Why Does VoIP Drop Calls?

A reliable business telephone system is a crucial business asset. That’s why some business owners are wary of moving over to a VoIP system when rumour persists that VoIP calls regularly drop. While it’s true that VoIP calls do sometimes drop, you can mitigate the risk of calls dropping in numerous ways.

Why does VoIP drop calls? VoIP calls drop for numerous reasons, from insufficient bandwidth to faulty hardware. In most cases, you can troubleshoot these issues to reduce the chances of calls dropping in the future.

So while VoIP calls can drop, you can troubleshoot these issues to avoid long-term recurring problems. I’m going to explain why VoIP calls drop, as well as detail some tips for creating a robust environment for your VoIP system.

Why Do VoIP Calls Drop?

As I said above, there can be numerous issues that cause VoIP calls to drop. Sometimes the issue can be something unrelated to the call or the VoIP telephone system, such as insufficient bandwidth. Here are some common reasons for VoIP calls dropping.

Insufficient Bandwidth

Insufficient bandwidth is likely one of the biggest causes of VoIP calls dropping. For a high-quality VoIP call, you need approximately 3Mbps up and down available. While the minimum bandwidth required is much lower (around 100Kbps up and down), if your internet connection falters, the call could drop.

Concurrent CallsMinimum BandwidthRecommended Bandwidth
1100Kbps Up and Down3Mbps Up and Down
5500Kbps Up and Down10Mbps Up and Down
101Mbps Up and Down15Mbps Up and Down

If you look at the above estimations, you might imagine that any internet connection would provide a stable VoIP call. However, there are lots of applications and devices contending for bandwidth in the average commercial premises. From web browsing and file uploading to point-of-sale systems, there’s plenty of competition for bandwidth. If you have a poor internet connection or little bandwidth available, it’s easy to see how VoIP calls can be impacted.

Overcoming Bandwidth Limitations To Ensure High-Quality Calls

So, how do we overcome the problem of limited bandwidth? This is handled in numerous ways, depending on your budget and the number of users on your telephone system.

One way you can ensure dedicated bandwidth for your VoIP telephone system is by installing a dedicated line. If you use this line solely for VoIP, the other processes and devices taking up bandwidth in your office will not impact the quality of your calls. Depending on your budget and how many calls you make and receive, this could be expensive and/or unnecessary. However, it is one way to ensure consistently high call quality.

Some VoIP providers will configure your network to prioritise voice traffic over any other type of traffic. Many routers come with Quality of Service (QoS) settings that you can configure to prioritise voice traffic. Unfortunately, these settings won’t make much of a difference if your internet service provider doesn’t have their network configured in such a way that prioritises voice traffic.

If it’s an option, choosing a business that can provide both your internet and VoIP telephone system is a good idea. A business specialising in both will be able to effectively configure your network to ensure VoIP call quality. If you have separate providers, you may find that they don’t work together effectively to get your VoIP telephone system working as it should if you encounter any problems with calls dropping.

Malfunctioning SIP Session Timers

Keep-alive messages are frequently exchanged between endpoints. This is to prevent ‘orphan calls’, where the call fails but the end session signal isn’t sent. If the keep-alive message isn’t received, the server could incorrectly assume that the call has dropped and thus end the call.

Unfortunately, it isn’t uncommon for SIP session timers to go wrong, resulting in the call being dropped. This is a malfunction that I see a lot, albeit less over the last few years, and is a very likely issue if you experience calls dropping regularly.

Diagnosing a problem with the SIP session timers can be fairly easy. If you notice any or multiple of the following, it would point towards an issue with the SST mechanism:

  • Calls drop at the same point every time. For example, 5, 10, or 15 minutes into the call.
  • Calls only drop on a certain model or make of handset and don’t at all on others.
  • It happens regardless of who is talking or whether there is any audio at all.

If the SIP session timers are faulty, you will likely notice a pattern. While the intervals between keep-alive messages differ from system to system, you may notice that the call ends at roughly the same duration every time. If you notice this pattern but only on certain handsets, it would suggest incompatible implementation of the keep-alive mechanism in the end-point device.

Failed Connection Acknowledgement Signal

When the person you call answers the phone, a connection message is sent from their telephone system to yours. When your system receives this acknowledgement, your IP PBX/VoIP gateway confirms the connection via a connection acknowledgement.

If it takes longer than a certain period of time for the connection acknowledgement message to be received by the recipient system, the call could get timed out and drop. If you have noticed that calls are consistently failing only a short period of time after it was answered, this would suggest a SIP ACK issue.

If your call dropping issue is because of a SIP ACK fault, you will observe that the call will fail at exactly the same number of seconds after it was answered every time. Usually, this will be 10 to 20 seconds into the call. You will only have to test this a few times to quickly find out whether the issue is a SIP ACK issue or not.

SIP ACK issues may only occur when certain destinations are called or when certain call routes are selected. If you notice you’re only encountering issues when phoning a particular person or selecting certain call routes, it would immediately highlight some form of incompatibility.

The Key To Identifying Why VoIP Calls Are Dropping

Identifying why VoIP calls are dropping doesn’t require fancy technology or years of experience. The key to identifying why VoIP calls are dropping is speaking to users that are encountering issues.

Far too often users are ignored by the technicians trying to ascertain why VoIP calls are dropping. This simply makes the technician’s job much harder and results in a issues taking much longer to correct than they should.

By asking users encountering issues a few simple questions, you can quickly find out what’s causing calls to drop. Here are some examples of questions that you can ask users, which should help you to get to the bottom of why calls keep dropping.

  • Do calls drop after a certain period of time?
  • If calls drop after a certain period of time, how long into the call does it happen?
  • Do calls drop at exactly the same call duration every time?
  • Do calls only drop when calling a certain person?
  • Is anyone else encountering the issues that you are?
  • Is anyone on the call talking when the call ends?

If you look at the examples of why VoIP calls drop that I’ve detailed above, you will see how easily you can ascertain what’s causing the issue by getting the answers to these questions.

If you need any other advice, please let me know in the comments below. I’m happy to advise you and help you figure out why your VoIP calls are dropping.

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.

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