How Many SIP Trunks Do I Need?

Many businesses are thinking about using SIP trunks. After all, statistics show that SIP trunks can reduce a business’s telephone bill by up to 40%. Naturally, many businesses considering the move to SIP trunks ask “how many SIP trunks do I need?”

How many SIP trunks does your business need? The number of SIP trunks your business need will depend on:

  • The number of concurrent calls you’ll be making
  • The provider that you choose
  • Your plans for growth in the future
  • Any factors that impact the number of calls you receive

If you already know the answers to the above questions, or how you can work them out, brilliant. If not, I’m going to explain each factor in more detail. By the end of this blog post, you’ll have all the information you need to figure out how many SIP trunks you require.

Working Out How Many SIP Trunks Your Business Needs

SIP trunking often works out much cheaper than ISDN lines but how much you save really depends on the number of SIP trunks you require. The key decider in how many SIP trunks you need is how many calls you be making or receiving at any given time.

So let’s look at the information you need to work out how many SIP trunks you require.

How Many Calls Will You Be Making Concurrently?

As I said previously, the biggest piece of information you need is the number of concurrent calls you’ll be making and receiving.

In the SIP trunking world, one call takes up one SIP channel. The SIP trunk is basically the ‘pipe’ and the calls travel through it as digitised packets.

A SIP trunk replaces the ISDN line that some businesses still use.

Concurrent calls are calls that you are making and receiving at the same time. So some businesses, despite having 50 employees, will only have 5 employees on the phone at any given time. On the other hand, some businesses will have their entire staff on the phone at the same time.

So before looking at providers, you need to know how many calls you will be making and receiving simultaneously. Next, let’s have a look at how the provider you choose will impact how many SIP trunks you need.

How Many Channels Are Available With Your Chosen Provider?

After finding out how many calls you make concurrently, your next question is likely “how many concurrent calls are possible using one SIP trunk?” Unfortunately, that question is somewhat difficult to answer as it all comes down to the provider that you choose.

As I’ve mentioned plenty on this website, providers aren’t made equal. The SIP trunks available from providers aren’t made equal either: some providers can only support a few channels per trunk. On the other hand, other providers can support hundreds of channels per trunk.

Why do some providers offer so many channels per trunk, whereas others only offer a few? It usually comes down to the provider’s target market rather than any technical limitations. If a provider’s target market is primarily small and medium-sized businesses, what’s the point in them offering SIP trunks that support 200 simultaneous calls? Similarly, if a business targets large enterprises, they’re unlikely to advertise a SIP trunk product that only supports 5 concurrent calls.

As part of researching this blog post, I spoke to two providers. One primarily works with micro and small enterprises, the other usually works with large enterprises. Unsurprisingly, the provider working with micro and small enterprises offered SIP trunk packages advertised as supporting up to 100 simultaneous calls. The other provider offered SIP trunks offering an unlimited number of calls (which wasn’t technically unlimited but capped at 100,000 simultaneous calls, setup dependent). You know the size of your business, so only you can decide which of these providers would be appropriate for your company.

Since this isn’t a case of anything technical holding businesses back, it’s perfectly plausible that you can choose any provider. However, it’s always best to choose a provider that primarily works with businesses similar in size to yours. If you choose a provider that normally works with businesses a lot smaller than yours, they may be unable to support your SIP trunking and VoIP requirements. That’s why you must take the time to find an appropriate provider.

The point here is that the provider you choose will impact how many SIP trunks you need. If your provider offers a SIP trunk product that supports 30 concurrent calls and you average 100 concurrent calls, you will need at least 4 SIP trunks. If you choose a provider offering SIP trunks that support 200 channels and you average 150 simultaneous calls, you may require only the one SIP trunk.

Moving on, there are other factors that can impact the number of SIP trunks you require. For example, your plans for the future.

Will Your Business Be Making And Receiving More Calls In A Years’ Time?

With any telecommunications solution, planning ahead is paramount. Modern solutions, such as VoIP and SIP, are designed with scalability in mind. However, if your business is growing and you know you’ll be making and receiving more calls within the next few months or years, you can prepare your telephone system in advance by adding and configuring more SIP trunks now. Here some questions to ask yourself:

  • Is my business’s call volume increasing? If you aren’t sure, there are several ways that you can find out. For example, an employee survey. Alternatively, your current telephone system might give you statistics that show call trends over time.
  • Is my team growing in the coming months? If you are planning to expand your team in the coming months, chances are your call volume will increase.
  • Are we launching a new product or service? Depending on what your business does, a new product or service could result in an influx of calls.

If your organisation is growing and you’re receiving more calls than you have in the past, It’s best to make sure you have enough SIP trunks configured now to cope with future demand. If you go for a SIP trunk that can support 20 channels and you try and exceed that number, you will start having problems.

Here’s a quick example of what can happen if you don’t have enough SIP trunks. If all your channels are in use and another customer tries to call you, they will get a busy signal or your voicemail (it depends on how your system is configured). The customer can ring you back later, of course, when your lines might be available. But this wouldn’t give off the best impression to your customers. I would always advise that businesses forecast their growth and predict how many calls they expect to make and receive 6 to 12 months down the line. Once you have done this forecast, that will tell you how many SIP trunks you should get.

Don’t Just Consider The Average Number Of Calls You Receive: Consider Potential Peak Times

When deciding how many SIP trunks you need, it’s important that you don’t just work out the average calls that you receive over the year. You also need to consider peak times and ensure you have enough SIP trunks to support your business in those times where you will be making and receiving a lot of calls.

For example, does your business get really busy at Christmas time, or another time of the year? How much would your business stand to lose if calls weren’t getting through to your team because all your channels were in use? You need to ensure that you have enough SIP trunks configured should you have a sudden spike in calls.

So, How Many SIP Trunks Do You Need?

Hopefully this blog post has given you all the information that you need to decide how many SIP trunks your business needs.

If you’re struggling to decide how many your business needs, it’s probably a good idea to choose a provider and contact them. Most providers will offer a free consultation and advise you on the SIP trunk setup that your business needs.

Please feel free to leave a comment below and let me know if this blog post has helped you to decide how many SIP trunks you need.

Need help? This is a free service for Business Tech Planet readers. Pop in your problem below and we'll be in touch soon!

Jack Mitchell

Jack Mitchell has been the Operations manager at telecoms and MSP Optionbox for more than 4 years. He has played a crucial role in the company, from marketing to helpdesk, and ensures that the IT requirements of over 300 clients are continuously met. With his innate passion for technology and troubleshooting and a particular interest in Apple products, Jack now delivers the most comprehensive tech guides to make your life easier. You can connect with Jack on LinkedIn.

Recent Posts