9-Minute VoIP Troubleshooting Guide

Updated: Apr 2

Edit: run this internet test before you spend much time reading the whole article only to find out the problem is your Internet.

VoIP problems suck don’t they?

You are busy enough during the day then problems appear without notice and your whole office seems to be down, some one has to do something!

I hate it when a customer calls me because they’re experiencing issues with their phone system, they’re frustrated and upset and I feel it in their voice.

I take pide in our products and our work.

More importantly our job is to ensure their systems are always working properly, that’s why they hire us, right?

Even though this rarely happens, when it does our amazing team diagnoses and fixes the problem fast but I feel their frustration and desperation for a brief moment.

I made this guide to help troubleshoot Hosted VoIP or UCaaS Phone systems

Advantec is a Texas based VoIP company

This guide is intended to help business owners or office managers.

According to Wix, this post is 8 minutes I just don’t know anyone who reads this fast.

Depending on your experience level you may have to invest a few minutes or a few hours on this project but you CAN fix your system and you'll learn about networks!

Feel free to email it to yourself to work on it later.

VoIP Explained

VoIP is powerful and very customizable with hundreds of helpful features.

Those same features can make it seem complicated and scary to some (even IT technicians and that’s what we do for a living haha).

Are you ready for a fun challenge?

Let me know in the comments how long it takes you to find the problem

Get ready to dissect how VoIP works while identify the issues that may arise when dealing with VoIP systems.

How does VoIP work?

I highly recommend this section.

When you pickup your VoIP Phone and make a call, a series of packets travel first through your local area network (LAN) to your router or gateway. Let’s call this our first stop.

Your router pareces and sends the packets to the public internet but before they leave it adds a small piece of code called a header to each packet.

This header will tell your packets where to go in the public internet. Imagine they are like a label in your Amazon box.

What is the destination for this package?

Sip Server

A sip server is a high powered cloud computer that connects phone calls with the PSTN (Public Switch Telephone Network).

Think of it like an old style switch board that operates faster than The Flash!

Most of these Sip servers are maintained and secured by large companies including Verizon and AT&T.

To connect to a cloud sip server all VoIP calls run on a network, most of them use the public internet.

Actually this is what the internet actually is: a huge network, simple just super computers connected together.

Most VoIP issues happen in transit

Transit between the client (your VoIP phone) and the sip server.

After your VoIP packets/traffic reach the sip server, you “should” be in the clear with relatively no issues assuming you use a serious sip service provider.

If you have or manage your own sip server we could have much deeper issues

That won’t be covered here because much more troubleshooting is required.

Let’s begin with the first line in the diagram above.

WiFi VoIP Phones

We all love the idea of WiFi phones for the office but unless you have a very solid infrastructure with WiFi 6, we recommend all VoIP phones to be physically connected to your network switch with Cat5 (or higher) cable.

If you’d like to add an extra layer of security and you have a managed switch we recommend V-Lans for your mission-critical devices (we won't go into detail this time), this can also make QoS easier to implement and manage.

If you must have your VoIP phones on WiFi try some of the following simple actionable items:

∙ Move phones closer to the Access Point or Router

∙ Add WiFi Access Points to your network with at least 1 Cat5 or higher cable

∙ Remove obstructions between the phone and the broadcasting device

As a quick note: there are many small businesses like us out there that can run cable for you for no more than $179/run (our price in Houston commercial buildings).

This may be a good investment to consider if this is your problem.

If you just moved into a new building and the Ethernet cable jacks are already there, it could be just a matter of toning them, checkout this video here.

Ethernet Cable

If your phones are connected using a network cable:

∙ Ensure all your phones have an IP address in the same range. When all phones are in the same network, they will all show a similar IP address for the first 3 sets of numbers (the technical name is octets) Example:

o If you have 10 phones and 8 phones have an IP address like 192.168.1.X but the other 2 have a 10.1.10.X then there's something going on (not necessarily bad but it's something you want to be aware of as you troubleshoot)

Stay Tuned to watch our video on how to look at the IP addresses of Yealink phones. We expect to release it by September 15th.

∙ Inspect the cable and the connector for imperfections (usually only when 1 or 2 phones are acting up and the others are fine)


What you're doing with this last step is inspecting for network problems on Layer II, good job becoming a Network Tech!

Disclaimer: from this point on it gets a little more technical. We can help out remotely with consulting fee of $9.99 for the first hour. We think you won't need more than an hour.

Fix VoIP Routers

I'm going to use fictional company Zylker AC, Inc if you caught it I'll buy you a beer

The Zylker AC, Inc team is formed by 4 office admins and 8 field technicians.

  • Mike

  • Sue

  • Mary

  • Doug

Their LAN (Local Area Network) looks like this:

(I forgot to add the label lol but the blue device is the router)

This is the device we'll be working on next.

First thing when working on routers is to identity it's IP Address on the Lan side aka private IP address (all routers have both Lan IP addresses and WAN IP Addresses)

Open up a terminal by clicking start on your windows machine and type "command prompt". Once it's running type: IP Config /all

This command will display a lot of information including the "Gateway" in other words, your router. Once you have the IP address of the Gateway, access the GUI (Graphic User Interface) - think of it like a website that controls your router - in reality this is one way you access the device. Enter your username and password. NOTE: Some small business routers will have a tag with some information maybe including the username and password for default access (it's probably what it is, most people don't change it. but now you will and your business will be better protected!) Feel free to click around and get to know the router but PLEASE o-please: if you don't understand what you're doing, don't make any changes. It could bring down your entire network. Disclaimer: if this this happens we are not responsible but we will help you fix it remotely, you'll get 1 hour free!

Since there are thousands of different routers out there, there is no way we can cover them all but please email us your model and serial number for detailed information.

Once you're in the router, these are the main things you have to check for:

Double NAT

You will need to find the routing table on the router (or run a trace). If the next hop is a private IP Address, your network is in double NAT, an issue that causes confusion in the routing tables and can translate into very choppy voice, no one-way audio, no two-way audio, a phone rings but call doesn't connect and even other phones continue to ring even after a call has been answered or terminated. Learn more about Private IP vs Public IP addresses here.


Your firewall (usually part of your router) has a lot on the type of sip server or cloud system you're using, if possible, contact the support group of the carrier and get protocol types and port numbers used in the transport of the data. After that, enable port forwarding as required. Email us your router model for detailed information and instructions.


This is a common setting that has to be turned off entirely for smooth calls when using Hosted VoIP, RingLogix makes a GREAT tool, it's a small .exe file that runs on your computer and it tells you if SIP ALG is active or not, visit them here.

Packet Loss and Jitter

Sometimes there is just packet loss upstream from your ISP router. This happened recently with one of our customers in Magnolia, TX. the Comcast Business or XFinity router was experiencing significant packet loss on their side and honestly we wish the solution would have been faster but they were eventually able to address and fix the issue with ZERO downtime. That was sweet!

Related: Test your Internet Speed and Ping to troubleshoot your internet circuit

Quality of Service

Another big consideration happens locally (in your LAN). When someone decides to play a video on YouTube or stream a movie on Netflix during the middle of the workday, for a few seconds the router in your office will send most of the “juice” to the computer, tablet or phone that is trying to download a large file. If there are multiple calls happing simultaneously in your LAN, it can cause issues with the quality. There are plenty of affordable routers you can use to alleviate this problem, heck yours probably does it. With Quality of Service (QoS) rules you will tell the router that it needs to prioritize your VoIP calls over any social media or streaming platform to avoid these issues. These are complicated, we only establish these on a handful of routers because if not done well, your entire network could have issues.

Depending on the type of connection you have, your internet can be unstable, most small and medium size businesses in America rely on a broadband-type connection meaning it’s usually shared between all subscribers in a footprint therefore your internet service provider (ISP) can only do so much to ensure your internet connection running smoothly. These types of connections are referred to as “best effort”. Thankfully there are a few other options.

Dedicated Internet Access

The most reliable connection is a dedicated internet access (DIA) which is usually be more expensive than broadband but works much better. There is always a service level agreement (SLA) with these connections which guarantee the uptime and speeds of your internet. Make sure to ask about this when you’re buying your new connection. We also have a tool available to see if there's any fiber optic available in your neck of the woods:

For the best solutions contact us today! We act as an independent agent in the telecom industry to tailor-make solutions, we have relationships with many carriers in the Channel such as AT&T, Comcast, Spectrum Business, Windstream, Consolidated, Sudden Link, Lumen (Century Link) and many others to offer true engineered solutions for your connectivity and IT, CRM, Analytics, Business Intelligence and more.

The Unbreakable Internet

We have partnered with one of the biggest players in the software defined world and we highly recommend SD-Internet or SD-WAN networks, a true solution for your business that routes traffic with help of AI and an incredible algorithm so your mission critical applications (such as VoIP, video conference software, PoS systems, Credit Card Processing and more travel faster, more securely and more efficiently. In addition to that, it enables your internet (with the help of 2 or more circuits) to stay up no matter what happens, the failover is so fast that even if your team is on video calls, they won't even cut off when your prime circuit blinks or disconnects. The "Unbreakable Internet" starts at $49/ month. We highly, highly recommend it specially if you're having trouble with your internet connection, this magic box can help even if your running on old phone company DSL circuits in rural communities.

WISP (Wireless

Internet Service Providers)

If you're in a rural community (like many of our customers in Texas) you may have options you didn't even know about. This is where WISPS come in. Wireless Internet Service Providers tend to be smaller, family owned and operated internet service providers in local communities that bring good solutions to both residential and businesses. They deliver (usually) stable connectivity with state-of-the-art, discrete antennas that are mounted on rooftops for high speed connectivity. We've established wireless links that provide up to 3.2 gigs of bandwidth, that's over 3,000 Mbps! There is an excellent resource here to look for a WISP in your area. If you are nerdy like us you can even set up your very own internet service provider!

Some of the VoIP problems this troubleshoot guide will help with are:

  1. Choppy Audio

  2. Dropped Calls

  3. Echo During VoIP Calls

  4. Unable to Make Calls

  5. Call Connects with no Sound

  6. Low-Quality Audio

  7. Delays in Audio

Test your Internet Speed, Ping and Jitter

Use our free tool to test your internet service connection, bear in mind this tool usually only tests one server but there are a multitude of other tools available. Click Here to use the tool now.

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