Grandma’s Phone, DSL, and the Copper They Share

My DSL line downloads at 6 megabits per second. I just ran the test. This is over a pair of copper twisted wires, the same Plain Old Telephone Service (POTS) twisted pair that connected your Grandmother’s phone to the rest of the world. In fact, if you had that phone you could connect and use it today.

18zbmki8n3xgkjpgI can remember the old 110 bps acoustic coupler modems. Maybe some of you can also. Do you remember upgrading to 300 bps? Wow! Triple the speed. Gradually the speed increased through 1200 to 2400, and then finally, 56.6k. All over the same  of wires. Now we feel short changed if were not getting multiple megabits from DSL over that same POTS line. How can we get such speeds over a system that still allows your grandmother’s phone to be connected and dialed? How did the engineers know these increased speeds were possible?

shannon_maze_hr
Claude Shannon with his maze running mechanical mouse

The answer lies back in 1948 with Dr. Claude Shannon who wrote a seminal paper, “A Mathematical Theory of Communication”. In that paper he laid the groundwork for Information Theory. Shannon also is recognized for applying Boolean algebra, developed by George Boole, to electrical circuits. Shannon recognized that switches, at that time, and today’s logic circuits followed the rules of Boolean Algebra. This was his Master’s Thesis written in 1937.

Shannon’s Theory of Communications explains how much information you can send through a communications channel at a specified error rate. In summary, the theory says:

  • There is a maximum channel capacity, C,
  • If the rate of transmission, R, is less than C, information can be transferred at a selected small error probability using smart coding techniques,
  • The coding techniques require intelligent encoding techniques with longer blocks of signal data.

What the theory doesn’t provide is information on the smart coding techniques. The theory says you can do it, but not how.

In this article I’m going to describe this work without getting into the mathematics of the derivations. In another article I’ll discuss some of the smart coding techniques used to approach channel capacity. If you can understand the mathematics, here is the first part of the paper as published in the Bell System Technical Journal in July 1948 and the remainder published later that year. To walk though the system used to fit so much information on a twisted copper pair, keep reading.

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Is Your Cat 6 Ethernet Cable Cat 6? Probably Not.

Though we’ve never used their cables, [Blue Jeans Cable] out of Seattle, WA sure does seem to take the black art of cable manufacture seriously. When they read the Cat 6 specification, they knew they couldn’t just keep building the cables the way they used to. So they did some research and purchased a Fluke certification tester for a measly 12,000 US dollars. While they were purchasing the device, they ran across an interesting tidbit in the fluke knowledge base. Fluke said that 80% of the consumer Cat 6 cables they tested didn’t begin to meet the Cat 6 specification.

This is the part where [Blue Jeans Cable] earns our respect; like good scientists, they set out to replicate Fluke’s results. Sure enough, 80% of the Cat 6 cables they tested from big box stores etc. failed the specification. More surprising, many of them didn’t even pass the Cat 5e specification. [Blue Jeans Cable] asserts that this is possible because the Ethernet cable specification is policed via the honor system, allowing manufacturers to be fairly brazen about what they label as Cat 6.

Link Trucker is a Tiny Networking Giant

If you’re a networking professional, there are professional tools for verifying that everything’s as it should be on the business end of an Ethernet cable. These professional tools often come along with a professional pricetag. If you’re just trying to wire up a single office, the pro gear can be overkill. Unless you make it yourself on the cheap! And now you can.

[Kristopher Marciniak] designed and built an inexpensive device that verifies the basics:

  • Is the link up? Is this cable connected?
  • Can it get a DHCP address?
  • Can it perform a DNS lookup?
  • Can it open a webpage?

What’s going on under the hood? A Raspberry Pi, you’d think. A BeagleBoard? Our hearts were warmed to see a throwback to a more civilized age: an ENC28J60 breakout board and an Arduino Uno. That’s right, [Kristopher] replicated a couple-hundred dollar network tester for the price of a few lattes. And by using a pre-made housing, [Kristopher]’s version looks great too. Watch it work in the video just below the break.

Building an embedded network device used to be a lot more work, but it could be done. One of our favorites is still [Ian Lesnet’s] webserver on a business card from way back in 2008 which also used the ENC28J60 Ethernet chip.
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Custom Siri Automation with HomeKit and ESP8266

Knowing where to start when adding a device to your home automation is always a tough thing. Most likely, you are already working on the device end of things (whatever you’re trying to automate) so it would be nice if the user end is already figured out. This is one such case. [Aditya Tannu] is using Siri to control ESP8266 connected devices by leveraging the functionality of Apple’s HomeKit protocols.

HomeKit is a framework from Apple that uses Siri as the voice activation on the user end of the system. Just like Amazon’s voice-control automation, this is ripe for exploration. [Aditya] is building upon the HAP-NodeJS package which implements a HomeKit Accessory Server using anything that will run Node.

Once the server is up and running (in this case, on a raspberry Pi) each connected device simply needs to communicate via MQTT. The Arduino IDE is used to program an ESP8266, and there are plenty of MQTT sketches out there that may be used for this purpose. The most recent example build from [Aditya] is a retrofit for a fiber optic lamp. He added an ESP8266 board and replaced the stock LEDs with WS2812 modules. The current version, demonstrated below, has on/off and color control for the device.

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Inject Packets with an ESP8266

[Kripthor] sent us a link to his blog where he writes the Hello World of low-level networking. Basically he’s constructing his own packet and sending it. By itself this isn’t a bad thing. You could use this power for all sorts of networks-diagnostic good. And so, despite the ominous name of his blog post “ESP8266 Jamming”, he’s not really doing anything that bad — he’s just creating many fake WiFi beacon frames and sending them out every so often.

Which can apparently do bad things to some vulnerable routers. Who knew? Want to test yours?

Naturally we wanted to see how he was doing it, and we opened up the Arduino code in GitHub. It turns out that Espressif has written a wifi_send_pkt_freedom() function that just sends out whatever packet you’d like to the network. That was easy.

It also turns out that the ESP8266 will enter monitor mode, where it listens to all WiFi traffic regardless of the MAC address that it’s directed toward. [Pulkin] seems to have done the work for us and posted the code in his GitHub. Now things get nasty. Combining promiscuous monitor mode with some carefully constructed management frames can end up with a classic WiFi deauth denial-of-service attack on a $2 piece of hardware.

We think it’s tremendously cool that the ESP8266 packs such power, and we beg you all to use it responsibly. The last thing we want to see is the world littered with WiFi-DOS throwies. And the last thing you’d want is a visit from the FCC.

Zedboard Multiport Ethernet

The Zedboard uses Xilinx’s Zynq, which is a combination ARM CPU and FPGA. [Jeff Johnson] recently posted an excellent two-part tutorial covering using a Zedboard with multiple Ethernet ports. The lwIP (light-weight Internet Protocol) stack takes care of the software end.

Vivado is Xilinx’s software for configuring the Zynq (among other chips), and the tutorial shows you how to use it. The Ethernet PHY is an FPGA Mezzanine Card (FMC) with four ports that is commercially available. The project uses VHDL, but there is no VHDL coding involved, just the use of canned components.

The real issue when using an FPGA and a CPU is the interface between the processor and the FPGA circuitry. In this case, the ARM standard AXI bus does this task, and the Ethernet component properly interfaces to that bus. The IP application in the second part of the post is an echo server.

We’ve seen the Zynq used in flying machines and also in a music synthesizer. Although this project doesn’t use any Verilog or VHDL that you create, it is still a great example of configuring using Vivado and using common components in a design.

Free Cell Data Transfer with Slowest Morse Code Ever

Readers of a certain age will remember the payphone trick of letting the phone ring once and then hanging up to get your quarter back. This technique was used with a pre-planned call time to let someone know you made it or you were okay without accruing the cost of a telephone call. As long as nobody answered you didn’t have to pay for the call, and that continues to be the case with some pay-per-minute cellphone plans.

This is the concept behind [Antonio Ospite’s] ringtone data transfer project called SaveMySugar. Don’t judge him, this work has been ongoing for around ten years and started back when cellphone minutes were a concern. We’re just excited to see that he got the excruciatingly slow thing to work.

Those wanting to dig down to the nitty-gritty of the protocol (and you should be one of them) will want to read through the main project page. The system works by dialing the cellphone, letting it ring once, then hanging up. The time between redials determines a Morse code dot, dash, or separation between characters. Because you can’t precisely determine how long it will take each connection to read, [Antonio] built ‘noise’ measurement into the system to normalize variations. The resulting data transfer works quite well. He was able to transfer the word “CODEX” in just six minutes and thirty seconds. But it is automatic, so what do you care? See the edge-of-your-seat-action play out in the video below.

If you can’t stomach that baud, here’s a faster Morse code data transmitter but it doesn’t use the phone.

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