Predict SIP Trunking QoS by Doing an Internet Speed Test (In Under 10 Minutes)

An internet speed test can help determine if SIP trunking is a good option

You can predict the Quality of Service (QoS) you’ll get from your SIP trunk by doing an internet bandwidth test in under 10 minutes.

When you’re migrating a telephone system from traditional platforms such as the public switched telephone network (PSTN) or PRI/T1 to a SIP trunk, or just trying to determine if a particular SIP trunk is the right fit, having the right amount of bandwidth is a key factor.

Your local geography can also play a role (just ask Canada) but, as reliable broadband becomes more common, worrying about rural locations will become a mitigating factor.

If you currently do not have reliable or fast internet, SIP trunks may not the best option.

Before Considering Bandwidth, Know Your Concurrent Call Volume

As important as bandwidth is for your SIP trunk decision, you need to determine how many average concurrent calls you have on a daily basis.

Read our blog post here about figuring out concurrent call volume. You’ll need to know three things:

    1. Determine the codec and how much bandwidth it consumes per call.
    2. Determine call volume for a typical hour.
    3. Multiply the number of current calls (channels) x the amount of bandwidth each call will take (based on the codec selected)’s SIP Trunks use the G.711 codec (85 Kbps)

Compare your current internet speed (upload speed must be adequate) to the number of concurrent calls required.

When you have a strong internet connection, you will most likely be able to accommodate SIP trunks with your existing internet connection.

To determine how much bandwidth is needed, we recommend factoring in about 1 concurrent call for every 3 employees.

You can raise that number if your business is a contact center, or if you have an active sales team with a heavy call volume.

There’s an old telephony meausurement that’s used to calculate bandwidth requirements called the Erlang. For an in-depth description check out Andrew Prokop’s post here.

Or, click here to try out the Erlang calculator yourself.

Internet Speed Test to Determine QoS

Once you have your bandwidth needs figured out now you can do the fun part, checking the speed of your internet connection.

One of the easiest ways to test your speed is by using

Download and upload speeds are measured in Mbps whereas SIP trunk codecs are measured in Kbps (multiply Mbps x 1000 to Kbps to convert the number).

You want to take the lower of the two numbers, the upload speed, to make your determination.

Here was my upload/download speed test:

g.711 codec bandwidth

So if I have a SIP Trunks using the G.711 codec at 85 Kbps and I have a 20 person business with what I estimate to be an average of 10 concurrent calls (I have busy sales guys), here’s the calculation:

  • 85 Kbps bandwith needed per call
  • 10 concurrent calls x 85 Kbps = 850 Kbps of bandwidth needed to cover these calls
  • Upload speed = 5.97 Mbps (per my speed test pictured above)
  • Convert 5.97 Mbps  x 1000 = 5970 Kbps
  • 5970 Kbps of Available Bandwidth / 85 Kbps needed for each call = 70 calls

As you can see from the sample calculation above, my internet speed actually allows me to have up to 70 concurrent calls.

Of course you’ll want to err on the conservative side for your business but with my example 20 employees / 10 concurrent calls, I have enough bandwidth to cover it so SIP trunking would be a good fit for me.

Need help determining if SIP trunks are right for you? Call us today at 800-250-6510.