yoursunny blog
computer, Internet, and life

Let the World Reach Your NFD

Junxiao Shi
last updated

UPDATE 2021-11-15:

  • nfdc command syntax changed since NFD 0.6.0, in which nfdc register has been renamed to nfdc route add, but the underlying protocol remains the same. If you want to follow along, type nfdc route add in place of nfdc register.
  • remote-register-prefix command is replaced by register-prefix-remote. If you want to follow along, type ndn6-register-prefix-remote in place of remote-register-prefix.
  • The command output may be different.

Named Data Networking (NDN) is a potential future Internet architecture designed as a distribution network. My last post described how to connect an end host running NDN Forwarding Daemon (NFD) to the NDN Testbed, a backbone NDN network for research purposes, and retrieve contents from that network. An equally important topic is: how can you publish contents into the backbone network?

As mentioned in the last post, NDN communication is receiver driven. Interests expressed by the consumer application are forwarded toward the producer following the routing table, and Data packets carrying contents flow back on the reverse path of Interests. Every end host and router along the path between consumer and producer needs to have a route in its routing table, so that NFD can forward the Interest, hop by hop, toward the producer. On your own machine, nfdc register command adds a route to the routing table; however, if you want to publish contents into the backbone network and make them available for others to retrieve, you won't be able to directly execute nfdc register command on a terminal of the routers. How can you add a route without console access?

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Do Evil with ESP8266: Slow Down the WiFi

Junxiao Shi

While hackers do good most of the time, we occasionally do evil and play a prank. The ESP8266, unlike JSON, allows me to do evil. Thus, I programmed the microcontroller for an evil purpose: slow down the WiFi.

How it Works

802.11 WiFi typically operates in infrastructure mode, where a router acts as an access point, and other hosts (stations) connect to the router on a wireless frequency (a channel).

One property of the wireless channel is that, at any moment, only one party (station or access point) can be transmitting. If multiple senders are transmitting at the same time, the wireless signal will be jammed, and the recipient is unlikely to receive the packet correctly. In this case, the sender would have to transmit the packet again at a later time.

Packets can be transmitted at different speeds on the wireless channel. With 802.11g standard, the maximum speed is 54Mbps, and the minimum is as slow as 1Mbps. The sender (station or access point) dynamically chooses a speed for every packet depending on its perception of wireless channel quality. Usually, we prefer to transmit at a higher speed, so that the wireless channel can be freed as soon as possible for other senders to use. However, if the sender and recipient are far apart, high speed transmission is less likely to succeed because signals can be faded, and a slower speed is necessary to increase the chance of a successful transmission.

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Flash ESP8266 Witty Cloud Board with 6 Wires

Junxiao Shi

Witty Cloud board is an ESP8266 development board that has a unique two-PCB design: the top PCB carries the ESP8266 microcontroller and an AMS1117 voltage regulator, and the bottom PCB carries a CH340G USB-serial chip. The top PCB can operate independently. It has a pair of 8-pin male headers that expose ESP8266's GPIO pins, which can be used to control peripherals such as LEDs and buttons. The bottom PCB is needed only for flashing the ESP8266. It has a pair of 8-pin female headers. The top PCB should be inserted into the bottom PCB when the firmware is being flashed from a computer, or when we want to use Arduino's serial monitor.

Sometimes, we may want to simultaneously connect ESP8266's GPIO pins to peripherals, and keep the ability of flashing the firmware or monitoring the serial console from a computer. Can we achieve that?

From electric point of view, when the male headers on the top PCB are inserted into the female headers on the bottom PCB, each of the 16 pins on one PCB is connected to the corresponding pin on the other PCB via a wire. Thus, if we connect the two PCBs with 16 jumper wires, everything should work.

But it's tedious to connect 16 wires every time. Can we connect the two PCBs with less jumper wires? Let me find out.

I started with four wires:

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Understanding the Photoresistor on Witty Cloud Board

Junxiao Shi

One of my favorite electronic elements is the photoresistor, an element whose resistance decreases with increasing incident light intensity. I played with a photoresistor as part of an electronic building blocks toy kit when I was in elementary school, and made a geocaching trackable out of that experience. But I want a deeper understanding of the photoresitor: what's the correlation between its conductivity and the light intensity?

photoresistor circuit symbol

Recently I acquired some Witty Cloud boards. This board is built around an ESP8266 microcontroller; a photoresistor (aka Light Dependent Resistor, LDR) is connected to the analog input port of the ESP8266. With one line of code in Arduino (analogRead(A0)), we could read the light intensity as a number between 0 and 1023. However, what's the unit of this number, and how does it translate to the standard units such as lumens?

I couldn't find any formula for this translation, because it does not exist. Adafruit explains photoresistor readings nicely:

The readings taken are not in any useful units of light intensity. Photoresistors are not carefully calibrated sensors. If you wanted to make a light meter, with absolute measurement of light intensity in meaningful units, you would need to create a lookup table that related readings with readings taken from a properly calibrated light meter.

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First Impression on ESP8266 Witty Cloud Board

Junxiao Shi

I get addicted to ESP8266 ever since Losant sent me a builder kit which includes an Adafruit Feather HUZZAH. Witty Cloud GitWits is one of the cheapest ESP8266 device you can get on the market. It has a microUSB port with USB-Serial interface, which means no soldering! The board also contains an RGB LED and a button, which allows me to use it without a breadboard. So, I decide to go for it!

I ordered the Witty Cloud board from AliExpress, a Chinese E-commerce site. Ordering experience isn't so good. For some reason, they cancelled my order due to "difficulty in verifying payment". I had to upload a scanned copy of my passport and credit card statement, before they would ship my items. After getting past those non-technical steps, the Witty Cloud development board is in my mailbox 2 weeks later. There's no doubt I'm excited!

Appearance

The board is very small and lightweight. Its dimension is 31mm x 30mm x 18mm. Its weight is roughly the same as an Adafruit Feather HUZZAH.

Witty Cloud board has two PCBs connected via a pair of 8-pin headers.

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Monitor Uptime of a Losant Device

Junxiao Shi

Losant is a simple and powerful IoT cloud platform. Sensor devices, such as the Losant Builder Kit, can connect to their MQTT broker over the public Internet, and report state in real time. Based on those state reports, the software running in the cloud (call "workflows") can take actions such as sending an alert over email or text message, or deliver a command to be executed on an actuator device over MQTT.

One important question to ask is: how stable is this system? There are many elements in this system that can fail:

  • Losant MQTT broker
  • workflows in the cloud
  • connected device (sensor or actuator)
  • power supply to the connected device
  • the Internet connection

Hopefully, the good folks at Losant has deployed enough redundancy for their MQTT broker and machines to execute workflows, and the user is careful enough when modifying the workflows. A failure is more likely to occur in the connected device, its power supply, or Internet connection. Failure in any of these three elements will result in the device being disconnected from the Losant MQTT broker. Thus, we can find out how stable the system is from the cloud end: monitor MQTT connection from a workflow.

Brent Crawford has designed a workflow to alert the owner when a device has been offline for more than 10 minutes. While it's useful for a device deployed in the field, it's unnecessary for me to receive alerts because my device is right across the room and I can just glance at an LED that indicates its connectivity. I'm more interested in the history of device uptime.

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LosantPingPong: End-to-end Losant Connectivity Test

Junxiao Shi
last updated

Losant is a simple and powerful IoT cloud platform. The platform provides a MQTT broker that sensor devices can connect to and report state in real time; the reported states are stored in the cloud, and can be visualized in several formats.

Recently, Losant sent me a Builder Kit which contains an ESP8266 WiFi chip on Adafruit Feather Huzzah, a TMP36 temperature sensor, and some other components. Following the official instructions, 1.5 hours later, my room temperature shows up on a webpage.

I'm excited, and I decide to leave it running continuously so that I can monitor the activities of @TheTucsonHeat. However, Losant platform shows the device as "offline" from time to time, and sometimes it never comes back online unless I press the hard-reset button. This is mostly because of the bad WiFi in my apartment: 1000ms huge delay, 10% or more packet loss, etc. Since MQTT is based on TCP, it's severely affected. To make things worse, our WiFi connects to the Internet through two levels of Network Address Translation (NAT) gateways; it seems that the ESP8266 sometimes is unable to detect the TCP connection to Losant broker is broken, and thus does not take recovery actions.

As a computer networking student, the first thing coming through my mind is the end-to-end principle: the reliability of an application should be ensured by the end hosts, not by the network. To test whether my temperature sensor remains connected to Losant, I should send a message to the Losant platform, and let the platform send back a reply. And that's the idea of LosantPingPong: an end-to-end connectivity test between a connected device and the Losant platform.

LosantPingPong protocol

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How to Survive a Weekend Offline?

Junxiao Shi

I'm a heavy smartphone user. I read emails, access Twitter, check in on Swarm/Foursquare, watch YouTube, and look at weather forecast, multiple times a day. I use smartphones so much that my primary phone, the Nexus 5, needs to be charged 2~3 times per day, and I am reluctant to stay in places without free WiFi.

But, everything is changing in the past weekend: I joined a camping trip to Grand Canyon National Park. There is no electricity. There is no cellular signal, because national parks do not want cell towers to ruin the beautiful landscape. There is no WiFi, except in the cafeteria which we may or may not visit. Without electricity, I cannot keep my smartphones charged. Without cellular or WiFi, I cannot receive emails, access Twitter, check in on Swarm/Foursquare, watch YouTube, or use weather forecast apps. How can I survive the weekend in the national park, without electricity or Internet access?

Preparation

Internet access is unavailable, but it's not the only way to communication with the outside world. On many smartphones, there's a forgotten app called the FM radio, which allows you to receive information without Internet access or cellular signal. Therefore, I packed an old smartphone, the T-Mobile Comet, which has an FM radio tuner. This would allow me to listen to the weather forecast, and maybe some news and music.

My camping trip is a short one: we depart on Friday and return on Sunday. The lack of electricity can be solved by a few USB PowerBanks. I brought two USB PowerBanks, which contain a total of 12800mAh of electricity, enough to charge the Nexus 5 five times, or the T-Mobile Comet ten times.

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My Experience at Hack Arizona 2016

Junxiao Shi

Hack Arizona is the largest collegiate hackathon in southwestern United States. I attended Hack Arizona 2016 and had a great experience, and I want to share what I experienced during this event.

Why I didn't attend in 2015

I heard about Hack Arizona when it started in 2015, but I decided against attending last year because 37 sleepless hours is harmful for health and won't produce high quality project.

Many of my friends went in 2015, and they shared their experiences and showed me their projects. The situation sounds less scary than I imagined:

  • Although you are provided enough coffee and Red Bull energy drinks to stay up, you are permitted to leave and re-enter at anytime, and you can sleep in the venue as well.
  • There's free food, and it's not just pizza.
  • Projects aren't of poor quality.
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parallelize.sh: run commands in parallel with bash

Junxiao Shi

Recently I'm doing some heavy research work. One part of my work involves invoking a simulation script with different inputs and parameters and then an analysis script to analyze the simulation output.

At first, this is an easy bash loop:

(
  echo 3 11
  echo 3 11
  echo 5 19
  echo 5 19
) | while read -r -a L; do
  X=${L[0]}
  Y=${L[1]}
  python2 simulation.py --x=$X --y=$Y < input.tsv > $X-$Y.simulation.log
  gawk -f analysis.awk $X-$Y.simulation.log > $X-$Y.analysis.tsv
done

The loop works fine, but it takes too long time when the input gets larger, because scripts are running sequentially. Since we have a big server with 32 CPU cores, can I run the scripts in parallel?

So I wrote this nifty little script, parallelize.sh:

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