Spid is the process ID on the server, corresponding to the current connection. This information is sent by the server to the client and is useful for identifying which thread on the server sent the TDS packet. It is provided for debugging purposes. The client MAY send the SPID value to the server. If the client does not, then a value of 0x0000 SHOULD be sent to the server. This is a 2-byte value and is represented in network byte order (big-endian).