Shad-o-Box 1K/2K HS User Manual
p. 12
Optimizing Settings
The performance of the gigabit Ethernet connection on the host computer generally can be improved by adjusting
some settings in the NIC. The below advices refer to the Intel Gigabit CT desktop adaptor. For a more detailed
explanation please refer to “Network Optimization Guide (PDF)” and “Network Imaging User’s Manual (PDF)”
which is part of the Sapera LT software package.
To reduce the interrupt overhead in the host the following settings in the NIC are advised.
Packet Size
For a good Gigabit Ethernet connection with minimal packet resend conditions, host computer performance can
generally be improved by increasing the data packet size. Each streaming video packet causes an interrupt in the
host computer. Therefore increasing the packet size reduces the CPU overhead required to handle video data from
the GigE Vision detectors.
A standard packet can have a size up to 1500 bytes. Many network cards support a jumbo packet mode that can
extend that size up to 16Kbytes. In theory, a packet could be as large as 16 KB, but the CRC (cycle redundancy
check) containing the checksum of each packet is not as efficient when the packet size grows larger than 9000 bytes.
For this reason
we advise to set the packet size to 9014 bytes
(jumbo packet enabled).
Interrupt Moderation
Normally, each time a packet is received by the network card, the associated driver will receive an interrupt.
Obviously, when the packet rate is very high (that is, at high transfer rate which is common for GigE Vision
systems), this represents significant overhead. Most network cards have introduced an interrupt moderation mode
where the card waits to have received a certain number of packets over a maximum period of time before issuing the
interrupt. This helps reduce the burden on the CPU as it can process multiple packets during the same interruption.
The Intel Gigabit CT Network adapter provides a configuration parameter to manually adjust the NIC interrupt
moderation rate. By default the NIC driver sets this to Adaptive where the interrupt rate automatically balances
packet transmission interrupts and host CPU performance. In most cases no manual optimization of the Interrupt
Moderation Rate parameter is required.
In some conditions, video frames from the GigE Vision detector may be transferred to the host display or memory
buffer as data bursts instead of a smooth continuous stream. The NIC may be over-moderating acquisition interrupts
to avoid over-loading the host CPU with interrupts. If priority is required for acquisition transfers (i.e. a more real-
