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What is VoIP QoS, and How Can It Improve Call Quality?

what is VoIP QoS

VoIP call quality issues are not uncommon but can threaten your credibility and cost you valuable business opportunities. Businesses must be quick and seamless when addressing quality of service (QoS) problems.

If you haven’t yet optimized your QoS network, this guide is for you. In it, you’ll learn QoS, why it matters, and how to troubleshoot recurring problems. 

What is VoIP QoS?

VoIP QoS (Voice over Internet Protocol Quality of Service) is a set of techniques and mechanisms that ensure voice communication (phone calls) delivered over the Internet using VoIP technology maintains high quality, reliability, and performance.

Traditional phone systems carry voice calls over dedicated circuits, ensuring consistent call quality. However, with VoIP, voice data is transmitted over IP networks and shared with other data types, such as web browsing, file downloads, video streaming, etc. This shared network environment can lead to potential issues like packet loss, jitter, and latency, which can degrade the quality of voice calls.

Is QoS Necessary for VoIP?

QoS is necessary for VoIP systems to ensure a reliable and high-quality voice communication experience. Without QoS, VoIP calls are susceptible to various network issues like packet loss, jitter, latency, and congestion. Implementing QoS for VoIP helps address these issues by prioritizing voice traffic over other types of data traffic on the network.

Troubleshooting VoIP Call Quality with QoS

The best way to troubleshoot VoIP call quality issues is to address the root of the problem. Below are a few steps you can take to ensure high QoS.

  • Identify call quality issues: Common issues include choppy audio, dropped calls, echo, delays, and distorted sound. Gather feedback from users to understand the nature and frequency of the problems.
  • Analyze network performance: Use network monitoring tools to assess network performance. The information you gather will contextualize the overall health of the network and the areas that need improvement.
  • Configure QoS settings: Properly configure network devices to implement QoS. Prioritize VoIP traffic by prioritizing it over other types of data. 
  • Allocate the appropriate bandwidth: Allocate sufficient bandwidth for VoIP traffic to prevent congestion and ensure smooth voice transmission. Adjust bandwidth allocation based on the number of concurrent calls and the expected traffic load.
  • Prioritize packets: Ensure VoIP packets are marked with the appropriate QoS tags (e.g., Differentiated Services Code Point or DSCP) to ensure preferential treatment as they traverse the network.
  • Configure jitter buffer: Jitter buffers can temporarily store incoming voice packets and smooth out variations in packet arrival times.
  • Upgrade network infrastructure: If your network is outdated or experiencing frequent issues, consider upgrading to more capable networking equipment that can handle the demands of VoIP traffic.
  • Monitor and adjust: Continuously monitor network performance and VoIP call quality. Adjust QoS settings as needed based on real-time performance data and user feedback.
  • Check for external factors: Sometimes, call quality issues may be caused by factors beyond the internal network, such as the VoIP service provider, internet service provider (ISP) points, or problems on the other end of the call.

Recommended VoIP QoS Settings

Your specific VoIP QoS settings may vary depending on your network infrastructure, the number of users, the available bandwidth, and the VoIP application or service you use. However, these QoS settings are generally dependable:

  • DSCP Marking (Differentiated Services Code Point): Use this to mark VoIP traffic with the appropriate priority. The recommended DSCP value for VoIP traffic is AF31 (Assured Forwarding 31).
  • Priority Queuing: Implement priority queuing on your network devices (routers, switches) to experience lower delays in traffic and ensure higher priority in the transmission.
  • Jitter Buffer Size: Set the jitter buffer based on your network’s typical levels. A larger buffer can help smooth out variations in packet arrival times.
  • Bandwidth Allocation: Allocate a dedicated portion of your available bandwidth for VoIP traffic to ensure enough bandwidth through heavy data usage, preventing congestion and call quality degradation.
  • Traffic Shaping: Implement traffic shaping to regulate data flow and prevent sudden spikes in quality.
  • Call Admission Control (CAC): Use CAC to manage the number of simultaneous VoIP calls on the network. CAC prevents overloading the network with VoIP traffic, ensuring that call quality remains stable.
  • Packet Loss Concealment: Enable packet loss concealment mechanisms to mask the effects of lost packets, providing a smoother audio experience during packet loss events.
  • QoS for Voice Signaling: Apply SIP (Session Initiation Protocol) and RTP (Real-time Transport Protocol) to control messages. Prioritizing signaling traffic helps ensure smooth call setup and teardown processes.

Understanding Common Network Benchmarks

Understanding and measuring key network benchmarks is essential o ensure a well-performing and reliable network infrastructure. Below are a few standard network benchmarks you should know:

  • Latency: Often called ping time, latency measures how long data packets travel from source to destination. Lower latency indicates faster data transmission. 
  • Network jitter: This variation in packet delivery or inconsistency in the time it takes for packets to travel happens when networks become congested, or routes change. Excessive jitter can lead to packet loss and degraded call quality.
  • Packet loss: This occurs when data packets don’t reach their destination and can result from network congestion, faulty hardware, or other errors. On the receiver’s end, packet loss may sound like choppy audio or like frozen video.
  • Bandwidth: This refers to the maximum amount of data transmitted over the network in a given time, typically measured in bits per second (bps) or megabits per second (Mbps). Sufficient bandwidth allows for faster data transfer.
  • LAN and WAN: LAN (Local Area Network) and WAN (Wide Area Network) are two common types of networks. LAN covers a smaller geographic area, while WAN connects over multiple LAN distances. LAN is ideal for local communications and sharing resources, whereas WAN may experience higher latencies on public connections. 

How to Set Up VoIP QoS

Your VoIP QoS setup will vary depending on your chosen service provider and specific needs. However, a typical process looks like this:

  1. Assess your network: Consider current capabilities and potential bottlenecks. Determine the available bandwidth, analyze network traffic patterns, and identify areas where congestion or performance issues may occur.
  2. Enable QoS on network devices: Ensure your network devices support QoS and can handle QoS settings.
  3. Classify VoIP traffic: Protocols like SIP (Session Initiation Protocol) and RTP (Real-time Transport Protocol) create rules or policies to match VoIP traffic based on source/destination IP, port numbers, or DSCP markings.
  4. Apply DSCP markings to VoIP packets: DSCP markings allow network devices to recognize the priority of each packet, ensuring proper handling and prioritization during transmission.
  5. Set up priority queuing or traffic prioritization: This ensures that VoIP packets are processed and transmitted with minimal delay.
  6. Allocate sufficient bandwidth for VoIP traffic: Calculate the expected bandwidth requirements based on the number of concurrent VoIP calls and the codec used for voice compression.
  7. Configure jitter buffers on VoIP endpoints: Minimize the potential effects of network jitter.
  8. Enable error correction and concealment mechanisms: These mechanisms can help recover lost or corrupted packets or conceal the effects of packet loss, resulting in improved call quality.
  9. Thoroughly test the VoIP system: Ensure the call quality meets the desired standards. Use network monitoring tools to track network performance and identify any QoS-related issues.
  10. Monitor the network regularly and adjust QoS settings as needed: Periodically review QoS configurations and make optimizations to ensure optimal performance.

VoIP QoS Best Practices

There is no one correct way to establish VoIP QoS, but these best practices may help ensure a stable and high-quality connection:

  • Upgrade your internet speed: Ensure your network has enough bandwidth to handle call traffic, upgrading your connection if necessary.
  • Test connections regularly: You never know when you’ll run into a connectivity issue, so always review ping, jitter, and latency. 
  • Use wired Ethernet connections: If your WiFi experiences frequent disruptions, a Category 6-certified Ethernet cable lowers latency.
  • Switch providers: If troubleshooting doesn’t solve your latency issues, consider upgrading providers.

VoIP QoS Limitations

Despite its obvious benefits, VoIP QoS does pose some limitations, including the following:

  • It’s dependent on the Internet, which can impact call quality during peak usage hours.
  • Implementing end-to-end QoS can be challenging, especially when calls traverse multiple networks, including the public internet.
  • Sharing networks can cause data traffic.
  • While QoS can help mitigate the impact of jitter and packet loss to some extent, network conditions can vary over time.
  • Older or less sophisticated network devices may not fully support QoS features or have limited capabilities. 
  • Users may have to adjust QoS settings dynamically based on network conditions and traffic patterns. 
  • Setting up and managing QoS configurations can be complex and require specialized IT knowledge. 
  • When using VoIP services from third-party providers, you may have limited control over their QoS settings and infrastructure. 


Does QoS slow down the internet?

Correctly implemented QoS won’t slow down the Internet. Instead, QoS aims to improve the overall efficiency and fairness of the network by prioritizing critical traffic like VoIP and real-time applications while ensuring that other types of data still have sufficient bandwidth for their needs.

What are common causes of VoIP Quality of Service disruptions?

Common causes of VoIP QoS disruptions include congested networks, noise, and interference, WAN/LAN issues, packet loss, latency, jitter, and downtime.


Improving your VoIP QoS may seem like a pain, but it is necessary for business success. Without streamlined communications, you miss potentially lucrative opportunities with clients you couldn’t reach. 

Fortunately, ULTATEL’s reliable cloud business phone system can withstand heavy traffic and high usage. Plus, we’re always available to help you.

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