If you are still experiencing this issue, here are some tips you may want to try.
You can always check online services status here http://www.callofduty.com/ghosts/status
If online services are fully operational and you are still unable to connect, you may want to try the following.
Here are the port numbers you will need:
Xbox 360: Activision Support
Should you have any questions on how to port forward, please contact your ISP or the router manufacturer.