Large segment 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 a large segment offload (LSO ) or generic segmentation offload ( GSO).

If large amounts of data are sent over a computer network, limits on the package size must be observed to ensure that all areas of the network, such as switches and routers that can handle the packet size. The data are divided into smaller segments, this process is known in the jargon as segmentation.

The segmentation is applied conventionally by the transport layer ( Transmission Control Protocol) of the sending computer, and then takes some considerable CPU load. If this function is transferred from the computer to his network card, TCP segmentation offload it is said (TSO ). The computation speed of the computer and / or network speed can be accelerated, this is all the more relevant, the higher the network speed increases (eg, Gigabit Ethernet).

For example, a 64 kilobyte large package is normally divided into 46 segments of 1448 bytes before it is sent over the network adapter. With an intelligent network interface card of the computer can pass the full 64 kilobytes in one piece to the network card and the network card which then in turn divides the large package into smaller packages of 1448 bytes. The TCP / IP headers and other management information from the network card to be added to the individual segments then. Many newer network cards support TSO.

However, not all operating systems support TSO completely. The company Microsoft does not recommend the use of TSO on Windows 2000 and Windows XP.

Under Linux, the TSO functions are present in some network cards only in non-free driver packages. Here, only the conventional network function is supported by the free Linux driver, the use of TSO may require the involvement of a non-free manufacturer driver.