Frame Transfer Delay - Smartek UCC User Manual

5.6.3 Frame Transfer Delay

The Frame Transfer Delay sets the frame transfer start delay (in ticks) for the selected stream channel.
This value represents a delay between the point in time when a frame is ready for transmission and when
transmission actually starts. Frame Transfer Delay feature is useful in situations where there are many
simultaneously triggered cameras on the network requiring more bandwidth than is available. In such
scenario network can become overwhelmed with incoming data and start losing packets triggering packet
resend mechanism.
To calculate required Frame Transfer Delay use the formula shown below:
FrameTransferDelay - Frame Transfer Delay expressed in time unit [ns]
packetTransferTime - time required to transfer a packet over the network
numberOfPackets - amount of packets contained in one frame
byteTransferTime - time to transfer one byte over the network. It is 8ns on Gigabit Ethernet network
totalBytesInPacket - total number of bytes transferred in one packet
totalBytesInPacket = GevSCPSPacketSize + sizeOfEthernetHeaders
where sizeOfEthernetHeaders is 38 bytes which includes inter-frame gap, preamble, header and CRC.
Payloadsize - frame size in bytes (retrieved from camera)
effectiveBytesInPacket - number of effective bytes transferred in packet without headers
effectiveBytesInPacket = GevSCPSPacketSize − (IPHeaderSize + UDPHeaderSize + GVSPHeaderSize)
where IPHeaderSize is 20 bytes, UDPHeaderSize is 8 bytes and GVSPHeaderSize is 8 bytes.
camerasvtriggered
Camerav1
...
framevtransfervdelayv0ms
Camerav2
framevtransfervdelayv10ms
Camerav3
framevtransfervdelayv20ms
eachvcameravtakesv10msvtovtransfervfullvframe
tovPCvandvitvusesvwholevbandwithvwhilevtransferring
Figure 52 shows a case where three simultaneously triggered cameras are streaming frames to one PC
and each camera utilizes 100% of available bandwidth when transferring frame. In this particular sample it
takes 10ms to transfer one whole frame for each camera so Frame Transfer Delay needs to be adjusted in a
way that only one camera is transferring data at a time. In presented case Camera 2 will start sending data
after frame from Camera 1 is transferred and Camera 3 will start sending data after frame from Camera 2 is
transferred. Next trigger is not allowed until all cameras finish sending data.
FrameTransferDelay = numberOfPackets × packetTransferTime
packetTransferTime = byteTransferTime ∗ totalBytesInPacket
numberOfPackets =
Framesvsendingvflow
framevtransfervready
Frame1
10ms Frame1
20ms
Figure 52: Example flow of frames when GevSCFTD is used
PayloadSize
effectiveBytesInPacket
nextvtriggervallowed
Camera1vFrame1v
100%vbandwithv
utilization
Frame1
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User Manual - twentynine
Framesvreceivingvflow
Camera2vFrame1 Camera3vFrame1
100%vbandwith 100%vbandwith
utilization utilization
SMARTEK Vision | User Manual - twentynine | Doc. v1.0.2
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