There's a lot going on there. First a few points, then we'll get to some options.
I can't believe that Apple would implement such a crap routing scheme, so right now I'm assuming its the 2102.
While it is an Apple box and everything inside the box can be built the way Apple wants to do it, most of its wireless features require interoperability and so are based on wireless standards, including WDS. So while they can work their magic with putting USB harddrives ON the network, the wireless network itself must still conform to the standard.
The box does get too hot for my taste, that's for sure. I wonder if the router part of the 2102 is less than great.
Boxes that just do routing/QoS often cost more than the 2102 does with all the VoIP. The 2102's router is not high performance and has limited memory, with a particular weakness when it comes large numbers of transactions (as opposed to volume of data). As long as its not hot enough to auto-restart, its not *to* hot, but do what you can keep it cool, like mounting it vertically or laying it on a metal plate.
Okay, getting down to business. Your biggest challenge is that two big variables changed at the same time that a problem started, so there is not an obvious culprit. Take the voip box out of the network for an hour and see if the problem goes away.
My landlord also uses my wireless network, and my old WRT54GL with DD-WRT and the power cranked to 240 mW/m worked just fine to cover his side of the house and out to the barns.
AEBs have an option to turn down the power, is it possible its not maxed out? Otherwise the AEB's antenna is not as strong. A definite drawback to the cleaner design, no external antenna. Option #1, add one:
http://www.quickertek.com/products/80211N_upgrade_BS.php
But when I got the AEB, it wouldn't reach as far and he was having issues. So, I got another AEB for him and used the 2nd one to extend the wireless network. Which it did.
So far so good. But since then, I've noticed that the performance of the connection using wireless is CRAZY variable. Like sometimes nearly the full 2 mbps down and 7 or 8k up, and other times like 350kbps down and 20kbps up. Meanwhile, the desktop Mac Pro, which is connected via internet cable to the LAN port of the primary AEB, always gets pretty good performance, even when other wireless clients are on the LAN.
WTF is going on? I've googled to see if people have had trouble doing WDS with two AEB's, and I get zero reports of problems.
Back in the b/g days, I tried to make WDS work and was so :hairpull: that I gave up. N is supposed to have an improved version, but 1) any non-N devices connected to either AEB may require b/g use and 2) N WDS may not be as good as advertised.
So, the 2nd AEB gets half service, let's say. Then it divides that half among maybe up to three or four wireless clients. So, if I'm downstairs and connect to the 2nd AEB, which is in my landlords house, but just on the other side of the wall, then I get absolute crap for bandwidth.
This is my issue with WDS. You've got an antenna in a box. Any time that antenna is doing one thing, it can't also do another. So thats fine if a relay is only doing relay. But when a relay is also providing service for one or more clients, thats a lot to do. Bit 01 comes in from client, bit 02 has to wait for bit 01 to be retransmitted before bit 02 can come in. Then bit 03 has to wait for bit 02 to do its thing. The solution would be dual antennas, which the new AEB has, so maybe...
I'm going to try reconfiguring things for a test, so that the AEB1 is not bridged to the 2102, but is rather the first in line downstream of the modem. Then I will plug the Mac Pro and 2102 into the AEB1, and will keep the AEB2 wirelessly bridged to the AEB1, to extend the network.
So, I'll need to forward port 80 to the 2102, right? I assume this is straightforward, but I haven't read up on it.
Let us know how it goes. Again, I suggest pulling the 2102 off the network for this test. Its a lot faster to reverse and completely removes it as a cause if the issue continues.
If you don't want to access the web interface of the 2102 during the test, all it needs is an internet connection and a phone. If it works when you reconnect, don't bother changing anything unless you 1) need to or 2) want to leave the new configuration long enough to change settings with it.
To answer your question, don't bother with port forwarding. All it should need is WAN access to the web interface.
Is this what you do with your TimeCapsule? And if so, do you have a permanent DHCP lease to the 2102, or is it a static IP? Or what?
With Airport Admin, log into AEB1. Under Internet > DHCP > DHCP Reservations, click +. Type in something like 2102 > Mac Address > Continue. Then just type in the MAC ID of the 2102 and an IP you want it to have.
The best way (#2) to expand the range of a wireless network is to connect AEB2 to AEB1 via an ethernet cable, then configure them with the same network name. Are we talking separate buildings here? If so (#3), is AEB1 against the wall closest to house2?