Efficient Network Flooding and Time Synchronization with Glossy by John Rahat

Review & PResentation

Efficient Network Flooding and Time Synchronization with Glossy Federico Ferrari, Marco Zimmerling, Lothar Thiele, Olga Saukh Computer Engineering and Networks Laboratory ETH Zurich, Switzerland

outline Glossy

outline Background ~ Introduction ~ Research Objective ~ Glossy Research Contribution & Road Map Detailed Study ~ Interference & temporal displacement ~ Fast Packet Propagation in Glossy Experimental Results Concluding Remarks References and Fun Thoughts

wiReless sensoR netwoRk (wsn) Wireless sensor network (WSN) consists of spatially distributed autonomous sensors to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location

802.15.4: IEEE standard for embedded wireless sensor applications

netwoRk Flooding Definition Packet transmission from one node (initiator) to all other nodes in the network (receivers)

Fundamental service in wireless sensor networks Dissemination of commands Time synchronization Network wake-up and group formation Routing tree creation

eFFicient Flooding in wiReless sensoR netwoRks Main objective Propagate packet reliably and as fast as possible

Challenge in multi-hop wireless networks Uncoordinated transmissions  Packet loss  Retransmission delays  Flooding Storm [Broadcast Storm (Tseng, Mobicom 1999)]

eFFicient Flooding in wiReless sensoR netwoRks

Current approaches Identify which nodes relay packet CF [Zhu et al., NSDI ’10], RBP [Stann et al., SenSys ’06] Overhead to maintain network state Exploit properties of wireless radios (e.g., capture effect) Flash [Lu and Whitehouse, INFOCOM’09] Challenging in dense networks

glossy

Flooding architecture for wireless sensor networks Key Techniques Temporally decouple network flooding from application tasks Exploit concurrent and synchronous Transmissions for fast network flooding Main Contribution of Glossy  considers interference an advantage rather than a problem  makes simultaneous transmissions of the same packet interfere constructively  allows receivers to decode the packet even in the absence of capture effects  implicitly synchronizes nodes as the flooding packet propagates through the network

glossy

Flooding architecture for wireless sensor networks

Advantages Fastest possible propagation, by design Highly reliable (> 99:99 %) Requires no network state information Efficient also in dense networks Time synchronization at no additional cost

ReseaRch Road MaP

Road MaP They find out why and under which conditions overlapping transmissions of the same packet interfere constructively They show that the temporal offset among concurrent IEEE 802.15.4 transmitters must not exceed 0.5 s to generate constructive interference with high probability They introduce Glossy, which exploits concurrent transmissions, time synchronizes nodes, and decouples flooding from other network activities. Also They talk about design and radio-driven execution model They demonstrate the feasibility of Glossy with an implementation in Contiki based on Tmote Sky sensor nodes They evaluate Glossy using experiments under controlled settings and on three wireless sensor testbeds, including Twist and MoteLab

ReseaRch inFo

Operating systems

Contiki

Industry standards

802.15.4

Programming languages

Hardware

Tmote Sky

Software

Cooja

Applications

Glossy Flooding

Conferences/Journals

IPSN

detailed study

concuRRent tRansMissions The paper exploits concurrent transmissions for efficient flooding in sensor networks

inteRFeRence If the amplitudes of two waves have the same sign (either both positive or both negative), they will add together to form a wave with a larger amplitude. This is called constructive interference. If the two amplitudes have opposite signs, they will subtract to form a combined wave with a lower amplitude. This is called destructive interference. They investigate the conditions for making concurrent transmissions of the same packet interfere in a constructive way, so that a receiver detects the packet with high probability

inteRFeRence & teMPoRal disPlaceMent They first review the specifications of the IEEE 802.15.4 standard. Then, we derive an upper bound on the temporal displacement Δ among multiple concurrent transmissions of the same packet

Δ 1.1. Identical Identicalpacket packet 2.2. Small SmallΔΔ

iMPact oF teMPoRal disPlaceMent Matlab simulations

A and B synchronously relay packets to C

IEEE 802.15.4 transmitters interfere constructively if the temporal displacement is smaller than max = 0:5 ms.

iMPact oF teMPoRal disPlaceMent Requirements for generating constructive interference strongly depend on the communication scheme, especially on the modulation and the bit rate.

iMPact oF teMPoRal disPlaceMent

Glossy strive to satisfy the requirement of max = 0:5 ms

glossy oveRview

• Decouples flooding • Concurrent transmission • Constant slot length

glossy oveRview

glossy in detail

Fast Packet PRoPagation in glossy

glossy in detail

iMPleMentation & exPeRiMent Three test bed used

exPeRiMent inFo Operating systems Industry standards Programming languages Hardware Software Applications Conferences/Journals Platform Sensor nodes Tmote Sky MSP430F1611 + CC2420 MCU and timer source by DCO

Contiki 802.15.4 C Tmote Sky Cooja Glossy Flooding IPSN Challenges Deterministic execution timing Start execution at same time Compensate for hardware variations

contiki Contiki is an open source, highly portable, multi-tasking operating system for memory-efficient networked embedded systems and wireless sensor networks. Contiki is designed for microcontrollers with small amounts of memory. A typical Contiki configuration is 2 kilobytes of RAM and 40 kilobytes of ROM. Implicit network time synchronization in Contiki 2.5 This crude and simple network time synchronization module synchronizes clocks of all nodes in a network. The time synchronization is implicit in that no explicit time synchronization messages are sent: the module relies on the underlying network device driver to timestamp all radio messages, both outgoing and incoming. The code currently only works on the Tmote Sky platform and the cc2420 driver.

telosB/tMote sky Developed by the University of California, Berekely. It was a new mote design based on experiences with previous mote generations

telosB/tMote sky

contRolled exPeRiMents

• Setup 1 – One initiator, two receivers – Delay one receiver by [0,8]us – Non-delay receiver@-20dBm, delayed@-13dBm

contRolled exPeRiMents

• Setup 2 – One initiator, variable # of recievers – No delay

contRolled exPeRiMents

• Setup 3 – – – –

One initiator, four receivers Start a Glossy phase, computes reference time Schedules next phase All nodes activate an external pin when a phase start

testBed exPeRiMents Evaluation on three sensor network testbeds Differ in number of nodes, node density, and network size Vary packet length Vary transmit power Metrics MoteLab (Harvard) 94 nodes (unevenly spread over three floors), 5 to 8 hops Twist (TU Berlin) 92 nodes (evenly spread over two floors), 3 to 5 hops Local testbed (ETH Zurich) 39 nodes (two nodes located outside), 3 to 7 hops

Flooding latency L Time between first transmission at initiator and first reception at a receiver

Flooding reliability R Fraction of floods in which a receiver successfully receives the packet

Radio on time T Time a receiver has radio turned on during a network flood

testBed exPeRiMents

Node density no noticeable dependency Performance depends on network size Increase N significantly enhances flooding reliability

MaxiMuM nuMBeR oF tRansMissions • Vary N

iMPact oF Packet length

concluding ReMaRks

• Flooding and time sync are two important services • Well written, systematically analysis • Promising results • Testbed evaluation • Integrate with application might not be easy

Back uP slides & ReFeRences RFID & Discussion

tiMeline

iMPleMenting synchRonous tRansMissions in glossy

ReFeRence Authorâ&#x20AC;&#x2122;s Website

Websites http://www.capsil.org/capsilwiki/index.php/TELOSB/TMote_Sky http://www.cse.iitk.ac.in/users/braman/courses/ictp-feb2007/topic02-802-15-4.pdf http://www.mics.org/MV2003-Present/Ma14/ReceiverScolari.pdf http://www.windows2universe.org/earth/Atmosphere/tornado/beat.html http://en.wikipedia.org/wiki/Wireless_sensor_network http://compilers.cs.ucla.edu/emsoft05/CullerEstrinSrivastava04.pdf http://arri.uta.edu/acs/networks/WirelessSensorNetChap04.pdf http://www.sics.se/~adam/contiki/docs/a01741.html

Articles [1] The Contiki operating system. http://www.sics.se/contiki/. [2] B. C. Arnold, N. Balakrishnan, and H. N. Nagaraja. A First Course in Order Statistics. SIAM, 2008. [3] Atmel. AT86RF230 datasheet, 2009. [4] G. Barrenetxea, F. Ingelrest, G. Schaefer, M. Vetterli, O. Couach, and M. Parlange. SensorScope: Out-of-the-box environmental monitoring. In ACM/IEEE IPSN, 2008.

Source code publicly avalable at: http://www.tik.ee.ethz.ch/~ferrarif/sw/glossy

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