The term Quality-of-Service (QoS) refers to defined measures of performance in networks, including end-to-end latency (or delay) and throughput, but also jitter (variation in latency) and packet loss (or error rate). The choice of a QoS metric depends on the type of application. Sensor networks performing target detection and tracking will require low end-to-end transmission delays for their time-sensitive sensor data, while data-intensive networks (e.g., multimedia sensor networks) may require high throughput. The Expected Transmission Time (ETT) is a common metric to express latency and is defined as (Draves et al. 2004):