TCP segmentation offload
TCP segmentation offload or TSO is a technology to reduce the CPU load of TCP / IP in fast computer networks. TSO is also often referred to as large segment offload ( LSO ) or generic segmentation offload ( GSO ).
When large amounts of data are sent over a computer network, upper limits for the packet size must be observed so that all areas of the network, such as e.g. B. Switches and routers that can handle packet size. To do this, the data is divided into smaller segments; this process is known as segmentation in technical terms .
The segmentation is traditionally taken over by the transport layer ( Transmission Control Protocol ) of the sending computer and then sometimes uses a considerable CPU load. If this function is transferred from the computer to its network card , it is called TCP segmentation offload (TSO). The computing speed of the computer and / or the network speed can be accelerated as a result; this becomes all the more relevant the higher the network speed increases ( e.g. Gigabit Ethernet ).
For example, a 64 kilobyte packet is typically split into 46 1448 byte segments before it is sent over the network card. With an intelligent network card, the computer can transfer the full 64 kilobytes to the network card in one piece, and the network card in turn divides the large packet into smaller packets of 1448 bytes each. The TCP / IP headers and other management information from the network card are then added to the individual segments. Many newer network cards support TSO.
However, not all operating systems fully support TSO. The company Microsoft advises against using TSO on Windows 2000 and Windows XP from.
Under Linux , the TSO functions are only available in non-free driver packages for some network cards. Only the conventional network function is supported by the free Linux driver, the use of TSO can require the integration of a non-free manufacturer driver.