Hm.... This sounds more like the propaganda of a Wireless operator who
wants to keep the little guys out.

I've been doing wireless internet provision off the side of my desk
for over a year. I provide service to residential areas just off the
end of the cable line. I use 900 MHZ units. My customers are getting
about 10 MB/sec . Downtime? Hm... not once in over a year.
Two power outages... but what the heck... power back on... system back
running.

Nick.

On 17 Oct 2007 14:02:36 -0700, dennis@etinc.com wrote:

>On Sep 2, 7:20 pm, Jeff Liebermann <je...@comix.santa-cruz.ca.us>
>wrote:
>> On Sun, 2 Sep 2007 10:59:11 -0700, "Mountain Mike^^"
>>
>> <rukidd...@aol.com> wrote:
>> >I'm just playing around with setting up a "mesh" wifi access for my entire
>> >neighborhood, and would like to discuss theory if possible.
>>
>> Why use a mesh? The only real benifit to a mesh network is the cost
>> savings on the wired backhaul to the ISP. Since you're probably only
>> going to have one or two backhauls, there's not much savings. Instead,
>> you get the deal with store and forward packet repeaters, that eat
>> airtime, mutual interference problems, bandwidth bottlenecks, complex
>> routing algorithms, and performance issues. More specifically, you
>> only use mesh when you absolutely must use mesh.
>>
>> Light reading:
>> <http://pdos.csail.mit.edu/roofnet/doku.php>
>>
>> Reality. Be sure to read this one carefully, especially the part
>> where there's typically 50% or less probability of delivering a packet
>> intact, and the reliability even at 1Mbit/sec.
>> <http://pdos.csail.mit.edu/roofnet/doku.php?id=interesting>
>>
>> The commercial version of Roofnet:
>> <http://meraki.com/products/outdoor/>
>>
>> >Am I right in that using a router as an AP only (or bridge) would cut the
>> >bandwidth in half?
>>
>> Not quite. One hop will cut the *MAXIMUM* thruput in half. Let's
>> pretend that you're very lucky and get a 36Mbit/sec association
>> (that's a wireless connection). Maximum thruput is about half or
>> 18Mbits/sec for TCP (assuming no interference, etc). However, if you
>> shove that through a mesh network or store-n-forward repeater, it gets
>> cut in half again to perhaps 9Mbits/sec. I say perhaps because it's
>> usually more than half if there are a number of mesh nodes nearby. If
>> you add a 2nd hop, it gets cut in half again or 4.5Mbits/sec *MAXIMUM*
>> TCP thruput.
>>
>> What you need is a good overdose of reality. Setup a mesh network in
>> a closed room, where everyone can hear everyone else. A dedicated
>> repeater or WDS bridge will suffice. Now, try to measure performance
>> from end to end using IPerf (instructions on request or Google this
>> newsgroup for my posting on IPerf). If you turn off the repeaters,
>> you should get something near the maximum theoretical performance.
>> Turn on the repeaters, and watch the thruput drop radically along with
>> a corresponding increase in retransmissions and errors. Try it.
>>
>> >And, for experiments sake, I'd like to get an idea of what kind of hardware
>> >to buy to allow access for, say, 100 homes, in a 6 block area.
>>
>> Ummm... 100 customers? Every time it goes down, you want 100 phone
>> calls? Have you perhaps been snorting, injesting, or smoking
>> controlled substances? Never mind the technology. Do you think you
>> can handle the complaints and service calls? Whatcha gonna do when
>> some clueless user comes home with a virus or worm and eats all your
>> bandwidth? How about the not so trivial problem that customers will
>> tend to call you first, before calling their computer guru (who
>> charges money), simply because you're cheaper? Do your really need
>> this headache?
>>
>> Anyway, the loading is easy:
>> 100 light email and web users
>> 10 business users
>> 1 file sharing user
>> It doesn't matter how many access points or backhauls. One user can
>> hog the whole system unless you have monitoring and traffic management
>> in place.
>>
>> Ummmm.... How big is a "block" in feet or meters? Is that a city
>> block or country block? Tall apartments of single family suburbia?
>>
>> >I know I'd need to convert the AP for outdoor use (I'd like to play with
>> >cheaper consumer stuff), which I can do using an oudoor box and power over
>> >the cat5, right?
>>
>> Right. It's called PoE (power over ethernet) or 802.3af. There are
>> vendors that will sell you the complete package, or just the pieces.
>> For example:
>> <http://www.hyperlinktech.com/web/power_over_ethernet_weatherproof_enc...>
>>
>> >Although I'd probably design a conduit to carry the signal
>> >and 12V seperately for easier maintenance. Any idea the wattage necessary?
>> >I'm thinking of using PSU's from scrap computers.
>>
>> The delivered power is limited by the resistance of the power wiring.
>> That's why PoE is normally done at 48VDC, so that the effects of the
>> wire resistance is minimal. Junk power supplies are only going to
>> supply 12VDC, make a bunch of noise, probably smoke the cable if you
>> short it, and are not terribly reliable. Look into real PoE adapters.
>>
>> >Then, how about the repeaters? I need the same brand usually, correct?
>>
>> Repeaters are not very well defined in the IEEE 802.11 specs. The
>> result is substantial incompatibility among vendors and versions.
>> That's one nightmare I suggest you avoid. Repeaters are also a basic
>> component of mesh networks, which I previously suggested are a bad
>> idea.
>>
>> >I know about the LOS issues, and plan on doing all roof mounts, and USB
>> >client adapters.
>>
>> Keep planning. You'll find that USB is limited to 16ft maximum cable.
>> You can get amplifiers that will go farther, but then you have to
>> supply power at the destination end. Use ethernet and PoE instead.
>>
>> >Also, any idea of the bandwidth necessary and how to limit it to each
>> >client? (100 users, typical home use).
>>
>> Look at the real bandwidth managers:
>> <http://www.etinc.com/index.php?page=bwmgr.htm>
>> and see what you might need. Also note that it's not enough to simply
>> configure a bandwidth manager and let the system free run. You gotta
>> monitor the traffic to look for abuse, changes, hackers, idiots, and
>> failures. You'll need to know the performance of each user and which
>> one's are hogging the system. Check out various traffic monitors.
>>
>
>Just to comment on this, you really DONT need to spend your life
>chasing abusers. We've been recommending per-IP controls for several
>years now. But using burst controls, you can identify those that are
>abusive automatically and implement effective controls that don't
>need to be monitored. As tunnelling and encryption become more and
>more prevalent in "abusive" protocols, you'll eventually have no
>choice but to monitor overall usage, so you might as well start now
>and save yourself a lot of headaches.
>
>As an ISP you are a reseller of bandwidth. I've always has
>philisophical problems with ISPs deciding which protocols are good and
>which are bad. The truth is, that "good" usage is identifiable by the
>fact that its not a continuous use of bandwidth. Web browsing pulls
>pages and stops for a while. Even downloading movies stops after
>awhile. Defining a fair slice, and then setting controls that enforce
>that slice, is a generic way to manage a network without having to
>care what specific users are doing with the bandwidth.
>
>Dennis Baasch
>Emerging Technologies