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Overview of Receive Segment Coalescing

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When receiving data, the miniport driver, NDIS, and TCP/IP must all look at each PDU's header information separately. When large amounts of data are being received, this creates a large amount of overhead. Receive segment coalescing (RSC) reduces this overhead by coalescing a sequence of received segments and passing them to the host TCP/IP stack in one operation, so that NDIS and TCP/IP need only look at one header for the entire sequence.

RSC is intended to support coalescing in a way that:

  • Doesn't interfere with the normal operation of TCP's congestion and flow control mechanisms.

  • Coalesces packets without discarding information that is used by the TCP stack.

RSC-capable miniport drivers for network cards must:

  • Follow a standard set of rules when coalescing segments.

  • Provide certain out-of-band information to the host TCP/IP stack.

The following sections provide an overview of RSC.