Quality of Service (QoS) metrics are essential measures used to evaluate and ensure the performance and reliability of a network. These metrics provide insights into various aspects of network service quality, helping network administrators and engineers to optimize and maintain efficient network operations. Key QoS metrics include:

1. **Jitter**: This refers to the variation in the time between packets arriving, caused by network congestion, timing drift, or route changes. High jitter can lead to poor audio and video quality in real-time communications, such as VoIP calls or video conferencing.

2. **Latency**: Also known as delay, latency measures the time it takes for a data packet to travel from the source to the destination. Low latency is crucial for applications that require real-time interaction, such as online gaming and live streaming.

3. **Packet Loss**: This metric indicates the percentage of packets that are lost during transmission. Packet loss can occur due to network congestion, hardware failures, or signal degradation. High packet loss can severely impact the quality of data transmission, leading to interruptions and degraded service quality.

4. **Throughput**: Throughput measures the rate at which data is successfully transmitted over the network. It is typically measured in bits per second (bps) and is a critical factor in determining the network’s capacity to handle data traffic. High throughput is essential for bandwidth-intensive applications like video streaming and large file transfers.

By monitoring and analyzing these QoS metrics, network professionals can identify potential issues, optimize network performance, and ensure that the network meets the required service quality standards for various applications and services.