What is Session Initiation Protocol (SIP)?

If you are looking into upgrading your business communications, you will likely have come across Session Initiation Protocol (SIP) alongside mentions of state-of-the-art VoIP business phones and communications software. So, what is SIP, and how can you and your business benefit from it?

Session Initiation Protocol (SIP)

A protocol is a set of rules that defines how two or more computing devices (such as laptops, smartphones, routers, etc.) communicate with each other. SIP is the protocol that helps video, voice and messaging communications flow. It is one Voice Over Internet Protocol (VoIP) deployment method, and so SIP is a specific technology that supports VoIP communications and allows users to make and receive calls over the internet.

A session is set up to initiate the transmission of communications over the internet and, once established, the data is sent, managed and ended by SIP. You’d never know this, as it all happens in a few milliseconds, and the call quality is even better than that provided by a traditional phone line.

What is the role of SIP in a VoIP call?

If you are familiar with the traditional PSTN or ISDN networks that routed calls using copper lines, just think of SIP working in a similar way to connect your device with the outside world by routing communications over the internet.

If you are going to use a device to communicate using the internet, as a VoIP user, you’ll have a SIP address. This enables you to establish a call connecting one SIP address to the other, then data transfer can occur. We already rely on SIP and VoIP to communicate — such as for smartphones, Zoom, and Microsoft Teams — and soon, we will all be saying goodbye to traditional landlines for good and making all phone calls using an internet connection as in 2025 PSTN, and ISDN services will be switched for everyone in the UK due to the ‘Big Switch Off.

How can I access SIP telephony?

If you want to connect your business communications to the cloud and enjoy the benefits of VoIP, you need to decide between hosted PBX or SIP trunking.

Hosted PBX is a cloud-based phone system hosted by a third-party service provider. SIP trunking upgrades your existing PBX equipment by connecting it to the internet, so you’ll be ready for the 2025 big switch-off.

First, work out your requirements. You need a setup that will serve your business needs now, as well as be able to scale in line with your future plans. VoIP is generally suited to smaller businesses as it is very easy to install, whereas SIP allows you to keep your existing phone system, so might be the best choice if you have an established communications network. SIP trunking enables you to continue using your company’s PBX via a SIP trunk: a direct virtual connection between your PBX equipment and VoIP.

SIP technology is rapidly becoming the method of choice for enabling business VoIP calls. To learn more about embracing the benefits of VoIP, visit and talk to us about bespoke solutions for your business.

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