Common SIP Myths Debunked

As we near the ISDN switch off, businesses that haven’t already adopted SIP or VoIP can’t be blamed for being skeptical. Luckily, the myths around SIP trunking can be swiftly debunked.

Mike Mead


SIP was first introduced to the UK market in the 2000’s and has since been widely adopted. Smart businesses realised that the benefits hugely outweighed the risks early on, which led to widespread adoption.

SIP trunking simply refers to a VoIP connection of a PBX to the Internet. During BETA programs, certain horror stories emerged with some companies still failing to implement SIP successfully. However, the common scenarios surrounding SIP trunking failure are often unpublished. Therefore, all anybody hears is “our trunks are down” or “the call quality was poor today” without truly assessing the problem.

As we near the ISDN switch off, businesses that haven’t already adopted SIP or VoIP can’t be blamed for being skeptical. Luckily, the myths around SIP trunking can be swiftly debunked. Let’s look at the most common SIP trunking issues and what the real causes are.


Despite the acceptance of cloud technology in most businesses today, IT security managers must still be diligent. The common scenario is the assumption that because calls occur over the internet they are not secure, this is only true to an extent. The public internet is not as secure as a private internet connection like MPLS or SD-WAN however, if you ensure that your connection follows security best practises, you don’t need to worry.

As long as your underlying connectivity is secure end-to-end, the technology will follow suit. Despite the worrying stories of telephone fraud, if your network is up to scratch, your telephony will also be secure.


Like security, the quality of your calls is reliant on your connectivity as SIP can quite happily run over an ADSL connection. Quality and performance will be impacted each time someone downloads a large file or starts streaming a live video so take that into account. SIP over any form of broadband may be fine for your needs however, if your business is reliant on the telephone, then you need a dedicated network.

The larger the company, the more complex you can get. Ultimately, a high bandwidth alongside a secure and resilient private connection with segregated sections for your SIP traffic to flow through will deliver the quality you correctly expect.


A common problem with ISDN and on-premises phone systems is scalability. Poorly configured trunks can lead to this problem being replicated in the SIP world. Ultimately, you can only take as many SIP calls as your bandwidth will allow.

The average SIP call uses 100kps of bandwidth so a dedicated connection of 10mbps will allow 100 concurrent calls. Of course, you may not need everybody on the phone at the same time. In this case, you can easily scale up and down with SIP trunks. Unlike a traditional copper telephone line or ISDN circuit, there is nothing to be installed or recovered each time you make a change to your network.


Assuming your connectivity and network components are in place, SIP trunking will almost always come with cheaper ongoing costs than your current fixed line environment. Typically, an ISDN circuit will cost around £30 per month. Per trunk, you are looking at around a tenth of the price – dependent on your requirements for resilience and feature enhancements.

If you don’t have any infrastructure in place, it’s likely the ROI on an SIP trunk implementation is going to be seen sooner than you think. To build a typical technology business case, you look at the next three years of expenditure. With SIP, you are getting a return from day one. Your calls are clearer and more secure, and you are safe in the knowledge that you will never need to pay another eye-popping bill for an ISDN installation.

By now, you should have seen a pattern emerge. SIP is safe as long as you take the time to ensure that your network is ready for SIP. To check whether your network is ready for SIP, or to talk more around your requirements, contact Nice Network today.

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