An IP PBX is a business telephone exchange that carries calls as data over an IP network instead of over dedicated telephone wiring. It provides the functions of a conventional PBX, such as extensions, transfers, routing and voicemail, but does so in software. Phones and outside lines usually connect to it using the SIP protocol.

IP PBX in simple terms

"IP" refers to internet protocol, the same addressing method computers use on an office network. In an IP PBX, a desk phone is effectively a small network device. It plugs into the same switch as a laptop, receives an address, and talks to the PBX server across the network.

Because the exchange is software, its capabilities are defined by configuration rather than by the cards fitted in a cabinet. Adding a user is mostly an administrative task, and a feature such as a call queue is something the administrator switches on and configures.

The building blocks

An IP PBX deployment has four parts.

The PBX server. Software that registers phones, applies routing rules and provides features. It may run on a machine in the office, in a data centre or in a cloud environment.
Endpoints. IP desk phones, softphones on computers and mobiles, conference units, door phones and similar SIP devices.
Outside connectivity. SIP trunks from a telecom operator, or a gateway that converts conventional operator circuits into SIP.
The network. Switches, cabling, routers and the internet link. Voice quality depends on this layer more than on any other.

What an IP PBX is not

A few terms are often mixed up with it.

It is not the same thing as VoIP. VoIP describes the general technique of sending voice over IP networks; an IP PBX is one system that uses that technique to run a business phone service.

It is not automatically a cloud service. An IP PBX can sit in a server room on site. When a provider runs it for the business, it is usually described as a hosted PBX.

It is not a consumer calling app. An IP PBX is built around business numbers, extensions, shared routing and administrative control.

Benefits businesses usually look for

One network. Voice and data share cabling and switches, which matters when fitting out a new office.
Location independence. A user at a branch or at home can register to the same system and keep the same extension, subject to connectivity and policy.
Software features. IVR menus, queues, hunt groups, voicemail to email and conferencing are configured rather than bought as hardware modules.
Easier changes. Moves, additions and menu edits are done from an administration interface.
Visibility. Call records and system status are available as data, which helps both operations and IT.

Limits and prerequisites

An IP PBX is only as dependable as what sits beneath it. If the office network is congested or poorly configured, callers hear choppy audio or delay. If power fails and the switches and phones have no backup, the phones stop. If outside lines arrive over a single internet link, that link becomes a single point of failure.

It also asks for different skills. Someone has to understand networking, firewalls and SIP, either in-house or through a vendor. A telephone system exposed to the internet needs sensible security: strong credentials, restricted access and monitoring for unusual call patterns.

For a small site with a handful of analogue phones, sound existing wiring and no plans to change, replacing a working conventional exchange may not be justified.

Where NetLumen fits

NetLumen CorePBX is an IP PBX that can be deployed cloud-hosted or on-premise. Its feature list includes SIP trunking, an IVR designer, call queues and ACD, hunt groups, voicemail to email, conference bridges, extension management and SNMP monitoring. See the CorePBX page for the product, the IVR system page for call menus, or get in touch with a description of your sites and users.

Frequently asked questions

Do I need special phones for an IP PBX?

Endpoints need to speak SIP, which means IP desk phones or softphones. Existing analogue phones can often be kept by connecting them through an adapter or gateway, though they will not gain every feature.

Is an IP PBX the same as a hosted PBX?

A hosted PBX is an IP PBX that a provider operates on the customer's behalf. The technology is the same; ownership and maintenance differ.

Can an IP PBX use ordinary telephone lines?

Yes, through a gateway that converts those lines to SIP. Many businesses use a gateway during migration and move to SIP trunks later.

What Is an IP PBX? Meaning, Components and Limits