Monthly Update - February 2023

This month we take another look at the Bay Area Backbone - a set of AREDN and non-AREDN radios located on towers around the Bay Area. We’ll describe what they are, how they work, and how you can take a peek.

Backbone

A year or so ago our local hams realized that, as their AREDN network began to connect cities and communities, some sort of backbone network would be necessary. They envisioned a group of high tower sites, meshed to each other with high bandwidth radios, providing a way for AREDN enthusiasts to connect without all those pesky hills and mountains getting in the way. We wrote about the process of building the backbone last year (see here for more). This time we’ll talk about the technology we’re using and how it all works.

Fiber Radios and Big Dishes

We encourage everyone to buy inexpensive radios with included antennas. They get the job done. For the backbone we need something with a little more … oomph. While the AREDN radios on my house can move a modest 20 Mbps across town, the backbone needs to move 10x as much; enough to connect neighborhoods, not just neighbors. So for the majority of the links in the backbone, we’ve been using Ubiquiti airFiber radios with 2 to 3 foot dishes. Depending on the location, these radios can transfer 500 to 800 Mbps. For our more modest goals, 200 Mbps for each point-to-point link is plenty.

The connections in our backbone are between high sites. We do this for a couple of reasons. First, there are fewer obstacles between high sites, making the point-to-point links easier to create. Second, for neighborhood hams connecting to the backbone, it's easier to find a path to a higher point - if nothing else, there are less trees in the way.

We’ve set up a number of backbone links in the last year, but today we’ll just talk about the link between San Carlos and San Bruno Mountain. AirFiber PtP (point-to-point) radios connect these sites with 30 dBi dishes at each end. The “AREDN-ness” for these radios is provided by a Mikrotik hAP ac2 (more on this in a bit). Each site also provides AREDN sector antennas for incoming local links.

The Techie Bit: Backbone VLANs and Routing

If you’ve ever plugged AREDN radios together with ethernet, you're probably familiar with device-to-device links (DTD links) and VLAN 2. VLANs (virtual LANs) are a way for a single physical network cable to carry multiple, independent networks, by giving each a number. VLAN 2 is the number AREDN gives for the network between locally connected devices.

When we’re connecting the AREDN radios together at different sites using the airFiber radios, we use VLANs to make this happen. We could just connect everything to VLAN 2 (and we have done this in the past) but then AREDN thinks we have one big radio site where everything is in one place. Obviously it isn’t. Instead, we run a unique VLAN per link across our airFiber radios. For example, we use VLAN 15 to connect San Bruno Mountain to San Carlos.

To make use of these VLAN links and connect them to our mesh, we still need an AREDN node. At each site we use a Mikrotik hAP ac2 - a quad core, ARM based, gigabit router - running AREDN. This device uses an AREDN feature introduced last year called “xlinks”. An xlink is like an AREDN tunnel running over a VLAN, but without the overhead or need for an internet connection. AREDN routes traffic over these xlinks just like any other radio. These xlinks send traffic over our point-to-point VLANs which, in turn, send traffic over our airFiber radios.

After all this, we’re left with high-speed radio connections between AREDN nodes. It’s just like the usual AREDN radios talking to each other .. but a little more engineered and a lot faster.

Want to Look?

So perhaps you’d like to take a look? You can if you’re connected to the mesh. Not all the radios support this yet but you can log into the airFiber radios as a guest and check out what they’re doing. For example, if you want to see the San Carlos radio (pointing at San Bruno Mountain) you can find it here:

Hostname: http://san-carlos-to-san-bruno.local.mesh/

Username: mesh

Password: aredn-back-bone

This is a read-only account. You can’t change the configuration, but you can take a look at what it’s doing. The AirView tool is particularly interesting and lets you “see” the local radio environment from the perspective of the antenna. Please take a look around. You can find more information about other backbone radios on our wiki - https://bamwiki.xojs.org.

Next

We have more backbone links planned - some a glint in the eye, and some ready to go. We’ll write more as they happen. These connections, and the mesh they support, make the links across the Bay stronger, provide an easier, more reliable way for us to communicate, and–when disaster strikes–one more way to reach out and help.

SCaLE 20x

SCaLE is the largest community-run open-source and free software conference in North America. AREDN has always been part of SCaLE and this year is no exception. We’ll be there proselytizing AREDN in general, and the SoCal and BAM networks in particular. The conference runs from March 10th to 12th at the Pasadena Conference Center in the greater LA area. Why not pop down for the day? Details can be found here - https://www.socallinuxexpo.org/scale/20x/

Changes to Slack

The Bay Area Mesh #sfwem slack channel has moved! We had been squatting in the San Francisco Radio Club’s Slack Workspace for years now; longer than we intended. You can now find us as #bayareamesh on the AREDN Community Slack (aredncommunity.slack.com).

AREDN News

The slow process of turning the nightly builds of AREDN into the next release continues. Presidents’ Day weekend saw a particular burst of bug reporting (and fixing!) which was greatly appreciated by the devs. At this point the adventurous amongst you are encouraged to get one of the new AC radios and put it into service. Bench testing is behind us, and field testing is the final step before the release.

73,

Tim - KN6PLV - tim@sfwem.net