Synonymous with IP PBX. A pure IPBX is based on a client/server architecture that generally is implemented on a switched Ethernet LAN platform running at 100 Mbps or more in support of VoIP. Client software residing on intelligent IP hardphones and softphones runs against one or more servers that can be distributed across an enterprise, perhaps in geographically diverse locations connected over the public Internet or, preferably, a private IP-based network. One or more telephony servers are responsible for all call control functions (e.g., call setup and teardown), telephony applications (e.g., feature content and class of service (CoS) assignments), and associated databases (e.g., IP and station numbering schemes and assignments, and directory information). Although the switched Ethernet LAN infrastructure is shared between voice and data, and perhaps video, each IP phone has a dedicated physical port on an Ethernet switch in order to minimize any issues of congestion at the port level. Further,VoIP generally runs in a logical virtual LAN (VLAN) partition to maintain an acceptable level of quality of service (QoS). A digital signal processor (DSP) embedded in each IP phone digitizes the analog voice signals in pulse code modulation (PCM) format and may compress the resulting voice data. Application software then forms VoIP packets, which are then inserted into Ethernet frames, and presented to the switch. There are several hybrid IPBX approaches that allow a user organization variously to maximize the embedded investment in conventional TDM-based PBX equipment and ease into a pure IPBX mode. An IP-enabled PBX is a conventional TDM PBX circuit switch platform with a VoIP module. A hybrid TDM/IP PBX has both TDM and IP components co-existing, side by side.The TDM component comprises TDM line and trunk cards and ports and a TDM bus.The IP component comprises Ethernet ports, an Ethernet switch, a router, and IP trunk ports. A gateway interconnects the TDM and IP components, both of which are under the control of a telephony server running a commercial operating system (OS). See also client/server, CoS, DSP, Ethernet, gateway, IP, IP Centrex, IP-enabled PBX, LAN, PCM, QoS, VLAN, and VoIP.