Attendant console: The larger, specialized phone an operator or attendant uses to answer incoming calls and route them to the appropriate extension. In an IP PBX, this may be replaced by software running on a PC.

Centrex: A traditional business telephone service that a local telephone company offers from a local central office. This is essentially a normal single-line telephone service with advanced business features.

CSU/DSU (channel service unit/data service unit): A device that terminates a digital channel. In this context, the device sits between the voice T1 line and the IP PBX.

Find-me/follow-me: A feature that allows calls to find you wherever you are, ringing multiple phones (such as your cell phone, home phone, and work phone) all at once. Such presence features are found in IP PBXs and offered by some hosted services. You activate them by pressing a soft key.

Gateway In VoIP systems: a network device that converts voice and fax calls in real time from a public switched telephone network.

(PSTN) to an IP network: A gateway can also convert calls between branch offices to VoIP so they can travel over the Internet.

High-availability: Refers to devices or deployment strategies designed to provide access to fully functioning systems at all times. One HA strategy is to cluster devices so that the primary device can fail over to the secondary one if necessary.

IP Centrex or hosted voice: An IP voice service delivered by an IP service provider or a phone company. On the surface it is like old-fashioned Centrex, but the features are much richer and the price is usually much lower.

IP PBX (Internet Protocol private branch exchange): A private telephone switching system that performs the same basic functions as a traditional PBX but operates using IP, making it easier to add features.

KTS (key telephone system): A system in which the telephones have multiple buttons representing separate phone lines. Users select external phone and intercom lines directly through these buttons. KTS solutions are less expensive and less flexible than PBX solutions.

PBX (private branch exchange) A private telephone switching system that connects outside phone lines from a telecommunications provider to extensions within a building or office, as well as providing such features as call forwarding and paging. Where older proprietary systems used handsets designed specifically for separate systems, new PBX devices are interoperable.

PoE (Power over Ethernet): A solution in which networking hardware transmits electrical power over Category 5 Ethernet cable or better. This eliminates the need for AC power cords, minimizing cabling and outlet requirements.

POTS (plain old telephone service): The typical, familiar single-phone-line-and-single-phone-number model. PSTN (public switched telephone network) The combination of local, long-distance, and international carriers that make up the worldwide telephone network.

QoS (quality of service): The ability of a network (including applications, hosts, and infrastructure devices) to deliver traffic with minimum delay and maximum availability.

SIP (Session Initiation Protocol): An Internet Engineering Task Force (IETF) standard for initiating, maintaining, and terminating an interactive user session involving video, voice, chat, gaming, virtual reality and more.

Soft keys: Buttons on a telephone handset that can be programmed to perform various functions—such as speed dialing or conferencing—depending on the interface on the handset's screen.

Soft phone: IP telephony software that lets users send and receive calls from non-dedicated hardware such as a PC or Pocket PC device. It is typically used with a headset and microphone.

VoIP (Voice over IP):The process of making and receiving voice transmissions over any IP network. IP networks include the Internet, office LANs, and private data networks between corporate offices. The main advantage of VoIP is that users can connect from anywhere and make phone calls without incurring typical analog telephone charges, as for long distance.