[Beowulf] Wireless clusters (Bridging 802.11a)

Alvin Starr alvin at iplink.net
Wed Jan 14 23:07:37 EST 2004

Jim Lux wrote:
> I'm building a cluster using wireless interconnects, and it is getting 
> to be a royal pain to figure out what sort of adapters/interfaces to 
> use.  I'm casting some bread upon the waters here to see if anyone has 
> fooled with this sort of thing.
> I want to go 802.11a because of spectrum usage, not because of data 
> rate.  If I go to 5GHz, I don't have to worry about accidentally 
> connecting to JPL's 802.11b (2.4GHz) network infrstructure, for 
> instance, which will keep netops off my back.
> The processors in the cluster are Mini-ITX widgets with Compact Flash 
> (CF) drives, and, while booting off the net might be nice, I'm going to 
> boot off CF for now.
> Here are some issues that have come up:
> 1) there's two ways to get the node to talk to the net:
>  via the ethernet connector and an external bridge
>  via a PCI card with a 802.11a adapter (most likely a 802.11a/b/g, since 
> that's what's available) (D=Link, Netgear, and Linksys all have them)

take a look at the Actiontec cards. They have a line of prism based cards that are supported by linux and when I was 
talking with them they made sounds like they were going to stay with the prism chipset for a while.

> In all cases, I'd have an "access point" of some sort to talk to my head 
> node/NFS, etc.
> Ideally, I'd like to set up the network in "ad-hoc" mode, where any node 
> can talk to any other directly, without having to be routed through an 
> access point. In "infrastructure" mode, many clients can talk to the 
> access point, but clients cannot talk to clients, except by going 
> through the access point, creating a single failure point (probably not 
> important for my initial work, but philosophically "bad").
> 2) It's unclear whether there are  Linux drivers for any of the PCI 
> based 802.11a cards. The mfrs don't seem to want to fool with that 
> market, and, chipset mfrs are quite reticent about releasing the 
> intellectual property needed to do a good job writing the drivers.
> 3) I could go with external bridging adapters (perhaps with integrated 
> routers, in case I add another ethernet device to the node, or, to hook 
> up a sniffer).  Here the problem is that not all mfrs appear to support 
> bridging, at least with more than 2 (i.e. they can set up a point to 
> point bridge, but not a many to many bridge)
>  From some reading of the various manuals, it appears that some "access 
> points" can be set up to appear to be a "client" in infrastructure mode, 
> however that's a problem philosophically (and in terms of latency).
> So, does anyone know which "access points" (i.e. a 802.11x to ethernet 
> box) can look like a client in an ad-hoc network.
> (possible candidates:  Netgear FWAG114, D-link DWL-774, DWL-7000AP, 
> Linksys WAP54A*, WAP51AB, WRT51AB.  *Linksys says that the WAP54A 
> doesn't do bridging)
> Part 2 of the quest.................
> I'm also looking for suggestions on performance and timing tests to run 
> on this cluster once it's assembled.  Aside from the usual network 
> throughput (benchmark program recommendations requested), I'm interested 
> in techniques to look at latency, latency distribution, and dropped 
> packets/retries, since I suspect that wireless networks will have very 
> "unusual" statistics compared to the usual cluster interconnects.

I think you will want to play with the payload size. It seems to make a big difference for what we are doing(net boot 
over wireless).

> And, bearing in mind our recent lengthy thread on timing and clocks, you 
> can be sure that I will do those sorts of tests too.
> James Lux, P.E.
> Spacecraft Telecommunications Section
> Jet Propulsion Laboratory, Mail Stop 161-213
> 4800 Oak Grove Drive
> Pasadena CA 91109
> tel: (818)354-2075
> fax: (818)393-6875
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Alvin Starr                   ||   voice: (416)585-9971
Interlink Connectivity        ||   fax:   (416)585-9974
alvin at iplink.net              ||

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