46
"Packet Delay" (PD)
9.5
To achieve optimal results in image transfer, several Ethernet-specific factors need to be
considered when using Baumer SXG cameras.
Upon starting the image transfer of a camera, the data packets are transferred at maxi-
mum transfer speed (1 Gbit/sec). In accordance with the network standard, Baumer em
-
ploys a minimal separation of 12 Bytes between two packets. This separation is called
"Packet Delay" (PD). In addition to the minimal PD, the
GigE Vision
®
standard stipulates
that the PD be scalable (user-defined).
Example 1: Multi Camera Operation – Minimal IPG
9.5.1
Setting the IPG to minimum means every image is transfered at maximum speed. Even
by using a
frame rate of 1 fps this results in full load on the network. Such "bursts" can
lead to an overload of several network components and a loss of packets. This can occur,
especially when using several cameras.
In the case of two cameras sending images at the same time, this would theoretically oc
-
cur at a transfer rate of 2 Gbits/sec. The switch has to buffer this data and transfer it at a
speed of 1 Gbit/sec afterwards. Depending on the internal buffer of the switch, this oper
-
ates without any problems up to n cameras (n ≥ 1). More cameras would lead to a loss of
packets. These lost packets can however be saved by employing an appropriate resend
mechanism, but this leads to additional load on the network components.
Figure 49 ►
Principle of Packet De-
lay
▲ Figure 50
Operation of two camer
-
as employing a
Gigabit
Ethernet switch.
Data processing within
the switch is displayed
in the next two figures.
Figure 51 ►
Operation of two cam
-
eras employing a
minimal inter packet
gap (IPG).
