Hardware
If your Xbox is close enough to your high-speed modem, you have the option of running a direct connection from your Xbox to the modem. If your Xbox is further away, connecting your modem to a wireless router is another option.
Connections
With any high-speed connection, your Internet service provider assigns you a minimum upload and download speed. DSL -- generally the slowest of the compatible high-speed connections -- has an average download speed of 1.0 to 1.5Mbps, which is enough to connect to Xbox Live.
Performance
Your Xbox Live connection is only as stable as the Internet connection you are using. Running other bandwidth-intensive applications, such as antivirus, firewalls and streaming video, may also affect your connection.