3CX - PSTN, ISDN and VoIP – Part 4 - Geek Guru

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3CX – PSTN, ISDN and VoIP – Part 4


In our penultimate blog post on line and connection types, we’ll look at specialist VoIP lines (Also known as SIP trunks) and how they work with the 3CX systems we offer.


SIP Trunks are special lines for dedicated VoIP services. They allow you to connect your 3CX system directly to the line, eliminating the need for a gateway; the connection between the VoIP / SIP trunk and the PSTN (telephone network) is managed by your SIP provider (known as an ITSP or Internet Telephony Service Provider).

Choosing a specialist SIP trunk to provider for your services means that you get a separate SIP connection installed. This is very much like any other kind of broadband internet connection, but deals only with SIP / VoIP traffic. This means that your business’ standard internet connection is not hampered or slowed if you have a lot of incoming or outgoing active calls – as your SIP trunk has its own dedicated bandwidth.

Because it’s based on internet telephony, VoIP/SIP systems can save a lot of money, particularly for larger businesses. For instance, if you replace a standard ISDN 30e connection with SIP trunks, the rental and installation costs can make thousands of pounds worth of difference.

It’s also very valuable for those who make many international calls. Because it’s using internet telephony, the call charges are far cheaper compared to standard calls made over a PSTN or ISDN line.

The uptime and quality of VoIP / SIP trunks has been increasing over the past few years, and right now they are able to compete with ISDN and PSTN lines for total uptime. This means that using VoIP / SIP, you won’t be without your phone connections any more than you would using a regular ISDN or PSTN line. The call quality of VoIP / SIP trunks is also constantly increasing as codecs are changed and compression gets more efficient, so currently the call quality is around equal to or better than you would achieve from an ISDN line – bearing in mind that call quality is also affected by the other party and their connection method and equipment.

People often choose to have a backup line such as a PSTN or ISDN line from a standard telephony provider. Some people still prefer to have the safety of a backup line, but if you wish to connect this line to the 3CX network, you will need a gateway. Some businesses also use a full hybrid connection of VoIP / SIP and ISDN – if this is something you’re interested in we’ll find you a package to suit while still saving you money.

You can maintain all of the efficiency and features provided by your 3CX system using VoIP – in fact, the system is tailored to use it just like a standard ISDN or PSTN connection. The only difference you should really notice is on the bill!

Next post we’ll be providing a short summary of the line types available to you, and how you can use them all together with a 3CX system.


If you’d like to discuss 3CX Systems, VoIP, ISDN or anything else IT or tech-related with us, give us a call and we’ll be happy to help you in any way we can!

Call us on 0845 234 0580 or email us at info@geek-guru.co.uk

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Posted on by Emily
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