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Chapter 8: Half of something is better than nothing, but why settle?

 

This is Chapter 8 of Rory Conaway’s “Tales From The Towers” seriesabout setting up a large scale Wi-Fi network. If you have not yet done so, read Chapter 7: One size does not fit all

Our network is pretty inexpensive...

but it suffers from first generation bandwidth problems of losing 50 percent of the bandwidth capacity with every hop.  Patton wouldn’t settle for a partial victory and neither will we since we can do it for very little additional cost.  It’s possible to virtually eliminate bandwidth loss per access point (AP) for up to $400 for the Gateway points ($100 for every direction it has to backhaul), $200 for midpoints and $100 for the end point.  Keep in mind you don’t need to do this at every AP, just the links that have a higher load or to extend the network further.  This is also something that can easily be added later as capacity increases.

We currently have the AP cost at about $200 and each AP can handle 30-50Mbps of traffic.  However, 2 hops down from the gateway point or backhaul point, we are now down to about half of that.  Go another hop and it is ¼ of that using single radio WDS functionality.  WDS has 3 other problems that we can’t get around with Ubiquiti’s Bullet 2M HP’s.  The first is that we lose the client isolation function.  The second is we lose a proprietary function that we will later cover called AirMax.  The third is that we lose advance WPA encryption methods and we are limited to the evermore useless WEP.  It’s easy to get around this though.  Keep in mind the motto, “it’s not a problem if it can be fixed with money”.

Ubiquiti sells a little radio called a Nanostation Loco M5.  It’s available in both 2.4GHz and 5.8GHz versions.  We will focus on the 5.8GHz version since that limits the interference for our backhaul and as we discuss later, opens up new options for our network for PTMP.  This little fellow only costs $70 and provides a 2×2 MIMO signal that can support up a total of around 100Mbps of total throughput with a 20MHz channel.  I’m going a little conservative on throughput numbers since different types of IP traffic can test between 60-150Mbps.  Put 2 of them on the pole with the Bullet M2 and your backhaul can now support all that bandwidth across several hops with a loss of about 1Mbps and about 2-3ms of latency added on each hop.  However, you have just added another $200 per AP to do this with a switch.  If you have two 5.8GHz radios on the pole along with the Bullet, you will need a switch.

The most cost effective switch I have found that is designed to handle reasonable temperatures is the Linksys SD205 unit.  Although they are rated for 122 degrees, I have never seen one fail and I have had them in temperatures far in excess of 140 degrees for years.  For around $25, they are the best little units for sealed outdoor installations and there is an SD-208 version if you need more ports.   Compared to an industrial switch which starts at $250 (cheapest ones I have seen), the Linksys units are a steal.  If you need a managed switch, then you are looking at industrial switches and the cost is going to start around $450.

The other good part of adding the Nanostation Loco M5 to our system is now if we have to add more APs in the middle of our network, we don’t have worry about the 1/n issue.  We can also use WPA or AES security on the 2.4GHz network and 5.8GHz backhaul hops.  This solves the wireless security issue.  If we have to go around corners or Y off an AP, we can add up to 4 Nanostation Loco M5’s per pole if we use a 20MHz wide channel.  Yes, I know that theoretically you can do 5 channels but that leaves no buffer between channels.  With 4 channels, you get a 5MHz buffer which although not ideal, it’s not bad.

The drawback to the Nanostation Loco M5 is that to get maximum throughput or MCS (15) rates, you will be limited to 17dBm output with a 13dBm antenna or a total of 30dBm EIRP.  If there are any tree obstructions or you need more power, the big brother, the Nanostation M5 has a 16dbi antenna and 21dBm of output for an extra $20.  Keep in mind that these radios will go to a much higher power level if necessary but it comes at a reduction in throughput which we discussed in article 2.  It does however, leave some room for increasing power if interference or obstructions start to cause issues later.

The Nanostation Loco M5 radios can also do one other thing.  If we get back to the idea of a PTMP hybrid system, that means that users that are within the beam pattern of the Nanostation Loco M5’s  can actually connect directly to the 5.8GHz backhaul.  I suggest this stay reserved for truck rolls and trained technicians.  5.8GHz is a lot more sensitive to LOS which makes it more difficult for clients to install themselves.  We are going to extend this concept further later also.

If the goal is that clients are going to install their own CPE’s, either indoors or out, it’s best if clients use a 2.4GHz product, preferably a Nanostation 2M or the upcoming Nanostation Loco 2M for indoor use with a window/wall mount.  There is also some new indoor equipment from Ubiquiti, the WiFiStation, with directional and omni-directional antennas that support 802.11N and only cost around $30.  The range is obviously lower but it also lowers the cost for clients.

Although our network also doesn’t support 2×2 MIMO on 2.4GHz yet, it is now supporting it on 5.8GHz so things are moving along.  We have a couple options coming upon the 2.4GHz 2×2 MIMO solution coming up.  There is also a way to customize the firmware on these units so that the CPE can be fixed only on your network with the proper settings and would allow you access to manage settings on the client side to optimize their connection quality.  Imagine the client connecting to the system and then you get to remotely upgrade firmware on every client device simultaneously, monitor their connection quality, and manage the connection all way to the computer.  That is the advantage to having all the radios from a single vendor.  Tech support calls would go way down and staff wouldn’t have to fudge their way through 100 different products.  Taking this a step further, if all the devices were Ubiquiti M series radios, you could also use the AirMax feature with polling for the clients.  Of course, you sort of kiss off the legacy devices, or do you?

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