Offline networking

Introduction

Offline and off-grid networking broadly refers to the practice of sharing information between devices without use of the global Internet. The advantage of this in a disaster scenario is to provide a fallback for access to critical information and communication services in cases where reaching the Internet is not possible. This can be done with a device acting as a WiFi access point and router, LoRaWAN devices sharing information over long distances using the LoRa radio specification, or with a digital radio service known as packet radio. Each of these will be covered here.

WiFi

WiFi (or Wi-Fi) refers to certain wireless protocols from the 802.11 collection of standards. WiFi is predominantly used for low power, short range networking, and centers around 2 popular bands, 2.4GHz and the faster 5GHz. In 2019, it was found more than 3.05 billion Wi-Fi-enabled devices are shipped globally each year. Each of these devices can connect to any wireless access point which is open, or for which they are authenticated. This presents a significant opportunity for the distribution of critical information where Internet access is otherwise not available.

Offline WiFi access points

Due to our habitual relationship with WiFi and connecting to the public Internet, we can often overlook WiFi's applications in 'offline' contexts. A WiFi access point (AP) does not need the public Internet to provide access to content, if the content is locally accessible to the AP. In such applications, either the WiFi router itself holds the data (perhaps on a USB stick), or the data is served from another device connected directly to the AP.

This is an interesting direction for those more technically minded wishing to provide basic services, like a source of information (WiKi or message board), when the Internet is down. Due to the short range of WiFi, such offline access point servers are best setup at a common communal area, like a community center or disaster meeting point.

OpenWrt

Some commercial routers provide ability for file sharing across their network using the factory firmware installed on the device. However in the majority of applications, an after market firmware is used, like OpenWrt. Suitable for those more technically inclined, OpenWrt is an open source project dedicated to writing and testing firmware that can be 'flashed' onto scavenged or bought WiFi routers, providing them with new functionality and customisation options. At the time of writing, 2043 wireless routers are supported by OpenWrt to some degree.

Many projects have been made exploring the practical application of offline networking in a wireless context using OpenWrt.

Turning a computer into an offline wireless server

Laptops and small form-factor computers can be repurposed as WiFi access points, that either route through to another network (like the Internet) or remain hermetic. Any GNU/Linux laptop or device (like Raspberry Pi) with a wireless network adapter can be repurposed as a wireless access point serving information and files from a locally hosted website. A popular webserver for use in such contexts is lighttpd. A popular daemon/service providing access point functionality is hostapd, often coupled with dnsmasq to provide automatic network configuration of clients using the DHCP protocol alongside domain name resolution.

WiFi mesh networks

Image showing connections between nodes of the Freifunk network in Berlin in 2007.

Mesh networks are computer networks that have in-built node redundancy, meaning that no central node is critical to the distribution of information across the network. Routing algorithms ensure that if a node is unavailable along the route, another optimised route is chosen. Mesh networks are in wide use throughout military and disaster response applications, but can also be deployed and managed by civilians with low cost equipment.

A low power mesh network run by a community atop dumpster-dived/recycled or bought wireless routers could provide a valuable means of distributing mission-critical information where cellular infrastructure or the public Internet is otherwise unavailable. Due to the short-throw of WiFi, for this to be useful in a disaster situation, a built-up urban area would require many such WiFi mesh nodes for there to be failure-tolerance and routing-redundancy. Further, most WiFi routers are wall-powered, and so in the event of a blackout a typical wireless router repurposed as a WiFi mesh node will be down.

Freifunk

Among the most well known and successful WiFi mesh networks in the world is Freifunk. Established in 2003 in Germany, one of the primary goals of the project is to build a large-scale free wireless Wi-Fi network that is decentralized, free of discrimination (net neutrality), owned by those who run it, and to support local communication independent of the public Internet. Comprising over 41,000 wireless access points run by civilians, the Freifunk firmware is based atop OpenWrt and runs the batman-adv (B.A.T.M.A.N) mesh networking protocol, which is actively developed by Freifunk activists.

The Freifunk firmware can be freely downloaded and modified to be deployed anywhere(DE).

Red Hook WiFi

Red Hook Wifi was established in Red Hook, Brooklyn, New York City in 2011. It was created by the Red Hook Initiative to provide access to broadband for the regions many residents. A survey found that many people in the area accessed the internet primarily through mobile phones and that over 30% of the population did not have broadband access at home. .

Red Hook serves as an excellent example of community-run infrastructure serving a critically important role in an environmental emergency. In 2012, when Hurricane Sandy hit the region, Internet and cellular communications systems were down. During this crisis the Red Hook mesh network not only remained active, but the Red Hook headquarters became a hub for volunteer coordination and food distribution, and residents came to the Red Hook Initiative's office to charge their devices and connect to the internet.

Soon after Hurricane Sandy hit, the Federal Emergency Management Agency of the United States connected itself to the Red Hook Network, providing a satellite uplink, connecting itself, the Red Cross and residents such that they could find out about food banks, shelters and emergency information.

SubNodes

SubNodes, by Berlin-based artist Sarah Grant, employs popular Raspberry Pi minicomputers as wireless access points, serving a website and chat application . Smartphones, for instance, can be used to connect to the access point, from which is served a website, alongside simple chat application. The project provides complete instructions requiring minimal prior knowledge for deploying a 'SubNode'. Such 'SubNodes' could be employed inside weatherproof plastic cases, like tupperware or a plastic lunchbox, powered off solar power bank or voltage-converted car battery, and used to provide valuable information without need for the Internet. SubNodes can also be used in a mesh networking capacity, connecting to other compatible nodes.

Other mesh networks by region

Wikipedia hosts a page dedicated to listing mesh networks by region.

LoRa/LoRaWAN

An Adafruit LoRa shield atop a Rasberry Pi Model 4, with 900MHz omnidirectional antenna.

A Meshtastic Station G2 LoRa mesh networking device with attached omnidirectional 900MHz antenna

LoRa (from 'long range') is a communication protocol that allows for the transmitting and receiving of data in license-free portions of the radio spectrum. Together with LoRaWAN, it represents is an interesting low cost, low power, wide area networking platform, that can be used to create robust mesh networks. Mobility, end-to-end security and location are all features implemented by the LoRa architecture. While the data rate of LoRa is significantly smaller than that of cellular or wireless networks, operating from 0.3 kbit/s to 50 kbit/s per channel, it is sufficient for a diverse applications such as the sending of location information, messages and chat, status updates, sensor output, etc. The longest 2-way conversation between LoRa devices using less than 1 Watt of power is 206 km (128 miles). Several kilometers of mesh contact are quite typical for even low-power off-the-shelf LoRa devices, making LoRa an especially interesting solution for emergency communications, both in urban and rural contexts.

One practical mobile application of LoRa is MsgLab, where it is employed as a small handset with keyboard and case such that it can be used for texting in off-grid contexts.

Meshtastic

The Meshtastic project is a unique LoRa implementation with a very large global community of user-operated mesh nodes. This consumer-facing solution provides a modular platform with broad selection of hardware options that is easy to get up and running for those less technical. Various interfaces to the hardware (including apps and web-based) are provided. Setup and configuration is done on a smartphone via an app over bluetooth, and requires little-to-no prior knowledge. A large community exists to support those in need of help.

Meshtastic leverages the fact that people are often already carrying smartphones, allowing messages to be sent from a paired smartphone over bluetooth to the device, the messages of which are in turn either broadcast to a public channel on the mesh, or to a user-configured encrypted channel of devices on the mesh (for instance to devices of friends and family in the region).. In this sense, Meshtastic can be considered to be a little like a very long range 'pager' using a smartphone as the messaging interface.

Low power, some portable Meshtastic devices can run for days on built-in batteries, and come in a small form-factor. The SenseCAP T1000 model, for instance, is little larger than a credit card.

A global map of Meshtastic nodes can be seen here.

Linkdump

(to be expanded out into text)

http://subnodes.org/

https://learn.adafruit.com/lora-and-lorawan-radio-for-raspberry-pi/overview

https://en.wikipedia.org/wiki/Packet_radio

https://meshtastic.org/

https://en.wikipedia.org/wiki/Freifunk

https://openwrt.org

https://qaul.net

https://open.janastu.org/

https://www.earthdefenderstoolkit.com/one-pager/guide-librerouter-and-libremesh/