3.1 Common Details

As described in section 1.3, TDS is an application-level protocol that is used for the transfer of requests and responses between clients and database server systems. The protocol defines a limited set of messages through which the client can make a request to the server. The TDS server is message-oriented. Once a connection has been established between the client and server, a complete message is sent from client to server. Following this, a complete response is sent from server to client (with the possible exception of when the client aborts the request), and the server then waits for the next request. Other than this Post-Login state, the other states defined by the TDS protocol are (i) pre-authentication (Pre-Login), (ii) authentication (Login), and (iii) when the client sends an attention message (Attention). These will be expanded upon in subsequent sections.