| Windows Telephony API | The Windows Telephony API defines the interface that applications use to access telephony functions in Windows. The API is a collection of C language function definitions, message definitions, types and data structure definitions, along with enough English verbiage to describe their meanings completely and unambiguously. |
| Windows Telephony SPI | The Windows Telephony SPI (Service Provider Interface) is the interface that a service provider must implement to make its telephony services available to applications via the API. The SPI is a collection of C language function definitions, message definitions, types and data structure definitions, along with enough English verbiage to describe their meanings completely and unambiguously. |
| Windows Telephony Application | Any software that uses the Windows Telephony API. The term "application" is used in its broadest sense possible; it need not necessarily be a user level program, but can also be a dynamic link library (DLL) that uses the API and provides higher level services via its interface. |
| Windows Telephony Service Provider | The conglomerate of software code (DLLs, device drivers, firmware) and hardware (add-on hardware, phone set, switch, network) that jointly implement the Telephony SPI. |
| client PC | The host environment for which the Windows Telephony API is defined. This is the Personal Computer (IBM/AT or compatible) running the Windows 3.1 operating system. |
| Desktop | The logical pairing of a user's PC and telephone. |
| Line | A pool of resources (i.e., communication channels) used by the application in performing telephony functions through the API. A PC may provide its applications with access to multiple lines and each line may provide different capabilities. It is the choice of the service provider for a line to decide how to model its resources. Note that a line need not correspond to a physical connection from the switch to the PC. For example, the realization of a line may involve a LAN-based server and a shared control link to the switch. |
| In essence, a line is any device that implements the line behavior defined by the API as the set of functions and messages for lines. |
| Phone | A device that behaves as a telephone set. This is usually, although not necessarily, the phone already on the user's desk located "next to" the PC. Phones need not be physically connected to PC. A LAN-based server with appropriate access to the switch may provide this logical connection. Note that the Telephony API treats the phone and the line as separate devices that can be independently controlled by the application. |
| In essence, a phone is any device that implements the phone behavior defined by this API as the set of functions and messages for phones. |
| call progress | Setting up a telephone call goes through several phases. Taking the phone offhook returns dialtone to indicate that a number can be dialed. Hearing the dial tone, the user dials the desired number. When the call reaches the destination phone, the caller will either receive a busy indication, indicating the called number is busy, or a ring back indication, indicating the dialed party is being alerted. Call progress is the process of monitoring the progress of a call through the various stages. |
| In analog networks, audible tones generated by the network provide the call progress indications to the user. Different tones allow the human ear to interpret the progress of the call. On digital networks (such as PBX or ISDN), the network may send indication messages to the phone to indicate the status of the call, and the phone may generate most tones locally, driven by those messages. |
| DTMF | Dual Tone Multiple Frequency. Pressing a button on the keypad of a TouchtoneTM phone, generates a pair of tones, of specified frequency and duration. The network or the equipment at the other end of the connection (such as a remote control for a phone answering machine), detects and interprets these tones. |
| Switch | Telephone switch. A piece of equipment capable of establishing telephone calls. Within the context of the API, a switch can be a PBX, a key system, or a central office. |
| analog line | A standard 2500-type phone line. Signals on an analog line use a set of standard in-band tones for call progress and DTMF signaling. |
| digital line | A digital station line on a PBX or digital key system. Signaling on a digital line uses vendor-specific (proprietary) protocols that exchange messages between the switch and the phone. A digital line typically requires a "matched" phone set. |
| BRI-ISDN | A basic rate ISDN (Integrated Services Digital Network) connection consisting of two bearer channels of 64 kbps each for voice or data, and one data channel of 16 kbps for control (2B+D). |
| POTS | Plain Old Telephone Service. Basic single-line telephone service for the public switched telephone network (PSTN). Only supports making and receiving calls. |
| PBX | Private Branch Exchange. A digital switch on the customer's premises that provides switching (including a full set of switching features) for an office or campus. PBXs typically use proprietary digital line protocols, although the user features provided by the different PBX vendors are generally similar. |
| central office | A public switch, directly connected to a number of telephones in a given geographical area. |
| Centrex | A service provided by central offices that provides a virtual PBX to a set of extensions. It offers features such as transfer, conference, forward, etc., within that set of extensions. |
| key system | A switching system where the phones have multiple buttons that permit the user to directly select incoming or outgoing lines. Key systems can typically support fewer users than can PBXs. |
| Call | Two or more parties exchanging information (or attempting to exchange information) using telephony equipment. Most of the functions in the Telephony API operate on calls. |
| Station | A peripheral device of the switch. This is any piece of equipment connected to a switch via a phone line. Examples are telephone sets, a fax machine, a PC with an add-in telephony card, an answering machine. |
| caller-ID | An identification (number, name) of the party initiating a call, as displayed to the called party prior to answering the call. A caller-ID may also be either unknown (due to telephone switch limitations) or blocked (concealed by the caller). |
| called-ID | An identification (number, name) of the party being called. This identification is of interest when you transfer or forward a call. For example, when you forward an unanswered call to a voice messaging system, you use the called-ID of the original call to locate the mailbox of the called party. |