a voice over Internet Protocol (VoIP) technology and streaming media service based on the Session Initiation Protocol by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based private branch exchange and unified communications facilities.

a proprietary link layer protocol developed by Cisco Systems for the purpose of negotiating trunking on a link between two VLAN-aware switches, and for negotiating the type of trunking encapsulation to be used.

a Cisco proprietary protocol that propagates the definition of Virtual Local Area Networks on the whole local area network.

a name that has been used for at least two proprietary network protocols.