AnteNnas

http://scratchpad.wikia.com/wiki/Sasecurity

part of MeshNetworking

Antenna deployment
* AntennaDeployment * PcmciaDiversity

Interference channels
>           I have been playing around with Mesh boxes for a few years >    in testing, >    and I have a few questions which I thought some of the experts on >     this >    list might be able to place some opinion on. >    1. There is a lot of controversy about antenna's. I am currently >    testing     the mesh concept in a rural area and have one main gateway which has a   omni antenna about 13 metres up in the air. The other repeater nodes are quite far apart with distances of around 1.5 to 2.5 km apart. The repeater nodes are using flat panel antennas directed at the gateway. The question I have on this setup is this, is it the best option to have  the omni as a gateway antenna, or should I use something different? I know that noise from the omni can be a problem, but remember that I am in a rural area where not that many people have wireless stuff operating so that is not a big problem.

> /If you are getting good signal to noise ratio, then I would leave > well alone - Antenna and propagation theory is only a guide, but you > never know until you try it. If SNR falls off due to noise, then you > may consider putting three sector antenna up in the same location, as > described by Kenny in a previous post (2 Mesh and one access point) Be > > >     2. Given the info above, on the repeater nodes, which are using >    the flat >    panel to connect to the gateway, would it be best to then use a >     second >    radio card in the node to provide local access to the repeater and >    connect this up to an omni, or would it be better to use something >    like >    a linksys 54 to provide local access and bridge that to the repeater >    using a wired link or place it in the path of the link to the gateway? > > > /This sounds like a candidate for the new 2100 series software on > www.locustworld.com  using a combination > of A and B, but assuming you are using the Open mesh software, a > second radio card - if you can prevent it interfering with the first, > or an access point on the wired side of the mesh box would work - my > preference would be for a good access point. / > > >     3. Given the above info, in order to provide the redundancy links >    to the >    gateway, should I use a second radio card to provide a flat panel >    link >    to another repeater node if possible? > > > /You can use quite a lot of money inducing redundancy - your call, > based on how reliable its been so far./ > >    4. I have a mixture of Wrap boards and white box pc's acting as nodes. >    On all of the nodes I use Senano wireless cards either pcmcia or mini >    pci on the wrap. These cards have two antenna connections, one for the >    main antenna and one for diversity. At the moment I only use the main >    one to connect to either a flat panel or omni as described above. >    Should >    I be using this second diversity antenna, and how does one us it. >    Do you >    connect a second similar antenna, or use a lower gain antenna? >    Where do >     you mount the second antenna in relation to the first one? I think I >    know the concept of the diversity antenna to help the card >    differentiate >    between signals, but will it make a difference to the kind of setup I >     have described? I have noticed and expected that people close to the >    gateway, in the effective dead zone of the omni based on it's >     height get >    poor performance from their connections. Would a diversity antenna >    help >    out with this dead zone? > > > /This is always the difficulty of how to get a radio shot over a good > distance, but still get the signal down into where its needed. All of > us use a variety of tools to achieve this, from antenna on the roof > connected to AP's in client mode, through to putting more mesh in. / > // > /I'd be wary of using diversity in the way that you describe. The > purpose of it is to provide two places where the signal can be > received, to account for the fact that the signal often bounces off > other objects, and the more antenna you have, then the more likely > that you are going to pick up a strong signal. The trouble with > Diversity is that it is not very intelligent. Simplistically it > switches off the antenna that is picking up the weakest signal. I > would not be sure until I had tried it, but it may cause issues with > meshing and talking to different customers, as you may end up meshing > on the wrong antenna. / > // > /If you have good line of site, and good height to account for the > fresnel zone, then a diversity antenna is probably not going to make > much difference./ > // > /Now MIMO - or 802.11 Pre-n - that looks interesting, as that receives > on all antenna similtaneously, then adds the signal together so that > the resultant signal to the receiver is that much higher./ > // > // > > >     I know this sounds like a long mail with lots of questions, but I have >    been sort of storing them all up and thought I would try and get >    advice >    on the whole setup, rather than just asking one question when not all >    facts are available. > > >  > /I note from your email address that you are in South Africa. I > believe that you have a 3Gb cap on standard ADSL. The 2100 > software, may be worth a closer look for the volume based user > accounting. In other words, you can set volume caps on your users, > also the PPoE authentication may be of some use, as I understand that > this is the way that you athenticate to ADSL in SA / > > /PS I'm not on commision from LW;-)/ > // > >     I would appreciate any information on or off list on these  questions, >     and thank everyone in advance for any assistance.

Many thanks for the detailed reply. I will stick with the Omni for now, and give the diversity a miss, as it sounds more hassle than anything else. I am only using the open mesh software as this is not a commercial venture and just an experiment on my side of things. The 2100 would be overkill and expensive. We are in South Africa and the cap on ADSL is not quite 3Gb, but bandwidth is expensive, so that needs to be controlled. For those who want to be shocked, we pay monthly about 50 pounds sterling to have a 512k ADSL line to a house, and then about 23 pounds sterling for a 3gb shaped account. So for about 75 pounds sterling, we get up and going, so it is expensive. We do you PPoE to connect, but in terms of connecting to the mesh, that doesn't really have much play on things.

splitting 802.11b channels
>I am getting to many customers and a lot of CSMA contention and busy >holdoffs on a mesh network. There are 40 - 50 dhcp leases on each >of 10 APs. A lot of duplication. I was thinking of putting some >APs on channel 11 and some on channel 1. I would have two gateway >APs at the data line backhaul, one on each channel. My concern is >having two gateway APs and their antennas mounted on one mast at the >headend of my network. Even though the channels are separated by >40Mhz, will it cause contention and busy conditions between the two >gateway APs? The two antennas on the mast would only be separated >by a few feet. Has anyone tried two gateway APs in very close >proximity running on two b channels?

I can go one better! Using a splitter, I am running two gateways through the same antenna - one is on channel 1, and the other is on channel 11. Although they can see each other using maxispy/sigspy, they are not meshing with each other, and there is no appreciable performance hit. I set up a test network at my shop with the two boxes/antennas 3 ft. apart - one channell 11, one channel 1. The boxes were each put on a switch to a 4MB cable feed. Set the owner download/upload to 4Mbit for two clients in the next room and got them to associate one with each box, and did concurrent downloads at over 1.6MB. By themselves they did 2.4MB. I turned off one access point and used one laptop and got the same 2.4MB. It might be contention at the switch, or the cable providers 4MB service. But I feel confident enough to take it out to the field and try, especially with the feed back from the user group. An interesting footnote is that one of the APs saw the other in sigspy, but the other one did not. I thought this to be a little strange. More - I do RV parks in the Naples, FL area. I'm using the VIA-MII motherboards with built on pci-pcmcia adapter, 2100 DDR RAM, CF to IDE, and Engenius/Senao 200mw cards. The installation of Locustworld's distro is really simple. I've had the older VIA boards in the field for three years now with no failures - zero. I am giving up on the PCEngine boards. Way to many problems especially in a dense environment. Those little pigtails and miniPCI cards are to intolerant. A little bit off on the pigtail to card adapter, or a little bit off on the other end and I get signal quality all over the place. And they simply don't have the capacity to handle many users and mesh. I think they might work fine for a single AP hotspot. I've also dropped the SMC 2532w-b cards for cpe. I use Zcom's XI-325HP cards. They are the same as the old SMCs. Zcom private brands for SMC. The new 2532w-b cards are not the same. Terrible signal quality and strength. I buy the Zcoms through O2 Secure Wireless in Atlanta. They have an Ebay store, but contact them directly for volume pricing. I use EUB-362(EXT) USB radios from Netgate. They are 200mw with an external antenna adapter. I love both of these radios, one for laptops the other for desktops, because if they cannot associate well with one of my APs I simply put an external 6dbi flat patch antenna with lmr195 wire and pigtails. Most of the time I can mount the antenna inside for GREAT improvement in signal strength and quality. Plus they're directional antennas that cut down on the rf. At last resort, I go outside with the anetenna. I've used over 60 Ft. of cable with insignificant RF loss. The most important thing is to not pinch or crimp the cable. The cpe costs me between $50 and $125 using this stuff. I've found nothing cheaper or better. And, I almost forgot, for the 6 Apple Macs I have that cannot hit the antennas with built in Airport, I use 2611CB3 bridges. They are great. Set them up on a laptop and plug them into the Apple Mac. A little expensive, but I'm dealing with Apple ... I have a Linux computer with three ethernet adapters running Fedora 4 at the headend. I bridge two ethernet adapters between the Wireless Gateways and the T1(2 of them) router. I use the third for access to the box to monitor the bridge. I run iptraf on the bridge to monitor the nework and iptables for firewall management. I block known p2p ports and other bad traffic as I see it. This has been invaluable. I tried Squid on this box, and it helped so little I took it off. It only cashes the obvious, and client web browsers all ready do a pretty good job of that. I'm still a little worried about dense cpe environments and the mesh. If I can get my complaints down to zero for a week or so I will be a happy camper. I hope my comments help those getting started with the mesh. And I really do appreciate the list. It's helped me many times.