Winsock allows the basic data transport capabilities of numerous transport protocols to be accessed in a generic manner. It also provides a generic way to use multipoint and multicast capabilities of various network transports. To simplify, the term multipoint is used hereafter to refer to both multicast and multipoint communications.

Current multipoint implementations, for example, IP multicast, ST-II, T.120, and ATM UNI, vary widely with respect to how nodes join a multipoint session, whether a particular node is designated as a central or root node, and whether data is exchanged between all nodes or only between a root node and the various leaf nodes. The Winsock WSAPROTOCOL_INFOWstructure is used to declare the various multipoint attributes of a protocol. By examining these attributes the programmer will know what conventions to follow in using the applicable Winsock functions to set up, use, and tear down multipoint sessions.

The following list shows the parts of Winsock 2.2 that support multicast:

• Three attribute bits in the WSAPROTOCOL_INFOWstructure.
  
  
• Four flags defined for the dwFlagsparameter of WSPSocket.
  
  
• One function, WSPJoinLeaf, for adding leaf nodes into a multipoint session.
  
  
• Two WSPIoctlcommand codes for controlling multipoint loopback and establishing the scope for multicast transmissions. (The latter corresponds to the IP multicast time-to-live or TTL parameter.)
  
  

  Note:
  A service provider must also support an existing protocol-dependent interface, such as the Deering socket options for IP multicast.

See Also