If you are having issues with the setup of you NS2's please review the Apple Extreme settings.

For Lion operating system.

Open Macintosh HD > Applications > Utilities > AirPort Utility 

Click on the AirPort Extreme icon, then click Edit

Click the Wireless tab at the top of the window

Click the Wireless options button

Edit the 2.4 GHz Channel and 5 GHz Channel accordingly by clicking on the selection box to
change the setting from Automatic to a channel that you choose

Click Save, then click Update and allow 25-30 seconds for the AirPort Extreme to restart

For Leopard or Snow Leopard.

Open Macintosh HD > Applications > Utilities > AirPort Utility

Select the AirPort Extreme and click Manual Setup

Click the Wireless tab below the row of icons

Edit the Radio Channel selection box by click Manual, then Edit

Change the 2.4 GHz and 5 GHz Channel accordingly

Click Done, then click Update and allow 25-30 seconds for the AirPort Exteme to restart