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Overview of IEEE 802.15.4 and Its Role in Standards-Based Protocol Stacks

The paper by Thomas Watteyne examines standards like IEEE 802.15.4, IETF's 6LoWPAN, and RPL, which are integral to low-power wireless networks. It highlights IEEE 802.15.4's features such as low-cost, low-speed communication for devices in proximity and emphasizes its suitability for real-time applications with energy-efficient communication. The standards provide a framework for various applications ranging from home automation to sensor networks, optimizing for low data rates and battery longevity. The discussion reflects ongoing efforts to enhance these protocols and their industrial applications.

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Overview of IEEE 802.15.4 and Its Role in Standards-Based Protocol Stacks

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  1. 3. Towards A Standards-Based Stack Thomas Watteyne @ EDERC 2010

  2. Protocol Stack IETF IEEE Thomas Watteyne @ EDERC 2010

  3. Section 3 - Overview 3. Towards A Standards-Based Stack 3.1 IEEE 802.15.4E 3.2 IETF 6LoWPAN 3.3 IETF RPL 3.4OpenWSN 3.5 Conclusions Thomas Watteyne @ EDERC 2010

  4. 3.1 IEEE802.15.4E Thomas Watteyne @ EDERC 2010

  5. 15.4-2006, 15.4 PHY, 15.4 MAC, 15.4E? • IEEE 802 LAN/MAN Standards Committee • standardizes a.o. 802.3 (Ethernet) 802.11 • http://www.ieee802.org/ • IEEE 802.15 Working Group for WPAN • wireless Personal Area Network • standardizes a.o. 802.15.1 (Bluetooth), 802.15.4 • http://www.ieee802.org/15/ • IEEE 802.15 WPAN Task Group 4 • low data rate solution with multi-month to multi-year battery life, very low complexity • operating in an unlicensed, international frequency band • sensors, interactive toys, smart badges, remote controls, and home automation, etc. • first standard in 2003, updated in 2006 • standardizes both PHY and MAC • http://www.ieee802.org/15/pub/TG4.html • IEEE 802.15 WPAN Task Group 4e • define a MAC amendment to the existing standard 802.15.4-2006 • enhance and add functionality to the 802.15.4-2006 MAC to better support the industrial markets • uses 802.15.4-2006 PHY • draft standard on 03/08/2010, integrated in next revision of the 802.15.4 standard (exp. 2011) • http://www.ieee802.org/15/pub/TG4e.html Thomas Watteyne @ EDERC 2010

  6. IEEE802.15.4 – Overview • Emphasis of IEEE 802.15.4 is: • low-cost, low-speed ubiquitous communication between nearby devices with little to no underlying infrastructure • basic framework assumes 10-meter communications area @ 250 kbit/s • lower transfer rates of 20, 40 and 100 kbit/s are now considered too • to meet embedded constraints, several PHY layers are available • Key technology features are: • real-time suitability by reservation of guaranteed time slots • collision avoidance through CSMA/CA • integrated support for secure communications (128-bit AES encryption) • power management functions such as link quality and energy detection • 16 channels in ISM bands for operation, i.e. 868-868.8 MHz (Europe), 902-928 MHz (North America), 2400-2483.5 MHz (worldwide) • star and mesh topologies can theoretically be built • support for low-latencies and dynamic device addressing Thomas Watteyne @ EDERC 2010

  7. IEEE802.15.4 – PHY Layer • The 2006 revision of the standard defines 4 PHY layers: • 868/915 MHz DSSS with binary phase shift keying (BPSK) • 868/915 MHz DSSS with offset quadrature phase shift keying (OQPSK) • 2450 MHz DSSS with offset quadrature phase shift keying (OQPSK) • 868/915 MHz PSSS, i.e. combination of binary keying and amplitude shift keying • The 2007 IEEE 802.15.4a version includes 2 PHY layers more: • Chirp Spread Spectrum (CSS) @ 2450 MHz ISM • Direct Sequence Ultra-wideband (UWB) @ < 1GHz, 3-5GHz, 6-10 GHz • Beyond these PHYs at the three bands, there are: • IEEE 802.15.4c for 314-316, 430-434 and 779-787MHz bands in China • IEEE 802.15.4d for 950-956MHz band in Japan Thomas Watteyne @ EDERC 2010

  8. IEEE802.15.4 – PHY Layer • binary phase shift keying (BPSK) • quadrature phase shift keying (QPSK) • offset quadrature phase shift keying (OQPSK) Thomas Watteyne @ EDERC 2010

  9. IEEE802.15.4 – 2.4GHz PHY • O-QPSK, 250 kb/s, 62.5 ksymbol/s • Direct Sequence Spread Spectrum • Max PSDU = 127B • Turnaround: TX-RX ≤ RX-TX ≤ 192us • ED over 8 symbol periods DSSS: 4 bits of information = 32 chips (raw data rate of 2Mbps) Thomas Watteyne @ EDERC 2010

  10. IEEE802.15.4 – MAC Layer • Some key attributes: • CSMA/CA channel access • manages access to the physical channel and network beaconing • controls frame validation, guarantees time slots, handles node associations • offers hook points for secure services • In more details: • networks which are not using beaconing mechanisms utilize an un-slotted variation which is based on the listening of the medium, leveraged by a random exponential backoff algorithm (acknowledgments do not adhere to this discipline) • confirmation messages may be optional under certain circumstances, in which case a success assumption is made; timeout-based retransmission can be performed a number of times • due to the maximization of battery life, the protocols tend to favor methods implementing periodic checks for pending messages, the intensity of which depends on application needs Thomas Watteyne @ EDERC 2010

  11. IEEE802.15.4 – MAC Layer • There are two general channel access methods: • Non-Beacon Network: • simple, traditional multiple access system used in simple peer networks • standard CSMA conflict resolution • positive acknowledgement for successfully received packets • Beacon-Enabled Network • can be used in beacon-request mode without superframes • superframe structure - network coordinator transmits beacons at predetermined intervals • dedicated bandwidth and low latency • low power consumption mode for coordinator Thomas Watteyne @ EDERC 2010

  12. IEEE802.15.4 – MAC Layer • Super-Frame Structure for Beacon-Enabled Mode: Thomas Watteyne @ EDERC 2010

  13. IEEE802.15.4 – Packet Format 0-127 4B of data(all 0’s) 0x7A synchronization header physical header 16-bit CRC beacon, ACK, DATA, command MAC header Thomas Watteyne @ EDERC 2010

  14. IEEE802.15.4 – Device Classes • Full function device (FFD) • any topology • network coordinator capable • talks to any other device • Reduced function device (RFD) • limited to star topology • cannot become a network coordinator • talks only to a network coordinator • very simple implementation Thomas Watteyne @ EDERC 2010

  15. IEEE802.15.4 – Star Topology PAN Coordinator Master/Slave Communications flow Full function device Reduced function device Thomas Watteyne @ EDERC 2010

  16. IEEE802.15.4 – P2P Topology Cluster tree Point to point Full function device Communications flow Thomas Watteyne @ EDERC 2010

  17. IEEE802.15.4 – Combined Topology Clustered stars - for example, cluster nodes exist between rooms of a hotel and each room has a star network for control. Full function device Reduced function device Communications flow Thomas Watteyne @ EDERC 2010

  18. IEEE802.15.4 Scenario • First node makes sure it is alone, scans for a “good” frequency and transmits beacons. • New node scans (active or passive) and hears beacon. Sends an association request (indirect response). Tracks beacon periodically. • Upstream data transmitted in CAP using CSMA/CA. If downstream data, coordinator set pending data field. • Device can ask to (dis)allocate a GTS to the coordinator. GTS slots are announced in beacon, CSMA is not used in GTS slot. • Secondary coordinators to create a generalized star topology. Thomas Watteyne @ EDERC 2010

  19. IEEE802.15.4 - Problems • Powered Routers • router nodes have their radio on all the time • if battery-powered: 2400mAh AA pack @ 81mA (CC2420) -> 29h of lifetime • assumption: mains powered • Single channel operation • WiFi-like: one channel for the whole network • suffers from external interference (WiFi, Bluetooth) • suffers from persistent multipath fading (especially indoors) • Topologies • works great in star topologies • e.g. multiple switches connected to a single lamp • extended star topologies are hard to manage Thomas Watteyne @ EDERC 2010

  20. IEEE802.14.4E - TSCH • Time Synchronized Channel Hopping • cut time into slots • have nodes follow a common schedule B D A C Thomas Watteyne @ EDERC 2010

  21. IEEE802.14.4E - TSCH • The channel offset is translated to frequency using a translation function • This insures that successive packets sent over a same link are sent over all frequencies • iff the superframe length and number if frequencies are mutually prime frequency = (absolute slot number + channel offset)%16 Thomas Watteyne @ EDERC 2010

  22. IEEE802.14.4e - TSCH A B Thomas Watteyne @ EDERC 2010

  23. Thomas Watteyne @ EDERC 2010

  24. Thomas Watteyne @ EDERC 2010

  25. TsPacketWaitTime Watchdog_TXACK TsRxOffset TsTxAckDelay Stopping_time Startup_time SETTING_CHANNEL STARTING STARTED RXDATA WAIT_TXACK TXACK STOPPING STOPPED 2 7 8 9 1 10 11 Guard_time_large Guard_time_small Watchdog_TXDATA TsAckWaitTime Watchdog_TXACK+Guard_time_small TsRxAckDelay TsTxOffset Startup_time+Guard_time_large SETTING_CHANNEL STARTING STARTED TXDATA WAIT_RXACK RXACK STOPPING STOPPED 1 2 4 5 6 10 11 SLOT_TIME >TsRxOffset+TsPacketWaitTime+TsTxAckDelay+Watchdog_TXACK+Stopping_time

  26. IEEE802.15.4e – Synchronization • clocks drift(10ppm typical) • Periodic realignment(within a clock tick) ∆t Thomas Watteyne @ EDERC 2010

  27. Improved Reliability Thomas Watteyne @ EDERC 2010

  28. Improved Connectivity Thomas Watteyne @ EDERC 2010

  29. Improved Throughput Thomas Watteyne @ EDERC 2010

  30. Improved Energy Consumption • 2ms maximum de-synchronization • 20ppm relative drift • Resynchronization every 100 seconds (10ms slots) 0.010% idle duty cycle • 25mA when mote is active • 2400mAh batteries(AA batteries) • lifetime of 109 years(>> shelf-life) Thomas Watteyne @ EDERC 2010

  31. Improved Throughput Thomas Watteyne @ EDERC 2010

  32. IEEE 802.15.4e - TSCH antenna humidity sensor IR light sensor • TelosB mote • TinyOS operating system • 30ms time slots • 19kB ROM / 3kB RAM • 10kbps over 14 hops visible light sensor CC2420 radio MSP430 microcontroller 1 2 3 4 Thomas Watteyne @ EDERC 2010

  33. Thomas Watteyne @ EDERC 2010

  34. 3.2 IETF 6LoWPAN Thomas Watteyne @ EDERC 2010

  35. IPv4 vs. IPv6 • Internet Protocol v4 (IPv4): • IPv4 (RFC 791) originates from 1981 • upper layer protocols responsible for end-to-end reliability • works over almost any layer 2 network and with many routing protocols • addressing is being pushed to extremes by Internet growth • Internet Protocol v6 (IPv6): • IPv6 (RFC 2460) is the next generation of the Internet Protocol • complete redesign on IP addressing: hierarchical 128-bit address with decoupled host identifier; stateless auto-configuration; etc • simple routing and address management • majority of traffic not yet IPv6 but most PC operating systems already have IPv6, governments are starting to require IPv6, most routers already have IPv6 support • IPv6 transition is coming slowly but quietly Thomas Watteyne @ EDERC 2010

  36. IPv4 vs. IPv6 • IPv4 ... ... versus IPv6 addressing: Thomas Watteyne @ EDERC 2010

  37. IPv4 vs. IPv6 Monday, September 26, 2011 Thomas Watteyne @ EDERC 2010

  38. IP headers IPv4 header [RFC791], 1981 IPv6 header [RFC791], 1998 Thomas Watteyne @ EDERC 2010

  39. IETF 6LoWPAN - Overview • Key properties: • IP for very low power embedded devices • IETF Standard for IPv6 over IEEE 802.15.4: RFC4944, to be obsolete by IPHC • 80% compression of headers • IPv6 40-byte header -> 2 bytes (best case) • UDP 8-byte header -> 4 bytes • end-to-end Internet integration • fragmentation (1260 byte IPv6 frame -> 127 byte 802.15.4 frames) Thomas Watteyne @ EDERC 2010

  40. Header Compaction RFC4944 Not compacted Well-known value Value inferred from IEEE802.15.4 header Thomas Watteyne @ EDERC 2010

  41. Internet Integration Thomas Watteyne @ EDERC 2010

  42. 3.3 IETF RPL Thomas Watteyne @ EDERC 2010

  43. IETF ROLL - Overview • Routing Over Low-Power and Lossy Networks (ROLL): • IETF information discussion started in 2008 • Finalizing “RPL: IPv6 Routing Protocol for Low power and Lossy Networks” • website: http://tools.ietf.org/wg/roll • list: http://www.ietf.org/mail-archive/web/roll/current/threads.html • Since WSNs are application specific, 4 scenarios are dealt with: • building applications: draft-ietf-roll-building-routing-reqs • home applications: draft-ietf-roll-home-routing-reqs • industrial applications: RFC 5673 • urban applications: RFC 5548 Thomas Watteyne @ EDERC 2010

  44. IETF ROLL – RPL • Adopted as a working document by IETF ROLL on August 3, 2009 • Close integration with IPv6/6LoWPAN • DAG Information Option (DIO) • Destination Advertisement Option (DAO) • Core operation: • build a Directed Acyclic Graph (DAG) onto the connectivity graph of the network, directed toward a DAG root • each node has at least one DAG parent; nodes send inward traffic to their DAG parent • nodes announce their presence to the DAG root using Destination Advertisement • Source routing is used for outward traffic Thomas Watteyne @ EDERC 2010

  45. IETF ROLL – RPL • Constraint Based Routing • finding the shortest path according to some metrics satisfying a set of constraints • Objective Code Point (OCP) included in DIO: • The set of metrics used within the DAGe.g. Expected Transmission Count (ETX) • The objective functions used to determine the least cost constrained paths in order to optimize the DAGe.g. minimize ETX • The function used to compute DAG Depthe.g. DAG Depth is equivalent to ETX • The functions used to construct derived metrics for propagation within a DIOe.g. additive Thomas Watteyne @ EDERC 2010

  46. IETF ROLL – RPL wsn.eecs.erkeley.edu Thomas Watteyne @ EDERC 2010

  47. IETF ROLL – RPL wsn.eecs.erkeley.edu Thomas Watteyne @ EDERC 2010

  48. IETF ROLL – RPL Thomas Watteyne @ EDERC 2010

  49. 3.4 OpenWSN Thomas Watteyne @ EDERC 2010

  50. Charter openwsn.berkeley.edu The OpenWSN project serves as a repository for open-source implementations of protocol stacks based on Internet of Things standards, using a variety of hardware and software platforms. Thomas Watteyne @ EDERC 2010

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