Thanks DT.. now it is about 340 packets/s.
what i understood with the 10ms delay is that i have 10ms maximum to pass a usbservice ( to avoid a disconnection) and it is not for the speed that's why if i made it bigger than 10 it will be better for me in case of delay from the pic for a calculus to do....but i was wrong this 10 ms affect the speed of communication; now it good ( i make it 1ms) .

i can send and receive about 340 packets /s (340 sent and 340 received)

in my program i send a packet, than wait the answer and in the "OnRead" subroutine i send the next one, so i think i have no delay in the VB part; about the PIC when it receive a packet i send it back directly ( it is for the test) so this is the maximum speed i can reach.

Thank you....