LCM lost package with UDP transfer

[hardybbs123]

hi, LCM friend,
I try transfer a Image with LCM , image is 640 * 640 * 3 = 1.2 M Bytes / with 30FPS. means 40M/S transfer rate.
sender is a high performance PC , receiver is ARM board (CPU 1G*4)
first I found it will lost frame , after run 5 seconds. ,it lost a frame every 5 frames.

• I change UDP buffer size with below , but not work

net.core.rmem_max=2097152
net.core.rmem_default=2097152
net.core.wmem_default=2097152
net.core.wmem_max=2097152

• I compress Image into JPG and decode on ARM , means only 100K pre frame(30HZ) = 3M /S , it reduce a lot of bytes.
  but not work

• I change Image size to 512*512 with JPG compress
  yes , It work good.

• Next I use lcm-logger record into a file , and use lcm-player play it again.
  It not work again , still lost frame

• I use netstat -su and get no UDP package error

So my question is :
since ARM board CPU is not full , why LCM lost data ?
since UDP transfer data is low , why LCM lost data ?
how can I found when and where it lost frame ?