Network Monitor uses a 1MB default capture buffer. When the amount of data is larger than the allocated buffers, it is discarded using FIFO logic ( First- In- First- Out) You can increase the capture buffer size up to 120MB, but never larger than the amount of available memory.
To increase the capture buffer size, open Network Monitor. On the Capture menu, click on Buffer Settings. Enter a value in ther Buffer Size (in MB) box and click OK. If you enter a number that is larger than available memory, you receive:
The buffer size you have requested may cause frames to be dropped due to swapping. Are you sure you want to allocate a buffer of this size?
Decrease the size of the capture buffer.
If you still have problems capturing data, and your buffer is at max, try decreasing the frame size.