One way of looking at this is to say that transport latency + processing time = response time.
Transport latency is the time it takes for a request/response to be transmitted to/from the processing component. Then you need to add the time it takes to process the request.
As an example, say that 5 people try to print a single sheet of paper at the same time, and the printer takes 10 seconds to process (print) each sheet.
The person whose print request is processed first sees a latency of 0 seconds and a processing time of 10 seconds – so a response time of 10 seconds.
Whereas the person whose print request is processed last sees a latency of 40 seconds (the 4 people before him) and a processing time of 10 seconds – so a response time of 50 seconds.