aries somewhat among different manufacturers, but the servers for call processing and gateway functionality are common to all. The gateway converts Voice over Internet Protocol (VoIP) signals to those compatible with the Public Switched Telephone Network (PSTN). These are located in a separate gateway or in a router. In addition, Layer 2 switches transmit calls to other devices connected to the switch and backbone switches. www.TechnicalPDF.com Connecting IP Telephones to Layer 2 Switches and RJ45 Jacks Computers and phones often share the same jack and cabling with the Layer 2 switch. In this configuration, the user's personal computer is plugged into a data outlet on the back of the telephone, and the telephone is plugged into the nearest RJ45 data jack. (IP telephones are often referred to as endpoints or nodes, terms for items such as PCs and printers connected to LANs.) RJ45 is the designation for a type of jack into which data devices are plugged to connect to networks. For greater redundancy and to create a dedicated path to the Layer 2 switch, the PC and telephone can each use a separate RJ45jack, cabling, and port on the Layer 2 switch. This requires additional hardware in the switch and an extra cable run from the telephone to the switch. In either case, voice, video, and data share the fiber-optic cabling and ports on Layer 3 switches that transmit traffic between floors and buildings. This is the enterprise backbone. Communications Servers and Voice as an Application on the LAN Communications servers perform call processing, sending instructions on how to set up calls. They send instructions for features such as three-party conferencing, speed dial, and transfer. Communications servers host the software for the system, trunking, and station features. These servers specify the trunks over which international, local, and interstate calls should be routed. A trunk is a fiber optical or copper cabling link to broadband or the public switched telephone network (PSTN). The servers have lists of user profile