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==== UDP Segmentation Offload ==== A device SHOULD support UDP Segmentation Offload (USO), for both IPv4 and IPv6. It MUST be possible to enable or disable the feature. USO allows sending multiple UDP datagrams in a single operation. The host passes to the device a UDP packet plus segment size field. The device splits the datagram payload on segment size boundaries and replaces the UDP header to each segment. USO is NOT the same as UDP fragmentation offload (UFO). That sends a datagram larger than MTU size, by relying on IP fragmentation. UFO is out of scope of this spec. Unlike UFO, USO does not maintain ordering. Datagrams may arrive out of order, same as if they were sent one at a time. The device SHOULD support IPv4 options and IPv6 extension headers in between the IPv4 or IPv6 and TCP header. The device SHOULD support IPSec ESP and PSP transport-layer encryption headers between IPv4 or IPv6 header and UDP header. UDP forms the basis for multiple high transfer rate protocols, including HTTP/3 and QUIC, and video streaming protocols like RTP. These workloads benefit from SO and form a sizable fraction of Internet workload. ''Header Field Adjustments'' Beyond CH/SP, USO requires an update of the UDP length field for the last segment if the USO payload is not an exact multiple of the segment size. It also requires the same IP and extension header field adjustments as TCP. A device SHOULD support this. Optionally, a device MAY only support USO for packets where payload is an exact multiple of segment size. The host then has to ensure to only pass such packets to the device. This mechanism forms the basis for Protocol Independent Segmentation Offload, next. <span id="protocol-independent-segmentation-offload"></span>
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