Engineering Radio – Page 90 – One Hundred percent Human Generated Content for your Reading Enjoyment

The neighborhood Mesh Network

Wireless IP Ethernet (802.11) technology has been around for a while. Many know it as “WIFI” but you could also call it “WLAN” or something similar. Like many other Ethernet technologies, WLAN relies on a spoke and hub connection system. The hub is the wireless access point or router and the individual hosts (PCs, tablets, phones, etc) are the end point for each connection. In a wired network, it is usually some type of switch that forms the center of the network data distribution system.

With a wireless mesh network or ad hoc network (802.11s), each wireless device can connect to any other wireless device within range. In this type of peer-to-peer network, there is no central access point, although something can act as an internet gateway or there can be several gateways. This type of topology functions much like the public network (AKA the internet), where there are many different paths to anyone (major) destination. If any one of those paths goes down, another route is quickly found.

This technology was developed by several vendors for military communications systems and for OLPC (One Laptop Per Child) programs in Africa and other places. Each link acts to extend the boundaries of the network, thus the more users there are, the more useful the network becomes.

Advantages of mesh networking:

Networks are self-forming; once the nodes are configured and can see other network nodes, the network automatically forms
Networks are self-healing; if one node drops offline, traffic is automatically routed to other nodes. If the node comes back up, it is included back into the network
High fault tolerance; in areas where many nodes exist and can see each other, the failure of any single node does not affect the rest of the network
Low cost to deploy; mesh networks use standard off-the-shelf WLAN (802.11) devices. The choice of software will dictate which hardware will work the best
Crowd-sourced infrastructure; as each network node is owned by an individual, the cost and responsibility is shared among the community

Several specific routing protocols have been developed for the network side of the system. Hazy Sighted Link State Routing Protocol (HSLS), BATMAN, OLSR HWMP and others. These work well with the existing 802.11 a/b/g wireless network hardware currently available.

On the host side, a good IBSS-capable wireless network adapter is needed, which many of the newer ones are. Several of the software programs have lists of WLAN adapters that work with their software. Open Garden is a free App for Windows, Mac OSX, and Android, and they are working on an iOS version. This leaves out certain devices like tablets and iPhones for now.

Since existing wireless adapter drivers do not yet support mesh networking, usually an additional piece of software is needed. There are several interesting ones, including HSMM-MESH, which was developed by Amateur Radio operators. Open-source programs for Linux, Free BSD and other are available as well as commercial versions for Windows.

I was thinking that this might be useful for broadcast applications. For obvious reasons, this type of system would work best in densely populated urban and suburban areas, which is exactly the type of area in which LPFM licenses might be hard to come by. For those who do not have the time or wherewithal to apply for an LPFM license, or for those that simply don’t get a license due to scarcity of available channels, this could be a great way to cover a neighborhood or section of a city. The more people participate in the mesh network, the stronger the network becomes. Additionally, by using FCC type accepted part 15 FM and AM transmitters as broadcast nodes, carrier current transmitters, and leaky coax systems, the presence of the mesh network can be advertized to potential listeners, including directions on how to take part.

Wireless mesh network example, courtesy of Meraka Institute

Wireless LAN bridges or broadband internet connections can act as a backbone between distant nodes.

For bandwidth efficiency sake, AOIP services should be limited to multicast addresses.

A good site with more wireless mesh network information is http://wirelessafrica.meraka.org.za/

Two subreddits on the subject: /r/meshnet and /r/darknetplan

Then there is project meshnet and the project meshnet wiki

Oh, by the way, go ahead and ask me what I have been learning about in school these days…

Oh, damn: la segunda parte

Emergency! The (AM) Transmitter keeps popping off the air and we can’t figure out why! YOU MUST HELP US!!1!!!

Really?

Some problems are easy to spot, difficult to fix

Well, with the ATU mounted about 1/4 inch away from the 90-degree, series-excited tower, I wonder why. It seemed to be especially problematic during rain, snow, and ice storms. When I asked how long this had been going on, I was told “About two years, ever since we put up the new tower!”

You don’t say.

We finally took care of this by moving the ATU back inside the shed after moving the transmitter to a different building. The funny thing is, this was installed by a guy who had a BSEE. I guess he must have been out sick the day they covered this in class.

End of the day, time to go home

I took a few shots during the boat ride back from the WICC transmitter site today. This has to be one of the more unique transmitter sites to access in the country. Most of the time, the boat ride takes about five to ten minutes, depending on other vessels in the channel. The dock at the island is in rough shape due to last month’s storm, but it is generally passable.

We are still working on repairing the damage from Sandy. Today was patching up the roof and troubleshooting the tower lights. The tower light wiring, junction boxes, and splices were all soaked by seawater, and there are several issues with malfunctioning side markers and beacon lights. We will be rewiring everything next week.

Departing Pleasure Beach Island, Bridgeport, CT

Shot over the stern looking at the two 1926 vintage Miliken towers. The square, self-supporting towers are nearly ninety years old, most of which was spent in a salt air environment, as such these towers are in excellent shape. They knew how to make things back then.

The Port Jefferson Ferry, Bridgeport Harbor, CT

The Ferry runs between Port Jefferson, NY (Long Island) and Bridgeport, CT carrying cars and pedestrians. There are no cars on this particular boat, so it must be out of service.

The pilot house on the Harbor Master boat

Looking into the pilot house of the Harbor Master boat. Looks a little crowded in there, I’ll just stay out on deck and enjoy the ride. Sometimes it is the small things.

Oh, damn: Una Parte

Guess what caught fire this time? It’s this thing, which has become the newest piece in my burned-up shit collection:

If you give up and are totally flummoxed, this is the IPA power supply regulator for a BE FM35A transmitter. Here it is in better days when it was actually working. The IPAs are in pull-out drawers on the right side of the transmitter cabinet, below the FX-30 exciter.

Said transmitter is aging not so gracefully, as it turns 26 this year. There does seem to be a finite life to transmitting equipment, something that should be kept in mind when planning out next year’s capital expense budgets. Regardless of all that, this event naturally occurred the day after Thanksgiving.

The good news, and there is always good news, we have many spare IPA regulators and PA modules in the shop ready to go. Upon investigation, there were numerous other problems with this transmitter, which have been or will be addressed.