Is GigE Vision® Over 10 GigE Up for the Challenge?

The idea of a video interface technology that could take advantage of standard Ethernet platforms took hold in 2003, and became ratified by the Automated Imaging Association (AIA) as the GigE Vision® standard in 2006. Not long after ratification, the machine vision market embraced GigE Vision and it quickly became the fastest growing standard for demanding applications.

But existing video interface standards are starting to come up short for high-performance vision system integrators. Market demand is intensifying for next-generation interface standards that can respond to the need for:

I. Solutions to evolving physical requirements
II. Higher data rates
III. Ease of integration and
IV. Cost-effective equipment

As a result, many system integrators and designers are now considering the move from GigE Vision over 1 Gb/s to GigE Vision over 10 Gb/s. Further, two other video interface standards have emerged as potential alternatives to GigE Vision over 10 GigE: CoaXPress and Camera Link HS™.
In the face of these contender video interface standards, the market is now wondering if GigE Vision over 10 GigE is up for the challenge? This article will consider this question in relation to the above noted market demands.

I.              Evolving Physical Requirements

Applications for real-time video transfer are expanding rapidly and as a result, the physical requirements sought out by system designers have evolved. Of most common consideration are (a) cabling characteristics and distance, (b) number of cameras, and (c) power consumption/heat.

I a.    Cabling characteristics and distance

Cabling is a major consideration in practical system design. While the physical characteristics of cabling can impact design, they also play a role in a system’s overall performance levels. This applies to cabling distance as well.

Cabling characteristics for consideration include off-the-shelf availability, size of connectors, and flexibility/bend radius. In terms of availability, CoaXPress, Camera Link HS, and GigE Vision over 10 GigE cables are all readily accessible. The three emerging interfaces all offer relatively small connectors, which can be attached after the cabling itself is in place, facilitating the process of running the cables through small conduits. Further, CoaXPress, Camera Link HS, and GigE Vision over 10 GigE all offer flexible cabling, which enables excellent bend radius.

While the three next-generation interfaces offer comparable advantages in terms of physical cabling characteristics, differences emerge when it comes to cabling distance. And distance is, arguably, the most important element to consider when it comes to cabling. Vision systems have long suffered from design limitations dictated by the distance limitations of their cabling. Such notable examples are Camera Link, with its maximum cabling distance of 10m, and USB, with a maximum of a mere 3m. With greater distances between cameras and PCs, systems designers have the flexibility to place processing systems away from harsh manufacturing or quality inspection environments. It also allows for inspection systems to be more compact, as the weight and size of bulky processing PCs do not need to be taken into account when the system’s mechanicals are designed.

As illustrated in Figure 1, the distance for CoaXPress cabling is 40m to achieve its maximum speed of 6.25 Gb/s. (It is possible to achieve a cabling distance of 130m with CoaXPress, but this severely reduces the throughput speed to 1.25 Gb/s.) This is in stark contrast to the practically endless cable lengths that are possible with fiber optic cables used with Camera Link HS and GigE Vision over 10 GigE, which can be run for kilometers.

I b.    Number of cameras

If a system requires more than one camera, then a camera manufacturer can respond by creating a single device that incorporates multiple sensors and a single transmission interface. Systems designers, on the other hand, may respond to this requirement by integrating appliances that convert, for example, multiple Camera Link Medium or Base interfaces into a single GigE Vision over 10 GigE link. They may also choose to add multiple cameras to an Ethernet switch, with an aggregated stream being sent to one or more PCs over a single link per PC.

Naturally, the requirement for more than one camera in a system design adds importance to maximum bandwidth (addressed in Figure 1) when selecting between one of the three emerging interfaces. If a system’s interface standard offers sufficient bandwidth, designers are then able to replace multiple cables with a single connection. For example, a quality implementation of GigE Vision over 10 GigE can easily carry video from four 2.0 Gb/s sensors or even five 1.6 Gb/s sensors (allowing for protocol overhead). This is particularly valuable for systems that have limited space to spare for routing cables and connectors, since cabling can be consolidated even while additional features and capacity are added.

I c.    Power consumption/heat

As system designers integrate higher speed, they face the trade-off of higher power consumption/heat. However, this is a trade-off that applies to all three of the choices for a next-generation advanced vision system interface. Since the speeds and functionalities are similar, cameras and systems developed using these interfaces will use FPGAs of the same class, and will have similar memory requirements, resulting in similar power consumption characteristics across all three interfaces.

II.            Higher data rates

As system designers seek out higher data transfer rates, video interface standards will increasingly be assessed in relation to the maximum speed over a single cable.