draft-rosenberg-midcom-turn-06: Why a client has to send data first before receiving any UDP data?

Hi all,

In the new TURN draft, it mentions that the client has to send data 
first (using TURN Send Request) before receiving any UDP data (Section 8.6).

I am using the TURN for two VoIP phones. I assume each of them will do a 
TURN allocation to request their own binding. Phone 1 will send RTP to 
Phone 2 via Phone 2's TURN binding, while Phone 2 will send RTP to Phone 
1 via Phone 1's TURN binding.

However, the specification mentions that Phone 1 will first send data 
out to Phone 2 using the TURN Send Request via Phone 1's binding. I am 
confused here, as I have no idea why I need to do this. Also, what data 
should I be sending? Any idea?

I am also using ICE with TURN.

Thanks.

Best Regards,
Tony Cheung