Important Reserved for future use with socket groups:
Windows Sockets 2 introduces a number of function parameters, data types, structure members, and manifest constant values that are reserved for future use in grouping sockets together. As of the version 2.2.1 of the specification, the intended future use of these items is fully described, however, none of the group-related parameters is interpreted in software releases corresponding to the version 2.2.1 specification. Since a client always has the option to elect not to use socket groups, there are always default values and behaviors defined for group-related definitions. It is simple for an application not employing socket groups to use default values in such a fashion that the application will not be harmed if and when socket groups are "turned on" in the future. Definitions related to socket groups are marked in version 2.2.1 specification with the phrase: "Reserved for future use with socket groups" preceding the description of the intended future use.
Windows Sockets 2 introduces the concept of a socket group as a means for an application (or cooperating set of applications) to indicate to an underlying service provider that a particular set of sockets are related, and that the group thus formed has certain attributes. Group attributes include relative priorities of the individual sockets within the group and a group's quality of service specification.
Applications needing to exchange multimedia streams over the network benefit by establishing a specific relationship among the set of sockets being utilized. This can include, as a minimum, an indication to the service provider about the relative priorities of the media streams being carried. For example, a conferencing application would likely give the socket used for carrying the audio stream a higher priority than the socket used for the video stream. Furthermore, there are transport providers (for example, digital telephony and ATM) that can utilize a group, quality-of-service specification to determine the appropriate characteristics for the underlying call or circuit connection. The sockets within a group are then multiplexed in the usual manner over this call. By allowing the application to identify the sockets that make up a group and to specify the required group attributes, service providers can operate with maximum effectiveness.
The WSASocket and WSAAccept functions are two new functions used to specifically create and join a socket group coincident with creating a new socket. Socket group identifiers can be retrieved by using getsockopt with option SO_GROUP_ID. Relative priority can be accessed by using get/setsockopt with option SO_GROUP_PRIORITY.