I have a 27" i7 though based on a short internet search this symptom is not constrained to specific models. I can't connect to 5GHz networks (it seems as "connected" but network performance is abysmal or nonexistent). Took me 2 days of frustration to sort this out - here are the details.
1. Had a perfectly working WiFi network with a 1st gen Airport Extreme gigabit base station, and numerous devices/computers all working without a hitch.
2. With a recently purchased 27" iMac connection was flaky at best, so decided it might be a low signal issue (hovered around 30% based on iStumbler) - purchased the latest (dual-band .n final) base station. Issues remained.
3. Set up an "extended" network with the old base station, and - though reception showed as excellent at 60%, it still refused to work properly.
4. Just out of curiosity, "downgraded" to WDS and voila - all was fine. The key difference between Apple's proprietary "extended" network and WDS is the band they use - 5GHz vs 2.4GHz.
Solution:
5. A spark of light - manually constrained the Extreme base station to 2.4GHz only (802.11abg) and that tamed my connection. Still not happy with 54mbps, hopefully a firmware update will fix this soon.
1. Had a perfectly working WiFi network with a 1st gen Airport Extreme gigabit base station, and numerous devices/computers all working without a hitch.
2. With a recently purchased 27" iMac connection was flaky at best, so decided it might be a low signal issue (hovered around 30% based on iStumbler) - purchased the latest (dual-band .n final) base station. Issues remained.
3. Set up an "extended" network with the old base station, and - though reception showed as excellent at 60%, it still refused to work properly.
4. Just out of curiosity, "downgraded" to WDS and voila - all was fine. The key difference between Apple's proprietary "extended" network and WDS is the band they use - 5GHz vs 2.4GHz.
Solution:
5. A spark of light - manually constrained the Extreme base station to 2.4GHz only (802.11abg) and that tamed my connection. Still not happy with 54mbps, hopefully a firmware update will fix this soon.