Long Term Measures of Performance of Queueing Systems

• time-averaged number of customers in the system (L) and in the queue (${\rm L_Q}$)
• average time in system (W)
• average time in queue (${\rm W_Q}$)
• Little's Law (consevation equation) in a queueing system, if the queue length is denoted by L, the arrival rate is denoted by ${\rm lambda}$, and the waiting time is denoted by ${\rm W}$ then
  
  $$L = \lambda W$$
  
  
  intuitively, it says the queue length is proportional to the arrival rate and the waiting time. Waiting time is affected by two parameters the arrival rate and the service rate.