At 6/18/2010 07:21 PM, Greg Ihnen wrote: >Are you seeing benefits from the mesh approach that you wouldn't get >from backhaul/APs? Doesn't the mesh gear usually have >omni-directional antennas which can be problematic in an RF polluted >environment.
There's more than one type of "mesh" out there, and I may need to be clearer. The first generation "WiFi" mesh, with the same frequency used for access and meshing, was a bad joke. It reminded me of the AX.25 digipeater networks that we played with in the 1980s. They demonstrated, in slow motion, what didn't work! The early Trangos, I think, were like that. They could "mesh" about one hop from the injection point. At that point in time I discounted "mesh networks" as a bad idea. Then came multi-frequency meshes. These do the backhaul on one frequency and access on another. (Okay, SkyPilot can use the same frequency for both, but it's layer 1 synchronous. That works too.) This is what I'm talking about. >Probably a better way would be to use a standard back haul with >access point network and if you want redundancy put in extra back >hauls and extra access points. The back hauls could switch over >automatically, and the AP's would just need be commanded on or off. Well, that's what the hardware might look like. A typical box would have three radios, two for a backhaul chain and one for access, or maybe more access radios if sectorized. We can't use "standard" one-hop backhaul because the customers are in a tough location (basically wedged between a rock and a wet place) that's a few radio hops away from anywhere. And that's one reason why per-hop latency is all-critical. I could put a chain of back-to-back radios there, but would run out of frequencies and room on the poles/towers before I got a few hops in... I need to extract some of the signal at several stops along the chain. I've been playing with RadioMobile and while I think its land cover forest-loss computations are *way* optimistic (even pushing it to 180%), it has helped identify the only possible ways in and out. I call that a mesh... but it has nothing in common with urban meshes, LAN meshes, or those awful home-router toys. Aaron added, ..> and layer 3 meshing gets the job done. > > Why layer 3? Because you don't want it all to be a single layer 2 > broadcast area :) I don't want a layer 2 broadcast mesh, actually. I'm thinking more in terms of Carrier Ethernet, if I can make that work. It's switched, not bridged. Huge difference. I've got some bridged-network horror stories to tell myself, and I don't like bridging. But suffice to say that the project in question is not exactly a pure IP network. That's a story for another time though. > > Your spectrum is just too valuable to send every broadcast > message to all others in the network. > > Combine that with BGP/OSPF/whatever backbone links which are > built point to point (or point to a few multipoints) > > with high capacity and you are set. > > This way you can even have layer 2 meshes interoperating with > different meshes or OSPF/BGP/IS-IS/whatever protocol > > backbone networks. HMWPplus seems to be doing an SPF protocol among nodes, at a layer below IP. That seems right to me. BTW I'm pretty familiar with SPF routing concepts. Way back in 1986 or so, I started writing RSPF, an SPF routing protocol for IP over radio. A couple of guys implemented it, more or less, in Linux, in the 1990s. But it's pretty much forgotten. I've moved past IP; it's just so T.C. So I am really open to suggestions, and I hope I've made my requirements clearer. This is a challenge to serve the most impossible place we know of; our second expected project area some miles away looks to be just a bit easier. (Still convex beach and wooded hills, but it doesn't look as steep.) -- Fred Goldstein k1io fgoldstein "at" ionary.com ionary Consulting http://www.ionary.com/ +1 617 795 2701 -------------------------------------------------------------------------------- WISPA Wants You! Join today! http://signup.wispa.org/ -------------------------------------------------------------------------------- WISPA Wireless List: wireless@wispa.org Subscribe/Unsubscribe: http://lists.wispa.org/mailman/listinfo/wireless Archives: http://lists.wispa.org/pipermail/wireless/
