Voip Terms

SS7 (Signaling System No. 7) is a set of telephony signaling protocols developed in 1975, which is used to set up and tear down the vast majority of the world's public switched telephone network calls.

E.164 is an ITU-T recommendation that defines the international public telecommunication numbering plan used in the PSTN and other data networks.

Q.931 is a network layer protocol in the ISDN protocol suite used for establishing, maintaining, and terminating network connections between the two DTEs.

A trunk is a communication line or link designed to carry multiple signals simultaneously to provide network access between two points, typically between two switching centers or a switch and a PBX.

G.711 is an ITU-T standard for audio companding, widely used in telephony and VoIP, which provides a bandwidth of 64 kbps.

A Central Office (CO) switch is the facility where subscriber lines are connected to the PSTN and where call routing and signaling are managed.

A Digital Signal Processor (DSP) is a specialized microprocessor designed to perform mathematical functions on digital signals, such as converting analog voice to digital packets.

The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks, commonly used in VoIP.

Mean Opinion Score (MOS) is a numerical measure of the human-judged quality of voice communications, often used to evaluate the performance of different voice codecs.

A Key System (or Key Telephone System) is a small-scale telecommunications system used in small businesses that allows users to select lines manually.

A Private Branch Exchange (PBX) is a telephone system within an enterprise that switches calls between users on local lines while allowing all users to share a certain number of external phone lines.

Common-channel signaling (CCS) uses a dedicated channel for signaling information, separate from the voice traffic channels, as seen in SS7.

Time Division Multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line.

Ground start signaling is used in PBX environments to provide a positive indication of a request for service, which helps prevent glare by ensuring the line is seized before a call is attempted.

PVDM (Packet Voice Data Module) is a hardware module used in Cisco routers to provide DSP resources for voice processing, such as transcoding and conferencing.

Glare occurs in telephony when both ends of a trunk attempt to seize the same line at the same time, leading to a collision.

RTCP (RTP Control Protocol) provides out-of-band statistics and control information for an RTP flow, such as packet loss and jitter.

PSTN (Public Switched Telephone Network) is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telephony operators.

The local loop is the physical link or circuit that connects from the customer premises to the edge of the carrier or telecommunications service provider's network.

Channel Associated Signaling (CAS) is a method where signaling information is sent within the same channel as the voice traffic, often using bit-stealing.

G.729 is a widely used audio codec in VoIP systems, specifically designed for low bandwidth (8 kbps) while maintaining high voice quality. Other options like PBX and PVDM are hardware or system components, not codecs.

A loop start circuit is the standard signaling method for home phones, where the phone company detects an off-hook condition by sensing a closed loop of current. Ground start is typically used in business trunk lines to prevent glare.

Quantization is the process of mapping continuous analog signal values to a finite set of discrete digital levels. Sampling and coding are other steps, but quantization is the specific mapping process.

A Central Office (CO) is the physical building where the telephone company houses switching equipment and connects local loops to the public switched telephone network.