Throughput over 34 klms

[bobski]

I have 2 wifi links of 12 ks and 22ks each link uses 2 Senao 2611's. The first has the 2611's bridged and the second has them point to multi point. I'm getting a throughput of about 3mbits/sec over the entire length. Is this all I can expect? Is there any other AP's that may be better?

[M/Q]

More details, please. Are you saying that the two links are connected for a total of 34km? What are you using for antennas etc. I sound like a broken record, but we do not have a clue as to what you are using. So it would be hard to offer any kind of worthwhile help..

[bobski]

Thanks for the reply. The overall setup I have is a Billion 7402vl adsl modem for the 1.5 MBit broadband connection being fed to a Senao NL 2611 CB3 + in bridge mode with a 24 dB mesh antenna. This has a clear LOS to the top of a mountain 12 klms away about 1200 ft above the first ap. The receiving AP on the mountain is up a 100ft tower and is another Senao NL 2611 CB3 + in bridge mode. This link the APs indicate a connection of 11 Mbit. This then goes through a switch to 2 more Senao 2611 CB3 + in access point mode each with a 24 dB mesh antenna. One of these goes 22klms to another Senao NL 2611 CB3 +, with a 24 dB antenna, which is in bridge mode. This link the bridged AP indicates a 40% signal strength with Current communications quality (%):57. The other link is the same configuration but only 4.5 klms with 100% comms quality and 80% signal strength. This then goes to another Senao NL2611 CB3+ in access point mode. The originating point is in a town of about 2500 people and after that it is open farm land with no interferance from other networks. The APs on the mountain are in access point mode so that we have broadband access on the mountain. The World paragliding championships will be held there in 2007 and that is why I'm trying to optimise this setup ready for that. There will be an ip camera setup on top of the mountain in the near future as well as a weather station accessible from the net. The throughput I tested was over the 12 k and 22 k links combined. Also the 12 k and 4.5 k links tested much the same.

[M/Q]

Just like to diagram it to make sure we are on the same page.

ADSL Modem
|
| Signifies Ethernet cable
|
>- Senao 2611/24dBi Dish (Bridge1)
...<>
...<> Signifies 12Km wireless link (Fresnel Clearance=20m)
...<>
....>- Senao 2611/24dBi Dish (Bridge2)
........|
........>- Switch
...........|..|
...........|..>- Senao 2611/24dBi Dish (AP1)
...........|......<>
...........|......<> Signifies 22Km wireless link (Fresnel Clearance= 26m)
...........|......<>
...........|.......>- Senao 2611/24dBi Dish (AP Client 1)
...........|...........|
...........|...........>- Senao 2611/? (AP3)
...........>- Senao 2611/24dBi Dish (AP2)
...............<>
...............<> Signifies 4.5Km wireless link (Fresnel Clearance= 12m)
...............<>
................>- Senao 2611/24dBi Dish (AP Client 2)
....................|
....................>- Senao 2611/? (AP4)

Does this look like the setup? If so it is a neat setup and seems to be working quite well. There are a few questions that might help improve the throughput.

What is the channel distribution on the system? Also did you notice the Fresnel Clearance values I have posted? That refers to a very important distance that needs to be clear of any physical obstructions. This link I postes will give you a good idea as to what is required and why it is needed.

http://www.terabeam.com/support/calculations/fresnel-zone.php#meters

The other calculations on that website are also very useful in determining how to optimize your systems.

So, as an example the first link minimum would be having two antennas at least 20m off the ground and the ground has no topological changes or other physical obstructions. This has to do with multipath interference as well as the curvature of the earth when you get on some of the longer links. It is significant as you can see from the 22Km link.

One last question is to how you have the antennas and systems situated when there are multiple devices in relatively close proximity? There could be some interference issues if there is an overlap of coverage areas and backside emissions.

[bobski]

This is a good representation of the setup. Looks like a change in channels would help!! This setup has been working for about 9 months now. The main problem I've had has been batteries going flat on the mountain after prolonged cloudy weather. Just need a bigger solar panel and battery bank I guess. The 22 k link suffers when there is heavy cloud but still works reasonably well. The access point indicates a sig level of 25% sometimes and speed drops to 1mbit.
If the dishes are mounted higher at each end of the system I could expect some improvements or is the throughput as good as I can expect?




ADSL Modem
|
| Signifies Ethernet cable
|
>- Senao 2611/24dBi Dish (Bridge1) Channel 1 Dish 10m high
...<> Good line of sight but has some trees at this end
...<> Signifies 12Km wireless link (Fresnel Clearance=20m)
...<>Easily 30m clearance this end
....>- Senao 2611/24dBi Dish (Bridge2) Dish 30m high
........|
........>- Switch 3 dishes all at same level on tower only inches apart
...........|..|
...........|..>- Senao 2611/24dBi Dish (AP1) Channel 9 30 m high good los and clearance
...........|......<>
...........|......<> Signifies 22Km wireless link (Fresnel Clearance= 26m)
...........|......<> Good los
...........|.......>- Senao 2611/24dBi Dish (AP Client 1)dish only 3m high on side of house
...........|...........|
...........|...........>- Senao 2611/? (AP3)
...........>- Senao 2611/24dBi Dish (AP2)Channel 7 dish 30m high good los and clearance
...............<>
...............<> Signifies 4.5Km wireless link (Fresnel Clearance= 12m)
...............<>
................>- Senao 2611/24dBi Dish (AP Client 2) only 3m high good los and clear
....................|
....................>- Senao 2611/? (AP4)

[M/Q]

I would be concerned about AP client 1 and 2, especially 1. You lose line of site due to the curvature of the earth at approximately 24km. So, you have less than minimal Fresnel clearance. You maybe getting most of your signal from a bounce. Has the signal been different in the winter? I guess I should ask if you have winter first.

What channels are you using? Or are they all on the same channel?

Also where are you located, as I was wondering what kind of logon you are thinking about. Reason I ask is that if you are going to have it wide open, you need to have some sort of liability disclaimer on a sign in web page just to protect yourself.

[bobski]

Sorry I should have highlighted the changes of your discription of the setup. the channels and heights of the dishes are noted on my last reply as additions on your post of the setup. The tower in the centre of this setup is about 1200 ft above the surrounding terrain so don't have a problem with the fresnel except maybe at each end where the dishes are mounted low down. The main reason I'm concerned about the throughput is because I wanted to add another 1.5 mbit adsl connection to the network to distribute to some other people. This is also why I was trying to connect the D-Link AirPlus DWL-G520 to the ap 4.5 klms away as this would be the cheapest option to connect more people. I have already connected another broadband connection to the network as a temporary trial and it seemed to work ok but I thought the throughput being just 3mbit would give me no leeway for the second 1.5 mbit broadband connection. I don't know if I've exp[lained this very well but I hope you get the general idea. As it is all the speed tests that I do at the modem end are the same as at the distant end of the network so the one BB connection is working well.
I'm located in rural Australia about 300klms North of Sydney. The setup is only used for private purposes at the moment and any extra people given access to it would be to try and offset the cost of it.

[M/Q]

That is exactly what I was referring to as you only have the dishes 3m off of the ground . That is just asking for multipath interference, IMO. And as I mentioned the 22km link is near Loss of LOS because of the curvature of the earth. You stand on the ground you can only see 24Km due to the earth's curvature and you are very close to that limit right now.

Again what channels are you using????

[bobski]

The mountain with the 30m tower is 1200 ft high. The 12 klm link is on channel 1.
The 22k link is on channel 9. The 4.5k link is on channel 7. I see that these should be at least 3 channels apart where they can interfer with each other.

[M/Q]

You should only use channels 1, 6, and 11, unless you are allowed to use up to 14 in AU. I do not remember the regulations.

Also I realize the tower is that high but the other endpoint is only 3m off of the ground. It is way less than the required Frensel Clearance. You are most likely picking up multipath signals as a direct link is most likely covered as I mentioned.

You asked how to maximize this setup and I am trying to tell you what to do to improve it. You do not want to listen that is fine, I do not want to waste my time either. One more time maybe this link will help.

http://www.zytrax.com/tech/wireless/fresnel.htm

[bobski]

I really appreciate your input into this. I was trying to work out if I had to have the dish at 26m high at the end of the 22k link. I thought the fresnel zone tappered at each end and therefore I need to work out the minimum height to have the dish for best effect. It would be prohibitively expensive to try and get the dish at the full 26m height. Should the signal strength increase as the dish is mounted higher or will the quality improve without an improvement in strength? Thanks for your input thus far.

[M/Q]

Whether there will be any improvement is some what subjective. I was just trying to point out a possible improvement. The only way to know for sure is to test. I suspect it would not be an improvement in signal strength, but an improvement in throughput bandwidth. Did you read the last link and the effects of phase cancellation? That is what I am concerned about. But, in any real situation, you maybe just right phase-wise for that particular topology. And moving an antenna may even make it worse. If you get a chance read that link it is very informative and accurate.

[bobski]

Yes I have read it. Thanks for your help. I am beginning to understand there are no definites with these sorts of problems.

[M/Q]

Once that is understood, working with RF becomes great fun as well as frustrating. Testing and experience help, but changes in any of the multitude of variables will have an affect.

[EastCoastWiFi]

Hate to rain on anyone's parade.

You will not see anymore than 3 megs of throughput on the CB3's. Period. Well known problem that there isn't any resolution to.

You get what you pay for.

[Alan87i]

Ouch Sounds similiar to my problem with the DI-624's I was using for my small 700 foot bridge. Anyone who followed the post knows I messed with antennas, cables and trees. All the while the equipment was the main cause of the problem.
Still the Knowledge gained was worth all the time & effort I put into the project and more.
Allan

[bobski]

I originally used Senao 3054 CB3+ for these links but could only get dial up speeds.
What would be the best brand of ap's to use over these distances for best throughput and what would be the max throughput to expect for 12klms and 22klms.

[Jet Broadband]

Cisco 350 equipments with 24dbi antennas can be used to distribute 25miles upto 7mbps with security encryption.

I need some help on iptables/tc for running bandwidth management on linux.
I went thro' some examples. Is there any kind of doc, which can walk thro' iptables/tc for "bandwidth management for dummies " kind of stuff?

You can also email me at prabb@stamfordsystems.com