher frame rates.

Both high resolution and high speed have a direct effect on the bandwidth between camera and host system. In such applications, the performance of the entire image processing system is limited by the capacity of GigE Vision. 10 GigE with 1.1 GBps bandwidth is the ideal solution to keep up with increasing requirements and to maintain access to the knowledge and experience made with the established and widely used GigE interface.

10 GigE Vision

The 10 GigE Vision standard allows for the use of high-resolution sensors and very high frame rates in mainstream industrial image processing applications. By increasing the bandwidth by a factor of 10 to 1.1 GBps, the established and common GigE Vision standard remains suitable for the next generation of applications.

Cables

Standard copper cables (Cat 6, Cat 6a and Cat 7) used in 10 Gb connections support up to 100 m length. Cat 6 cables can even be used for up to 55 m length, and longer calls for Cat 6a or Cat 7 cables. Fibre-optic cables enable considerably longer distances and ensure reliable data transmission even in interference-critical environments thanks to their immunity against electrical and electromagnetic fields. 10 Gb Ethernet also supports Power-over-Ethernet (PoE+) and cuts down on costs for the camera connection. At the same time, it reduces possible system errors due to the reduced number of cables used in the camera connection.

Alternative interface standards

Standards like Camera Link or CoaXPress used to be the conventional approach in applications with very high demands on bandwidth. However, the need for frame grabbers and pre-assembled cables turns them into complex and cost-intensive solutions in terms of purchasing and system integration. This is the reason they are not recommended in mainstream applications. The latest developments such as edge computing operating on small ARM-based boards also cannot be completely used due to the necessary use of frame grabbers.

Figure 1: Overview of different interfaces with image data throughput versus maximum cable length. For a larger image click here.

Compatibility and reliability

10 Gb Ethernet, having been established in large data centres for many years, means mature technology. Many providers offer high-quality tested network components such as switches and adapter cards. Such common products can be directly implemented in the environment of industrial image processing, without the typical drawbacks of being an early adopter.

10 GigE was already described in the GigE Vision 2.0 standard in 2011. The changes from version 1.0 are minimal, so that cameras compliant with the GigE Vision 1.0 standard operate on 10 Gb Ethernet without problems. There is no need to change the application software for camera integration, since it is completely independent from the physical Ethernet interface.

Image processing applications must ensure very reliable and stable operation. Every individual image must be received by the host in order to perform the required inspection task. To ensure this, 10 GigE uses the Packet Resend feature known from the GigE Vision standard, which means the optional repeated sending of lost packets (forward error correction).

Speed and latency

The main benefit of using 10 GigE is certainly higher transmission speed. A 1.1 GBps interface is 10 times faster than GigE Vision and 35% faster than Camera Link Full. In addition to high bandwidth, the latency — the delay between the request from the host and the arrival of the response — has been significantly improved. While latencies between 50 and 125 μs used to be standard in GigE systems, 10 GigE provides latencies ranging from 5 to 50 μs.

IEE1588 PTP

Precise time synchronisation is essential in multi-camera systems and of ever-increasing importance in view of the increasing adoption of Industry 4.0 and the IoT. For this reason, the Precision Time Protocol (IEE1588 PTP) is an integral part of the Ethernet standard and thus also 10 GigE Vision. PTP synchronises various system components to within a few hundred nanoseconds and minimises jitter.

Multicast

Being a network standard, GigE provides some features that are of particular interest at high frame rates. Using Multicast, the Ethernet client can send data packets to several receivers simultaneously. This is an easy way to assign processing power to several host systems (for example, one system to detect image features and another for image archiving or monitoring).

Costs

Right from the start, 10 Gb Ethernet without the need for frame grabbers was intended as a low-cost standard. High-performance standard network adapters with up to four ports are cheap and available from many vendors. Common copper cables are not expensive either and can be easily assembled onsite. Individual cable assembly at the user’s site cuts down on system costs and at the same time significantly reduces inventory compared to other interfaces. Additionally, in the event of failure, cables can be immediately and easily exchanged right on the spot.

Another benefit in terms of cost is GenICam compatibility. Widely used in the image processing industry, many individual application requirements for specific scenarios are conveniently met by configuration. In addition, many years of experience allow for reliable estimates in customer-specific software projects and minimise implementation risks.

Reverse and future compatibility

Typically, the maximum transmission bandwidth in Ethernet networks is limited by the slowest network component (eg, network adapter, switch, router or camera). The same applies to 10 GigE Vision for reasons of reverse compatibility.

To invest in new technologies means to invest in the future. 10 Gb Ethernet is the next Ethernet upgrade and already existing knowledge must remain relevant to support the versions to come. 10 Gb Ethernet came into being in 2010, and since then the Ethernet standard has considerably evolved. Today, 40 Gb Ethernet networks are already operated by data centres throughout the world, and the development of 100 Gb Ethernet is constantly pushed forward. Induced by internet giants such as Google, ever increasing speed under the name Terabit Ethernet is now the subject of present-day discussions.

Host system requirements

High transmission rates and the requirement of 100% image data transmission with 24/7 operation must be taken into account when selecting the host PC. Even short interruptions at the processing host system — for example, caused by parallel or background processes — can result in packet loss, which might result in the loss of images in the worst-case scenario. It is of vital importance that the entire component chain is capable of processing the data stream provided by 10 GigE.

The full 10 GigE bandwidth tested on a system with an i7-7820X processor revealed that about 5% of the overall processing power is required for image reception. This processor is only one possible alternative, but it works well in terms of price–performance ratio, high clock rate and turbo frequency.

The system memory must also be capable of the required bandwidth. The common DDR3-1866 memory module provides a maximum data rate of 14.9 GBps. However, since it is not only image transfer that consumes memory capacity, but also other processes and the operating system itself, the system configuration must always consider the memory bandwidth.

Figure 2: Overview of frame rates for different sensors and interfaces .For a larger image click here.

The network card is another factor in the maximum possible system bandwidth. The different bus levels (PCIe gen 1, 2, 3 and 4) together with bandwidths from 1 to 16 lanes can be confusing. Therefore, the slot of the installed network card should operate at least on PCIe gen 3 and should provide four lanes. The slot should be directly connected to the CPU without an intermediate chipset. Usually, the mainboard manual describes the different PCle slot properties.

Transmission errors are often caused by processes running in the background of the operating system. Bursts of activity by antivirus software and indexing services have a significant effect on the performance of the overall system and must also be taken into consideration.

Summary

Data processing at 10 Gb Ethernet bandwidth is certainly challenging, but not in the implementation of standard network components. A wide choice of manufacturers, low prices and Ethernet flexibility speak positively for the deployment of 10 GigE cameras in high-speed image processing. Present developments for the evolution of even higher speed Ethernet show that the Ethernet standard will meet the future required bandwidths and will ensure reverse compatibility to carry the experience and knowledge of the past into the next generations of machine vision.

Top image: ©iStockPhoto.com/kynny