If you are receiving any multiplayer connection issues, or having trouble connecting to a multiplayer game please try the following:
Start by testing your network connection with the following steps:
1. Start at the PS3 XMB.
2. Scroll to Settings.
3. Choose Network Settings.
4. Select Internet Connection Test.
If this test shows your connection as NAT type 3, then you will most likely have some sort of interference within your connection to the online servers.
Alternately, you can view your NAT type directly within the multiplayer menus in the top right corner.
Selecting Online from within the AC3 multiplayer menu will provide a more detailed description of your NAT settings.
There are three possible NAT types
Moderate NAT will have some restrictions and will be unable to communicate or play with users with a strict NAT.
Strict NAT may not be able to join or communicate in certain game sessions. Average matchmaking wait times will be affected.
If your NAT type is moderate or strict, please try the steps below:
1. Restart your network hardware. Turn off your PS3, Modem, and Router and wait about 15 - 30 seconds
2. Fully power up your modem
3. Fully power up your router
4. Turn on your PS3 and test the network connection again
At this point if you still have trouble then you may have a firewall interfering with your connection. Please configure the following network ports and enable UPnP through your router.
PlayStation Network Required Ports
TCP: 80, 443, 5223
Assassin's Creed III Required Ports
TCP (remote port): 80, 443
UDP (local port): 3658
Finally, if this does not solve your problem, try establishing a direct connection to your modem (bypass the router) and retry.