The Genius of DAG®
The real Genius of DAG® Card technology is that it:
- Provides guaranteed 100% packet capture at full line rate
- Removes packet-processing load from the server CPU freeing it up for application processing
- Provides highly accurate timestamping of every packet
DAG's unique capability results from the onboard FPGA (field-programmable gate array) that enables smart, packet-processing to be managed in hardware, and a large FIFO memory buffer that allows packets to be captured off the wire at full line rate without a single packet being dropped.
Eliminating the interrupt storm
Packet capture using traditional NIC hardware is subject to the Inconvenient Truth of packet capture. Even at moderate line-rates the interrupt rates of standard NICs overwhelms CPUs - causing packets to be dropped.
DAG's onboard FIFO memory buffer enables packets to be captured and stored on the card itself, where the DAG card driver makes it available to the CPU via Direct Memory Access (DMA).
This ability to deliver captured traffic to the CPU and consuming applications via DMA without requiring an interrupt or a memory copy every time a packet arrives effectively reduces CPU interrupt rates to an "idling" level - even on heavily loaded links.
The DAG's DMA is optimised for modern multi-core processors. Each CPU or core can have its own allocated memory space in the buffer so captured packets can be directed to specific CPUs or cores. This enables efficient load-balancing (with full session continuity) across multiple CPUs, multiple cores and multiple applications or application instances.
