Mobile and Wireless Computing CITS4419 Week 6: Software Architecture

Rachel Cardell-Oliver2014

Software architectures for co-ordinating Sensing and Actuation in Smart Homes

Smart Homes (Pilich 2004)

• Controllable– Integrated remote control– Interconnected devices– Voice, gesture or movement control

• Programmable– Reacting to time and simple sensor inputs– Assessing and recognising situations

• Intelligent– Learns repeated actions and reacts automatically

SOFTWARE ARCHITECTURE

What is Software Architecture

• Process of defining a structured SW solution to given technical and operational requirements

• Optimises common quality attributes (performance, security, manageabilty)

• A series of decisions • “the decisions that are hard to change” [Fowler]

• Further reading: http://msdn.microsoft.com/en-us/library/ee658098.aspx

Software ComponentsSource: http://msdn.microsoft.com/en-us/library/ee658124.aspx

SW Architectures for Smart Homes

• Client/Server– System comprises 2 applications: client(s) makes

requests to a server (2-Tier architecture)• Service-Oriented (SOA)– Applications expose and consume functionality as

loosely-coupled services that use contracts and messages

• Component Based / Resource Oriented (ROA)– Reusable functional/logical components expose well-

defined communication interfaces

Client / Server

• 1 or more clients send requests to a server• Server listens for requests and responds• Example: desktop UI and database server• Processing can be client-side or server-side• PRO: simple maintenance, high security of data, central

data management• CON: one point of failure, close coupling of application

data and business server = poor extensibility• 3-Tier and N-Tier client server can be used to improve

extensibility and reliability

Service Oriented (SOA)• SW components provide application functions as services to

other systems. • A service is a distinct, self-contained function such as

submitting, changing or retrieving data. • Protocols define how services exchange data.• For the web, XML is used to describe data and metadata,• Web service description language (WSDL) for defining

services, and• Simple Object Access Protocol (SOAP) as comms protocol• Services are combined to build large ad hoc applications• PROS: domain alignment, abstraction, discoverable,

interoperable, removes duplication• CONS: data overhead

Resource Oriented (ROA)ROA supports internetworking of resources

Resource = anything important enough to be referenced as a thing itself

Resource name = unique identification of the resource (uniform resource identifier (URI))

Resource representation = useful information about the current state of a resource

Resource link = link to another representation of the same or another resource

Resource interface = uniform interface for accessing the resource and manipulating its state

In a ROA each device has its own URI, HTTP GET requests query its state and POST request sets a value.Fielding, R.T., Architectural Styles and the Design of Network-based Software Architectures, Ph.D. dissertation, in University of California, Irvine. 2000. Leonard Richardson, S.R., RESTFul Web Services. 2007: O'Reilly. http://inspire.ec.europa.eu/rports/ImplementingRules/network/Resource_orientated_architecture_and_REST.pdf

SOA vs ROA for smart homes

• Bovet [2007] argues:• Since, large overhead of XML and • complexity of the service description language

WSDL, • So, Service-Oriented arch (and its SOAP

protocol) is not well suited for sensor/actuator things

• But, resource oriented architecture (ROA) offers new ways for accessing things

Incorporating Low Power Sensors

ROA is not suitable for energy harvesting (really low power) sensors and actuators such as enoceanSolution: 1. gateway listens to sensor telegrams and saves info (values and

ids) which are used to respond to get requests2. actuators can not be discovered so their name is filled by user,

and then actuation telegrams can be sent using data from POST requests.

3. One solution is for a bridge to brokers enocean requests, but this does become a single point of failure.

4. They propose a hybrid mode in which both gateway and sensors know about actuators and can drive them

SERVER EXAMPLES

FHEM http://fhem.de/

• FHEM is an open source PERL web server designed for home automation

• Users can control the program via the web, smartphones, telnets or TCP/IP

• In addition, the project offers various contributed front end user interfaces and back end protocols and modules for many proprietary sensor protocols including enocean, Zwave, KNX.

• It supports house automation devices, audio/video devices, weather services, online calendars and more.

Lighttpd http://www.lighttpd.net/

• Lighttpd is a lightweight webserver with a small memory footprint compared to other web-servers.

• It can easily be setup to serve PHP websites.• It is more suitable than Apache for Raspberry Pis,

since Apache can use up to 30% of the Pis resources in idle mode

• Source: http://www.scandio.de/2012/11/setting-up-a-lightweight-webserver-with-lighttpd-php5-and-sqlite3/

Python http.server

• Python 2 supports SimpleHTTPServer • In Python 3 see http.server • On the Raspberry Pi, call python3 for version 3 and

just python for version 2.7.x• To use the web server, use one of the following

• python3 -m http.server 8000• python -m http.server 8000 --bind 127.0.0.1• python -m SimpleHTTPServer 8000

COMMUNICATION PROTOCOLS

MQTT

• MQTT stands for MQ Telemetry Transport. It is a publish/subscribe, extremely simple and lightweight messaging protocol, designed for constrained devices and low-bandwidth, high-latency or unreliable networks.

• http://mqtt.org/faq• http

://www.sigfox.com/static/media/Files/Documentation/SIGFOX_Whitepaper.pdf

• There is a python library Mosquitto for MQTT that can be used with Raspberry pi.

• http://mosquitto.org/documentation/python/

Zigbee• ZigBee is used in applications that require only a low data rate, long battery life, and

secure networking. ZigBee has a defined rate of 250 kbit/s, best suited for periodic or intermittent data or a single signal transmission from a sensor or input device. Applications include wireless light switches, electrical meters with in-home-displays, traffic management systems, and other consumer and industrial equipment that requires short-range wireless transfer of data at relatively low rates.

• Zigbee is for personal area networks built from small, low-power digital radios. ZigBee is based on an IEEE 802.15 standard. Though low-powered, ZigBee devices can transmit data over long distances by passing data through intermediate devices to reach more distant ones, creating a mesh network

• As one of its defining features, ZigBee provides facilities for carrying out secure communications, protecting establishment and transport of cryptographic keys, cyphering frames and controlling devices. It builds on the basic security framework defined in IEEE 802.15.4. This part of the architecture relies on the correct management of symmetric keys and the correct implementation of methods and security policies.

Z-Wavehttp://en.wikipedia.org/wiki/Z-Wave

• Z-Wave is one of the most popular home automation protocols• Supported by the Z-wave alliance of 250 technology companies.• Lots of products: sensors, lighting switches and dimmers, thermostats and

radiator valve actuators, alarms• Z-wave creates a mesh network, with low power radio protocol designed

for remote control applications• Optimised for reliable, low-latency communication of small data packets

with data rates up to 100kbit/s.• Unlike Wi-Fi and other IEEE 802.11-based wireless LAN systems that are

designed primarily for high-bandwidth data flow, Z-Wave operates in the sub-gigahertz frequency range, around 900 MHz.

• Z-wave mesh network can contain up to 232 nodes: control and slave devices, which can use multi path up to 4 hops to relay messages.

• Security includes encryption, authentication and key exchange protocols.

EnOcean

• EnOcean self-powering sensors come with their own proprietary ultra-low-power protocol

• Devices publish data telegrams • Packets only 14 bytes long, trans. 125 kbit/s• RF only tx for 1s (saves energy on 0s)• Devices at 902, 928.35, 868.3, 315 MHz

6LoWPAN and COAP6LoWPAN (IPv6 over low power wireless personal area networks)

IPv6 packets sent over IEEE 902.15.4 networks for limited form factor devices(sensors and actuators)

Compressed headers, low data rate, IETF working group

Constrained Application Protocol CoAP is a draft internet standard IETF for constrained devices

Application layer protocol, multi-cast, designed to translate to HHTP

URI and content support, resource discovery, requests and responses

CoAP for the Web of Things: From Tiny Resource-constrained Devices to the Web Browser, M. Kovatsch, WoT 2013: Fourth International Workshop on the Web of Things, http://dx.doi.org/10.1145/2494091.2497583Shelby, Z., Hartke, K., and Bormann, C. Constrained Application Protocol (CoAP). I-D: draft-ietf-core-coap-17, 2013

FURTHER READING

Universal Remote Console

• URC standard for devices that can be used remotely.

• Remote devices = “controller”• Controlled device = “target”• Controller presents a user interface for the

target• FHEM

Zero-Configuration Networking

• Automatic discovery of devices on a local network

• Publish and Discover TCP/IP services• Apple implementation Bonjour, See also

Windows version