DACS App Note

What is the limit of DIS PDU packets that the DACS can handle? (#4)

The theoretical limit is based on the memory size of the ethernet board and the polling rate between Modelbuilder and the ethernet driver. All of our systems are DSP based which generates an accurate real time signal that Modelbuilder uses to poll the ethernet driver. Our ethernet driver is not interrupt based, but implements a check of the ethernet controller every 10 milliseconds for all new packets received since the last check. All new packets are loaded into ethernet memory and stored until Modelbuilder comes and checks it. The buffer size of the ethernet board is 16K bytes.


Maximum ethernet packet size 1500 bytes
Maximum number of packets that can be held in ethernet memory (16K/1.5K) 10 packets
Maximum number of packets per second (10 packets / 10 milliseconds) 1000 pkt/sec
Maximum network bandwidth (1000 pkt/sec * 1500 bytes * 8bits/byte) 12M bits/sec

This is larger than the theoretical limit of ethernet which is 10M bits/sec.

Under real life testing conditions of 30% -50% loaded ethernet networks, the DACS has not lost any packets.