Past EED rants


Live leaderboard

Poker leaderboard

Voice of EED

Sunday, 11 June 2006

Lurks2Houmous WAN link phase 1 [Lurks]

We moved house into our dream home, at last. It's a bungalow just a row off from the sea on the very south coast of England. Of course a move brings all the usual difficulties with broadband. I was hit up with a triple whammy of having no Vodafone signal for my 3G/GPRS card, no ADSL and my order being cancelled due to the presence of the former owners ADSL on the line, and even my fallback plan of Wi-Fi to Houmous across the road was foiled by the presence of not one but three garages in the direct line of sight (LOS).
The only issue I could realistically do anything about was wireless, so fresh from having dealt with the move of all our stuff from the previous house, I spent probably an hour on a constantly disconnecting crappy GPRS link ordering some wi-fi boosting stuff from Dabs. I decided to choose two solutions for redundancy. We hadn't even gotten up the new name of the house yet but this was the new billing address for credit cards etc so the missus bunged up an impromptu bit of paper proclaiming 'Stormwind'.
The access point I'm connecting to is one of those Belkin Pre-N Wireless Routers. Houmous kindly rejigged his cables to give enough play to set it up on the window sill with all three antennas placed the other side of a metallic set of venetians. Quite frankly given the previous location well inside the room, I'm amazed I picked up the SSID at all earlier on my laptop adaptors. Testament to how much better wireless gear works when there's not 20 nearby screaming access points and other sources of noise like we had in London.
So anyway, what we have here is what I'll call Solution A and Solution B.

It'd never have occured to buy something like the Hawking dish thing but there was an actual banner for it when I was shopping on Dabs and some direct-click is most welcome when every page took 3 minutes to load. It's pretty well rated on the net too. It's a pretty cheap and toy looking plastic widget with a USB mini jack on it and an adjustable dish on the front. 8dB of gain is pretty substantial on something this compact and inexpensive. It also has the advantage that you could use a long USB lead and position it where you like. I was desperate enough to run a huge USB lead out the window and up to the roof and put the damn thign in a plastic bag and gaffa tape it to the guttering if needs be.
Getting it up and running was straight forward and it weirdly scans around the channels but doesn't give an update on found SSIDs until you hit refresh. It reported 40% signal from the access point which you'd think would be quite healthy. However this was at the minimum 1mb bitrate. The ping rate was kinda all over the show but worse still, it just kept sort of pseudo disconnecting. This would happen every 10-30 seconds or so and they'd no more IP connectivity even though it says it's still connected. I'd go into the control software and hit connect again and it'd come instantly good. Why it can't do this itself transparently is entirely beyond me.
The bottom line is that Solution A, despite a good 8dB gain, was ultimately failing to provide any kind of link at all. Strangely moving the dish around didn't improve matters very much. I gave up on the crappy control software for trying to detect signal levels and installed Net Stumbler which has a handy S/N graph. Moved the dish around and not much difference within 20-30 degrees or so. In essence without a direct line of sight, we're relying on microwave reflections for our link. I could have moved the dish outside via a long USB lead but some experimentation with just holding it in the open window at various positions and angles didn't boost S/N appreciably.
Having failed with Solution A, I thought at this point that there may well simply not be enough signal for any solution to work effectively. Solution B consists of a cheap PCI Wi-Fi card, a Dabs value unit but actually quite a respected brand, Edimax, coupled with an SMC directional antenna. The idea was I could actually sit this outside on the window cill if required however there proved to be not quite that much lead unless I moved the entire PC right next to the window.
Here's the thing, I switched Net Stumbler from looking at the Hawking Dish to the Solution B and whammy, S/N is immediately higher. Hang on, the SMC is pointed in the wrong direction! I place it up onto my speaker, angle it towards the access point and the signal pulls up nicely. Blimey! Sat right next to the Hawking, pointing in the same direction, I could toggle A/B between the adaptors and no question, Solution B was at least 10dB higher and it was much more stable too with the Hawking dropping out from time to time.
Was it enough for a link? Kill Stumbler, disable the Hawking (sometimes close adaptors interfere with eachother), fire up Windows wireless networking and connect. Signal strength is measured as low but I'm getting a bitrate which bumps up and down between 18 and 24 megabits. Time for the ping test. Constantly 1ms, the occasional spike up to 20 odd milliseconds. I leave it running, I tilt the SMC around a it and it doesn't really change. Turns out, it's absolutely rock solid and stays up for horus without a single disconnection. Web browsing etc is like I've got a local ADSL connection. Success!
The distance and the lack of LOS here are certainly challenges for Wi-Fi. The fact I've got a decent link is certainly assisted by the multipath technology in the Belkin router. I'm going to surmise that the lack of LOS is why the Hawking dish failed so completely compared to the SMC. I think the SMC has a much wider gain 'lobe' if you like, and is picking up wider path of reflections and it's transmission likewise results in more reflections getting to the access point. Rather like firing at a squirrel behind a rock. If you fire a rifle your chances of a richochet hitting the squirrel are much less than if you fired a shotgun. Of course I have no data to back up this view.
I do suspect the Hawking would do quite well in line of sight test but I remain highly unimpressed with it's performance given it reports 40% signal strength and 60% link quality and dropped out constantly yeilding a completely unusuable connection. I'd be loath to recommend this expensive little toy for any real networking.
Praise here, I think, I can't exactly lavish on the PCI card since I'm sure there's a million like it with similar performance. However if I'm buying one again, I don't thin you can fault one of these for 12 quid. Where I can definately lavish praise is the SMC external antenna. This also came with a couple of adaptors to the tiny 'pigtail' type connections (which you should be able to find on laptop Wi-Fi cards!) and the large N-type connections. Those leads are bound to come in handy at some point and ultimately it's a smart-looking, Wi-Fi antenna with a decent gain. Bargain for 16 quid, highly recommended.
This isn't the end of the experiment in Wi-Fi between our houses. This was a quick and dirty emergency effort to get us through our broadband drought. Next up though will be the implementation of a fixed high performance LOS link from rooftop to rooftop. Signal strength will not be a problem here but we'll be requiring the highest performance Wi-Fi available to give us as close to LAN speed networking as possible. The new draft 802.11n equipment appearing on the market is interesting but so far I note that no one has really applied external antennas to multipath (MIMO) Wi-Fi that I have seen. I'm considering using some of this equipment and hacking on three external el-cheapo home-made antennas in various configurations.
Why the need for a high-performance wireless link? A street-wide WAN for sharing of movies, music and the goal of an eventual distributed LAN party with a live video link-up. Exciting stuff.

1 comment:

  1. I never did update about this project. It's actually now fully up and running. What I'm using is a pair of cheap 802.11g 'Super-G' D-Link DWL-2100AP units which cost about £40 each. In addition some 9dBi external antennas were used, sourced off a small outfit that manufacturers them on ebay, quite a bit cheaper than big brand ones.
    The difficulty in network topography was the issue of routing. If the LANs were to be on different subnets, which is desirable, then you need to have static route entries in routers on each end. That's possible at my end but at the other end there was a simple domestic ADSL router. In the end I just opted for a straight bridge mode and joined the two LANs up together. This is called WDS on the D-Link and my access point is happy to act both as an access point and a bridge at the same time, which is handy.
    Initially I wanted some high speed solution based on MIMO and 802.11n-draft equipment but there still remains nothing on the market that supports bridging, merely client/access point type stuff. The access points have, in theory, antennas with substantial gain which aren't that far away but in practice I found the signal strength on the DWL-2100AP when used with the external antennas wasn't very good at all. It's now no more than 'adequate'.
    Throughput is a little better than a straight 802.11g network thanks to the bonded Super-G channels, but it's still not particularly fast. Faster than using the Net between the two houses, that's for sure, with around about eight megabits of throughput I'd say. Still, it's been completely reliable and having another Internet connection on the same LAN via someone else's DSL is very handy indeed.
    In fact on the remote end, the DSL has to be disconnected occasionally to run a private VPN so there's one PC over there which uses my Internet connection during the day for continuous service. Also my PFsense-based embedded computer does the DHCP for the entire network and machines remotely which should be using the remote DSL connection use static entries.
    All in all it's not an uber solution but it works pretty well and didn't cost very much and has a low complexity. People on this LAN can browse shares on machines at the other end which wouldn't have worked any other way. Being able to switch Internet connection by just changing the gateway and DNS IP in your TCP/IP settings has already come in handy many times. For these purposes, not having the throughput what I'd like doesn't seem that much of a hardship. It still seems high enough to stream HDTV video.