Quality of Service

Customers expect your application to be responsive and reliable, but how can you meet their demands when facing networking issues? Quality of service is the set of techniques that make smooth, consistent traffic flow possible.

What Is Quality of Service (QoS)?

Quality of service (QoS) is the practice of managing network traffic to ensure the most important data is delivered quickly, reliably, and without interruption.

Instead of treating all network traffic equally, it uses rules and priorities to guarantee better performance for critical applications.

It benefits real-time applications the most, like web conferencing solutions and online games. For example, during a video call, it prioritizes voice and video packets over less urgent data flows, such as file downloads.

How Does QoS Work?

Let's look at the underlying systems that make quality of service function.

Traffic Shaping

Traffic shaping smooths out sudden bursts of traffic to prevent network congestion.

Instead of dropping excess data, it delays transmission so that traffic conforms to a defined bandwidth profile.

Typically, traffic shaping is deployed on the network edge (routers, firewalls, or gateways) and relies on rate-limiting algorithms to regulate flow, such as token or leaky bucket. This is done to control how packets enter the network to maintain a predictable QoS.

Traffic Classification and Labeling

Traffic classification identifies and categorizes packets based on application type, protocol, or user. Labeling refers to marking and tagging these packets accordingly.

Together, classification and labeling enable consistent enforcement of QoS policies.

Once identified, packets are labeled using mechanisms like Differentiated Services Code Point (DSCP) or Class of Service (CoS). These labels signal to routers and switches how to handle ‌traffic along its path.

Scheduling Algorithms

Scheduling algorithms determine the sequence in which packets are transmitted. By controlling packet order, they directly influence how well policies achieve their performance goals, particularly in managing delay, jitter, and bandwidth allocation.

Priority queuing is often the scheduling algorithm of choice when implementing QoS. It allows time-sensitive data, such as voice or video streams, to take precedence over best-effort data, like file transfers.

Strict priority queuing can lead to bandwidth starvation for lower-priority flows. It's typically combined with rate-limiting or class-based policies to maintain fairness while still protecting important data transfers.

Traffic Policing

Traffic policing enforces network usage limits by monitoring the rate of incoming and outgoing data against predefined thresholds.

Unlike rate limiting or traffic shaping, which delay and smooth excess traffic through buffering, policing is strict and immediate.

When packet flow exceeds the allowed rate, it may drop the packets outright, forward them somewhere else, or remark them to a lower priority. This prevents bandwidth abuse and helps maintain fairness between competing services.

As part of QoS, policing protects critical applications from congestion caused by non-compliant or greedy traffic sources.

Resource Reservation

Resource reservation allocates network capacity for critical applications, guaranteeing performance levels.

It's often implemented through models like Integrated Services (IntServ), where protocols such as the Resource Reservation Protocol (RSVP) establish end-to-end guarantees before traffic flows.

Unlike best-effort delivery, resource reservation creates a predictable service level by isolating critical traffic from congestion. While powerful, it can be resource-intensive and is typically reserved for mission-critical services.

How Does QoS Work in a Modern Tech Stack?

Modern application stacks extend these principles beyond the network layer. 

Packet Marking and Cloud Equivalents

At the infrastructure level, packet marking with DSCP is still relevant. However, equivalent mechanisms are built into managed services.

For instance, cloud load balancers and API gateways often support network flow prioritization rules that function like QoS, ensuring latency-sensitive APIs are processed ahead of bulk and background traffic.

Application-Layer Prioritization 

At the application layer, you can apply these principles to prioritize message delivery and request handling. This is especially valuable when applications multiplex different types of traffic over the same connection.

For example, a real-time service using WebSockets might prioritize event notifications and chat messages over analytics, batch uploads, or background syncs.

Examples

Quality of service is especially valuable in scenarios where real-time or mission-critical traffic needs to be prioritized. Some common examples include:

• Video conferencing: During a live call, QoS ensures that audio and video packets are transmitted with priority over background tasks like file syncing, reducing lag and jitter.

• Online gaming: Competitive games use QoS to minimize latency and packet loss, delivering smoother gameplay even when network congestion occurs.

• Telehealth platforms: Virtual healthcare providers depend on QoS to guarantee reliable, real-time video consultations and the delivery of critical patient data.

• Financial transactions: In fintech, QoS prioritizes trades and payment requests to avoid costly delays during market fluctuations.

• Industrial IoT: Manufacturing systems use QoS to ensure emergency signals (like an automated shutdown command) take precedence over routine sensor data.

Key Metrics To Track

Some key metrics reveal how traffic behaves and whether critical applications are receiving their required network resources. Let's see how they relate to QoS.

Bandwidth

Bandwidth is the total data capacity available in a network, covering both uploads and downloads. Tracking bandwidth usage helps determine if applications have sufficient throughput or if competing traffic is saturating resources.

Latency

Latency measures the time it takes for data to travel from source to destination. Keeping latency low is critical for interactive services, such as video conferencing, gaming, or telehealth sessions.

Packet Loss

Packet loss occurs when data packets fail to reach their destination. Even small amounts can degrade user experience, causing frozen video frames, missing words in calls, or interruptions in real-time apps.

Jitter

Jitter is the variation in packet arrival times. Excessive jitter disrupts the smooth flow of data, often leading to choppy audio, lagging video, or distorted visuals in latency-sensitive traffic.

What Are the Benefits of QoS?

Delivers Consistent UX

Consistent performance keeps users from leaving out of frustration, reducing churn and safeguarding revenue.

It also gives them the best possible performance across devices and varying network quality. While it can't overcome extreme bandwidth limits, it helps maintain stability and reduce disruption so interactions remain as smooth as their network allows.

Strengthens Brand Image

Platforms that reliably deliver smooth, high-quality interactions also garner a better reputation than the competition, which attracts new customers and enables business growth.

If you're launching a new online game, it can prevent the networking issues that drive bad reviews, protecting your image and potential revenue.

Enables Real-Time and Critical Services

QoS supports real-time communication, ensuring calls, file sharing, and chat remain responsive even under heavy network load. This reduces inefficiencies and keeps teams operating smoothly, whether it's internally at your organization or externally on your app.

It's also essential for mission-critical applications, enabling real-time computing in fintech, industrial, and healthcare industries. For instance, traffic policing can drop unnecessary sensor readings to guarantee the speedy delivery of an emergency shutoff command in a car manufacturing plant.

Best Practices for Implementing QoS

Effective quality of service comes down to setting the right priorities, monitoring them closely, and adjusting as needs evolve.

Set Priorities by Value

QoS rules should reflect what matters most both to the user and the business. Here are some ways to set priorities by value:

• Map traffic to business goals: Identify what applications and services affect revenue, compliance, and reliability for your business the most.

• Distinguish time sensitivity: Give precedence to traffic that's highly sensitive to latency and jitter (like live communication) over batch or background processes.

• Consider user impact: Rank services based on how performance issues would affect end-user satisfaction and retention.

• Reevaluate regularly: Update priorities as business models, user behavior, or application features evolve.

For example, a telehealth company should prioritize live video consultations over background data syncs.

Monitor in Real Time

Active monitoring lets developers fix problems during changing conditions. More advanced monitoring can also identify trends in user traffic to predict which tasks require a higher priority ahead of time.

Monitoring provides the necessary data that automated systems use to adjust priority values dynamically, without manual intervention.

Test Under Load

Load testing exposes how rules behave when networks are pushed to their limits. It helps uncover problems like starvation for lower-priority tasks and overly strict policing.

For instance, an edtech platform can prepare for its launch by simulating the peak usage at the start of a new semester when thousands of students register for classes. This highlights weaknesses that could seriously impact UX and reputation.

Frequently Asked Questions