Multiple cameras on a single network

If multiple GigE Vision cameras are connected to a network card through a switch, you may experience packet loss due to collisions.

If two cameras are synchronized and transmitting their images at the same time without using packet delay, it means that the total data rate is momentarily 2 gigabit per second on a 1 gigabit network.

All GigE Vision cameras share a feature to compensate for simultaneous streaming from multiple cameras: GigE Vision Stream Channel Packet Delay (GevSCPD for short, which is also the actual GenICam feature name).

This is also simply called packet delay or inter-packet delay.

It works by putting delays in between each of the packets that a camera transmits. By configuring all cameras on the network this way, the data packets can interleave on the switch.

Here it is shown with 3 cameras, where the data stream is marked with 3 different colors. All of the 3 cameras are configured to have an inter-packet delay, which is long enough to leave time for the other two cameras to transmit their data packets in between.

To calculate the minimum inter-packet delay, you can use the Excel sheet below. The calculation has been updated to work with 10GigE as well as GigE.

The calculation is a simple transmission time formula: On a 1 gigabit network, it takes one nanosecond to transmit one bit in a continuous stream.

Example: If the packet size including all headers is 2500 bytes = 10000 bits, it takes 10000 ns = 10 µs to transmit one packet. If there are three cameras connected via switch, all of them have to leave time for two other cameras. So the minimum delay between two packets would be 2 x 10 = 20 µs.

At the same time, it is necessary to keep the combined data rate below the total capacity of the network.