Allocating Bandwidth

The User Datagram Protocol (UDP) used by the GigE Vision standard provides no guaranteed transmission or fixed timing mechanism. Therefore, bandwidth must be managed by the Device Throughput Limit, based on desired resolution and frame rate.

Determining Bandwidth Requirements

The maximum bandwidth available is 125 MB/s. This includes image data, control data and image resends, which occur when frames are being dropped. Each image and each packet has a certain amount of overhead that will use some bandwidth. Therefore, when calculating your bandwidth requirements, you should not attempt to use the full maximum of 125 MB/s.

To calculate your bandwidth requirements:

Determine your required resolution, frame rate, and pixel format (bytes per pixel)

(Height x Width x Frame Rate x Bytes per Pixel)/1000000 = Bandwidth in MB/s

For example, for an image that is VGA, 82 FPS, Mono8:

640 (H) x 480 (W) x 82 (FPS) x 1 (BPP) = ~25 MB/s

Once you have calculated your required bandwidth, you can allocate an amount to each camera by adjusting the Device Throughput Limit. Allocating a specific amount to each camera helps to avoid dropped packets due to a data burst. You would do this in a set up with multiple cameras, or in a situation where the system bandwidth might be limited or shared due to hardware architecture.

Bandwidth Requirements for Multiple Cameras

Multiple cameras can be set up in two ways: 1) Each camera is connected directly to a single Ethernet port; or, 2) multiple cameras are connected to a single port through an Ethernet switch.

If using the first method, each camera has the full bandwidth allocation available to it. If using the second method, the combination of all cameras on a switch cannot exceed the available bandwidth.

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Setting Up Multiple GigE Cameras	Technical Application Note 10351

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