I have taken this article from Activisions Support page, let me know how you get on as i have tried it and it makes no difference to my game play at all. I am running on One GIG Network with 78 Meg Hard Wired Download Speed And 24 Meg Upload, the game is unplayable for me.
When playing the game online, the minimum speed of your network should be 128kbps. The ideal network speed for playing the game online is 768kbps. If you are having a problems with lag check the following:
Disable any firewall or security features on your router.
Set port forwarding on your router to the IP address of your Xbox 360. This game uses port 3074 (UDP/TCP). Additionally Xbox LIVE requires ports 80, 53 TCP and 88, 53 UDP.
Place your Xbox 360 into the DMZ of your router.
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 Microsoft's Xbox Live Connection Issues page for additional steps that may need to be done to resolve the issue you are having. You can also verify that you have an Xbox Live compatible router.
If you are having issues connecting while multiple Xbox 360 consoles are connected on the same network, try forwarding port 3074 (UDP/TCP) for one Xbox 360 and setting the other as DMZ. There is a chance that this may not resolve you issue, if it doesn’t then you may want to consider getting an additional public IP address by contacting your Internet Service Provider and assigning it to one of these two consoles.
NOTE: If setting port forwarding or DMZ helps your connection issue, you may want to assign your Xbox 360 a static IP address within your home network. This can help to ensure that the configurations you made do not need to be done again. You can visit PortForward's Static IP Guide for a detailed guide on how to do this.
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 the following:
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.
Run the Xbox Network Self Test to see how strong your NAT is currently set to. Once the test is completed you will be notified if there is an issue with your connection. If you select "More Info" you will be given information about your NAT type and some steps to resolve any issues with your connection.
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 port 3074, or placing your Xbox in your router's DMZ may resolve this issue. Please consult your router documentation for instructions on how to do this.