Standard Xbox 360 consoles require an active connection to official Ubisoft and Xbox Live servers to play online. When those servers go offline, standard multiplayer dies.
Ensure your Title Update (TU) version matches the host precisely. Check the Media ID of your game file; mismatched Media IDs can sometimes pull different TUs. tom clancys ghost recon future soldier jtag rgh link
You must register a free account at XboxUnity.net. This account links your console to the homebrew server database. Standard Xbox 360 consoles require an active connection