First, you should check the status of the Call of Duty servers, as the servers may be down for maintenance. Links to the Call of Duty server status pages can be found on the homepage of this website.
 
If you are still having a problem connecting to an online game, try the following:

1. Due to the inconsistent nature of wireless connections, try connecting with a wired connection.
2. Disable any firewall or security features on your router.
3. Set port forwarding on your router to the IP address of your PlayStation 3. This game uses ports 36081, 3074, 3075, 3478 UDP (User Datagram Protocol) and ports 80, 81,443, 3074, 5223 TCP (Transmission Control Protocol.)
4. Disconnect your router and try the game. If it works regularly at this point something about your router may not be completely compatible with the specific needs of this game. Check with your router manufacturer and Sony’s PlayStation 3 Connection Issues page for additional steps that may need to be done to resolve the issue you are having.
5. Place your PlayStation 3 into the DMZ of your router.

If you are having issues connecting while multiple PlayStation 3 consoles are connected on the same network, try forwarding the ports (36081, 3074, 3075, 3478 for UDP and 80, 81,443, 3074, 5223 for TCP) for one PlayStation 3 and setting the other as DMZ. There is a chance that this may not resolve your issue, if it doesn't, you may want to consider getting an additional public IP address by contacting your ISP and assigning it to one of the consoles.
 
NOTE: If setting port forwarding or DMZ helps your connection issue, you may want to assign a static IP address to your PlayStation 3 within your home network. This can help to ensure that the configurations you made do not need to be done again.

NOTE: Many broadband internet modems are coming with routing capabilities built in. Please contact your internet service provider to determine if your internet modem has an integrated router. If it does, they should be able to assist you with the steps above for setting up your router.

Once you have verified that your network setup is not the cause of the issue, try connecting to a different server. Some servers may have other players connected to them that you do not have an optimal connection with. In most games this is accomplished by backing out to the main menu and then selecting multiplayer again. From there you can try connecting to another online game.
 
Moderate and Strict NAT types may have issues connecting to online matches. You may get the error "Notice - The game session is no longer available." If you do then enabling UPnP, forwarding ports  (36081, 3074, 3075, 3478 for UDP and 80, 81,443, 3074, 5223 for TCP), or placing your PlayStation 3 in your router's DMZ may resolve this issue. To do this, please consult your router documentation for instructions.