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What is the difference between VoIP and SIP?

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The ISDN switch off draws a little closer.  Many businesses are faced with a choice, SIP (Session Initiation Protocol) or a Hosted Solution using VoIP (Voice over Internet Protocol)?


They’re terms you’ll hear when doing some research but unless you know the difference, you can very easily adopt a system that isn’t right for the business size or structure.

Essentially VoIP and SIP are two different entities. Technically they’re quite similar.  VoIP refers to hosted seats, whereas SIP is a direct replacement for ISDN.  Hosted seats use SIP signalling to initiate the session to send calls to an Internet Protocol (IP) provider.


VoIP Solutions

When we talk about VoIP, we’re talking about hosted seats.

Hosted seats are often sold in package deals, bundled with calls usage. This makes them ideal for small businesses who want flexibility and scalability from their phone system.  One monthly ongoing cost makes it easy to budget for, where single or multiple user licenses, new IP handsets and mobile or desktop softphone clients are offered.  These IP handsets are plugged into a broadband router and/or Power over Ethernet (POE) switches to provide a single line replacement to the PTSN line over some form of broadband connection.


SIP Trunking

SIP or SIP Trunking as many in the industry like to refer to it as, is a more of a ‘like for like’ replacement to ISDN channels.

It features an onsite system, known as a Private Branch Exchange (PBX), which would be serviced by ISDN channels, usually between 2 and 30.  By using SIP Trunking, businesses are able to replace their ISDN channels with SIP channels, retaining their existing PBX.  The cost is monthly but spread over a 5 year plan a business owns the system and has something to show for their investment!


So, there are a couple of key differences between VoIP and SIP.  If you want to keep your existing on-premise PBX, you need to use SIP but if you want to replace it, you need to look at VoIP.

Then there are the costs.

Long term, an on premises communications system is more cost effective, because, for example, at the end of the 5 year plan a business will own their phone system, but for smaller businesses looking for lower monthly costs, a VoIP solution may be more suitable.


If you’re concerned about the ISDN switch off, get in touch.


We’re here to provide advice and support and with our consultative approach, you can be assured of the right phone system for the business you are in.

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