DirectPlay

From Wikipedia, the free encyclopedia

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

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 stable, effective and 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 Xbox 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 summer of 2004 the headers and libraries - vital components if developers wanted to develop new programs that utilize the technology - were absent.

DirectPlay, as the rest of DirectX, runs in COM and it is accessed through COM (Component Object Model) interfaces. Per 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.

[edit] Interfaces

The primary interfaces (methods of access) for DirectPlay are:
- IDirectPlay8Server, which allows access to server functionality
- IDirectPlay8Client, which allows access to client functionality
- IDirectPlay8Peer, which allows access to peer-to-peer functionality
Secondary interfaces are:
- Various lobby interfaces that allows players to find and prepare a game before it actually commences.
- Thread management interfaces that allows the programmer to fine-tune resource usage. This also allows for a general disabling of worker threads so that tricky multi-threaded issues are avoided at the cost of decreased responsiveness.
- Various network address translation (NAT) interfaces that make it easier for players behind routers to host games. Most players on broadband internet connections face this problem.
- Various voice communication interfaces that make it easier to support audio communication and voice input in games.
- Various queue monitoring interfaces that allow the application to get feedback on how much data has been sent and received as requested. This allows an application to decrease/increase the amount of data sent in accordance with the capabilities of the receiver.

[edit] Networking model

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

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

On layer 4, DirectPlay can handle the following tasks if requested by the application:
- Message ordering, which ensures that data arrives in the same order it was sent.
- Message reliability, which ensures that data is guaranteed to arrive.
- Message flow control, which ensures that data is only sent at the rate the receiver can receive it.
On layer 5, DirectPlay always handles the following tasks:
- Connection initiation and termination.