nRF24l01+ Library Roundup

Overview and Status of RF24 Arduino/Linux Comm. Stack

Six, seven years? Has it really been that long? According to GitHub that is in fact the case, as my first commits to my own fork of the RF24 library took place in early 2014. It all started by identifying existing limitations in the available libraries and working to achieve the highest level of performance and reliability possible. The main fork for RF24 at the time was written and maintained by ManiacBug, but he dropped off the scene shortly after publishing this very nicely designed library. Other users attempted to add support for various devices and address certain bugs, but nobody had really taken a thorough look at the capabilities of the hardware vs what was achievable at the time. Only through a lot of reading, testing and learning to program was I able to make those initial changes to begin work improving the RF24 core library. Looking back now, I am very grateful that I picked ManiacBugs code base as a place to get back into programming in C/C++, as it was well thought out and I discovered ways of doing things that I previously did not understand or know about.

And with that began a long and arduous journey into the internal workings of nrf24l01+, Arduino (AVR) and RPi (Linux) devices with the stated goal of optimizing the library to whatever extent possible. Once the RF24 library began to take shape, I began looking at the RF24Network library, another very nicely designed bit of code by ManiacBug, but it had its limitations and problems. Many issues were addressed, features and functionality added in order to push the nrf24 devices to the test in a multi-device scenario. It performed much better than expected using this OSI Layer 3 (network) library.

At that point, I began to really understand the OSI model, how the different layers actually work together and what they do down the last bit. Based on a number of conversations and user input, I came up with the idea for RF24Mesh, which is basically another layer on top of RF24Network -> RF24 that handles addressing, similar to DHCP, but able to verify connectivity and reconnect nodes at any point in the mesh. This allows nodes to move around and reconnect quickly as required while maintaining the mesh structure. The Network & Mesh layers use a 'master' node that acts like the gateway in a standard IP network, and it provides addressing and resolution for RF24Mesh.

Based on input and discussions with users and the performance of the radio modules when used in a multi-device mesh/network scenario along with the emergence of IoT and sensor networks, it seemed like the thing to do would be to work my way up the OSI model, so that is exactly what I did. Upon discovering the uIP stack for Arduino, I realized it would be possible to add ip4 support to some of the smallest devices like ATmega328 AVRs, and larger devices like RPi could just use their own IP stack and encryption etc. The uIP stack and related software was quite a challenge to understand and implement, as uIP is written in C and is designed to be as small and lightweight as possible as opposed to being human readable and easy to understand. The UIPEthernet library was also essential in helping me to understand and implement RF24Ethernet.

With that, an OSI RF24 comm. stack was established, with RF24, RF24Network, RF24Mesh, RF24Ethernet and RF24Gateway libraries all working together and inter-operational at any of the layers. This means that on a RF24Gateway/RF24Ethernet mesh network incorporating RPi and Arduino nodes, devices can choose to operate using OSI layer 2,3,4,5 and/or 7 (Data Link, Network, Transport, Session, Application). When using the higher layer libraries (RF24Gateway & RF24Ethernet) standard IP connectivity is established and devices can utilize standard encryption & authentication protocols (SSH, HTTPS etc.) to secure their traffic as per the OSI model.

The RF24 Communication Stack vs The OSI Model

With the associated libraries and enhanced functionality, the RF24 comm. stack is able to provide IoT and sensor network connectivity and capabilities to suit many different scenarios at a very low price point with much lower power consumption than WiFi networks. With the production of many devices like RPi, ESP8266 and ESP32 which support WiFi, users can construct and deploy IoT networks very easily, extending them as required.

Even now, it is really kind of cool to witness the system in action, using these little radios on tiny little computers we refer to as 'Arduinos'. The methodology and processes in place to manage a network of devices, fragmentation & reassembly, mitigate wireless data collisions and ensure delivery of data are quite effective, from the radio hardware and auto-ack functionality, all the way up to the TCP/IP and Mesh levels. With TCP/IP for example, using Raspberry Pi devices, the MTU is 1500-bytes, so each packet can require up to 63 sequential, successful data transmissions at the core RF24 layer, but this still works relatively well in real-world testing/usage.

It has been a lot of fun and a great learning experience so far. The creation of RF24Gateway really allowed the limits of the radios to be tested, and provided an excuse to play around with different network/IP configurations, routing scenarios and traffic handling at any level of the OSI model. A full and complete understanding of how devices operate on the internet or similar networks helps dramatically in troubleshooting, testing and development of systems and software that operate using these protocols.

Going forward, the development of the RF24 libraries has slowed significantly along with bug reports and issues. My focus has recently been on cleaning things up, finding and fixing bugs, mostly in the higher layers, and improving the user interface via examples and documentation. I had previously almost given up on the RF24Gateway and Ethernet layers as being too difficult to fix, but with the rise of more powerful MCUs and the potential for expanding their capabilities, it seems worthwhile to take another crack at working out bugs and issues.

 It would be nice to find another similar radio device with lower power consumption and/or more advanced capabilities and throughput to create more robust networks and mesh capabilities. The current design allows for speeds up to about 20KB/s over IP (RF24Gateway) using two Linux devices, but it would be nice to have a higher throughput to allow for more nodes, longer range and more advanced communication scenarios.

In conclusion I want to extend a big thank you to everybody who contributed ideas, analysis, information and programming skills along the way. An extra thank you to Avamander (GitHub) who has played a big part in ongoing maintenance, support and development!

Update: Aug 2020

Wow, I mentioned that I would be working on finding and fixing bugs due to the slowdown involving support, dev and maintenance etc, but did not expect to spend so much time, or that I would be able to identify so many issues, their root cause and a solution. Some pretty significant issues have been fixed throughout the RF24 stack, including 1 major bug in RF24, affecting all libraries, a number of bugs/issues affecting functionality and reliability in RF24Network and RF24Mesh, and a memory issue in RF24Ethernet affecting stability.
RF24Gateway has been updated with better handling of interrupts, a few corrections and the first release made, v1.0 due to all the issues that have been addressed. Again, a portion of these improvements are due to assistance, testing and input from a select few users. Users should notice a marked improvement in stability, functionality and the ability to recover from significant errors/hardware issues.

RF24 Communication Stack:
https://github.com/nRF24
https://nrf24.github.io/RF24Gateway
https://nrf24.github.io/RF24Ethernet

Summary: A Personal Experiment & A New Model for Open, Open-source, Anonymous & Secure Wireless Communication

Communication, Network, Protocol Design & Implementation Using Arduino & Raspberry Pi

Updated Nov 23, 2016

Over the course of the last few years, I have been working on a standardized, open-source communication stack that can be scaled from the biggest, most powerful devices, to tiny inexpensive devices like Arduino micro-controllers.

This looks familiar!

In the course of this time, I've made great progress in development of the core RF24 radio driver for nrf24l01+ radio modules. The overall goal of this project is independent of the radio devices, but these devices were chosen due to their relative capabilities vs cost, availability and ease of use. They are simply 2Mbps half-duplex wireless communication devices. Virtually any type of wireless devices can utilize the same theory of operation, including the mesh (RF24Mesh) style protocols.

What is it ? This system/communication stack allows nrf24l01+ radio/wireless devices to be utilized as a standard Network Interface Card (NIC) using TCP/IP & Mesh protocols. This is a summary of the experiment, system, general operation, and some of what I've learned.

Why? The programming, design and implementation of this system is part of a personal experiment I've been conducting involving the nature of wireless communication systems and protocols in relation to privacy, security, the Internet and the Internet of Things.

Theory of Operation & Design:

Consideration A: Open Networks + Anonymity + Automation

In general operation the basic principle of the communication stack is thus:
1. Each device utilizes a unique identifier while connected to a given access point.
2. This 'unique' identifier essentially represents an IP address in this implementation
3. For reasons of simplicity, this implementation also requires a 'static' identifier or IP address, but using more powerful micro-controllers and radio devices, the identifier can be assigned randomly or via DHCP
4. Devices simply attach, at any point in the network, using any available node(s) as an access point.

In a large scale model incorporating this type of design, with proper randomization of identifiers, individual devices and users are (potentially) indistinguishable from one-another initially and generally anonymous.

The next stage of course involves communication to enable the IoT/automation & allowing any capable device to connect. In this case there appear to be some options:

Option A: Leave the network open, and devices can choose to encrypt/authenticate their communications.This may require additional protective measures to prevent abuse in a large or publicly accessible system.

Option B: Assign selected devices a shared "network key" of sorts and incorporate encryption protocols into the network

Either way, it seems that wireless devices & users can inherently maintain their relative anonymity in a system that is designed a little differently.


Consideration B: Mesh Networks

The Network Layer: 
In studying the different layers involved in a capable communication stack, it seemed that many of the boundaries between layers were blurry, with many different systems 'breaking the rules' as it were. A good example of this is TCP/IP which does not strictly adhere to the OSI model.

In my design, a 'static' network architecture is used, which resembles a tree configuration. The simplicity of the RF24Network layer means that each node can handle routing of any type of information, and only needs to know which nodes it is directly connected to. 

Some of the features/functionality involving the RF24Mesh layer have been placed into the RF24Network layer directly. The reasons are mainly due to efficiency and limitations of small devices and this is under review.

Due to the limitations of the specific device used ( nrf24l01+ ) radio modules, each device is limited to 5 individual connections in the mesh, but this could be easily extended for use with more powerful radio devices.

The Mesh Layer:

The mesh layer utilizes its knowledge of the 'static' network architecture to allow individual nodes to attach themselves to the network at any given point where another node is active.

As mentioned above, each device is currently pre-assigned a unique identifier from 0-255 due to the 8-bit nature of very small & low power devices. In a large scale or commercial implementation, these identifiers can be assigned automatically & randomly, with devices then registering themselves in DNS if required, or simply acting as an anonymous client.

The fundamental benefit of a mesh style network is that nodes will automatically adjust their physical address and connection as required as they move around the network or lose connectivity. Any other nodes will provide connectivity by allowing other nodes to attach, and routing or accepting their traffic according to specifications.

Per RF24Network design, there is very little overhead for individual nodes, since they only need to keep track of which node they are connected to, and which nodes are using them as an access point.

Consideration C: Limitations

There are currently a number of fundamental imitations and odd 'quirks' that have to be dealt with due to the nature of really small devices like 16Mhz AVR devices.

AVR Devices: The chosen limitations in this case include some of the smallest and least power hungry devices available to any consumer. ATTiny devices can operate as low layer nodes & relays using RF24Mesh, and slightly faster 328 based AVR devices can run an actual IP stack.

uIP TCP/IP Stack:  One of main issues with small devices involves certain limitations of the IP stack. As soon as slightly larger devices are utilized, more robust IP stacks are available that make operation faster and more reliable. uIP has provided a very interesting learning opportunity and is quite amazing given what it can do with extremely limited resources.

Radio Devices: nrf24l01+ radio modules are max 2Mbps half-duplex communication devices with a specific 5-byte addressing scheme.


Consideration D: Fully Automated Networks

Software and wireless development capabilities have come to the point of enabling fully autonomous networks that essentially manage themselves, devoid of human interaction. This goal has been partly realized or demonstrated in theory and action with the RF24Mesh layer, and could easily be built upon and implemented by large scale commercial interests.

The concept of independent networks that configure and maintain themselves may seem to some as a wild idea or a bit of a pipe dream, but we have all of the tools and capabilities within our grasp. It is simply a matter of engineering and development.

Connectivity of individual users can be managed entirely via authenticated and encrypted connections, so there is clearly no need for individual identification of users or user management beyond the application layer.

This type of system could allow communities to simply put up hardware and provide access. The system would be automated to the point that if a device fails, nearby devices send out an alert and the equipment is replaced. That is all.

Consideration E: Wireless Technology and Potential Breakthroughs

Communications technology, aka the Internet, has become ubiquitous in many ways to the daily life of millions and millions of individuals and businesses. Unfortunately, this type of connectivity has not been available to consumers in poor, rural or remote areas in a real, usable way.

Even with existing satellite technologies showing great promise towards providing quality communications capabilities to new places, it seems that additional measures will need to be taken to provide for the age of automation. This is the kind of automation that will see real-time control scenarios, with vehicles communicating among themselves, drawing in information from traffic control systems, news, weather, and countless other systems.  This is the kind of automation that will see drone based grocery and package delivery, combined with, at some point, flying vehicles and high speed transportation systems.

The implementation of automation on a massive scale is going to require something better than the kind of service we get from existing cellular networks and current technology. This is going to require a lot more than what public cellular, 5G and fiber technologies can provide. What we need moving forward is not just a standard step forward in communications technology, but a giant leap forward, while keeping in mind all the things that make the internet and technology beneficial to everybody.


General Summary:

It now seems entirely possible and practical to design and implement fully featured, autonomous. large scale, wireless network architecture that fundamentally provides anonymity and promotes privacy among its users, while providing full mesh networking capabilities and automated network management.

With the emerging nature of communications devices, potential breakthroughs in communication technology, and wireless/IoT/automation technology emerging as a major component of our future progress, it seems very important to study, understand and develop networking and communication technologies with us, the users in mind.

It also seems that wired communications systems have already become a thing of the past, with more and more devices embedding chips and features to support Wireless and WiFi protocols and interfaces. The importance of privacy and security is fundamental to the operation of any large or public communication system, and any large, public & worthwhile communication platform will incorporate these basic ideals as inherent to its operation.


http://nrf24.github.io/RF24Ethernet

http://nrf24.github.io/RF24Gateway

RF24 Addressing: A review of NRF24L01+ radio addressing

Pipes, Addresses and Acknowledegments

There still seems to be a fair bit of questions, misconceptions and misunderstandings regarding the nature of RF24 radio addressing and how to set up communication scenarios. This is a review of RF24 pipes, addressing and acknowledgements that should provide any user with enough information to set up any supported configuration.



Acknowledgements (ACKs):

The radios support an automatic acknowledgement feature, enabled by default, in which the receiving radio switches into transmit mode after reception, and acknowledges reception of data.

1. A sends to B
2. B responds to A
3. A is now aware that B received the payload successfully

The acknowledgment process is very important to understand, because correct addressing is required for this feature to function properly.




Simplest Explanation/Rules of Addressing (Using ESB/Auto-Ack):

1. When using Auto-Ack, every radio can utilize a maximum of 6 unique addresses at once, which other radios can send data to.

2. Each address is assigned to a logical "pipe", and each radio has only 6 pipes that can be assigned addresses.

3. Since auto-ack implies a bi-directional communication channel, each address/pipe can only support communication to a single radio using acknowledgements. If two or more devices send data to a single pipe/address, auto-ack should be disabled to prevent ACK spamming and erroneous acknowledgements.
   Exceptions:
   a: Disabling Auto-Ack - This prevents excessive spamming of acknowledgements and errant acknowledgement.
   b: Timing of Transmissions - Using a token-ring style network or other method of preventing simultaneous transmissions would allow multiple radios to send data to the same pipe/address while maintaining the reliability of acknowledgements.

Note: At 1MBPS, a transmission can take up to 85ms or so, and overlapping transmissions are likely with any significant traffic

4. Per manufacturer design, the addresses assigned to pipes 1-5 must be the same, except for a single byte.



Basic Scenario - One to One Communication with AutoAck:

For purposes of standardization and to allow the system to be scaled, it is generally recommended to use two radio addresses. With auto-ack disabled, a single address can be used for all radios, or groups of radios.


Code:
Radio #1:
byte address_1[] = {0xCC,0xCC,0xCC,0xCC,0xCC};
radio.openReadingPipe(1,address_1);
Radio #2:
byte address_2[] = {0xC3,0xCC,0xCC,0xCC,0xCC};
radio.openReadingPipe(1,address_2);


Process - Radio #1 sending to Radio #2:

1. Radio #1 opens pipe 0 for writing (and internally, reading) using address of Radio #2 (CCCCCCCCC3)
2. Radio #2 receives the data on the first attempt, and (internally) opens a writing pipe using its own address (CCCCCCCCC3) and sends an acknowledgement back to Radio #1
3. Radio #1 receives the ACK, so does not engage in a series of timed retries





Basic Scenario - One to One or Many to Many Communication with Multicast:

With AutoAck disabled, radios can share the same address, and the system can still be scaled to support any number of devices.

Code:
byte address_1[] = {0xCC,0xCC,0xCC,0xCC,0xCC};
radio.setAutoAck(0);
radio.openReadingPipe(1,address_1);

In this situation, any radio can send a message to all other radios sharing the same address:

Code:

radio.stopListening();
radio.openWritingPipe(address_1);
radio.write(&data,sizeof(data));
radio.startListening();





Simple Mesh Scenario - Five-to-Five Communication with AutoAck:




In the above scenario any radio can send or receive data from any other radio in the mesh, thus creating a 'true mesh' of 5 nodes.

Radio #1 will always open a writing pipe using the address assigned to pipe#1 of the recipient.
Radio #2 will always open a writing pipe using the address assigned to pipe#2 of the recipient.
Radio #3 will always open a writing pipe using the address assigned to pipe#3 of the recipient.
... and so on

Process Confusion:
In this example of addressing, if Radio#2 and Radio#3 were to both open a writing pipe to Radio#1 using the same pipe/address, there would be confusion with acknowledgements. Radio#1 will respond to both devices with acknowledgements, since they have both opened a writing and reading pipe using the same address.




Complex Network/Mesh Scenario - Many-to-Many Communication with AutoAck:


As can be seen, this format of addressing is very similar to creating sub-nets with IPV4 addressing, except here we are using HEX instead of decimals, and there are 5 bytes per address instead of 4. Each radio is linked as shown in the image below, and each radio has a unique communication channel (pipe/address combination) to use when communicating with any of its parent or child nodes.

Due to the correlation of addresses and associated topology, each radio only needs to be aware of its parent and child nodes. Any traffic sent to a given node will either be a: Accepted b: Routed to parent c: Routed to a child

Address configuration, routing etc, can be managed very simply by masking and bit-shifting.





In the above example, pipe0 is NOT assigned a reading address, leaving it available to be used for broadcast or multicast. With AutoAck disabled on a single pipe, or by using selective acknowledgements, all radios or groups of radios can share an address, thus all radios will receive all messages sent to that address.

See the RF24Network Documentation and Source Code for more information regarding this type of configuration.



Summary:

In many low-throughput situations, the radios will appear to function correctly even with improper addressing, and may not cause any obvious problems, however, performance and functionality will most certainly be affected.

In any situation where reliability and acknowledged payloads are important, proper addressing and an understanding of the underlying processes behind acknowledged payloads is very important.

RF24Gateway - Creating Hybrid IoT Networks using TCP/IP and RF24Network

 RF24Gateway User Interface Example

RF24Gateway is a new complimentary library to RF24Ethernet, designed for RPi and Linux based devices with SPI and GPIO capabilities (BBB, Intel Edison, Galileo, etc).

The RF24Gateway library acts as a network/internet gateway, and allows Arduino/AVR based sensor nodes to interact with each other, the environment, and the world using TCP/IP and/or lower level RF24Network messages.

In short, it allows hybrid IoT networks to be created using Arduino and nrf24l01 modules. Some nodes are capable of internet or local network communication using standard protocols (TCP/IP) and/or RF24Network messages, while other nodes can communicate only at the network level, using only the lower layer RF24Network messaging.

Once RF24Gateway is configured, nodes can be controlled completely using standardized tools and protocols. Additional client examples have been added to demonstrate how to control and/or receive information from sensor nodes using standard tools and scripting methods via Bash, NodeJS and Python scripts. Any method of establishing a TCP connection can be used, with the examples generally using HTTP to some degree as well.

Libraries and code that utilizes RF24Network can utilize RF24Gateway in much the same way, since external data types (TCP/IP) are handled out of sight from the user. RF24Network is used exactly the same way, except that the gateway.update() function is called instead of network.update() or mesh.update(). The included examples demonstrate usage.

Note: RF24Gateway defaults to using a TUN interface with RF24Mesh enabled. RF24Ethernet examples have been updated to accommodate this.

Current Status:

April 2015: Near completion. Integrated fully with RF24Ethernet. Graphical (NCurses) interface example finalized.

Source Code:
https://github.com/TMRh20/RF24Gateway

Documentation:
http://nrf24.github.io/RF24Gateway

Download (See documentation for installation info):
https://github.com/TMRh20/RF24Gateway/archive/master.zip