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{{Short description|Application level throughput}}
{{More footnotes|date=April 2016}}
In computer networks, '''goodput''' (a [[portmanteau]] of [[wikt:good|good]] and [[throughput]]) is the [[Application layer|application-level]] throughput of a communication; i.e. the number of useful information [[bit]]s delivered by the network to a certain destination per unit of time. The amount of data considered excludes [[protocol overhead]] bits as well as retransmitted data packets. This is related to the amount of time from the first bit of the first packet sent (or delivered) until the last bit of the last packet is delivered.
For example, if a file is transferred, the goodput that the user experiences corresponds to the file size in bits divided by the file transfer time. The goodput is always lower than the throughput (the gross bit rate that is transferred physically), which generally is lower than network access connection speed (the [[channel capacity]] or [[Bandwidth (computing)|bandwidth]]).
Examples of factors that cause lower goodput than throughput are:
* ''Protocol overhead'': Typically, transport layer, network layer and sometimes datalink layer protocol overhead is included in the throughput, but is excluded from the goodput.
* ''Transport layer [[Flow control (data)|flow control]] and [[congestion avoidance]]'': For example, TCP slow start may cause a lower goodput than the maximum throughput.
* Retransmission of lost or corrupt packets due to transport layer [[automatic repeat request]] (ARQ), caused by bit errors or [[packet dropping]] in congested switches and routers, is included in the datalink layer or network layer throughput but not in the goodput.
==Example==
Over Ethernet, files are broken down into individual chunks for transmission. These chunks are no larger than the [[maximum transmission unit]] of IP over Ethernet, or 1500 [[byte]]s. Each packet requires 20 bytes of [[Internet Protocol|IPv4]] header information and 20 bytes of [[Transmission Control Protocol|TCP]] header information, leaving 1460 bytes per packet for file data ([[Linux]] and [[macOS]]<ref>{{cite web|url=http://www.stuartcheshire.org/papers/NagleDelayedAck/index.html|title=TCP Performance problems caused by interaction between Nagle's Algorithm and Delayed ACK|author=Stuart Cheshire|accessdate=2010-01-13}}</ref> are further limited to 1448 bytes as they also carry a 12-byte time stamp). The data is transmitted over Ethernet in a frame, which imposes a 26 byte overhead per packet. Given these overheads, the maximum ''goodput'' is 1460/1526 × 100 [[Mbit/s]] which is 95.67 megabits per second or 11.959 [[Megabyte per second|megabytes per second]].
Note that this example doesn't consider additional Ethernet overhead, such as the [[interframe gap]] (a minimum of 96 bit times), or collisions (which have a variable impact, depending on the network load). TCP adds the overhead of acknowledgements (which along with the [[round-trip delay time]] and the TCP window size in effect rate-limit each individual TCP connection, see [[bandwidth-delay product]]). This example does not consider the overhead of the HTTP protocol itself, which becomes relevant when transferring small files.
==Data delivery time==
The goodput is a ratio between delivered amount of information, and the total delivery time. This delivery time includes:
* Inter-packet time gaps caused by packet generation processing time (a source that does not use the full network capacity), or by protocol timing (for example [[Collision avoidance (networking)|collision avoidance]])
* Data and overhead [[transmission delay]] (amount of data divided by [[bit rate]])
* [[Propagation delay]] (distance divided by wave propagation speed)
* Packet [[queuing delay]]
* [[Network address translation|NAT]] translation delay
* Intermediate node [[store and forward delay|store-and-forward processing delay]]
* Packet retransmission time (in case of deleted packets in congested routers, or detected bit errors)
* Delayed acknowledge due to flow control, [[congestion avoidance]] and [[processing delay]]
==See also==
* [[Measuring network throughput]]
* Link and system [[spectral efficiency]]
==References==
{{Reflist}}
==Sources==
* [http://mailman.isi.edu/pipermail/ns-users/2001-June/015799.html Goodput calculation] {{Webarchive|url=https://web.archive.org/web/20100818222126/http://mailman.isi.edu/pipermail/ns-users/2001-June/015799.html |date=2010-08-18 }}
* [https://arxiv.org/abs/cs.IT/0604082 Energy-Efficient Power and Rate Control with QoS Constraints: A Game-Theoretic Approach]
* [http://tools.ietf.org/html/rfc2647 RFC 2647 — Benchmarking Terminology for Firewall Performance]
[[Category:Network performance]]