Goodput

In computer networks, goodput (a portmanteau of good and throughput) is the application-level throughput of a communication. In other words, goodput is the number of useful information bits 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). Examples of factors that cause lower goodput than throughput include: Protocol overhead: Typically, transport layer, network layer and sometimes data link layer protocol overhead is included in the throughput, but is excluded from the goodput. Transport layer 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 data link layer or network layer throughput but not in the goodput.