Networking - QoS (Quality of Service)

What is QoS?

Quality of Service (QoS) is a set of techniques used in networking to manage and prioritize traffic so that critical applications (like voice, video, or real-time services) get the bandwidth, low latency, and reliability they need.

Without QoS, all network traffic is treated equally — which can cause delays or poor performance for important services when the network is congested.

Why QoS is Needed

  • Voice & Video Calls (VoIP, Zoom, Teams) need low latency and no jitter.

  • Streaming needs steady bandwidth.

  • File downloads or background updates can tolerate delay but consume bandwidth.

  • Business apps (ERP, databases) require reliability.

QoS ensures that the right traffic gets priority when bandwidth is limited.

Key QoS Parameters

  1. Bandwidth – Amount of data that can be transmitted.

  2. Latency – Delay between sending and receiving data (critical for real-time apps).

  3. Jitter – Variation in packet arrival times (affects voice/video quality).

  4. Packet Loss – Dropped packets hurt performance (especially real-time traffic).

How QoS Works (Techniques)

  1. Classification – Identify different types of traffic (voice, video, web, email).

  2. Marking – Tag packets with priority (e.g., DSCP, CoS).

  3. Queuing – Place packets in different queues based on priority.

    • High-priority queues (voice) get served first.

    • Low-priority queues (downloads) wait if the network is busy.

  4. Policing/Shaping – Control traffic rate.

    • Policing = drops excess traffic.

    • Shaping = buffers and smooths traffic.

Example Scenario

  • Without QoS:

    • You’re on a Zoom call, but your roommate starts downloading a large file. The call lags and breaks up.

  • With QoS:

    • The router prioritizes Zoom traffic over downloads → smooth call experience.

Where QoS is Used

  • Enterprise networks → Prioritize business-critical apps.

  • Service Providers (ISPs) → Guarantee service levels (e.g., VoIP vs browsing).

  • Home routers (advanced ones) → Prioritize gaming or video calls.

 In short: QoS is like traffic control at an intersection.

  • Emergency vehicles (voice/video) get a green light first.

  • Regular cars (web browsing) wait their turn.

  • Trucks (large downloads) may be slowed down to avoid blocking others.