To reduce the risk of drop-outs, try:
Change 1:
Within wireless modem, change to 802.11g only and change is maximum connection rate to 18 Mbits.
Change 2:
Within wireless modem, change Authentication from default WEP to WPA-PSK or WPA2-PSK. For some unknown reason, some WEPs don't like the new iMacs, but ok with MBPs or other Apple end devices.
These 2 items resolve majority of drop-outs on the "new" iMacs.
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WEP-Open: Offers the same security offered by a wired network (LAN) with encrypted packets. This option offers either 64-bit or 128-bit encryption. In this mode, WEP keys are always authenticated at the device level. After authentication, data is then encrypted between the gateway and the connected device.
WEP-Shared: Similar to WEP-Open but in this mode, WEP keys accept a string of unencrypted data from a device. The wireless Home Networking modem encrypts with a WEP key and sends back the encrypted data to the attached device.
To use either of these two options, please enter one of the following in the Key field:
To enable 64-bit encryption, enter a 10 character key, using only hexadecimal characters. Alternatively, you may also use a 5 ASCII character key.
To enable 128-bit encryption, enter a 26 character key, using only hexadecimal characters. Alternatively, you may also use a 13 ASCII character key.
Note: Hexadecimal characters can only be numbers 0-9 and/or letters A-F.
WPA-PSK: This supports TKIP (Temporal Key Integrity Protocol) which allows verification of the security configuration after the encryption keys are determined, synchronizes changing of the unicast encryption key for each frame, and then determines a unique starting unicast encryption key for each pre-shared key authentication.
WPA2-PSK: This supports AES (Advanced Encryption Standard) which is a private key algorithm that ranges from 128- to 256-bits.
WPA-PSK and WPA2-PSK: Turns on both WPA-PSK and WPA2-PSK mode.
To use any of these three options, please enter one of the following in the Key field:
A 64 character key, using only hexadecimal characters.
An ASCII "pass phrase" between 8 and 63 alphanumeric characters. Click SAVE.
Important: If you changed the network name or key, you will need to reconfigure your wireless network on your computer.