1. Monday, 17 Oct 2011 A Low-Power CoAP for Contiki Matthias Kovatsch, Simon Duquennoy, and Adam Dunkels kovatsch@inf.ethz.chkovatsch@inf.ethz.ch simonduq@sics.seadam@sics.sesimonduq@sics.seadam@sics.se

2. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Internet of Things Protocol Stack 2 LayerProtocol ApplicationCoAP / REST Engine (Erbium) TransportUDP NetworkIPv6 / RPL Adaption6LoWPAN MACCSMA / link-layer bursts Radio Duty CyclingContikiMAC PhysicalIEEE 802.15.4

3. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Internet of Things Protocol Stack 3 LayerProtocol ApplicationCoAP / REST Engine (Erbium) TransportUDP NetworkIPv6 / RPL Adaption6LoWPAN MACCSMA / link-layer bursts Radio Duty CyclingContikiMAC PhysicalIEEE 802.15.4 / link-layer bursts

4. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich ContikiMAC 4 A D A D A ACK frame Data frame Radio on Sender Receiver Transmission detected DDDD Channel check

5. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Link-layer Bursts 5 A AD Sender Receiver Transmission detected DDDD Channel check A AD DA AD DA AD D D A ACK frame Data frame Radio on

6. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Constrained Application Protocol (CoAP)  RESTful Web services for networked embedded devices  Idealized architectural style of the Web  HTTP for the Internet of Things 6 coap://sky3/ coap://sky2/ coap://sky1/ GET /sensors/temperature

7. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich  Implements draft-ietf-core-coap-07  Available in the Contiki repository on SourceForge «Erbium» CoAP for Contiki 7

8. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich «Erbium» CoAP  Reliable UDP transport  Observing resources  Blockwise transfers  Resource discovery  Separate responses  Blocking client requests 8

9. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich «Erbium» REST Engine  Resource abstraction RESOURCE(handle, METHODs, URI-Path, Web Linking info);  Resource handler PERIODIC_RESOURCE(handle, METHODs, URI-Path, info, period);  Additional periodic handler EVENT_RESOURCE(handle, METHODs, URI-Path, info);  Additional event handler 9 Observable CoRE Link Format title="Hello world"; rt="TemperatureC";

10. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich «Erbium» Memory Footprint ROM [kB]RAM [kB] CoAP REST Engine total8.51.5 Measured stack usage–0.1 REST Engine0.70 CoAP-07 base4.50 CoAP-07 server1.90.3 CoAP-07 transport0.40.9 CoAP-07 observing0.90.2 CoAP-07 separate0.10 10

11. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Experimental Set-up 11 3 hops 2 hops 1 hop Energy data over USB 100 Requests each Laptop with border router Static routing 4 hops

12. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Energy vs Latency for 64B Payload 12 Number of hops Energy [mJ] Latency [s] No duty cycling ContikiMAC 1234 0 100 200 300 400 1234 0 0.2 0.4 0.6 0.8 1.0 8 Hz channel check rate 0.6% RDC

13. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Transmitting Large Data 13 Payload [Bytes] Energy [mJ] Latency [s] Bursts avoid steps in latency 23456 Steps become less noticable 4 hops 2 hops 1 hop

14. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Transmitting Large Data 14 A AD Sender Receiver Transmission detected DDDD Channel check AD AD ADA AD D D A ACK frame Data frame Radio on AD

15. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Separate Responses 15 Client Server Request processing Request Retry Retry … Response Request processing Response ACK Request ACK Benchmark and switch automatically Benchmark and switch automatically

16. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Separate Responses over 4 Hops 16 Without With Energy [mJ] Server processing time [s] Savings marginal

17. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Conclusion  Internet of Things stack  Isolated layers with different goals work together  Layered architecture lowers complexity  Optimize for single fragments  No need to optimize payload size once fragmented  CoAP  Draft 07 implementation for Contiki  Block size most important parameter for memory-constrained devices: Exponential sizes too coarse-grained 17

18. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Future Work  Extend «Erbium» CoAP  Blocking resource handler for UART  Hierarchical resources / URI-Path handling  Improve observer handling (only one buffer)  Study RESTful approach  Long-term deployment with smart appliances  Separate application logic from device firmware and combine with «Californium» App Server 18

19. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich THANK YOU Questions? 19

20. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Radio Duty Cycling 20

21. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Constrained Application Protocol (CoAP)  RESTful Web services for networked embedded devices  Idealized architectural style of the Web  Usually implemented with HTTP  Central mechanisms  Reliable UDP transport («confirmable»)  Group communication (IP multicast)  Push notifications («observing»)  Resource discovery («CoAP link format»)  Larger data transport («blockwise transfers») 21 coap://sky3/ coap://sky2/

22. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Blockwise Transfers Automatic or controlled by handler RESOURCE(handle, METHODs, URI-Path, Web Linking info);  Resource handler handle_handler(void* request, void* response, uint8_t *buffer, uint16_t preferred_size, int32_t *offset); 22 Unaware: fill buffer up to REST_MAX_CHUNK_SIZE Chunk-aware: use offset and fill buffer up to preferred_size (update offset and set to -1 when finished)

23. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Observing Resources Post-handler registers observers automatically PERIODIC_RESOURCE(handle, METHODs, URI-Path, info, period);  Additional periodic handler EVENT_RESOURCE(handle, METHODs, URI-Path, info);  Additional event handler int handle_event_handler(resource_t *r) {... REST.notify_subscribers(r->url, CON/NON, seqno, buf, len); } 23 Every x-th is CON to resolve orphans

24. A Low-Power CoAP for Contiki Matthias Kovatsch – ETH Zürich Erbium REST Engine  Manipulate messages with REST API  REST.set_header_etag(response, etag_buf, etag_len);  REST.get_query_variable(request, name, value_buffer);  Link implementation  coap-03  coap-06  coap-07  …  HTTP (not yet implemented for Erbium) 24