Which two scenarios... quality of service (QoS) to the network?

Which two scenarios would benefit the user the most by adding quality of service (QoS) to the network? (Choose two.)

A student is communicating via Skype with a friend in another country.
Students are updating information about their sport activities on the class Facebook page.
A student is sending emails to a friend.
Students are watching a lecture from a YouTube site.

The two scenarios that would benefit the most from adding Quality of Service (QoS) to the network are:

A student is communicating via Skype with a friend in another country.
Students are watching a lecture from a YouTube site.

These scenarios are more dependent on consistent, reliable, and high-quality network performance compared to the other options. To understand why these scenarios benefit more from QoS, we need to delve deeper into how QoS works, the nature of the network traffic in these scenarios, and why these specific activities would see the greatest improvement.

What is QoS?

QoS (Quality of Service) is a networking technology that manages bandwidth and prioritizes certain types of network traffic over others. It helps improve performance for applications that are sensitive to delays, jitter, and packet loss, which can severely affect user experience.

For instance, real-time applications like voice and video communications (e.g., Skype, YouTube) require low latency, minimal jitter, and minimal packet loss. These applications can benefit greatly from QoS because QoS ensures that the necessary bandwidth is allocated to these services and that their traffic is prioritized over less time-sensitive applications, such as email or browsing Facebook pages.

Scenario 1: A Student is Communicating via Skype

Skype, or any other Voice over IP (VoIP) application, depends on real-time voice and video communication. Any delay, packet loss, or jitter will significantly degrade the quality of the call. This results in poor audio quality, video freezing, or delays between when one person speaks and the other hears it. Let’s break down the key issues that can occur without QoS:

Latency: If packets (small units of data sent over the network) take too long to reach their destination, the conversation will have noticeable delays. A delay longer than 150 milliseconds is generally considered detrimental to a natural conversation.
Jitter: Jitter refers to variations in packet arrival times. In real-time communications, a consistent stream of packets is essential. If packet timing varies, it can lead to choppy audio or video, disrupting the conversation.
Packet Loss: If packets are lost during transmission (which can happen if the network is congested or experiencing interference), parts of the conversation will not be heard or seen, resulting in incomplete or garbled communication.

By applying QoS to prioritize Skype traffic, these issues can be mitigated. The network can ensure that Skype packets are transmitted first, reducing the chances of latency, jitter, or packet loss affecting the call. Without QoS, Skype might have to compete with less time-sensitive traffic (like file downloads or web browsing), resulting in a poor communication experience.

Scenario 2: Students Watching a Lecture from a YouTube Site

Streaming a video from YouTube is another activity that greatly benefits from QoS. Like Skype, YouTube requires a continuous and reliable flow of data. Although YouTube videos are typically buffered to help reduce the impact of short-term network issues, the quality of the video can still degrade without QoS, particularly in environments with high network traffic.

Buffering: In environments without QoS, when there is a network bottleneck, YouTube will pause and buffer, resulting in interruptions in the video stream. This is especially frustrating for students trying to watch a live or time-sensitive lecture.
Video Quality Reduction: To adapt to poor network conditions, YouTube automatically lowers the quality of the video stream (i.e., from 1080p to 480p or even lower). This can lead to a suboptimal viewing experience, particularly when detailed visuals, such as diagrams or text on slides, are essential to understanding the lecture content.
Delay in Streaming: Similar to Skype, YouTube streaming is also susceptible to delays due to latency and packet loss. While buffering can mask some network issues, if the network performance is too poor, even buffered videos will eventually encounter problems, leading to an extended delay in streaming.

With QoS, the network can prioritize YouTube traffic to ensure that students watching the lecture receive the bandwidth they need. QoS can allocate higher priority to YouTube traffic, ensuring minimal buffering, smoother video playback, and better video quality overall. In a scenario where many students are accessing the network for various purposes, QoS ensures that the video lecture, which is more bandwidth-intensive and latency-sensitive, gets the resources it needs over less critical traffic.

Why the Other Scenarios Don’t Benefit as Much from QoS

Students Updating Information about Their Sport Activities on the Class Facebook PageThis type of traffic is generally less time-sensitive and less prone to disruption by network congestion. Posting updates to a Facebook page involves sending small bursts of data, typically text or images, which are not affected by minor delays or packet loss. Even if the upload takes a few extra seconds due to network congestion, the user experience will not be significantly degraded. Because this type of traffic can tolerate latency and packet loss without impacting user satisfaction, it does not benefit as much from QoS as real-time applications like Skype or video streaming.
A Student Sending Emails to a FriendEmail traffic is highly resilient to delays, packet loss, and jitter. Emails are typically small in size and do not require real-time delivery. Even if the email takes a few more seconds to send or receive due to network congestion, the user experience will not be significantly impacted. Since email can tolerate a high degree of delay, packet loss, and jitter, it does not benefit from QoS in the same way that real-time applications do.

How QoS Works to Improve Network Performance

QoS operates by classifying network traffic into different categories, or queues, based on the type of application or protocol. Network administrators configure QoS to assign higher priority to time-sensitive traffic, like voice and video, and lower priority to less critical traffic, like email and web browsing.

Traffic Shaping: QoS shapes traffic by controlling the rate at which packets are transmitted to ensure that time-sensitive traffic is sent as quickly as possible.
Traffic Prioritization: It can assign higher priority to Skype or YouTube streams over other activities like downloading files or sending emails.
Bandwidth Allocation: QoS can allocate a guaranteed minimum amount of bandwidth to high-priority applications. This ensures that even when the network is congested, critical services still receive the resources they need.

In summary, adding QoS to a network can dramatically improve the experience of users engaged in activities that require real-time communication or high-quality video streaming. Skype and YouTube are perfect examples of applications that can suffer from poor network performance without QoS. By ensuring these types of traffic are prioritized, QoS creates a smoother, more reliable experience for users in real-time communication and video streaming contexts, making it essential for modern, multimedia-heavy networks.