Posts tagged with “things that make me go hmm”


Fri 1 Feb

Teardown of an Ubiquiti Nanostation Loco M5

I was doing some work on a Ubiquiti Nanostation Loco M5 yesterday and wound up bricking it (protip: the 'erase all' command in uBoot also erases the bootloader itself... whoops!). Rather than getting out the JTAG I decided I'd do a full teardown of it since I hadn't seen one of this device before.

I'd long since removed the board from the case, so here's the board itself. The silver thing on top is shielding for the RF components. It's pretty easy to pop it off with a flathead screwdriver -- just jam it into the sides until it bends up.

There are a few chips on this board. The big one in the center is the 400MHz MIPS SoC, the Atheros AR7240-AH1A. The chip below that is the Winbond 25X64VFIG, a flash memory module. On the left side of the board, we have an M-Tek H16125MCG, an Ethernet transformer (I'm not sure if this is found on all ethernet devices, or if it has something to do with PoE). Directly above the transformer is a chip that's covered in stickers, the one "mystery chip" on this board (at least to me). Removing the stickers, I found three markings. On the top, it has a logo followed by "MIRA", which appears to be a custom IC manufacturer from Taiwan. There are two other markings: one next to the logo reading P3S56040ETP, and one on the bottom reading 944ANF74-G5. I found one reference to the latter, on this site, suggesting both that this is a 32MB SDRAM chip and that the Buffalo WHR-HP-G300N has a very similar bill of materials to the NSLM5!

Inside the shielded area, directly above the AR7240, is the radio chip, the Atheros AR9280-AL1A. The two chips to the left are both Skyworks SE2593A20, a dual-band WiFi frontend which does all the switching, filtering, and so forth. If you look closely towards the bottom left of the shielded area, you can see two leads running to a pair of connectors for RF pigtails (they're the golden squares with a dark circle). These are the antenna lines -- you can follow them back to the antenna port of each of the frontend chips. I guess they left those leads for testing purposes; I don't know if they're functional.

A couple other points of interest are the serial port on the lower right side of the board, just next to the Ethernet port. The reset button is on the bottom left, under the Ethernet transformer.

Flipping the board over, we see the antennas. These are two panel antennas layered on top of each other. They're attached with some plastic screws and solder to connect them to the antenna leads, along with one metal bolt which looks like it goes to ground. The lower layer of the antenna is the only one that's soldered to the board. The upper layer actually doesn't make any electrical contact with the lower one.

Up to this point, you could probably re-assemble the board. But this is a teardown, so I broke off the solder between the lower antenna and the board. It snaps in two pretty easily.

(Note my current favorite tool in the top right corner, vicegrips!)

There's nothing too exciting underneath, just the bottom of the Atheros chips.

I still have all the parts, so if you'd like better pictures or have questions about any parts I didn't discuss, let me know!


Thu 29 Nov

Syrian Internet Cut Off

Well, it's happened again: a country's been cut off the Internet. This time it's Syria.

There's good coverage of the technical details of this outage on the Renesys and CloudFlare blogs. The short version is that all Internet traffic into and out of Syria flows through a single, government-owned ISP, the Syrian Telecommunications Establishment (AS29386). This ISP withdrew their BGP routes from their providers, disabling access for all Syrian IP's (since every ISP in Syria relies on AS29386 for their international connectivity). This is effectively the same network structure that exists in Iran, and it makes it trivial to shut off an entire nation's Internet access: all traffic flows through a single point, and the government controls that point.

My TIER colleague Yahel Ben-David brought up the great point a couple months ago that it's kind of odd that method of choice for country-scale Internet blackouts seems to be withdrawing BGP routes, as opposed to just unplugging cables or powering off routers. The Syrian government tried to blame a cable cut for this blackout, but it's pretty hard to say all your BGP routes just "accidentally" got withdrawn. Withdrawing a BGP route is literally broadcast publicly around the world, so it's not particularly subtle either. I don't have a good explanation of why this is done: maybe the engineers tasked with implementing the blackout are just familiar with BGP? Maybe they don't want to disrupt their consecutive days of uptime numbers? If you're a network engineer who's implemented a national Internet blackout and has the answer, get in touch.


Fri 10 Sep

Landfill Diaries

I just discovered this fascinating blog, Landfill Diaries. From the about page:

"Landfill Diaries is maintained by Marijke Rijsberman, who accidentally fell in love with landfill in 2001, as she sat and watched the sun rise over San Francisco Bay at Candlestick Point. That put her almost on top of the city’s old garbage dump, right next to the current transfer station, poised to notice that endless stream of garbage trucks trundling by.

Authorities refer to garbage as the waste stream, as if, like a mountain brook, it burbles pleasantly to its final destination with no further encouragement besides gravity. The reality is a little different. Watching the sun rise and counting trucks, I finally got it: our garbage is huge and intractable. An almost invisible but very large industry takes care of it, behind the scenes, in places we rarely visit, don’t worry about, and usually don’t inquire into.

Even though our castoffs weigh on the land, it’s still possible just to drag our garbage to the curb every week and never think about it again. These pages are meant to change that situation at least a tiny bit: they examine and trace and pay respects to our invisible garbage. Landfill is not just real, it’s ours. And it is, upon closer inspection, very interesting."

And so is this blog. Definitely worth your time to check it out, especially if you've ever had an interest in the places your trash goes after the truck picks it up.


Sun 18 Oct

Fun with webcams

Back in middle school (or was it early high school?), I read an issue of 2600 that had a letter describing a technique to view a bunch of publicly accessible webcams worldwide. It turns out that this particular brand of webcam had a web-based viewer, and moreover that this web-based viewer had a unique URL string. All you had to do to get a list of these cameras was to do a Google search for "inurl:$THAT_UNIQUE_URL_STRING" and you'd get a bunch of results, all with cameras you could view and some that could even be controlled. Most turned out to be in Japan for some reason, and it was really cool to be able to watch busy city streets and trains from half a world away.

Fast forward a few years. I was recently using a webcam at my university that overlooks a construction site next to the CS building. One of my friends showed it to me over the summer, and it's been pretty fun to use it to watch the construction progress (as well as watch the workers eating lunch, driving trucks, etc). It hit me that this brand of webcam probably had the same "vulnerability" of a unique URL string that could be found on Google. Sure enough, it did:

http://www.google.com/#q=LvAppl/lvappl.htm

There seems to be a bit more geographic diversity in camera placement for this particular breed. I have found several in Japan, but others that are definitely closer to home (based on timezone). Here are a few interesting ones:

If you find any more interesting ones, leave a note in comments!


Tue 11 Aug

Do the internet and computers fundamentally alter existing socioeconomic power structures or do they merely exacerbate existing divides?

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