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QoS is a set of techniques and mechanisms used to manage and prioritize network traffic to ensure that critical applications and services receive the necessary bandwidth, speed, and reliability. QoS focuses on both performance and availability to guarantee an optimal user experience.

What problems does QoS address?

QoS addresses several common problems that can hinder network performance and impact the user experience. These include:

Latency refers to the delay or lag experienced when data packets travel across a network.  High levels of latency can negatively impact real-time applications and services and cause delays in interactions and communication.  QoS uses various techniques to minimize latency, such as prioritizing time-sensitive traffic and allocating sufficient bandwidth to critical applications.  Reducing latency ensures that data travels quickly across the network, facilitating real-time communication and enhancing the user experience.

Jitter is another problem addressed by QoS.  Jitter is the variation in the delay of packet delivery.  It can disrupt the smooth flow of data causing inconsistent performance, especially in time-sensitive applications such as voice and video transmission.  QoS addresses jitter by prioritizing packets and managing network resources to ensure a stable and predictable delivery of data packets. By mitigating jitter, QoS maintains the integrity of time-sensitive applications and guarantees consistent performance.

Packet Loss also impacts user experience. Packet loss occurs when data packets fail to reach their intended destination, resulting in gaps in the transmission. It can occur due to network congestion, errors, or insufficient bandwidth. QoS implements mechanisms to minimize packet loss by prioritizing critical traffic, utilizing error correction techniques, and allocating sufficient resources to handle network congestion. By reducing packet loss, QoS ensures reliable and uninterrupted data transmission, enhancing the overall quality of network services. Through packet analysis, network administrators can assess the impact of QoS mechanisms and fine-tune them for better performance.

Although Latency, Jitter, and Packet Loss are the biggest challenges addressed by QoS, there are additional issues mitigated by QoS:

  • Bandwidth Contention: In networks with limited bandwidth, different applications and services may compete for resources, leading to congestion and degraded performance. QoS allows network administrators to prioritize critical applications, ensuring they receive the necessary bandwidth and minimizing the impact of bandwidth contention. By allocating resources effectively, QoS helps prevent bottlenecks and maintains optimal network performance.
  • Network Congestion: When the volume of network traffic exceeds the available capacity, congestion occurs. QoS techniques help manage network congestion by implementing mechanisms such as traffic prioritization, queuing, and shaping. By controlling the flow of packets and allocating resources based on priorities, QoS minimizes the impact of congestion and ensures consistent network performance.
  • Service Differentiation: Not all applications or services have the same requirements in terms of network performance and reliability. Some applications, such as real-time communication or video streaming, require low latency and minimal packet loss for optimal user experience. QoS enables service differentiation by assigning appropriate priority levels to different types of traffic. This ensures that critical applications receive the necessary resources, while less time-sensitive traffic is allocated accordingly.
  • Network Security: QoS can also play a role in enhancing network security. By implementing QoS policies, network administrators can prioritize traffic related to security measures, such as firewall rules or intrusion detection systems. This ensures that security-related packets are given priority treatment, allowing for more effective security measures and timely response to threats.
  • Resource Optimization: QoS helps organizations optimize the utilization of network resources. By implementing appropriate QoS mechanisms, organizations can ensure that critical applications receive the required resources while non-critical traffic is limited or given lower priority. This efficient allocation of resources maximizes the overall performance and capacity of the network.
Image by Mohamed Hassan, courtesy of Pixabay

Why Is QoS Important?

In today’s highly connected world, where networks carry an array of data and services, ensuring reliable and efficient network performance is crucial. By controlling network traffic, QoS enables organizations to allocate resources efficiently, reduce latency, minimize packet loss, and enhance overall network performance.

QoS is particularly essential for networks that handle resource-intensive systems and services. Various applications and services, such as internet protocol television (IPTV), online gaming, streaming media, videoconferencing, video on demand (VOD), and Voice over IP (VoIP), demand consistent and reliable network performance to deliver high-quality user experiences.

How to Implement QoS

Implementing QoS involves a series of steps to ensure efficient resource allocation and optimal network performance. The process generally includes preparation, designing, testing, implementing, and monitoring of QoS settings and policies. Details of each step are explained below:

  1. Prepare
    In the preparation phase, organizations should gain a comprehensive understanding of each department’s service needs and requirements. This involves identifying critical applications, services, or devices that require priority access to network resources. Organizations should also choose a suitable QoS model based on their specific needs and cultivate buy-in from stakeholders. By considering the diverse requirements of different departments, organizations can tailor their QoS implementation to prioritize critical services effectively.
  2. Design
    In the design phase, organizations must consider any significant software and hardware changes within their network architecture. They should apply the chosen QoS model to the specific network infrastructure, ensuring that critical applications receive the necessary resources and bandwidth. By carefully designing QoS parameters, organizations can optimize network performance and allocate resources efficiently.
  3. Test
    The testing phase is crucial to ensure the effectiveness and stability of QoS settings and policies. Organizations should conduct tests in a controlled environment, simulating different network scenarios and traffic conditions. This allows them to identify any potential issues, fine-tune QoS configurations, and address any bugs or conflicts that may arise. Thorough testing helps organizations validate their QoS implementation and ensures optimal performance before deployment.
  4. Implementation
    In the implementation phase, organizations should roll out QoS policies in a phased manner. They may choose to implement policies by network segment or focus on specific QoS functions. This incremental approach allows organizations to monitor the impact of QoS on different parts of the network and address any issues that arise during deployment. By implementing QoS gradually, organizations can minimize disruptions and optimize network performance.
  5. Monitor
    Once QoS policies are deployed, ongoing monitoring is essential to evaluate performance and adjust as necessary. Organizations need to gather performance data and analyze it regularly to identify areas for improvement. By monitoring network performance metrics and user experiences, organizations can fine-tune QoS parameters, optimize resource allocation, and ensure consistent and reliable network operations.

QoS Key Concepts

Class of Service (CoS) and Differentiated Services Code Point (DSCP) are two key concepts related to Quality of Service (QoS). They are used to classify and prioritize network traffic, enabling effective QoS implementation.

Class of Service (CoS): CoS is a method for categorizing and prioritizing network traffic based on specific characteristics or requirements. It is often used in local area networks (LANs) and is primarily associated with Layer 2 switching technologies, such as Ethernet. CoS uses priority levels or classes to distinguish traffic types and assign them to appropriate queues or buffers for transmission.

CoS employs a 3-bit field in the Ethernet frame header, known as the CoS field or the 802.1p priority field. This field allows for eight different classes (0-7), with 0 being the lowest priority and 7 being the highest. Network devices, such as switches, use CoS to determine the order in which packets are transmitted or processed, giving higher priority to more critical traffic.

Differentiated Services Code Point (DSCP): DSCP is a field within the IP header of network packets that enables finer-grained differentiation and prioritization of network traffic. It is used in IP networks and is associated with Layer 3 quality of service. DSCP expands on the capabilities provided by CoS, allowing for more granular classification and prioritization of traffic based on service levels.

The DSCP field is a 6-bit field within the IP header’s differentiated services field (DS field). It allows for 64 different code points, which represent specific traffic classes or behaviors. These code points are assigned based on the requirements and characteristics of the applications or services generating network traffic.

Network devices, such as routers, use the DSCP field to classify packets and determine how they should be treated in terms of forwarding and QoS treatment. By examining the DSCP value, routers can prioritize or handle traffic differently, ensuring that critical applications receive the necessary resources and network conditions.

CoS and DSCP are often used together to provide end-to-end QoS across networks. CoS is commonly used within LANs, where switches use the CoS field to prioritize traffic. When traffic crosses different networks or domains, the DSCP field in IP headers can carry the CoS information or be mapped to specific DSCP values to ensure consistent QoS treatment across the network.

By leveraging CoS and DSCP, organizations can classify and prioritize traffic effectively, ensuring that critical applications receive the appropriate treatment and resources to maintain optimal network performance and deliver a satisfactory user experience.

 Quality of Service Techniques

QoS encompasses various techniques to manage network traffic effectively. Examples are as follows:

  • Classification and Marking
    Classification and marking involve identifying and categorizing network traffic based on specific criteria, such as application type, source, destination, or service level agreements (SLAs). Once classified, packets are marked with appropriate priority levels or differentiated services code points (DSCPs). This allows routers and switches to prioritize traffic based on its importance or the requirements of the applications or services.
  • Congestion Management
    Congestion management techniques aim to prevent network congestion and ensure fair allocation of bandwidth among competing flows. These techniques use algorithms and queuing mechanisms to prioritize and manage traffic during periods of high network utilization. By regulating the flow of packets, congestion management techniques help maintain consistent network performance and prevent bottlenecks.
  • Congestion Avoidance
    Congestion avoidance techniques work proactively to prevent network congestion from occurring. These techniques use feedback mechanisms to monitor network conditions and adjust the transmission rate accordingly. By detecting signs of impending congestion, such as increased packet drops or queuing delays, congestion avoidance mechanisms regulate the flow of traffic to maintain optimal network performance.
  • Shaping
    Shaping involves regulating the rate of outgoing traffic to match the capacity of the network or the receiving device. This technique is particularly useful when network resources are limited or when traffic needs to conform to specific bandwidth constraints. By controlling the rate at which packets are sent, shaping helps prevent network congestion and ensures smooth data transmission.

Quality of Service Best Practices

Implementing QoS effectively involves considering some best practices:

  • Regular monitoring and optimization: Continuously monitor network performance, collect data, and analyze it to identify areas for improvement. Adjust QoS settings as needed to optimize resource allocation and maintain consistent network operations.
  • Stay up to date: Keep abreast of new QoS technologies, standards, and best practices. Regularly update QoS policies and configurations to align with evolving network requirements and emerging technologies.

 What Tools Are Used for QoS?

Various tools and technologies are available for implementing and managing QoS. These include network monitoring  and management systems, traffic shaping and prioritization tools, quality measurement tools, and network devices with built-in QoS capabilities. Service providers and network administrators can leverage these tools to effectively control and optimize network traffic.

What Are the Three Main QoS Models?

A: The three main QoS models are Best Effort, Integrated Services (IntServ), and Differentiated Services (DiffServ).

  • Best Effort: In the Best Effort model, all network traffic is treated equally, with no prioritization or guarantees of service. It is commonly used in public internet connections where no specific QoS requirements exist.
  • Integrated Services (IntServ): IntServ provides individualized and predictable QoS for specific network flows. It requires resource reservation and signaling protocols to allocate network resources dynamically. IntServ is suitable for applications that require strict QoS guarantees, such as real-time voice or video conferencing.
  • Differentiated Services (DiffServ): DiffServ is a scalable and flexible QoS model that classifies and prioritizes traffic based on predefined service levels or DSCPs. It assigns different forwarding behaviors to different traffic classes, allowing network devices to prioritize traffic based on its importance. DiffServ is widely used in large networks and enables efficient resource allocation.

How Do You Measure QoS?

There are two styles of measuring the quality of service to optimize network traffic: passive multi-point measurement and active multi-point measurement.

Passive Multi-point Measurement: This method involves capturing and analyzing network traffic passively using specialized tools or network monitoring systems. It provides insights into network performance, identifies bottlenecks, and detects anomalies or issues affecting QoS.

Active Multi-point Measurement: In active measurement, synthetic traffic or test packets are generated and sent across the network to measure performance metrics such as latency, packet loss, and jitter. This approach allows organizations to proactively assess QoS and identify areas for improvement.

Both measurement styles provide valuable data for network administrators to evaluate QoS performance, diagnose problems, and optimize network configurations.

In Conclusion

QoS is a valuable combination of tools and techniques used to manage and prioritize network traffic so the user experience is optimized, and critical applications and services have the speed, reliability, and bandwidth needed for optimal network performance. For that reason, it is important that the network performance management system you choose allows you the QoS control you need to easily view, manage, and support the traffic your enterprise relies upon day in and day out.

LiveAction’s LiveNX network management platform lets you view and control application performance through a graphical QoS management interface.  This intuitive interface lets you configure and manage QoS to ensure the performance of VoIP, video, and other application traffic to ensure a high-quality user experience and reduce overall network latency while helping to secure the network.


— by Susan Short. Susan is Director of Product Marketing for LiveAction.