Setting up a mesh wifi

I'm just playing around with setting up a "mesh" wifi access for my entire
neighborhood, and would like to discuss theory if possible.

Am I right in that using a router as an AP only (or bridge) would cut the
bandwidth in half?

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.

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? 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.

Then, how about the repeaters? I need the same brand usually, correct?

I know about the LOS issues, and plan on doing all roof mounts, and USB
client adapters.
Also, any idea of the bandwidth necessary and how to limit it to each
client? (100 users, typical home use).

I bet Jeff has some ideas

Mountain Mike^^ 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.
>
> Am I right in that using a router as an AP only (or bridge) would cut the
> bandwidth in half?
>
> 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.
>
> 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? 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.
>
> Then, how about the repeaters? I need the same brand usually, correct?
>
> I know about the LOS issues, and plan on doing all roof mounts, and USB
> client adapters.
> Also, any idea of the bandwidth necessary and how to limit it to each
> client? (100 users, typical home use).
>
> I bet Jeff has some ideas
>
>

You have done some homework here?
http://en.wikipedia.org/wiki/Wireless_mesh_network

"curly Bill" <(E-Mail Removed)> wrote in message
news:bXECi.86200$(E-Mail Removed)...
>
> You have done some homework here?
> http://en.wikipedia.org/wiki/Wireless_mesh_network

No, I hadn't. My previous experience with any Wiki was not good for relevant
info. However, I've found this stuff pretty good, thanks!

Any idea what the Linux stuff on the Wiki is so, well, so obtuse?

thanks again.

On Sun, 2 Sep 2007 10:59:11 -0700, "Mountain Mike^^"
<(E-Mail Removed)> 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_enclosures.php>

>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.

In case it's not obvious, you're going to need EVERYTHING that a
typical wire line ISP uses, with the added enjoyment of an unreliable
means of delivery. If you want to do this for free, that only
eliminates the billing system. Everything else still has to be there.

>I bet Jeff has some ideas

Nope. I'm busy buying test equipment, updating up my lab, dealing
with the ultimate messy house and office, loafing, and playing hard to
find.

Well, ok... just one idea. Start small. Find a Linux based wireless
router and install it on your roof (using PoE) as an access point.
Deliver shared service to a few friends and neighbors. Keep it small
so that when you do something stupid, you don't have a torchlight
parade of irate neighbors banging on your castle door. Learn system
admin, bandwidth management, and abuse mitigation on a small scale.
Once you've made all the basic mistakes, grow the system so that you
can move on to making bigger mistakes.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 (E-Mail Removed)
# http://802.11junk.com (E-Mail Removed)
# http://www.LearnByDestroying.com AE6KS

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> What you need is a good overdose of reality.

Got it.

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.
>


OK, I'll take your word for it.

> In case it's not obvious, you're going to need EVERYTHING that a
> typical wire line ISP uses, with the added enjoyment of an unreliable
> means of delivery. If you want to do this for free, that only
> eliminates the billing system. Everything else still has to be there.
>
>>I bet Jeff has some ideas
>
> Nope. I'm busy buying test equipment, updating up my lab, dealing
> with the ultimate messy house and office, loafing, and playing hard to
> find.
>
> Well, ok... just one idea. Start small.

Nicely written, and imminately enjoyable to read. Great stuff, thanks.

Well, nice links, Jeff. One more question, please.

These guys:
http://meraki.com/products/outdoor/>

Seem to already make what I had in mind. Seeing as I don't have to re-invent
the wheel, are you saying that this (apparently a mesh for hobby types) has
the inherent problems you just mentioned?

So, the result is what I want, but I should consider another design? What do
you have in mind? (gotta be wireless for the ususal reasons).

Maybe a simple POE with long shots? Or what?

(BTW, this is going to be a lab experient similar to the Roof Net guys....)

"Mountain Mike^^" <(E-Mail Removed)> hath wroth:

>Well, nice links, Jeff. One more question, please.

Groan. Why me?

>These guys:
>http://meraki.com/products/outdoor/>
>
>Seem to already make what I had in mind. Seeing as I don't have to re-invent
>the wheel, are you saying that this (apparently a mesh for hobby types) has
>the inherent problems you just mentioned?

Yep. Overly simplified, you have several problems:
1. You're building a WISP (wireless internet service provider) but
are not very aware of how much work that really involves.
2. Mesh networks can be made to work and certainly have their place.
Servicing non-paying neighbors is not my idea of one of those. Others
(such as Earthlink, Meraki, and various manufacturers will disagree).
3. Delivering reliability and quality service via Wi-Fi is a dubious
proposition mostly due to self-interference.
4. Mesh systems do not scale very well. The problem is that you
discover this only AFTER you spend considerable money. Anything can
be made to work on a small scale.

Also, I can tell you did NOT read the MIT Roofnet article or you would
have some questions regarding thruput and reliability limits.

>So, the result is what I want, but I should consider another design? What do
>you have in mind? (gotta be wireless for the ususal reasons).

Well, you could just join Meraki and try their system. It's not that
expensive and certainly cheaper than a do it thyself system. If mesh
is what you want, you'll certainly get a clue on how it works very
quickly. If that's too much trouble, go unto the Google (free) Wi-Fi
complaint and help message board, and see what manner of problems a
real mesh system can generate. Remember, as system operator, owner,
and chief technologist, *YOU* get to answer these type of questions.
<http://groups.google.com/group/Google-WiFi-Network/topics>

As for what I had in mind, I'll answer your questions after you answer
mine. For example, how big is 6 blocks in feet, meters, cubits, or
furlongs? That's not intended to irritate you. It's because wireless
networks are designed to operate in specific environments and
topologies. What's suitable for a small coffee shop hot spot, is not
suitable for "illuminating" an office building or apartment complex.
Give me some numbers and I'll gladly spend your money for you.

>Maybe a simple POE with long shots? Or what?

Dream on. Sounds like you're thinking of an omnidirectional antenna.
Yeah, that might work for starters, but has some rather severe
limitations, especially when it comes to minimizing interference. I'm
a big fan of "sector antenna", where you have multiple access points
and multiple 90 or 120 degree sectors per access point. However, I
can't tell if this is suitable for whatever you're doing.

>(BTW, this is going to be a lab experient similar to the Roof Net guys....)

Yep. Learn By Destroying (tm). Nothing like repeating their mistakes
on a small scale. I recall the definition of insanity was doing the
same thing multiple times and expecting different results. As I
mentioned before, you're problems are NOT going to be technical.
They're going to be administrative and system management. Simply
identifying the cause of problems, separating them between user and
system problems, and doing something about it at 4AM, is going to be a
major challenge. That's why I wanted you to start with a small scale
system. You'll get all the experience with irate customers
immediately and will not have to wait until the system grows to get
the experience. Also no need for a mesh with a small system. I have
a neighborhood wireless and wired LAN that I run. I often regret
doing it simply because of the weird problems that tend to appear at
odd times. For what it's worth, I tried to use old 802.11b junk
radios and am now replacing them with much better and more reliable
802.11g equivalents.

There are other mesh networks out there being used. We have one
locally:
<http://www.surfnetc.com/mp_perform.asp>

Some light reading from my bookmark mess:

An Experimental Scaling Law for Ad Hoc Networks. (Also applies to
mesh)
<http://black.csl.uiuc.edu/~prkumar/ps_files/exp.pdf>

Doing mesh the right way, using multiple radios per node:
<http://www.belairnetworks.com/about_belair/solution.cfm>
<http://www.belairnetworks.com/resources/documentation_display.cfm?c_id=10>

Some comments on whether mesh networks scale:
<http://www.smallworks.com/archives/00000072.htm>
<http://wifinetnews.com/archives/003972.html>

Some articles on various mesh networks (2004):
<http://www.moskaluk.com/papers.htm>

Meshbox:
<http://www.locustworld.com>

OLPC (One Laptop Per Child) Mesh WIKI:
<http://wiki.laptop.org/go/Mesh_Network_Details>

Where some of the WISP crowd posts:
<http://isp-lists.isp-planet.com/isp-wireless/archives/>

--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Mountain Mike^^" <(E-Mail Removed)> hath wroth:

>
>"Jeff Liebermann" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed).. .
>> What you need is a good overdose of reality.
>
>Got it.

Here's a good start. How many wireless connections do you think a
typical WAP can handle before something pukes in the firmware? It's
not as many as you think. See list at:
<http://www.smallnetbuilder.com/component/option,com_chart/Itemid,189/chart,124/>

>Nicely written, and imminately enjoyable to read. Great stuff, thanks.

Y'er welcome.
--
Jeff Liebermann (E-Mail Removed)
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...

> Groan. Why me?
>

Because you're the guru around here. Plus, you let me pay your consulting
fees in antique Japanese relics. (old stereos, tube radios, wrecked Datsuns,
etc.)

> Also, I can tell you did NOT read the MIT Roofnet article or you would
> have some questions regarding thruput and reliability limits.
>

Oh, I read it all right. Just some things I may get a bit later. Plus, I'm
the persistent type.

> As for what I had in mind, I'll answer your questions after you answer
> mine. For example, how big is 6 blocks in feet, meters, cubits, or
> furlongs? That's not intended to irritate you.

I'm not irritated in the least. To answer your questions, the mileage is
exactly 584' 7" on one side, and 956' 2" on the other side. A slight
rectangle. LOS clear from the roofs. Mean temp is 75*F, no snow, no freezing
in winter. An earthquake once in awhile, not much else in the way of
topography to talk abut. I'll start with 25 or so clients, and thanks for
the link to max supported per router.


>>(BTW, this is going to be a lab experient similar to the Roof Net
>>guys....)
>
> They're going to be administrative and system management. Simply
> identifying the cause of problems, separating them between user and
> system problems, and doing something about it at 4AM, is going to be a
> major challenge.

No, I have the admin all figured out. I'm not going to do any It's gonna
be free, and free means no support. Later, I'll just jerk it all out.

AS you say, wifi is not designed for some applications. However, the need,
especially in third world places is enormous. I'm thinking that off the
shelf parts may not be perfect, but eventually they will. Remember, a
computer was not designed for long distance phone service either, but it
works reasonably well. Most technology grew from the tinkerers, me thinks.

So, yeah, it may not be optimal. What really is in this world? Windows
Vista? (sacarism dripping........).

Thanks for the brain massage

Mountain Mike^^ wrote:

>
> No, I have the admin all figured out. I'm not going to do any It's gonna
> be free, and free means no support. Later, I'll just jerk it all out.

Thats even worse. From my experience when you undervalue or give away
your services people don't appreciate it. And since everything is free
they will expect lots of extra free stuff. You are in for a real
experience about human nature if you become the free ISP on your block.



>