Glossary / VoIP Fundamentals
🌐 VoIP Fundamentals explains how voice calls travel over the internet instead of traditional phone lines. This section covers the core technologies, devices, and protocols that make internet-based calling possible. This section contains 14 terms.
On this page: VoIP · IP Telephony · Packet · Packet Switching · Circuit Switching · Softswitch · Media Gateway · VoIP Gateway · ATA · Softphone · Hard Phone / Desk Phone / IP Phone · WebRTC · SBC · B2BUA
VoIP (Voice over Internet Protocol)
The technology that lets you make phone calls over the internet instead of traditional phone lines. VoIP converts your voice into small data packets, sends them over an IP network, and reassembles them at the other end. It is cheaper than traditional telephony because it uses existing internet infrastructure. Almost all modern business phone systems use VoIP.
Related: PSTN · Packet Switching · SIP Trunking
IP Telephony
A broad term for any phone service delivered over an IP (Internet Protocol) network. IP telephony includes VoIP calls, video calls, and messaging. It also covers the hardware and software that makes these services work, such as IP phones, softphones, and SIP servers. In everyday use, "IP telephony" and "VoIP" are often used interchangeably.
Related: VoIP · Cloud PBX · SIP Protocol
Packet
A small unit of data sent over a network. When you speak during a VoIP call, your voice is digitised, compressed, and broken into packets. Each packet travels independently across the internet and is reassembled in the correct order at the destination. A typical one-second voice sample is split into dozens of packets.
Related: Packet Switching · VoIP · Jitter
Packet Switching
The method of sending data by breaking it into small packets that travel independently through the network and are reassembled at the destination. The internet uses packet switching. This is more efficient than circuit switching because the network resources are shared among many users. VoIP relies on packet switching to carry voice data.
Related: Packet · Circuit Switching · VoIP
Circuit Switching
The traditional method used by the PSTN, where a dedicated communication path (circuit) is established between two phones for the entire duration of a call. The circuit is reserved even during silence, which wastes bandwidth. Packet switching (used by VoIP) is more efficient because it only sends data when someone is actually speaking.
Softswitch
Software that controls and routes VoIP calls. A softswitch replaces the physical switching equipment used in traditional telephone exchanges. It handles call setup, routing, and teardown. Telecom providers use softswitches to manage millions of calls. In smaller deployments, the PBX software acts as the softswitch.
Related: PBX · FreeSWITCH · Media Gateway
Media Gateway
A device that converts voice data between different network types. For example, a media gateway converts VoIP packets into the format used by the traditional phone network (PSTN), and vice versa. This allows VoIP systems to communicate with landlines and mobile phones. Media gateways are essential at the border between IP and traditional networks.
Related: VoIP Gateway · PSTN · SBC
VoIP Gateway
A device or software that connects a VoIP network to the traditional telephone network (PSTN). It translates between SIP/RTP (used by VoIP) and TDM (used by ISDN or analogue lines). Small businesses use VoIP gateways to connect legacy analogue phones or fax machines to a modern IP phone system.
Related: Media Gateway · ATA · FXO
ATA (Analogue Telephone Adapter)
A small device that connects a traditional analogue phone to a VoIP network. You plug your old phone into the ATA, and the ATA connects to your internet router. The ATA converts your analogue voice signal into digital VoIP packets. It is the simplest and cheapest way to use an existing phone with a modern Cloud PBX.
Related: FXS · VoIP Gateway · Hard Phone
Softphone
A software application that turns your computer, smartphone, or tablet into a phone. You make and receive calls through the app using your internet connection. Softphones connect to your PBX or Cloud PBX using SIP. They offer features like click-to-call, contact integration, and video calling. No physical phone hardware is needed.
Related: Hard Phone · WebRTC · SIP Protocol
Hard Phone / Desk Phone / IP Phone
A physical phone device designed specifically for VoIP calls. It looks like a traditional desk phone but connects to your network using an Ethernet cable instead of a phone line. IP phones register with your PBX using SIP and offer features like HD audio, colour screens, programmable buttons, and built-in Bluetooth for headsets.
Related: Softphone · SIP Protocol · ATA
WebRTC (Web Real-Time Communication)
A technology built into modern web browsers that allows voice and video calls directly from a web page, without installing any plugins or software. WebRTC is used by many Cloud PBX providers to offer browser-based calling. Users simply open a web page, log in, and start making calls. It works on Chrome, Firefox, Edge, and Safari.
SBC (Session Border Controller)
A network device that sits at the edge of a VoIP network and controls which calls are allowed in and out. An SBC provides security (blocking unauthorised access), interoperability (translating between different SIP implementations), and quality management (prioritising voice traffic). Businesses and service providers use SBCs to protect their phone systems from attacks and ensure call quality.
Related: Firewall · B2BUA · SIP Protocol
B2BUA (Back-to-Back User Agent)
A SIP component that acts as an intermediary by terminating one call leg and creating a new one. Unlike a simple proxy that passes SIP messages along, a B2BUA fully controls both sides of the conversation. This gives it the ability to modify call parameters, record calls, apply billing, and hide internal network details from the outside world. Most SBCs operate as B2BUAs.
Related: SBC · SIP Proxy · Call Recording
Related Sections
🔗 Core Telephony Concepts — PSTN, ISDN, DID, and other foundational terms
🏢 PBX Systems — Cloud PBX, IP PBX, Hosted PBX, and open-source alternatives
📡 SIP Trunking — How your PBX connects to the outside phone network
🎵 Audio, Media and Codecs — Codecs, jitter, latency, and RTP
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