GOAL: To send one 20-byte data packet from an Android Galaxy S5 to nrf51822 and send three 20-byte packets from the nrf51822 to the S5 in a single connection interval of 10 milliseconds or less. PROBLEM: I have not been able to get both devices to send data simultaneously. Instead, one device always waits to receive data from the other before it starts sending, so the complete transaction always takes at least two connection intervals, often three or four. ADDITIONAL INFO: I am using Android Studio for the Galaxy S5 and mbed for the nrf51822.