TCP_OFFLOAD_STATE_CONST structure (ndischimney.h)

Article
05/26/2021

[The TCP chimney offload feature is deprecated and should not be used.]

The TCP_OFFLOAD_STATE_CONST structure contains the constant variables of a TCP connection state object.

Syntax

typedef struct _TCP_OFFLOAD_STATE_CONST {
  OFFLOAD_STATE_HEADER Header;
  USHORT               Flags;
  USHORT               RemotePort;
  USHORT               LocalPort;
  UCHAR                SndWindScale : 4;
  UCHAR                RcvWindScale : 4;
  USHORT               RemoteMss;
  ULONG                HashValue;
} TCP_OFFLOAD_STATE_CONST, *PTCP_OFFLOAD_STATE_CONST;

Members

Header

An OFFLOAD_STATE_HEADER structure. NDIS sets the Length member of Header to the size, in bytes, of the TCP_OFFLOAD_STATE_CONST structure. The RecognizedOptions member of Header is reserved.

Flags

A bitmask that can be set to zero or any of the following flags, combined with bitwise OR:

TCP_FLAG_TIMESTAMP_ENABLED

The host stack sets this flag to enable the TCP timestamp option on the connection. (For more information about the TCP timestamp option, see RFC 1323.) When this option is enabled, the offload target must place a timestamp in each TCP segment that it sends. The host stack clears this flag to disable the TCP timestamp option on the connection.

TCP_FLAG_SACK_ENABLED

The host stack sets this flag to enable selective acknowledgments (SACKs) on the connection. (For more information about the SACKs, see RFC 2018.) When this option is enabled, the offload target sends and receives SACK blocks over the TCP connection. The host stack clears this flag to disable SACKs on the connection.

TCP_FLAG_WINDOW_SCALING_ENABLED

The host stack sets this flag to cause the offload target to use scale factors (SndWindScale and RcvWindScale) to compute send and receive windows for the connection. (For more information about window scale factors, see RFCs 2883 and 3517.) The host stack clears this flag to disable this option.

RemotePort

The destination port number (see RFC 793).

LocalPort

The source port number (see RFC 793).

SndWindScale

The send window scale factor (see RFC 1323).

RcvWindScale

The receive window scale factor (see RFC 1323).

RemoteMss

The initial maximum segment size (MSS) advertised by the remote endpoint during TCP connection setup. (For more information about MSS, see RFC 2581.)

HashValue

A 32-bit hash value that the offload target uses for receive side scaling (RSS) processing on the TCP connection if the offload target supports RSS.

Remarks

The value of each TCP constant variable does not change during the life of a TCP connection. Neither the host stack nor the offload target changes the values of a TCP constant variable. When the host stack terminates the offload of the TCP connection state object by causing NDIS to call the offload target's MiniportTerminateOffload function, the offload target does not return the value of the offloaded TCP constant variables to the host stack.

When passed to an offload target, a TCP_OFFLOAD_STATE_CONST structure is associated with an NDIS_MINIPORT_OFFLOAD_BLOCK_LIST structure, which contains a header that is formatted as an NDIS_OBJECT_HEADER structure. The Revision member of the NDIS_OBJECT_HEADER structure, in this case, specifies the revision number of the TCP_OFFLOAD_STATE_CONST structure.

Requirements

Requirement	Value
Header	ndischimney.h (include Ndischimney.h)