Setting Inter Packet Delay - Smartek UCC User Manual

5.6.2.1 Setting Inter Packet Delay

The cameras provide the features GevSCPSPacketSize and GevSCPD . GevSCPD represents the Inter
Packet Delay and is expressed in microseconds. Its value can range from 0 to 1000
according to number of cameras connected to a certain network interface card and GevSCPSPacketSize .
The GevSCPSPacketSize feature represents the size of packets and is expressed in bytes, the default
camera packet size is at 1500 bytes, but can be larger if the network hardware supports Jumbo Frames.
Assuming that the GevSCPSPacketSize is 1500 bytes (effective Ethernet packet size including inter-frame
gap, preamble, header and CRC on the wire is 1538 bytes), maximum of 81274 packets are sent every
second via the Ethernet interface. It takes 8ns to transfer one byte over Gigabit Ethernet network, so time
required to transfer one packet of 1538 bytes is 12,3
required to transfer one packet, in order to ensure that packets from second camera will fit in the vacant time
slot. On the other hand, if the camera is producing 60000 packets per second (50 frames per second, 1200
packets per frame), total transfer time must not exceed 16,67
Example
Three cameras are connected to one PC, and are sending 1500 byte packets each. GevSCPD should be
such that packets from all three cameras are serialized to the PC's Network Interface Card. Setting inter
packet delay to 25 s (12,3
µ
gap between two consecutive packets.
Camera 1
Packet 3
Camera 2
Delay
Camera 3
Delay
Figure 51: Packet flow example with three cameras and inter packet delay
s + 12,3 s ≈ 25
µ µ µ
Delay
Packet 2
Packet 2 Delay
s. The GevSCPD should be a bit longer than the time
µ
s if frame rate is to be preserved.
µ
s) will ensure that packets from other two cameras will fit in the
Packet 2
Delay Packet 1
72
User Manual - twentynine
s and should be set
µ
Arriving packet flow
Packet 1 Packet 1
SMARTEK Vision | User Manual - twentynine | Doc. v1.0.2