VoIP (Voice over IP) is a well-established and widely adopted technology in business environments, particularly in call centers, thanks to its scalability, flexibility, and cost-saving benefits. However, VoIP call quality can be affected by multiple, often interconnected, factors. When call quality deteriorates, the impact is immediate: reduced agent productivity, compromised customer experience, and damage to the company’s reputation.
In this article, we’ll take an in-depth look at the main causes of VoIP call quality issues, how to diagnose them, and which technical interventions can be implemented to resolve them—both from a network and VoIP infrastructure standpoint.
Understanding VoIP Audio Quality Parameters
To effectively address quality issues, it’s essential to understand the technical parameters that define the audio experience during a VoIP call. The key metrics include:
- Jitter: the variation in packet arrival time. High jitter leads to distorted or choppy audio.
- Latency: the time a packet takes to reach its destination. Beyond 150 ms, conversations become difficult.
- Packet Loss: lost packets during transmission. Even a 2% loss can severely degrade call quality.
- MOS (Mean Opinion Score): a subjective quality rating from 1 to 5 that reflects users’ perception of the call.
Real-time monitoring tools can provide these metrics, helping isolate the root causes of issues.
Common Causes of Poor VoIP Call Quality
Network Congestion
The most common cause of jitter and packet loss is congestion on the LAN/WAN network. In a call center environment where voice and data traffic coexist, the absence of proper Quality of Service (QoS) mechanisms can lead to bandwidth competition.
The solution is to implement QoS at the switch and router level. VoIP packets (typically RTP over UDP) must be prioritized over best-effort traffic. It’s also advisable to create separate VLANs for voice and data to segment traffic.
Internet Connection Issues
The quality of your Internet connection is crucial, especially if you’re using external SIP trunks. High latency or bandwidth fluctuations can significantly degrade call quality.
To resolve this, assess your provider’s connection stability and minimum guaranteed bandwidth. In business-critical contexts, a dual uplink (automatic failover) is recommended, along with a dedicated MPLS channel for voice traffic if possible.
Inadequate Hardware Infrastructure
Unmanaged switches, consumer-grade routers, or underperforming firewalls can introduce bottlenecks. Outdated or misconfigured VoIP terminals also directly affect perceived quality.
In this case, the solution is to use professional-grade VoIP-compatible hardware, properly configured to handle real-time traffic. Features like SIP ALG can cause more harm than good and are often best disabled.
How to Diagnose VoIP Issues
Internal Checks
- Inspect network cabling: damaged or poorly shielded cables can introduce errors.
- Use tools like
ping,traceroute, andiperfto measure latency and bandwidth between internal endpoints. - Run SIP debug on the PBX to check for delays or instability in SIP dialogues.
External Checks
Run tests with other VoIP providers or use a softphone from a different network.
Also, record a call and analyze the RTP stream to detect jitter, latency, or packet loss.
Continuous Monitoring
Set up a continuous monitoring system (Zabbix, Grafana, or PBX-integrated tools) to collect QoS and call performance statistics over time.
Technical Solutions to Improve VoIP Quality
Quality of Service (QoS)
Proper QoS configuration is essential in environments with high call volumes. Key suggestions:
- Assign RTP packets a DSCP (Differentiated Services Code Point) value of
EF(Expedited Forwarding). - Segment voice and data traffic into dedicated VLANs.
- Set up priority rules on routers and firewalls for VoIP traffic.
Local Network Optimization
- Switch to managed switches supporting 802.1p and VLAN tagging.
- Minimize the use of Wi-Fi for business VoIP phones—prefer wired connections.
- Ensure firewall ports allow bidirectional RTP traffic.
Codec and Compression
Using the wrong codec can worsen issues on networks with limited bandwidth or high latency.
- Prefer codecs like G.729 or Opus for low-bandwidth networks, considering their CPU impact.
- On LANs or high-quality networks, G.711 delivers better quality without compression.
Session Border Controller (SBC)
An SBC is vital in professional environments:
- Protects against SIP-based attacks.
- Improves interoperability between PBXs and providers.
- Offers failover mechanisms and advanced traffic management.
Strategic Considerations for Call Centers Using VoIP
For call centers, VoIP quality isn’t just a technical detail—it’s a competitive asset. Consider the following:
- Proactive monitoring: integrate quality metrics into the CRM for every call.
- Redundancy: a backup line or secondary SIP provider ensures business continuity.
- IT staff training: your PBX managers should have strong networking expertise.
- Cloud or on-premise?: a cloud-based PBX simplifies management but requires stable, redundant connections.
How to Build a High-Performance VoIP Infrastructure for Your Business
Adopting VoIP without the right setup can result in a frustrating experience for both clients and agents. That’s why it’s critical to build a network with professional design principles, implement real-time monitoring tools, and choose partners who can support you at every stage—from consulting to operational management.
SiVoIP is the ideal partner for companies looking to adopt VoIP securely, scalably, and without compromising on quality. With industry experience and a technical infrastructure tailored for call centers, SiVoIP offers:
- Specialized assistance and advanced technical support
- Proactive call quality monitoring
- Design and maintenance of professional VoIP networks
- Reliable, redundant SIP trunks
If you’re facing call quality issues or considering a VoIP implementation in your contact center, get in touch with SiVoIP today for a free technical consultation. Quality is not an option—it’s the foundation of your business reputation.