Quality of service aims to provide better service to some data flows over others. It is defined by parameters like reliability, delay, jitter, and bandwidth. Techniques to improve quality of service include scheduling, traffic shaping, and resource reservation. Scheduling techniques like FIFO queuing and priority queuing determine how packets are processed. Resource reservation allows resources like bandwidth to be reserved beforehand for certain data flows. Quality of service is important for applications like mobile communication, real-time media, and traffic with performance guarantees.