Response time
Response time may refer to:
See also
Response time (technology)
In technology, response time is the time a system or functional unit takes to react to a given input.
Computing
Response time is the total amount of time it takes to respond to a request for service. That service can be anything from a memory fetch, to a disk IO, to a complex database query, or loading a full web page. Ignoring transmission time for a moment, the response time is the sum of the service time and wait time. The service time is the time it takes to do the work you requested. For a given request the service time varies little as the workload increases – to do X amount of work it always takes X amount of time. The wait time is how long the request had to wait in a queue before being serviced and it varies from zero, when no waiting is required, to a large multiple of the service time, as many requests are already in the queue and have to be serviced first.
With basic queueing theory math you can calculate how the average wait time increases as the device providing the service goes from 0-100% busy. As the device becomes busier, the average wait time increases in a non-linear fashion. The busier the device is, the more dramatic the response time increases will seem as you approach 100% busy; all of that increase is caused by increases in wait time, which is the result of all the requests waiting in queue that have to run first.
Round-trip delay time
In telecommunications, the round-trip delay time (RTD) or round-trip time (RTT) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the propagation times between the two points of a signal.
Computer networks
In the context of computer networks, the signal is generally a data packet, and the RTT is also known as the ping time. An internet user can determine the RTT by using the ping command.
Space technology
In space technology, the round-trip delay time or round trip light time is the time light (and hence any signal) takes to go to a space probe and return.
Protocol design
Network links with both a high bandwidth and a high RTT can have a very large amount of data (the bandwidth-delay product) "in flight" at any given time. Such "long fat pipes" require a special protocol design. One example is the TCP window scale option.
The RTT was originally estimated in TCP by:
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