Help- WDS with Extreme-N & 2x Airport Express with ~ 40% packet loss

Question

So this problem is driving me crazy. I recently moved into a house that has enough metal in the walls (don't ask) to prevent me from using a single base station so I expanded my network as a WDS utilizing an Airport Extreme (mixed NGB mode) and two Airport Express (one as a relay and one as remote). The configuration appears to work normally some times but other times (especially evenings) I get a very high rate of dropped packets between the client notes (which are connected through the WDS-enabled Expresses) and the base station (using a simple ping 10.0.1.1 to check connectivity to the APBS-N). The problem manifests itself from a users' perspective as very long DNS lookups which causes slow page loads in a browser but it's very reproducible via ping.
So far I've tried changing the channels on the network but I haven't seen a huge payoff there. iStumbler reports no additional networks on channel 2 which I'm using, there are some on channel 1, 5, and 13. I've also tried channels 7 and 11. We have no microwave in the house and our cordless phone (5.8ghz) never interrupted with our simpler Express-based network at our old house, n/m the fact that the phone is never in use when we have this problem.
I don't seem to see the problem when I'm local to (in the same room as) the AEBS; it really seems to happen only when I'm on the WDS-enabled remote and/or relay.
Other data points that may help are that the AEBS-N drops out of the Airport utility at the same time. Sometimes isn't gone for 30 seconds, other times for > 30 minutes. The other base stations continue to report "Green" in that they are not having any WDS problems. If I disconnect the remote node the relay will correctly reflect a status of yellow, so I know it somewhat works.
It's an open network (no encryption, open SSID) so it's unlikely that there's an issue there.
Clients include an Apple TV, iBook G4, MacBook, Tivo Series 3, Intel Mini and Dell Latitude D810. Because of the diversity of clients I don't think it's a driver or NIC adapter issue on any of the clients.
Does anyone have any experience working in a similar environment? Suggestions on troubleshooting packet loss (or other performance issues) in a WDS network?
Thanks,
Mike

Answer 1

Hello errorsupply. Welcome to the Apple Discussions!
I suggest downloading a copy of iStumbler. Use iStumbler's Inspector feature (select Edit > Inspector from iStumbler's menu) to determine the Signal-to-Noise Ratio (SNR) at different points around your house, by performing a simple RF site survey. Within the Inspector, note the values for "signal" & "noise" at these locations. Start with your MacBook near the main base station, note the readings, and then, choose the locations where you have the relay and remote base stations.
SNR is the signal level (in dBm) minus the noise level (in dBm). For example, a signal level of -53dBm measured near an access point and typical noise level of -90dBm yields a SNR of 37dB, a healthy value for wireless LANs.
The SNR, as measured from the MacBook, decreases as the range to the base station increases because of applicable free space loss. Also an increase in RF interference from microwave ovens and cordless phones, which increases the noise level, also decreases SNR.
SNR Guideline
o 40dB+ SNR = Excellent signal
o 25dB to 40dB SNR = Very good signal
o 15dB to 25dB SNR = Low signal
o 10dB to 15dB SNR = Very low signal
o 5dB to 10dB SNR = No signal
If the SNR is 20dB+ at each of these locations, then you should be getting reasonable performance from your AirPorts. If less, either try to locate/eliminate the source of the Wi-Fi interference or try relocating the relay and/or remote base station until they are within a 20dB SNR range of the main (and for the remote, of the relay).