DirectPlay

DirectPlay is a deprecated API that was part of Microsoft's DirectX API. DirectPlay is a network communication library intended for computer game development, although its general nature allows it to be used for other purposes.

DirectPlay is a high-level software interface between applications and communication services that makes it easy to connect games over the Internet, a modem link, or a network. DirectPlay features a set of tools that allow players to find game sessions and sites to manage the flow of information between hosts and players. It provides a way for applications to communicate with each other, regardless of the underlying online service or protocol. DirectPlay also resolves many connectivity issues, such as NAT.

DirectPlay, like the rest of DirectX, runs in COM and it is accessed through COM (Component Object Model) interfaces. By default, DirectPlay uses multi-threaded programming techniques and requires careful thought to avoid the usual threading issues. Since DirectX version 9, this issue can be alleviated at the expense of efficiency.

Under the hood, DirectPlay is built on the (UDP) to allow it speedy communication with other DirectPlay applications.

DirectPlay sits on layer 4 and 5 of the OSI model.

DirectPlay Voice was introduced in Windows Me as part of DirectX 7.1 for multiplayer games. It is a voice communications, recording and playback API that allows gamers to use voice chat in games written to take advantage of the API, through a DirectPlay network transport session itself.

DirectPlay was traditionally one of the components of DirectX that received less attention, but for DirectX version 8 it received a major overhaul and became a relatively lightweight networking library. However, as part of Microsoft's unveiling of XNA in 2004, Microsoft revealed that DirectPlay would be deprecated in favor of Games for Windows - Live technology already available on Xbox and being ported for use on Windows PCs. DirectPlay will be supported in DirectX DLLs for the lifetime of Microsoft Windows XP, but from the autumn of 2007 the headers and libraries — vital components if developers wanted to develop new programs that utilize the technology — were absent from the DirectX SDK.

...
Wikipedia