The third phase was known as 3G, characterized by digital transmission of both voice and data through the medium of the internet. The technology was pioneered by NTT DoCoMo in 2001. 3G facilitated applications requiring higher bandwidth, such as video conferencing. The 3G market did not grow as quickly as system operators expected because handset makers could not keep pace with the progress in technology. By 2009 the penetration of 3G handsets was still only 15 percent. Even though 3G had still not covered all the markets, 4G was being developed simultaneously. The chief improvements of 4G over 3G were mobile ultra-broadband access and multi-carrier transmission.