I was creating a really basic turn-based 2D isometric strategy game using DarkGDK with Visual Studio C++ 2008. The nice thing about DarkGDK is that it took care of the graphics functions in addition to the networking functions. However, it is currently not support any more and I would like to switch over my project to OpenGL.

However, OpenGL appears to only contain functions for handling graphics. What are you using to handle data transfer between two computers over TCP/IP?