Next step: 10 GigE?
By Ann R. Thryft, Contributing Technical Editor- August 1, 2010Scaling issues in 10 GigE haven't been solved, said Arndt Bake, GM of Basler Vision Technologies. If 1-Gbps speeds create a CPU load of 3%, then 10-Gbps speeds will create a 30% CPU load, which is definitely a problem. Even if a 10 GigE card existed today to do the job, it's a frame grabber. "The main task of GigE was to replace the frame grabber, so why not just use Camera Link in the first place?" he said. "Now, the question becomes not ‘how can I use 10 GigE?,' but ‘why should I?'"
But prototypes have already been demonstrated that run 10 GigE over GigE Vision, said John Phillips, Pleora's senior product manager. And although 1 Gbps is enough for most vision applications today, some sensors exceed the 2-Gbps speeds possible with link aggregation.
"One example is flat-panel display inspection with high-speed linescan cameras, each with multiple outputs from the sensor," he said. "Eight or more taps at 40 Mbps gets you over 3 Gbps. Some have said that 10 GigE is too power-hungry or too expensive. But those arguments are falling apart. We've seen a 10-Gbps NIC [network interface card] priced at under $500, and according to the Dell'Oro Group, the total number of 10-GigE ports shipped [in networking equipment] doubled in 2009 Q3 over 2009 Q2. These trends will drive costs down for machine vision, too."
Really fast CMOS sensors from Cypress Semiconductor, Cmosis, and Photon Focus with global, or snapshot, shutters are making the machine-vision industry take CMOS sensors more seriously, said Paul Kozik, product manager for Allied Vision Technologies. "They hold the promise of greater sensitivity than CMOS was capable of in the past," he said. "This need for higher data-transfer speeds is the reason we began offering link aggregation in our cameras." The IEEE's LACP (Link Aggregation Control Protocol) groups two cables into one data pipe. "When you set up a link aggregate group on your computer, the computer perceives that group as a single link at twice the normal speed, and so does the camera," said Kozik. The connection also looks like a single adapter to the application, simplifying application development.
One major challenge in shifting to 10 GigE speeds over GigE Vision is increased power consumption on the interface hardware, said Kozik. "The other main factor is the cost of off-the-shelf network components: The networking industry is still ramping up to 10 GigE, and those component prices are still higher than for 1 GigE." Kozik therefore believes that link aggregation makes GigE Vision an even more serious contender to Camera Link.
But some think link aggregation is only a stopgap: As soon as vendors provide 2 Gbps, the market will demand yet higher bandwidth. And the LACP does not specify exactly how image reconstruction and control will be performed, said Phillips. The protocol separates data into two streams to go over two Ethernet links, but there's no standard way for cameras to split an image and reassemble it on the other end, or for software to understand how it was done so it can be correctly reassembled.