VoIP (Voice over Internet Protocol) carries voice calls as data over IP networks. It is the foundation of most modern business phone systems, whether the system is hosted in the cloud, installed at an office or split between both.
VoIP in one minute
A microphone turns speech into an electrical signal. A codec converts that signal into digital audio, divides it into packets and sends those packets across an IP network. At the other end, the process is reversed. A separate signalling system sets up, manages and ends the call.
For many business systems, SIP handles signalling while RTP carries the audio. They are related but distinct: a call can signal correctly and still have one-way or missing audio if the media path is blocked.
The main parts of a business VoIP service
- Endpoint: a desk phone, conference phone, softphone, mobile app or analogue telephone adaptor.
- Phone system or PBX: manages extensions, call routing, queues, voicemail, schedules and other features.
- Carrier or SIP trunk: connects the business system to public telephone networks and supplies or hosts phone numbers.
- IP network: the local network, internet connection and provider networks that carry signalling and media.
- Supporting services: DNS, time synchronisation, provisioning, identity, recording and integrations.
Hosted, on-premises and hybrid VoIP
Hosted or cloud phone system
The provider operates the central platform. Phones and apps connect to it over an IP service, usually the internet. This can reduce local infrastructure and simplify remote work, but service design must consider internet dependence, provider access and commercial lock-in.
On-premises phone system
The organisation operates the PBX at its own site or data centre. This provides control and can support specialised integrations, but the organisation owns more of the lifecycle, security, resilience and upgrade work.
Hybrid phone system
Hybrid designs combine local and hosted components—for example, local gateways with cloud calling, or an on-premises PBX with cloud applications. They can solve migration and resilience requirements, although extra components add operational complexity.
What affects VoIP call quality?
Voice is interactive and time-sensitive. Raw download speed is not enough. Good calls depend on consistent latency, low jitter, low packet loss, sensible queue management and a stable media path. Wi-Fi coverage, overloaded upload links, faulty cabling, firewall behaviour and provider routing can all matter.
Quality of Service (QoS) can prioritise voice on a network you control, but it cannot repair a poor internet service or reserve capacity across the entire public internet. Start with capacity and stability, then use QoS as part of a complete design. See our voice-ready network guide.
Is VoIP the same as a business phone system?
No. VoIP is a way of transporting voice. A business phone system is the wider service that provides call routing, extensions, voicemail, auto attendants, queues, reporting, recording and integrations. Most current business phone systems use VoIP, but the terms are not interchangeable.
Australian considerations
Australian organisations should confirm how their service handles Triple Zero (000), location information, number portability and outages. ACMA notes that 000 is available from certain VoIP services and recommends another means of calling during a power outage, such as a charged mobile phone. Keep the service address held by the telco accurate because emergency processes use information supplied to the Integrated Public Number Database.
Frequently asked questions
Does VoIP require the internet?
Not always. VoIP requires an IP network. A hosted service normally uses an internet connection, while calls inside a private on-premises network may remain local.
Can I keep my existing phone numbers?
Often, through number portability, but eligibility, documentation, timing and supported number types vary. Do not cancel an existing service before a port completes unless your providers explicitly direct you to do so.
What happens when the power fails?
IP phones, routers, switches and network termination equipment need power. Use suitable backup power and an alternate calling method. Design this deliberately rather than assuming a cloud service makes the premises resilient.