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 notion of a socket group as a means for an application to indicate to the 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 quality of service specification.
Applications needing to exchange multimedia streams over the network are benefited by being able to establish a specific relationship among the set of sockets being utilized. As a minimum, this includes a hint to the service provider about the relative priorities of the media streams being carried. For example, a conferencing application would want to have the socket used for carrying the audio stream be given higher priority than that of the socket used for the video stream. Furthermore, there are transport providers (e.g. digital telephony and ATM) which 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, such service providers can operate with maximum effectiveness.
The following paragraphs define what a service provider must do in order to implement socket grouping.