the main advantages and disadvantages of a layered model the relationship between average queuin

what sort of question is that?I'm confused.what is the main advantages and disadvantages of a layered model ？what is the relationship between average queuing delay and traffic intensity?In telecommunication networks, traffic intensity is a measure of the average occupancy of a server or resource during a specified period of time, normally a busy hour. It is measured in traffic units and defined as the ratio of the time during which a facility is cumulatively occupied to the time this facility is available for occupancy.In telecommunication and computer engineering, the queuing delay (or queueing delay) is the time a job waits in a queue until it can be executed.The above text is quoted from wikipedia. My own understanding is as following:traffic intensity: a period during which the route is jammed with overwhelming jobs.queuing delay: a period during which a job is waiting to be done.The two conception is stated from two different view, yet they both mean the same period.