49
11.4 "Inter Packet Gap" (IPG)
To achieve optimal results in image transfer, several Ethernet-specific factors need to be
considered when using Baumer LXG cameras with
Visual Applets
.
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
"Inter Packet Gap" (IPG). In addition to the minimal PD, the
GigE Vision
®
standard stipu-
lates that the PD be scalable (user-defined).
11.4.1 Example 1: Multi Camera Operation – Minimal IPG
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 30
Packet Delay (PD) be
-
tween the packets
▲ Figure 31
Operation of two camer-
as employing a Gigabit
Ethernet switch.
Data processing within
the switch is displayed
in the next two figures.
◄ Figure 32
Operation of two camer-
as employing a minimal
inter packet gap (IPG).
