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Quality of Service (QoS) in Networking

Author : PyNet Labs
Last Modified: June 12, 2024 
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Enterprise networks must offer dependable and quantifiable services to enable the transmission of delay-sensitive data, voice, and video. In today’s interconnected world, where various applications, such as video streaming, voice-over-IP (VoIP) calls, online gaming, and cloud services, coexist on the same network infrastructure, it becomes essential to prioritize certain types of data packets over others. QoS mechanisms allow network administrators to assign different levels of importance to various types of traffic, ensuring that critical data receives preferential treatment and is delivered promptly.

So, QoS in networking is employed by enterprises to fulfill the traffic demands of sensitive applications, such as real-time voice and video, and to stop the quality from degrading as a result of packet loss, delay, and jitter. Throughout this article, we will explore various QoS techniques, protocols, and algorithms that enable efficient traffic management.

By understanding the principles and practices of QoS in networking, network administrators and engineers can effectively design and configure networks that can deliver the desired level of performance, prioritize critical applications, and provide a seamless user experience.

What is QoS in networking?

QoS in networking stands for Quality of Service. QoS is managing network traffic based on priority. It is exclusively applied to network traffic generated for video on demand, VOIP, Streaming media, Video conferencing, online gaming, etc.

In short, QoS is the mechanism or technology used in networking that work to control traffic and ensures the performance of critical applications with limited network capacity. It allows network devices to adjust the overall network traffic by prioritizing them.

Do you know how Quality of Service works? If not, the next section is perfect for you.

Types of Network Traffic and its requirements

To have QoS in networking, a user must understand the different types of traffic in the network. So that priority can be assigned as per different network traffic.

Here are some of the issues that occurs in a network and how these traffics are measured by QoS is listed below –

  1. Dropped Packets

Some routers will drop packets if they receive a packet while their buffer is full. If the receiving application is waiting for the packets but doesn’t get them, it will usually request that the packets be transmitted. The amount of data loss occurs due to network congestion.

QoS enables organizations to decide which packets to drop in this event, and the least packets are dropped in this event. For internet access, file sharing, and electronic mail, Reliability becomes more crucial.

  1. Delay

The transmission delay between the source and destination is another flow feature. There should be a minimum amount of delay when using telephony, audio conferencing, video conferencing, and remote conferencing.

When real-time applications are used in the network, the best reason to implement QoS is to prioritize delay-sensitive traffic. So, QoS creates queues by prioritizing certain traffic to avoid delay.

  1. Jitter

Basically, it is the difference in the delay for packets belonging to the same flow. Jitter is, therefore, essentially a variance in packet delay. A higher jitter value indicates a longer delay, and a lower jitter value indicates a smaller variation.

The varying speed of packets on the network means packets arrive late and out of sequence. This can cause a gap in audio/video being delivered.

  1. Bandwidth

Bandwidth is nothing but the speed of a link. Different applications need different bandwidths, so we can split bandwidth for different traffic by configuring QoS on the router, for example, assigning 40% of the bandwidth for video conferencing, 20% for audio, 15% for FTP traffic etc.

How does Quality of Service work?

QoS works by identifying traffic to assign priority and then configuring it on the router with some marking so that router will send packets or traffic as per priority. 

Instead of using the traditional traffic forwarding method, i.e., FIFO (First In, First Out), the router can forward traffic as per priority. So that instead of making one large queue, it can be divided into small queues as per classification of traffic. 

Quality of Service (QoS) operates through several key mechanisms.

  • First, traffic classification categorizes packets based on their characteristics like application type or content. This allows administrators to differentiate between traffic types
  • Next, traffic prioritization assigns priority levels or classes to each type, ensuring critical applications receive preferential treatment.
  • Queuing and scheduling algorithms manage packet transmission order, giving higher priority packets precedence.
  • Bandwidth management controls resource distribution, preventing a single application from monopolizing network capacity.
  • Lastly, congestion control techniques like traffic shaping and policing regulate network traffic to avoid congestion and maintain performance.

By employing these mechanisms, QoS optimizes network performance and user experience. Let’s discuss these mechanisms in detail.

Quality of Service (QoS) Mechanisms

1 – Classification and Marking

Let’s discuss both one by one.

  • Classification

The process of categorizing the type of IP packets or traffic is referred to as QoS classification. Data, video, and voice traffic are all possible traffic types. Traffic categories are split into classes according to how similar they are.

  • Marking

In order to allow other devices’ QoS tools to categorize traffic based on the marked values, QoS Marking entails setting specific bits inside a data link or network layer header. This is done after IP packet headers are classified based on their contents.

There are various layers at which marking can be applied, including layer 2 for Ethernet headers, layer 2.5 for MPLS labels, layer 3 for IP packet headers, Network-Based Application Recognition (NBAR), and deep packet inspection (layer 7).

2 – Policing, Shaping

Policies and shapers are two tools that identify and respond to traffic problems and are both rate limiters. Policers and shapers identify traffic violations similarly, but they differ in their responses: –

  • Policers

Policers make instant decisions if we want to deploy them on the ingress if possible. When traffic exceeds, policers don’t delay it, which means they do not introduce jitter or delay; they just check the traffic and can drop or re-mark it. It means there’s a higher drop probability.

  • Shapers

They are usually deployed between an enterprise network, on the egress side, and the service provider network to ensure you stay within the carriers’ contract rate. If the traffic does exceed the rate, it will be buffered and not dropped directly.

3 – Tools for Managing Congestion

When congestion occurs, the congestion management tools are activated, which are of two types:

  • Queuing

It is the logic of ordering packets in output buffers. It is activated only when congestion occurs. When queues fill up, packets can be recorded so that higher-priority packets can be sent out of the exit interface.

  • Scheduling

This is the process of determining which packet should be sent out next, and it occurs whether or not the link is congested.

Why is QoS in Networking Important?

QoS (Quality of Service) is important for several reasons –

  • QoS in networking optimizes performance for critical applications, minimizing latency and packet loss.
  • It efficiently manages and allocates limited network resources, preventing resource exhaustion and ensuring fair distribution.
  • It helps service providers meet performance guarantees outlined in SLAs, enhancing customer satisfaction.
  • QoS enables differentiated treatment of traffic, prioritizing critical applications over less time-critical traffic. Thus, helping businesses.
  • It also contributes to network stability and reliability by managing congestion, minimizing packet loss, and maintaining consistent performance levels.

In summary, QoS is important because it optimizes performance, manages resources effectively, meets service level agreements, enables differentiated treatment of traffic, and contributes to network stability and reliability.

QoS Use Cases

Some of the use cases of QoS in Networking are –

  • It ensures that critical traffic is given higher priority or restricted to non-critical traffic by managing application and network traffic.
  • In a network, QoS helps to achieve equal bandwidth transfer between different classes, subnets or users.
  • It can be used to determine bandwidth usage by traffic profiling of applications.
  • In an enterprise, QoS can be used to determine revenue-generating traffic and low latency for customers.
  • QoS can be used to allocate bandwidth internally or externally, or both. It can also be used for uploading and downloading traffic.

How to implement Quality of Service (QoS) in Networking?

Implementing QoS (Quality of Service) in networking involves several key steps:

  1. Traffic Classification: Begin by identifying and classifying different types of network traffic based on their characteristics, such as application type, protocol, or content. This classification forms the basis for applying specific QoS policies.
  2. Determine QoS Policies: Define the QoS policies based on the requirements of different traffic types. Specify parameters such as priority levels, bandwidth allocations, and delay limits for each traffic class.
  3. Configure Network Devices: Configure network devices, such as routers and switches, to support QoS. This includes enabling QoS features and assigning appropriate QoS policies to specific interfaces or ports.
  4. QoS Mechanisms: Select and configure QoS mechanisms that align with your network requirements. Common QoS mechanisms include traffic shaping, traffic policing, queuing algorithms, and link efficiency techniques.
  5. Traffic Prioritization: Assign appropriate priority levels to different traffic types based on their importance and performance requirements. Ensure that critical traffic, such as voice or video, receives higher priority over less time-sensitive traffic.
  6. Traffic Queuing and Scheduling: Configure queuing algorithms and scheduling mechanisms to manage the order of packet transmission. This ensures that higher priority packets are serviced first and prevents lower priority traffic from experiencing starvation.
  7. Bandwidth Allocation: Allocate and manage available bandwidth to ensure that critical traffic receives the necessary resources. This may involve reserving a portion of bandwidth for specific traffic types or implementing bandwidth guarantees.
  8. Congestion Control: Implement congestion control mechanisms to prevent network congestion and mitigate its impact on QoS. This can involve traffic shaping to smooth out bursts, traffic policing to enforce rate limits, or implementing mechanisms like Random Early Detection (RED) to control congestion at network bottlenecks.
  9. Monitoring and Optimization: Continuously monitor network performance, traffic patterns, and QoS metrics to identify areas for improvement. Make necessary adjustments to QoS policies and mechanisms to optimize network performance and meet changing requirements.
  10. Testing and Validation: Conduct thorough testing and validation of the implemented QoS configuration to ensure that it operates as intended. Test scenarios involving different traffic types and network conditions to verify the effectiveness of the QoS implementation.

Implementing QoS in networking requires careful planning, configuration, and ongoing monitoring to ensure the desired performance levels and resource allocations. It is recommended to consult network documentation, vendor-specific guidelines, and industry best practices when implementing QoS in a specific networking environment.

Quality of Service Best Practices

  • Always conduct a network assessment. It is crucial because it informs the creation of QoS regulations by revealing network conditions, including any issues that might affect deployment.
  • Select the network traffic types that should be given top priority. Think carefully about what matters most to your company’s success.
  • Classify all data flows that are susceptible to delay, such as audio and video.
  • Do not forget to include executives from the business, not just network managers. It will be evident to leadership which apps are really important.
  • For non-essential data flows, don’t employ QoS. This lessens bandwidth restrictions without requiring QoS intervention.
  • Assign a class to every application.
  • Avoid configuring too many QoS classes. It is not necessary to create QoS policies for each and every kind of data flow. The easier it will be to deploy and maintain, the fewer classes there are.
  • Make sure that QoS class identifiers are applied to network traffic as close to the source network devices as feasible.
  • QoS is not a project that should be set and forgotten. It is a cyclical, ongoing process that needs ongoing oversight and auditing.
  • It is dynamic so changes as needed are equally important as observing.

Application of Quality of Service

Below, we have discussed some of the key applications of QoS.

  • Real-time Communication: With the help of QoS, high-quality voice as well as video communications are possible. It prioritizes traffic and allocates sufficient bandwidth in order to ensure low latency and jitter.
  • Mission-Critical Applications: It supports critical applications such as online trading, financial transactions, and healthcare systems. In such cases, network downtime or errors can have severe consequences.
  • Cloud Computing: With QoS, it is possible for reliable and efficient cloud computing by means of prioritizing traffic and allocating resources to critical applications.
  • Online Gaming: It assists in prioritizing gaming traffic in order to minimize latency, jitter, and packet loss. It offers a responsive and immersive gaming experience to the users.
  • Internet of Things (IoT): It manages IoT traffic that ensures efficient communication between devices and side-by-side optimizes network resources.
  • Network Congestion Management: QoS assists in mitigating network congestion by prioritizing critical traffic and limiting non-essential traffic. This will ensure the network reliability.

Advantages of Quality of Service (QoS)

Here are the advantages of Quality of Service (QoS) –

  • Enhanced user experience through reduced latency and consistent performance.
  • Efficient allocation of network resources, preventing resource monopolization.
  • Customization to meet the specific requirements of different applications.
  • Meeting Service Level Agreements (SLAs) and ensuring consistent service quality.
  • Effective traffic management, congestion control, and avoidance of packet loss.
  • Prioritization of critical applications for improved performance and reliability.
  • Flexibility and scalability to adapt to changing network conditions and demands.

Disadvantages of Quality of Service (QoS)

Here are some of the disadvantages associated with QoS –

  • Increased complexity in network configuration and management.
  • Additional overhead in terms of processing power and network resources.
  • Scalability challenges as network traffic volume increases.
  • Introduction of additional network overhead due to signaling and packet marking.

While these disadvantages exist, proper planning and implementation can help mitigate their impact and ensure effective use of QoS in networking.

Frequently Asked Questions

Q1 – What is QoS in networking?

QoS in networking refers to the set of techniques and mechanisms used to manage and control network traffic, ensuring that different types of data packets receive the necessary resources and treatment to meet specific performance requirements.

Q2 – Which layer is QoS in networking?

QoS (Quality of Service) in networking is typically implemented at the network layer (Layer 3), specifically within the IP (Internet Protocol) layer. However, QoS mechanisms and techniques can also be applied at other layers, such as the transport layer (e.g., TCP or UDP protocols) and the application layer (e.g., application-specific QoS settings).

Q3 – When should QoS be used?

QoS (Quality of Service) should be used when there is a need to prioritize or manage different types of network traffic based on their specific requirements. It is particularly beneficial in situations where there is limited network bandwidth, congestion-prone environments, or when certain applications require consistent performance and low latency.

Q4 – What are QoS parameters?

QoS (Quality of Service) parameters are the specific metrics or settings used to control and manage network traffic. These parameters define how different types of traffic should be treated and prioritize resources allocation. Common QoS parameters include bandwidth, latency, packet loss, jitter, queuing algorithms, traffic shaping, and policing mechanisms


Quality of service, or QoS in Networking, is a crucial concept to keep in mind as networking and connection grow more pervasive. It serves as a performance indicator for enterprise SLAs and regulates how network and cloud companies apply their products. Additionally, QoS solutions are crucial in connected environments such as smart campuses, smart cities, and smart homes because they guarantee proper routing and prioritization of application traffic.

If you want a better understanding of QoS in Networking, you can join our CCNA training program, where you will learn the basics of QoS. To know more, you can visit PyNet Labs’ CCNA training.

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