In order for us to help determine what your issue is you will need to provide us with some information about your network:
What Country do you live in?
What make and model modem do you have?
What make and model router do you have?
Wired or Wireless connection to the console?
If wireless, are you using any encryption? If yes, what type?
Do you have one or more of these enabled? uPnP/DMZ/Port Forward?
What is your NAT type?
Any Error Codes you encounter?
What type of internet do you have? Cable/DSL/T1/3G?
Who is your ISP (Internet Service Provider)?
Do you have the most current version of router firmware? You can check the manufacturer website for this information and compare it to your router information.
Go to speedtest.net and run three tests; one close to you, one far from you and one in between. Then post your results here, including the ping.