How do I play multiplayer?

I have bought DOOM 3 BFG edition, which includes The Ultimate DOOM and DOOM 2, in addition to the expansion packs for Doom 3. I know the original incarnations and many of the source ports of DOOM and DOOM 2 supported multiplayer, but I don't seem to be able to find the option to start or join a multiplayer game in the version of The Ultimate DOOM that is bundled with the DOOM 3 BFG edition.

How do I play multiplayer The Ultimate DOOM - BFG edition?

There is no native option to play multiplayer DOOM with the version bundled with DOOM 3 - BFG Edition. When you start the game you're presented with the game selection screen;

When you select either DOOM or DOOM 2, you're presented with a limited version of the traditional start menu;

Selecting 'New Game' or any of the other options does not provide you with a multiplayer option.

As a workaround, however, it is possible to use the data files for both DOOM and DOOM 2 with one of the game engine ports and many of these (for example DOOMSDAY/jDOOM) do provide multiplayer support, allowing you to play multiplayer games of DOOM.