Implementation of CoAP and its Application in Transport Logistics Koojana Kuladinithi, Olaf Bergmann, Thomas Pötsch, Markus Becker, Carmelita Görg koo@comnets.uni-bremen.de bergmann@tzi.org tpoetsch@uni-bremen.de mab@comnets.uni-bremen.de cg@comnets.uni-bremen.de TZI, University Bremen, Germany IP+SN2011, 11th of April 2011 Becker: CoAP , IP+SN 2011 1 / 23
Outline Introduction Machine-2-Machine Communication Implementation of CoAP libcoap libcoap & Contiki libcoap & TinyOS Evaluation of libcoap CoAP vs HTTP Conclusions & Outlook Becker: CoAP , IP+SN 2011 2 / 23
Introduction ◮ IETF CoRE Working Group ◮ Constrained Application Protocol (CoAP) ◮ RESTful protocol Becker: CoAP , IP+SN 2011 3 / 23
CoAP in a nutshell ◮ Methods: CON, NON, ACK, RST ◮ Pre-processed URI in different options ◮ Resource discovery built-in /.well-known/core ◮ Caching/Proxying ◮ HTTP like response codes ◮ Mapping to HTTP Becker: CoAP , IP+SN 2011 4 / 23
Machine-2-Machine Communication ◮ http://www.intelligentcontainer.com Becker: CoAP , IP+SN 2011 5 / 23
CoAP Resources (1/2) Resource GET PUT Comments /st X Temperature /sh X Humidity /sv X Voltage /r X Temperature, humidity and voltage together /l X X LEDs /ck (X) X AES Encryption Key Table: CoAP Resources on Sensor Nodes Becker: CoAP , IP+SN 2011 6 / 23
CoAP Resources (2/2) Resource GET PUT Comments /ni X Inform about node integration into 6LoWPAN/RPL network /warntemplow X Below Warning Temperature Low /warntemphi X Above Warning Temperature High Table: CoAP Resources on the FSU Becker: CoAP , IP+SN 2011 7 / 23
libcoap ◮ http://libcoap.sourceforge.net ◮ Implements ◮ draft-ietf-core-coap-03 ◮ draft-ietf-core-link-format-01 ◮ draft-ietf-core-block-00 ◮ draft-ietf-core-observe-00 ◮ draft-bormann-coap-misc-06 ◮ Provides ◮ Sample server ◮ Sample client ◮ Participated in several plug-fests of the CoRE working group Becker: CoAP , IP+SN 2011 8 / 23
libcoap & Contiki ◮ CoAP for Sensinode N740 ◮ Based on uIP ◮ Contiki & libcoap stripped to fit into 3 memory banks of 32 KB each ◮ TCP removed ◮ Shared global variables ◮ libcoap : ∼ 12 KB ROM ◮ rest-coap shipped with Contiki: ∼ 26 KB ROM Becker: CoAP , IP+SN 2011 9 / 23
libcoap & TinyOS ◮ Installation instructions at http://docs.tinyos.net/index.php/CoAP ◮ CoAP server and client ◮ Only GET + PUT support (POST + DELETE do not fit component model) ◮ Based on TinyOS blip-1.0 (working on blip-2.0) ◮ Block & observe drafts not supported yet (time.h → Timer) ◮ Synchronous/asynchronous a.k.a immediate/deferred a.k.a. piggy-backed/separate supported through TinyOS timers ◮ multiple end-points on different ports possible Becker: CoAP , IP+SN 2011 10 / 23
libcoap & TinyOS components CoapBlipP Init Boot IPConnectivity SplitControl CoAPServer MainC IPDispatchC Init CoapUdpServerC Leds Mount R eadR esource[uint8_t] R eadR esource[uint8_t] R eadR esource[uint8_t] LibCoAP R eadR esource[uint8_t] W riteR esource[uint8_t] R eadR esource[uint8_t] W riteR esource[uint8_t] R eadR esource[uint8_t] CoapReadResourceC CoapReadResourceC CoapReadResourceC CoapReadResourceC CoapLedResourceC CoapFlashResourceC LibCoapAdapterC (CoapReadVoltResource) (CoapReadHumResource) (CoapReadT empResource) (CoapReadAllResource) (CoapLedResource) (CoapFlashResource) R ead<uint16_t> R ead<uint16_t> R ead<uint16_t> UDP R ead<val_all_t> Leds ConfigStorage CoapBufferHumT ranslateC CoapBufferT empT ranslateC UdpSocketC CoapResourceCollectorC LedsC ConfigStorageC (CoapBufferHumT ranslate) (CoapBufferT empT ranslate) (UdpServerSocket) CoapBufferVoltT ranslateC R ead<uint16_t> R ead<uint16_t> R ead<uint16_t> R ead<uint16_t> R ead<uint16_t> (CoapBufferVoltT ranslate) SensirionSht11C CoapBufferVoltT ranslateC CoapBufferHumT ranslateC CoapBufferT empT ranslateC R ead<uint16_t> (HumT empSensor) (CoapBufferVoltT ranslateAll) (CoapBufferHumT ranslateAll) (CoapBufferT empT ranslateAll) R ead<uint16_t> R ead<uint16_t> R ead<uint16_t> VoltageC SensirionSht11C (VoltSensor) (HumT empSensorAll) Becker: CoAP , IP+SN 2011 11 / 23
libcoap & TinyOS call/signal ◮ LibCoAPAdapterC translates between callbacks and call/signal ◮ LibCoAPAdapterC wired to UDPSocketC’s ◮ Resources wired, but registered with URI at boot time ◮ Generic index calculated from URI Becker: CoAP , IP+SN 2011 12 / 23
Interfaces (1/3) interface LibCoAP { command error_t bind(uint16_t port); command coap_tid_t send(coap_context_t *ctx, struct sockaddr_in6 *dst, coap_pdu_t *pdu, int free_pdu); event void read(struct sockaddr_in6 *from, void *data, uint16_t len, struct ip_metadata *meta); } Becker: CoAP , IP+SN 2011 13 / 23
Interfaces (2/3) interface ReadResource { command error_t get(coap_tid_t id); event void getDone(error_t result, coap_tid_t id, uint8_t asyn_message, uint8_t* val, uint8_t buflen); event void getPreAck(coap_tid_t id); } ◮ E.g. for Temperature, Humidity, Voltage ◮ Default handlers catch not supported methods on resources and return the appropriate error code Becker: CoAP , IP+SN 2011 14 / 23
Interfaces (3/3) interface WriteResource { command error_t put(uint8_t* val, uint8_t buflen); event void putDone(error_t result); } ◮ Readable and writable resources implement both interfaces ◮ E.g. for Led, FlashStorage Becker: CoAP , IP+SN 2011 15 / 23
libcoap & TinyOS Read/ReadResource interfaces ◮ CoapReadResourceC translates between val_t and uint8_t* ◮ CoAPBuffer{Volt | Hum | Temp}TranslateC transform buffer reading to SI units using fixed-point calculations ◮ Over-the-air only fixed point values (SI value * 100) are transmitted ◮ The corresponding side does not need to know which sensor and its characteristic line ◮ Characteristic line might be discoverable by resource discovery and resource description of link-format standard Becker: CoAP , IP+SN 2011 16 / 23
Evaluation of libcoap (Time & Size) Resource Type Retrieval Time Num. of Bytes Transmitted /st GET 297.04 ms 223 bytes /sh GET 143.57 ms 119 bytes /sv GET 92.69 ms 119 bytes /r GET 369.99 ms 229 bytes /l GET 69.55 ms 117 bytes /l PUT 71.12 ms 116 bytes /ck PUT 101.51 ms 142 bytes ◮ GET /st and /r are deferred/asynchronous/separate → higher retrieval time and number of transmitted bytes ◮ With coap-04 not necessary to be deferred, RESPONSE_TIMEOUT now 2 s Becker: CoAP , IP+SN 2011 17 / 23
Evaluation of libcoap (ROM) ROM Usage in Bytes 50000 45000 40000 35000 30000 25000 20000 15000 10000 5000 0 ◮ UDPEcho - CoAP without resources: 3708 Byte ◮ Increase to CoAP with resources is mostly because of additional components Becker: CoAP , IP+SN 2011 18 / 23
CoAP vs HTTP (RTT) ◮ Test on GPRS, not 802.15.4, because of ◮ HTTP not available on 802.15.4 ◮ CoAP wasn’t available for TinyOS at that time ◮ CoAP might be of interest for M2M on GPRS as well ◮ Similar RTT for multi-hop 6LoWPAN Access Method Time (sec) Apache2-Firefox 38.774 Apache2-Epiphany 31.972 Apache2-wget 2.660 Apache2-bareHTTP client 3.032 bareHTTP(TCP) 3.076 bareHTTP(UDP) 1.104 CoAP 1.029 Becker: CoAP , IP+SN 2011 19 / 23
CoAP vs HTTP (#Bytes) Total Number of Bytes Transmitted 2500 1928 2000 1500 1201 1186 1115 885 1000 500 132 107 0 ◮ Firefox downloads favicon ◮ Bare server and clients are ◮ Firefox, Epiphany, and less chatty wget add user agents ◮ UDP reduces at lot ◮ Apache2 adds ◮ CoAP has retransmission Content-Type etc. Becker: CoAP , IP+SN 2011 20 / 23
CoAP vs HTTP (#Bytes) Header HTTP/TCP HTTP/UDP CoAP/UDP Link Layer 160 32 32 IP 200 40 40 TCP/UDP 340 16 16 HTTP/CoAP 181 41 17 Data 4 4 2 Table: Separation of Bytes at each Layer ◮ Note: IP without 6LoWPAN Becker: CoAP , IP+SN 2011 21 / 23
Conclusions ◮ CoAP for M2M enabled logistic applications ◮ libcoap for Contiki and TinyOS ◮ libcoap is a generic library, specific custom-made implementations might be smaller ◮ Adaptations necessary, e.g. split-phase operation ◮ More compact than HTTP/TCP , but reliable on UDP ◮ JNI interface to libcoap for Java available, and possibly other languages Becker: CoAP , IP+SN 2011 22 / 23
Outlook ◮ Measurement of CoAP in deployments ◮ Port to blip-2.0 ◮ Move to coap-05/06 ◮ Simulation with TOSSIM Becker: CoAP , IP+SN 2011 23 / 23
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