#print packets from Nth connection
#connections are started every I secs
BEGIN { I=3000; syn_time=0; prev=0; k=0} 
	$2 - prev > I/2 { if (k>0) print prev - syn_time; syn_time=$2; k++}
	{if (k==N) print}
	{prev = $2}
END  {print prev-syn_time}