The DNP3 driver sends and receives data in packets that are known as Frames. For large amounts of information, more than one frame may need to be transmitted.
DNP3 application messages are broken into fragments. The fragment size is determined by the receiving device’s buffer. For systems operating in environments with high levels of interference, communications are often found to be more successful if the fragment size is further reduced.
Use these fields within the relevant DNP3 section of the tool to specify the maximum size of each frame and fragment:
- Maximum size of Data Link Frame—Enter the maximum frame, or packet, size that the Geo SCADA Expert DNP3 driver can transmit to the receiving device. You need to enter a value between 100 and 292 (inclusive).
- Large amounts of information may need transmitting using more than one frame. Where this occurs, the frames are reassembled into the complete application fragment by the receiving device.
- Maximum size of Application Fragment—Enter the maximum fragment size that the Geo SCADA Expert DNP3 driver can transmit to the receiving device. The size is determined by the receiving device’s buffer, and have to fall within the range of 100 to 2048 (inclusive).
- Messages that are larger than one fragment are sent using multiple fragments. Large fragments and multiple fragments are transmitted using more than one frame (for instance, a fragment of 2048 bytes needs breaking into at least 9 frames). Where this occurs, the frames are reassembled into the complete application fragment by the receiving device.