Data Over Cable Service Interface Specification enables the addition of high-bandwidth data transfers to existing cable-TV (CATV) systems. Developed by CableLabs and others, it was first released in 1997, and is now widely used by cable television operators to provide Internet access over their existing hybrid fiber-coaxial (HFC) infrastructure. The communication is via the free spectrum that is otherwise used for TV channels: 6 MHz in North America and 8 MHz in Europe – where EuroDOCSIS, a variation of DOCSIS, offers greater data rates. DOCSIS 3.0, introduced in 2011, has provided services up to 100 Mb/s, and beyond. That same year UK broadband provider Virgin Media announced trials with a download bandwidth of 1.5 Gb/s and upload 150 Mb/s. DOCSIS 3.1 (2013) introduced an OFDM modulation system (as used in DVB TV) using smaller 20 kHz to 50 kHz-wide subcarriers which can be aggregated into a block of up to 200 MHz.