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Learn / Blog

Sip Trunking: How Many Is Too Many?

|  3 min
Voice Terminals
In this article

For an SMB, especially in its early stages, VoIP is an easy decision. Why would a business founded in this decade take on the cost and complexity of a PSTN system? VoIP is ideally suited to a young, growing company that needs flexible, low cost, high quality communications. 

It’s not all straightforward, however; there is some thinking to be done. The lines have to carry not just voice traffic, but also video and data. Downloading/uploading large files over the internet means considering not just bandwidth and latency but also prioritisation. 

A key criterion is how many calls will be active at any time. On an old-fashioned switchboard, where there were a finite number of lines, an operator would plug in a physical line to connect a call. Thankfully VoIP is much simpler, but requires a feature known as SIP trunking to handle multiple concurrent calls. 

International VoIP wholesale provider

We are an international VoIP wholesale provider, here to help your business. Here we take a brief look at SIP trunking, and how it allows small, medium and large businesses to use VoIP successfully. 

What is SIP trunking?

SIP trunking allows multiple end-users to share bandwidth for their calls, by connecting nodes and switches. It brings a high level of scalability – as there are no physical constraints – and thus a reliable call experience. 

SIP trunking allows employees to work in remote locations, perhaps in a regional sales office, or work from home. This would be impractical for a company using an ISDN-based system such as BRI or PRI as this would require additional hardware. 

SIP trunking connects ALL the end-users, via the company’s PBX, to the Internet telephony service provider (ITSP). Not all of them can be active on calls at the same time however, so planning a telephony system means thinking hard about how many calls will be active. 

How many SIP trunks?

A small business should start with, say, 5 trunks. Ironically 5 trunks may still be needed with less than 5 employees. This limits the cost of telephony to begin with, but allows the business to scale up. More trunks can be added quickly and seamlessly. 

A medium to large business may well require hundreds of trunks, especially if the firm has a global presence with employees working in different locations. The IT budget will still benefit from being able to scale up and down the number of trunks. 

A simple rule of thumb is to calculate the number of trunks based upon the number of end-users. At around 5 employees there should be an equal number of trunks. At 100 employees and above, there should be approximately 1 trunk for every 3 employees. There is an online calculator here [1] which allows detailed analysis. 

While VoIP is an obvious decision for young, growing companies, SIP trunking is a must for any business using VoIP. Small, medium and large companies can all benefit from the quality, flexibility and cost of SIP trunking. 

[1] https://www.owenduffy.net/traffic/erlangb.htm 

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