在文件传输以及某个比较大的Buffer传输的时候，可能会考虑通过压缩方式传递，但是系统API中有TransmitFile and TransmitPackets两个函数，可以起到这个作用。

IOCP2.1计划：
       增加两个功能函数，TransmitFile 和 TransmitPackets。

http://msdn.microsoft.com/zh-cn/magazine/cc302334(en-us).aspx 提到：

Winsock offers two functions for transmitting data that are optimized for file and memory transfers. The TransmitFile API is present on both Windows NT 4.0 and Windows 2000, while TransmitPackets is a new Microsoft extension function that is expected to be available in a future release of Windows. TransmitFile allows the contents of a file to be transferred on a socket. Normally, if an application were to send the contents of a file over a socket, it would have to call CreateFile to open the file and then loop on ReadFile and WSASend until the entire file was read. This is very inefficient because each ReadFile and WSASend call requires a transition from user mode to kernel-mode. TransmitFile simply requires an open handle to the file to transmit and the number of bytes to transfer. The overhead is incurred when opening the file via CreateFile, followed by a single kernel-mode transition. If your app sends the contents of files over sockets, this is the API to use.
      The TransmitPackets API takes the TransmitFile API a step further by allowing the caller to specify multiple file handles and memory buffers to be transmitted in a single call. The function prototype looks like this:
BOOL TransmitPackets(   SOCKET hSocket,                               LPTRANSMIT_PACKET_ELEMENT lpPacketArray,   DWORD nElementCount,                   DWORD nSendSize,                   LPOVERLAPPED lpOverlapped,                     DWORD dwFlags                               );
      The lpPacketArray is an array of structures. Each entry can specify either a file handle or a memory buffer to be transmitted. The structure is defined as:
typedef struct _TRANSMIT_PACKETS_ELEMENT {     DWORD dwElFlags;     DWORD cLength;     union {         struct {             LARGE_INTEGER     nFileOffset;             HANDLE            hFile;             };             PVOID             pBuffer;     }; } TRANSMIT_FILE_BUFFERS;
The fields are self explanatory. The dwElFlags field identifies whether the current element specifies a file handle or memory buffer via the constants TF_ELEMENT_FILE and TF_ELEMENT_MEMORY. The cLength field dictates how many bytes to send from the given data source (a zero indicates the entire file in the case of a file element). The unnamed union then contains the memory buffer of file handle (and possible offset) of the data to be sent.
      Another benefit of using these two APIs is that you can reuse the socket handle by specifying the TF_REUSE_SOCKET flag in addition to the TF_DISCONNECT flag. Once the API completes the data transfer, a transport-level disconnect is initiated. The socket can then be reused in an AcceptEx call. Using this optimization would lessen the overhead associated with creating sockets in the separate accept thread, as discussed earlier.
      The only caveat of using either of these two extension APIs is that on Windows NT Workstation or Windows 2000 Professional only two requests will be processed at a time. You must be running on Windows NT or Windows 2000 Server, Windows 2000 Advanced Server, or Windows 2000 Data Center to get full usage of these specialized APIs.