AirTight

A C implementation of the AirTight protocol from the Real-Time Systems group at the University of York.

Introduction

AirTight is a protocol for critical wireless communication based on the IEEE 802.15.4 MAC and physical layers.

AirTight is described in the paper:

A. Burns, J. Harbin, L. Indrusiak, I. Bate, R. Davis and D. Griffin, "AirTight: A Resilient Wireless Communication Protocol for Mixed-Criticality Systems," 2018 IEEE 24th International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA), Hakodate, 2018, pp. 65-75, doi: 10.1109/RTCSA.2018.00017.

An existing implementation of AirTight, for TinyOS using NESC, is available at: https://github.com/RTSYork/airtight.

This implementation itends to be more platform independent than the existing implementation and more extensively documented. For the purposes of development, testing, and as an example, the Pi-Puck platform was used for testing, and the XBee module on the platform was targeted for the example radio port.

Updating & Building the XBee Library

To build the XBee library:

cd xbee
make

If you wish to make sure you are using the latest version:

git clone https://github.com/digidotcom/xbee_ansic_library.git
cd xbee
./import_library.sh

Then build as before.

Building Docs

To build the docs you will need Doxygen.

With doxygen installed simply run:

make doc

Bulding the Project

The XBee library is a dependency and therefore must already be built.

From the project root simply run:

make

Configuring AirTight

At it's core AirTight features a Priority Critical Queue (PCQ) which stores packets due to be sent or forwarded. To configure the PCQ use the following:

• To set the number of priority levels edit AIRTIGHT_PRIORITIES in src/airtight_types.h.
• To set the depth of each queue edit PRIORITY_CRITICAL_QUEUE_SIZE in src/airtight_priority_critical_queue.h.
• To set the criticalities of each queue edit AT_CONF_CRITICALITIES in src/airtight_mac_config.h.

The other core structure is the scheduling table used to organise transmissions and receptions on the AirTight network. To configure the schedule table use the following:

• To set the number of rows and columns in the schedule table edit AT_CONF_SLOT_TABLE_ROWS and AT_CONF_SLOT_TABLE_COLUMNS respectively in src/airtight_slots_config.h.
• To set the contents of the table edit the file src/airtight_slot_table.txt.

The full network of connections between nodes and the hops required to route packets around the network is specified in the file src/airtight_routes_config.txt with each HOP rule having a node ID to which it applied, a final packet destination, and a "hop" destination. Unspecified routes will be assumed to be direct with a single hop.

Further configuration parameters can be found in src/airtight_mac_config.h and are documented there.

Configuring the XBee Modules

The XBee module must have the 802.15.4 firmware and the following configuration must be set:

AT Command	Description	Value
MM	MAC Mode	Strict 802.15.4 with ACKs (2)
AP	API Mode	API Mode Without Escapes (1)
BU	Baud Rate	Same as configured in airtight.c

Debugging

Debugging is enabled by default but can be disabled by undefining AIRTIGHT_DEBUG in src/airtight_utilities.h.

Logging

Logging is enabled and prefixed with "LOG" by default. Logging can be disabled by undefining AIRTIGHT_LOGGING in src/airtight_logging.h.

License

This project is licensed under the BSD 3-Clause license, see LICENSE for details.

The XBee ANSI C library is Copyright Digi International, 2013 and licensed under the Mozilla Public License, v. 2.0. See https://github.com/digidotcom/xbee_ansic_library for further details.