Managing VoIP infrastructure at scale – from mobile operators using IMS cores to voice service providers supporting nationwide SIP trunking platforms – comes with its share of challenges. Even the most mature deployments run into issues like choppy audio, failed registrations, or dropped calls, all of which can impact thousands of users and require immediate attention.
Luckily, having a structured approach to VoIP troubleshooting makes these problems easier to resolve. In this guide, we share practical steps and tips to help simplify troubleshooting for network engineers running large-scale VoIP and UC environments.
Whether you're running a BroadWorks cluster or managing a nationwide SIP backbone, narrowing down the issue is the first step toward smart VoIP troubleshooting.
Here's a structured workflow used by experienced telecom engineers:
Start by asking these questions:
When you understand the scope of the problem, you can focus your investigation on the right systems, which may include the Session Border Controller (SBC), core call server, edge routers, or interconnect partners.
Whenever possible, replicate the issue using known endpoints. For example, if a carrier interconnect is misbehaving, try routing a test call to the same destination using different signaling paths to identify the issue. For voice service providers, this might involve testing calls through various SIP trunking partners or multiple PSTN gateways to identify and isolate the problem routes.
Gather SIP call traces and RTP statistics from key network devices – SBCs, softswitches, application servers, and edge routers. You can use tools like Homer, VoIP Monitor, Metaswitch SAS, BroadWorks XSLogs, or NetSapiens Traces to gain visibility into SIP and media behavior.
If SIP traffic simply isn't making it to the destination, DNS misconfigurations or SRV record inconsistencies could be the root cause. Use tools like dig, nslookup, or your SBC's DNS debug tools to confirm that endpoints are resolving to the correct IPs and that failover behavior follows expected priorities.
Configuration changes – no matter how minor – can introduce unexpected behavior in complex VoIP networks. Review your teams' and connected partners’ recent activity, including:
Voice service providers should maintain change logs to easily correlate any recent updates with incoming problem reports. But don't forget to check maintenance notifications received from your interconnected voice network partners.
If you still haven't found the cause of the problem, you have to test each component separately. For example:
Essentially, you’ll want to conduct a test that will help you determine whether each component is the culprit of the problem.
Once you've found the problem, make a change to restore service. Often, this will be a quick fix that won't be permanent. It could be a "workaround," or it may be a solution that's not economical long term. The goal here is to ensure that the services keep working.
Sometimes the most immediate fix can be the permanent one, but that's rarely the case. Even if the immediate fix seems simple, the underlying problem remains: why did a customer have to discover this problem for us?
Once your temporary fix is in place, plan how to make the repair permanent. Sometimes this will involve a software upgrade, but other times it means adjusting your procedures.
For example, if a customer couldn't call a destination because it's a new dialing code (NPA-NXX in the US, or a new mobile carrier in France), then you should ask how you can keep your dialing codes table up-to-date without having to hear from a customer when they cannot make a call.
Troubleshooting can be stressful work! You need to celebrate your wins. Healthy organizations have a way to share what they've learned with each other and congratulate one another. Finally, make sure to reflect on the process and tools.
Call quality problems are often subtle – audio sounds distorted, calls drop intermittently, or there’s dead air on one side. Here are some common VoIP call quality issues and steps you can take to resolve them:
Choppy audio or dropouts typically indicate problems with media delivery, including jitter, packet loss, or inconsistent routing across the WAN. Any kind of network problem, from bad Ethernet cables to malfunctioning fluorescent lighting, can lead to packet loss and audio problems.
QoS misconfigurations, hardware bottlenecks, or bursty traffic from other applications can also introduce too much delay, which causes real-time audio to suffer.
Troubleshooting tips:
Distorted audio usually stems from network problems, but can also come from more exotic sources like overloaded transcoding equipment. This can also happen when packet delivery is inconsistent due to network congestion or Wi-Fi instability.
Troubleshooting tips:
One-way audio issues often stem from problems in the RTP path. These can happen when NAT devices fail to maintain proper mappings or when firewalls block media streams on the return trip. In deployments that span multiple networks, issues like inconsistent NAT port forwarding and asymmetric IP routing may also interfere with one side of the call.
Troubleshooting tips:
While most VoIP and UC problems are media-related, some of the most frustrating issues come from SIP signaling failures – calls not connecting, unexpected 404 or 403 responses, or phones failing to register. Common VoIP signaling problems include:
Intermittent registration failures may result from timing issues in the registration process. Clients may have tried to register before DNS has fully resolved, or NAT bindings might have expired, causing timeouts between keepalives. Credential mismatches can also cause this issue, especially when provisioning systems are out of sync or authentication headers aren’t formatted correctly.
Troubleshooting tips:
When a call fails with a 404 or 403 error, it’s usually due to a routing or authorization mismatch. The SBC might not recognize the request URI, or the domain in the SIP headers may not match the settings. Inconsistently formatted phone numbers, such as mixed E.164 and local formats, can also result in rejected calls.
Troubleshooting tips:
Slow call setup can happen when there are DNS delays, TCP timeouts, or heavy processing loads on the SBC or intermediary proxies.
Troubleshooting tips:
UC and VoIP problems don't always originate within the systems themselves. Network infrastructure issues can manifest as VoIP-specific symptoms, and identifying this early can save hours of wasted troubleshooting.
If calls drop or degrade when another service (e.g., video conferencing or backup uploads) is active, investigate your WAN QoS policies by:
VoIP and UCaaS platforms that support dual-stack environments may default to IPv6, which can expose gaps in NAT/firewall rules. If IPv6 traffic isn't properly handled, calls may fail to connect or deliver audio despite successful SIP registration. Check this by:
Troubleshooting individual VoIP phone issues is very different from resolving systemic issues across a SIP trunking platform or a nationwide IMS core. Here are some ways large telecom providers approach it:
Capture systems like Oracle Communications Operations Monitor (OCOM) or Metaswitch SAS can help your teams trace calls through SIP and RTP flows without requiring full packet storage. These platforms index call metadata, making it easier to locate and isolate the problem quickly.
Monitoring tools like Grafana Dashboards, Nagios, or vendor-native analytics can track key performance indicators and generate alerts when thresholds are exceeded. Some KPIs to monitor include:
Proactive monitoring lets engineering teams address issues before they can affect customers. For example, a voice service provider might identify degrading audio quality on a specific trunk and reroute traffic to maintain service levels.
Carrier VoIP systems are complex and often unique to each organization, so institutional knowledge must be retained across shifts and engineers. Keep a searchable knowledge base of all known issues, SIP behaviors, and platform-specific bugs for faster diagnosis and more consistent support. Often, a simple system like Slack with public channels can be a great way to share information.
SBCs and softswitch application servers (like BroadWorks, Metaswitch, or NetSapiens) are central to the call path, making them the best places to start VoIP troubleshooting in most cases. Tools you can use to check these include:
Metaswitch Perimeta and Oracle SBCs provide trace tools that allow session correlation and reveal codec negotiation mismatches or routing failures, while BroadWorks’ XSLog tools expose device-level and application-level issues in detail. For BroadWorks operators, Alpaca shows the history of individual users and devices.
Effective VoIP troubleshooting takes more than guesswork – it demands expertise in SIP, RTP, SBC behavior, codec negotiation, NAT traversal, and signaling flows across large, distributed systems.
The ECG team has decades of experience supporting telcos, internet service providers, and enterprise-grade voice networks. We’ve helped resolve everything from obscure TLS handshake failures on Oracle SBCs to audio dropouts in Teams Direct Routing environments, and we can help you, too.
If you’re running into persistent VoIP problems and need fast answers, let’s talk. Contact us to get started.