PyNet Labs- Network Automation Specialists

QoS in Networking

Last Updated : September 16, 2022
qos in networking

Enterprise networks must offer dependable and quantifiable services to enable the transmission of delay-sensitive data, voice, and video.

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.

What is QoS in networking?

QoS 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 QoS work? If not, the next section is perfect for you.

How does QoS 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., FIFA (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. 

Types of Network Traffic and its requirements

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

Different types of traffic have different requirements. These are as follows:

  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.

QoS can be implemented using some mechanism to avoid delay, jitter, and drop of packets. Here are some of the QoS mechanisms used.

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).

  1. 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.

  1. 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.

Quality of service, or QoS, 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.

We hope you have a better understanding of QoS now. If you have any suggestions/complaints, you can leave a comment in the comment box below.

Topics you would find interesting

INTRODUCTION to Network Protocols 
What is Versa SD-WAN Certification?
EIGRP Interview Questions
What is IPv6?

If you want a better understanding of QoS, 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 page.

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