In Voice over IP (VoIP) telephony, voice information is transmitted over an IP network in form of digital data. However, the a/b interface is also still common in IP telephony. Many VoIP systems also feature a/b ports for connecting analogue phones, therefore allowing these to still be used on a digital network. Several new features of VoIP telephony, however, cannot be used with analogue devices. To take full advantage of all the VoIP features, using IP-compatible devices is recommended.