Skype for Business Server (formerly
Microsoft Office Communications Server and
Microsoft Lync Server) is real-time communications
server software that provides the infrastructure for enterprise
instant messaging,
presence,
VoIP, ad hoc and structured conferences (
audio,
video and
web conferencing) and
PSTN connectivity through a third-party gateway or
SIP trunk. These features are available within an organization, between organizations and with external users on the public internet or standard phones (on the PSTN as well as SIP trunking).