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In a startling series of events, Cincinnati Bell managed to get my new DSL line working. No one is more shocked than me! Evidently my loop length was in fact no where near 22 k feet, because I'm seeing download speeds between 3 and 4 Mb/s, which would be impossible at that distance. So basically I've been putting up with the cable company for over two years, for no good reason. Thanks AT&T!
The CinBell tech came out and determined that my DSL problems were caused by noise or other problems on the line, rather than the loop length. They dispatched AT&T (ILEC who owns the lines) to fix it, and they were onsite within two hours. They found and removed a bridge tap, and after a few more changes on the ISP's side, I was suddenly able to keep my DSL line mostly stable at about 3.5 Mb/s.
I say mostly because I've seen a few disconnects and some sporadic packet loss, but I'm going to give it a few weeks to settle and see how it does. So far it's been up almost a week and things seem to be improving. I don't know what my actual loop length is now, but I still don't think it's super-short because my speeds to seem to fluctuate, which tells me that the modem isn't always able to keep the same number of channels active. (If you don't know WTF I'm talking about, check out the DSL article at wikipedia) The speed tests I'm using have put my download speed as low as 2.9 Mb/s and as high as 4.3 Mb/s at different times, but my upload speed is solid at around 650 kb/s which is pretty nice. I'll happily go from 4800 / 350 kb/s on cable to ~3500 / 650 kb/s on DSL, plus I'll finally be able to get a static IP for a reasonable fee.
While I evaluate the new service, I wanted both cable and DSL active, which meant adding another NIC to my router. It's getting a little crowded -- seven ethernet interfaces now (I could really use a nice VLAN switch 
). Then I got to play with "ip route", "ip rule" and iptables on linux to send internet traffic out the different pipes depending on it's source ip, subnet and/or protocol, destination port, etc. Right now the private wireless subnet and a few servers are going out the DSL line, and the rest are using cable. I'm really hoping the DSL has no significant issues for the next couple weeks, allowing me to cancel the cable service for good. The monopolistic cable company has screwed me so many times, both at my home and at client offices we support, that I die a little inside every month when I pay the cable internet bill.
