Analogue PSTN lines were the norm before the more advanced digital ISDN systems arrived. It is still the most basic form of connection for small businesses and homes in many parts of the world.

Compared to digital connections like ISDN, an Analogue PSTN line is usually more expensive in terms of line rental cost and offers only limited features and services.

ISDN2 lines provide 2 voice channels when connected to a telephone system. Multiple ISDN2 lines can be combined to provide 4, 6, or more voice channels if required.

The arrival of Integrated Services Digital Network (ISDN) lines caused a telecommunications revolution, as they allowed the simultaneous transmission of voice, video and data over PSTN circuits. ISDN lines are currently the most common type of voice lines used by businesses, but since the arrival of DSL broadband, are no-longer used for data services.

ISDN systems are typically cheaper when compared to analogue PSTN lines, whilst offering more powerful call setup and routing features and superior call quality.

ISDN30 lines provide 30 voice channels when connected to a telephone system.

The arrival of Integrated Services Digital Network (ISDN) lines caused a telecommunications revolution, as they allowed the simultaneous transmission of voice, video and data over PSTN circuits. ISDN lines are currently the most common type of voice lines used by businesses, but since the arrival of DSL broadband, are no-longer used for data services.

ISDN systems are typically cheaper when compared to analogue PSTN lines, whilst offering more powerful call setup and routing features and superior call quality.

If you are moving to a new office building or are having a brand new business telephone system installed, it is possible your calls might be delivered via VOIP - otherwise known as Voice Over Internet Protocol.

The term VOIP refers to technologies delivering voice and multimedia over IP (Internet Protocol) networks, such as the Internet.

You might also hear VOIP systems referred to as IP phones or Internet telephones.

Other jargon you might come across whilst looking at VOIP systems include:

• μ-law

• a-law

• G.711

• G.722

• iLBC G.729

These terms relate to the types of encoding used to stream media across IP networks. Each of these 'codecs' allows streams to be carried over lines depending on their different bandwidth capacities and the stream's final application. One codec might be used to heavily compress a stream for delivery over narrowband connections, whereas another supporting high fidelity stereo would be used to send high-quality streams over broadband, for example.

SIP (Session Initiation Protocol) is the standardised protocol for VOIP phone calls. A SIP “session” could be a phone call between two participants, a conference call or even a video call.

A SIP Trunk refers to a “virtual” phone line which is provided by a SIP trunk provider. It uses your data connection to connect your phone system to the Internet.

Analogue PSTN and ISDN business lines are directly connected to internal handsets and devices via a telephone switching system called a PBX (Private Branch Exchange).

VOIP systems do not require the telephone handset to be connected directly to a PBX but can be connected over a standard network connection instead. This makes it possible to reduce the complication and cost of wiring and provides flexibility for businesses when planning phone system installations, effectively making deployment and management of phone systems lot simpler.

Using this system, incoming lines can be PSTN, ISDN2, ISDN30, SIP or a combination of these and the business will still have a PBX on the premises, but all the handsets are connected via the computer network and Wi-Fi, rather than via a dedicated cable.

This system enables the business to be in complete control of their telephony environment, provide resilience with a mix of inbound services, such as SIP and ISDN2, for example, and enable complex software integrations to allow reporting, analysis, call recording and screen popping technologies.

Importantly, this system is not reliant on an internet connection in order to maintain a service.

With a Hosted VOIP system, the business does not require PSTN, ISDN2, ISDN30 or SIP lines or connections, simply a good internet connection capable of handling the volume of voice data transmitted and received. In addition, there is no PBX on site. Instead, this function is moved to the hosted cloud VOIP provider and delivered as a subscription-based service over the internet.

In addition, there is no PBX on site. Instead, this function is moved to the hosted cloud VOIP provider and delivered as a subscription-based service over the internet.

Each of the business' telephone extensions connects via VOIP back to the VOIP providers servers, which handle the management of the calls and the call routing.

Hosted VOIP systems are heavily reliant on the availability of a good quality internet connection.

Hybrid systems use a combination of On-Premise PBX and Hosted VOIP running together as a single system.

A hybrid solution could be a compelling option if you are;

• Phasing migration from an On-Premise PBX to Hosted VOIP

• Retiring a system

• Adding advanced services (via the On-Premise PBX).

• Seeing out the remainder of a contract on incoming lines

• Providing services across multiple offices

• You need flexibility

An IP PBX switches calls between VoIP users on local lines while allowing all users to share a certain number of external phone lines. The typical IP PBX can also switch calls between a VoIP user and a traditional telephone user, or between two traditional telephone users in the same way that a conventional PBX does.