sDDS: An Adaptable DDS Solution for Wireless Sensor Networks
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The document describes an adaptable DDS solution called sDDS for wireless sensor networks. sDDS uses a model-driven software development approach to tailor DDS middleware functionality and generate optimized code for heterogeneous sensor nodes. It includes a custom protocol called SNPS that is influenced by RTPS but optimized for low bandwidth wireless networks. SNPS allows aggregation of data from different topics into single messages to reduce overhead. An example shows how sensor nodes can selectively process only relevant data from SNPS messages to further reduce resource usage.
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SNPS – Message Sizes
Version No. of
SubMsgs
Domain
α
Topic
A
Data
1
Payload
1
Data
2
Payload
2
Topic
B
Data
3
Payload
3
Header
Minimum Submessage Sequence
Size: 5 + [payload] Bytes Same Topic:
1 + [payload] Bytes
Different Topic:
2 + [payload] Bytes
● Minimum: Header, Domain, Topic, Data
● Data aggregation in one message adds little overhead
● Assumption:
● Switching transceiver on and off => base cost of energy
● Protocol layer 1, 2 and 3 overhead is significant too
● The overhead of the additional data is acceptable](https://image.slidesharecdn.com/sddsddsforwirelesssensornetworks-rheinmainuniversity-londonconnextconference1-141022140536-conversion-gate02/85/sDDS-An-Adaptable-DDS-Solution-for-Wireless-Sensor-Networks-18-320.jpg)
sDDS: An Adaptable DDS Solution for Wireless Sensor Networks
- 1. DDOOPPSSYY ggrroouupp PPrrooff.. DDrr.. RR.. KKrrööggeerr KKaaii BBeecckkmmaannnn MMaarrccuuss TThhoossss {{ffiirrsstt..ssuurrnnaammee}}@@hhss--rrmm..ddee LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb hhttttpp::////wwwwwwvvss..ccss..hhss--rrmm..ddee sDDS An adaptable DDS Solution for Wireless Sensor Networks Kai Beckmann Distributed Systems Lab RheinMain University of Applied Sciences RTI Connext Conference, London, 08.10.2014
- 2. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 22 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Personal Introduction ● RheinMain University of Applied Sciences, Wiesbaden, Germany ● Distributed Systems Lab (headed by Prof. Dr. Kröger) – Management of Distributed Applications – Embedded Systems, Industrial automation ● 2010 M.Sc. in computer sciences ● Research associate, Ph.D. student and assistant lecturer ● Interests: ● Application of distributed and embedded systems ● Middleware (esp. OMG Data Distribution Service) ● Wireless sensor networks ● Application of model-driven software development in embedded systems ● Model-based software testing
- 3. QoS? 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 33 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Motivation Wireless Sensor Networks Sensor-Actor-Networks Automation Often Data-Centric
- 4. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 44 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Problems with WSN ● Requirements ● Cheap ● Limited resources ● Low energy consumption ● Heterogeneity ● Hardware architectures ● Network technologies / protocols / standards ● Software / middleware ● Interoperability ● Proprietary products, different standards ● No consolidation so far ● Often IP as compromise ● DDS an approach?
- 5. Wireless transport IEEE 802.15.4 127 byte frame size 8 bit uC 8 kB RAM 128 kB Flash Finite energy source 32 bit ARM 64 kB RAM 4 GB Flash Wall-Socket dynamic node 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 55 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb DDS for WSN - problems ● Need for customised DDS functionality 32 bit ARM 2 GB RAM *nix OS Temperatur sensor ➔ publisher Switch sensor ➔ publisher Movement sensor ➔ publisher ➔ router Controllable Socket ➔ publisher ➔ subscriber ➔ router static link
- 6. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 66 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Our Approach: sDDS ● sensornetwork DDS (sDDS) ● Minimal individual customisable DDS solution ● DDS API conform ● Model-driven Software Development (MDSD) process ● WSN-System / Structure ● WSN-DDS-Application ● WSN-Node ● DDS middleware adaptation ● Tailoring of functionality of modules to be deployed ● Supporting heterogeneous middleware nodes ● Exploit existing target facilities ● SNPS protocol specialised for WSN environment
- 7. DSL DDS UML Profile 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 77 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb MDSD Tailoring Process HW Spec Deployment Topics QoS Application Requirements ● DDS func. ● QoS DSL DSML DSL DSL IDL PIM PSM Optimisation Templates Code
- 8. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 88 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb sDDS - Features ● Extensible MDSD process ● Eclipse environment (EMF, Xtext), with alternative lightweight python scripts ● Proof-of-concept realisation ● Many optimisations, customisations possible ● Integration of other models, specifications ● Platform independent, easy to port ● Plain C ● Abstract interfaces for system and network ● Fast integration of new platforms (Contiki: 2 weeks only, by undergrad student) ● Small footprint ● 20 kB for static routing with 2 - 4 topics
- 9. ● Reliable Transport ● Dynamic Discovery 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 99 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Problem - Network ● Heterogeneity ● Different Subsets of DDS ● Still need for cooperation ● Special layer 1-3 protocols ● Frame sizes ● Routing ● Energy consumption ● Transmitting data expensive – Amount of data – Transceiver on/of ● Natural Broadcast ● Limited resources on nodes ● Best Effort ● Only Publish ● Reliable Transport ● Static link ● Reliable Transport ● Static link
- 10. system protocol Enterprise DDS RTPS 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1100 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Protocol SNPS ● Sensor-Network Publish-Subscribe (SNPS) ● Influenced by RTPS ● Small footprint, small frame sizes, limited bandwidth ● Aim: Low average protocol overhead ● Data aggregation even for different receivers ● Utilises radio network features WSN sDDS SNPS
- 11. MMeessssaaggee 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1111 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb SNPS - Structure VVeersrsioionn SSuubbMMssggCCoouunnt t 1 1 1...* SSuubbMMeessssaaggee parameter: 4bit type: 4bit EExxtetennddeeddSSuubbMMeessssaaggee extType: 4bit type = extSubMsg_t SSuupppplelemmeenntStSuubbMMeessssaaggee ● Small atomic information units ● Submessage ● Sequential processing ● Self-description and implicit structure ● Skipping unknown parts ● Small protocol footprint ● Different classes of sizes ● From frequency of use ● “Squeeze” as much information into a byte as possible
- 12. SSuubbMMeessssaaggee DDoommaainin TTooppicic DDaatata EExxtetennddeeddSSuubbMMeessssaaggee PPaayyloloaadd Handshaking Ack SSeeqqNNr r Ack NNaacckk Data Addressing EExxtTtTooppicic 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1122 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb SNPS – Data transmission ● Addressing => Domain, Topic ● Data => header for payload ● Handshaking => Ack, Nack, SeqNr (different sizes) ● Sequentially assembled state used for interpretation
- 13. Data reader Subscriber Data writer Publisher Global data space (domain α) Data writer Topic A Publisher Data reader 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1133 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Example – Data Transmission ● SNPS protocol semantics limited to data transmission ● Subscription etc. handled at DDS level – BuiltIn-Topics ● Realisation is the task of the middleware Subscriber Topic B Topic C Domain participant Domain participant Domain participant Node1 Node2 Node3 Data reader Data writer
- 14. Data reader Subscriber Data writer Global data space (domain α) Data writer Topic A Publisher Data reader 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1144 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Example – Data Transmission ● Node 1 publishes data for topic A and B ● Node 2 needs reliable transmission, node 3 does not ● SNPS message of node 1: Publisher Subscriber Topic B Topic C Domain participant Domain participant Domain participant Node1 Node2 Node3 Data reader Data writer Version No. of SubMsgs Domain α Topic A Data 1 Payload 1 Topic B Data 2 Payload 2 SeqNr
- 15. Topic B Topic C Data reader Subscriber Data writer Publisher Domain participant Global data space (domain α) Data writer Topic A Publisher Data reader Subscriber Domain participant 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1155 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Example – Data Transmission ● Node 3 needs only topic B ● Skipping part related to topic A ● Processing data of topic B, skipping SeqNr and done Domain participant Node1 Node2 Node3 Data reader Data writer Version No. of SubMsgs Domain α Topic A Data 1 Payload 1 Topic B Data 2 Payload 2 SeqNr
- 16. Data reader Subscriber Publisher Global data space (domain α) Data writer Topic A Publisher Data reader 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1166 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Example – Data Transmission ● Node 2 needs only topic B as well ● Node 2 processes data of topic B ● Acknowledgement required Data writer Subscriber Topic B Topic C Domain participant Domain participant Domain participant Node1 Node2 Node3 Data reader Data writer Version No. of SubMsgs Domain α Topic A Data 1 Payload 1 Topic B Data 2 Payload 2 SeqNr
- 17. Topic B Topic C Data reader Subscriber Data writer Publisher Domain participant Global data space (domain α) Data writer Topic A Publisher Data reader Subscriber Domain participant 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1177 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Example – Data Transmission ● Node 2 publishes data for topic C ● And an acknowledgement for topic B ● Node 1 ignores topic C and processes the Ack Domain participant Node1 Node2 Node3 Data reader Data writer Version No. of SubMsgs Domain α Topic C Data 1 Payload 1 Topic B ACK SeqNr
- 18. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1188 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb SNPS – Message Sizes Version No. of SubMsgs Domain α Topic A Data 1 Payload 1 Data 2 Payload 2 Topic B Data 3 Payload 3 Header Minimum Submessage Sequence Size: 5 + [payload] Bytes Same Topic: 1 + [payload] Bytes Different Topic: 2 + [payload] Bytes ● Minimum: Header, Domain, Topic, Data ● Data aggregation in one message adds little overhead ● Assumption: ● Switching transceiver on and off => base cost of energy ● Protocol layer 1, 2 and 3 overhead is significant too ● The overhead of the additional data is acceptable
- 19. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 1199 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb sDDS - Status ● Development system: Linux and UDP/IP ● Target systems ● TI SoC CC2430 ● Atmel Atmega128 platform ● Transports ● UDP/IP ● 6LoWPAN (on Contiki OS) ● ZigBee Layer 3 (TI zStack) ● First concepts for CAN ● Work in Progress -> limited support of DDS functionality ● Used in an Ambient Assisted Living (AAL) research project and university courses
- 20. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 2200 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb sDDS - Future Work ● Currently funded by small internal research project ● Clean up, documentation, integration of functionality ● Aim: Publish as Open Source within next year ● Rework MDSD process ● Functionality ● Dynamic discovery ● QoS ● History on qualified nodes ● Connect WSN to “normal” DDS ● SNPS integration in RTI Connext DDS ● Vertical integration ● New application fields: Industry 4.0, IoT ● Base for new research projects
- 21. 08.10.2014, RRTTII CCoonnnneexxtt CCoonnffeerreennccee KKaaii BBeecckkmmaannnn 2211 DDOOPPSSYY ggrroouupp LLaabboorr ffüürr VVeerrtteeiillttee SSyysstteemmee DDiissttrriibbuutteedd SSyysstteemmss LLaabb Questions ?