## S

secure session
  A session in which all the users have been authenticated against a database of known users before being allowed to join a session. In a secure session, all DirectPlay system messages are digitally signed to verify the identity of the sender. Certain system messages that carry sensitive information are encrypted. System messages that originate from one player and need to be broadcast to all the other players in the session are first sent to the server. The server then puts its signature on the message and forwards the message to all the other computers in the session. Player to player messages are not signed by default and are not routed through the server.
service provider
  A dynamic-link library (DLL) used by DirectPlay to communicate over a network. The service provider contains all the network-specific code required to send and receive messages. Online services and network operators can supply service providers to use specialized hardware, protocols, communications media, and network resources. Microsoft includes four generic service providers with DirectPlay: head-to-head modem (TAPI), serial connection, Internet TCP/IP (using Winsock), and IPX (also using Winsock).
session
  An instance of several applications on remote machines communicating with each other. Before an application can start communicating with other computers, it must be part of a session. An application can enumerate all the existing sessions on a network and join one of them, or it can create a new session and wait for other computers to join it. Once the application is part of a session, it can create a player and exchange messages with all the other players in the session.
system message
  A message from the player ID DPID_SYSMSG. All system messages begin with a double-word value. You can cast the buffer returned by the IDirectPlay3::Receive method to a generic message (DPMSG_GENERIC) and switch on this DWORD value. The DWORD value is equal to one of the messages with a DPSYS_ prefix, for example, DPSYS_SESSIONLOST. After the application has determined which system message it is, the buffer should be cast to the appropriate structure (beginning with the DPMSG_ prefix), for example, DPMSG_SESSIONLOST, to read the data.

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