User Manual - twentynine
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
=
numberOfPackets
×
packetTransferTime
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
packetTransferTime
=
byteTransferTime
∗
totalBytesInPacket
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.
numberOfPackets
=
PayloadSize
effectiveBytesInPacket
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.
Frame1
Camera1vFrame1v
100%vbandwithv
utilization
Camerav1
Framesvsendingvflow
Framesvreceivingvflow
Frame1
Camerav2
Frame1
Camerav3
framevtransfervdelayv0ms
framevtransfervdelayv10ms
framevtransfervdelayv20ms
Camera2vFrame1
100%vbandwith
utilization
Camera3vFrame1
100%vbandwith
utilization
eachvcameravtakesv10msvtovtransfervfullvframe
tovPCvandvitvusesvwholevbandwithvwhilevtransferring
...
camerasvtriggered
framevtransfervready
nextvtriggervallowed
10ms
20ms
...
Figure 52: Example flow of frames when GevSCFTD is used
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.
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SMARTEK Vision | User Manual - twentynine | Doc. v1.0.2