What is Quality of Service (QoS)?

September 1, 2020

Quality of Service (QoS) Improve Application Performance?

Quality of service (QoS) is a qualitative measurement of the overall performance of services like telephony, computer networks, and cloud computing. QoS may also refer to the set of technologies and strategies that organizations deploy, aimed at optimizing network traffic in order to improve the user experience of their apps. QoS approaches are commonly applied to real-time applications, such as VoIP, video-on-demand, streaming video or online gaming where transmission quality is at a premium.

How do you measure QoS?

Quality of Service (QoS) monitors four key measurements:

  1. Bandwidth or throughput—Bandwidth is the measure of the theoretical amount of data that can be sent, whereas throughput is the actual amount of data sent and received.
  2. Latency or delay—Latency measures the overall time it takes for data or a request to be sent and received.
  3. Jitter or variance in latency—This is the average of the variance of delays between data packets in a transmission.
  4. Error rate—Signifies the degree of errors in a transmission, this is closely associated with packet loss.

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

Passive Multi-point Measurement—This method begins by connecting QoS agents to the network along the path to be tested. In transmissions these packets are analyzed by the QoS agents, and then sent along a separate measurement connection than real-time network traffic. Measurement flows are matched using IP address, protocols, and ports, while packet time-stamps are collected and analyzed to determine delay.

Passive measurements have a great hindrance, because the packets travel along a separate measurement connecting, it is not measuring real-time traffic. Additionally, if along the route, Network Address Translation (NAT), which obscures packet routing information, is deployed network flows cannot be matched, and therefore cannot be measured.

Active Multi-point Measurement—More intrusive than passive methods, active multi-point measurement methods place QoS agents on the real-time network path being tested. Probe packets are sent across the network path through serially installed QoS agents, and because of this active measurement methods can be performed even if NAT is being used.

Application Performance and Quality of Service (QoS)

Quality of service attempts to measure, maintain, improve, and guarantee in advance transmission performance. By installing and configuring QoS devices on a network and measuring the common characteristics of that network’s traffic, insights about the weak points in the network can be addressed.

In continuous transmission and high bandwidth cases, such as real-time communications or streaming video, these services cannot simply live by a best-effort delivery policy. Therefore, to ensure quality service, these networks deploy QoS methods, rules and device to ensure a steady, low-latency experience.

Related Terms

Network Latency

Network latency is the duration of time it takes a data packet to travel from its source to its destination across a network. In terms of user experience, network latency translates to how fast a user’s action produces a response from a network, say how quick a web page accesses and loads over the internet, or the responsiveness of an online game to the gamer’s commands.

Network Jitter

Network jitter, a.k.a. packet delay variation (PDV), is a stuttering like effect in signal quality because of inconsistent packet delays in a data transmission. Each packet in the transmission may be routed differently to its destination causing packets to arrive out of order or not at all (called packet loss). Though technology will handle this situation and put the packets back in order, it does cause delays. To illustrate the impact, in cases of high jitter video calls or VoIP, users will experience stuttering video, intermittent voice or dropped calls when speaking to others over the internet.

Packet Loss

Packet loss is the occurrence of missing data packets in a network transmission resulting in an incomplete transmission, which is dire enough can noticeably degrade real-time transmissions. Incomplete file transmissions typically trigger a recall of missing data packets, which can be noticed, for example, when web pages load slowly. In real-time video and voice, packets typically are not recalled if they are not available when it is time for their playback (known as deadline expiry), this is what gives weak real-time transmissions their “stuttering” characteristic.

MOS Score

The mean opinion score (MOS) measures the quality of experience of real-time telecommunications such as video, audio, and audiovisual applications.