MERLIN: A Synergetic Integration of MAC and Routing for Distributed Sensor Networks A.G.Ruzzelli, M.J.O’Grady, R.Tynan, G.M.P.O’Hare. Adaptive Information Cluster project (AIC) and Smart Media Institute (SMI) Department of Computer Science University College Dublin Ireland. http://www.adaptiveinformation.ie MERLIN: Integrating energy-efficient MAC and Routing Summary • Overview of WNSs and protocols • Motivation • Phase1: MERLIN design – – – – Motivation and objectives Fundamental concept MAC details Routing details • Phase2: Simulation and results – Scheduling performance – Comparison against SMAC+ESR • Conclusion MERLIN: Integrating energy-efficient MAC and Routing Sensor network characteristics • Energy consumption: primary objective • The wake-up concept • Very low duty cycle (even less than 5%) • Small packets smaller than in ad-hoc networks (e.g. temperature data is few bytes) • Low data traffic per node MERLIN: Integrating energy-efficient MAC and Routing Important issues of protocols for WSNs Communication reliability: Nodes are prone to fail and bad channel condition might affect the transmission Scalability: Medium Access control should be able to deal with large scale networks Unique global addressing: Low processing capability High end-to-end latency of packets MERLIN: Integrating energy-efficient MAC and Routing Protocol generality What does MERLIN address? Energy-efficiency • by an adaptive node activity scheduling End-to-end latency reduction • Separate MAC and Routing layers in low duty-cycle multi-hop networks cause an extremely high latency – (e.g. SMAC +DSR at 5% duty >35s delay for packets of 10 hops away nodes ) Communication reliability • failure, interference, depletion, mobility Addressing a single node can result in high error probability Node-to-Gateway routing What MERLIN does NOT address: •Node-to-node routing located at several hop distance Initial idea presented at IWWAN04: A.G. Ruzzelli, Evers, Dulman, Van Hoesel, Havinga. “ On the design of an energy-efficient low-latency integrated protocol for Wireless Sensor networks" MERLIN: Integrating energy-efficient MAC and Routing Design goals •MAC+Routing integration into a simple architecture; •No usage of handshake mechanisms; •No specific node addressing; •Reduce latency while ensuring a very low energy consumption •Increasing communication reliability while limiting packet overhead; MERLIN: Integrating energy-efficient MAC and Routing Initial idea: Timezone division (European EYES project, NL) Gateway Node Every node sets its zone and forward the sync packet to more distant nodes. A node division both in time and space is generated, i.e. timezone Nodes with the same color are in the same time zone MERLIN: Integrating energy-efficient MAC and Routing Division of the network in timezones Nodes report to the closest gateway Nodes within the same zone wake up, transmit and go into sleep simultaneously MERLIN: Integrating energy-efficient MAC and Routing Timezone data traffic Zone 3 Zone 2 Zone 1 Downstream multicast: Packets transmitted to higher zones Upstream multicast: Packets are forwarded to lower zones Sleeping MERLIN: Integrating energy-efficient MAC and Routing Local broadcast: Packets reach all neighbours. No forwarding performed Global allocation Frame Frame Zone 1 Zone 2 Zone 3 Zone 4 Frame Zone 5 Zone 6 Zone 7 Zone 8 The allocation of further zones can be obtained by appending the same table. The allocation of further frames is obtained by flanking the same table. MERLIN: Integrating energy-efficient MAC and Routing Accessing the table NZONE = 4 NSLOT =9 To access the current slot in the table: SLOT# = GlobalTime/SLOTTIME currentSlot = Mod(SLOT#, NSLOT) Nodes in the same timezone contend the slot for local broadcast only once each 4 frametimes If Mod(FRAME#, NZONE) = Mod(myZone,NZONE) MERLIN: Integrating energy-efficient MAC and Routing Intra-zone MAC features Zone N+1 Zone N Zone N-1 Recall that • Nodes in the same zone share the same slot for activity • transmission in MERLIN (multicast) do not address a specific receiving node How can simultaneous transmission be handled? How can correct/incorrect receptions be notified? MERLIN: Integrating energy-efficient MAC and Routing Burst tones can help • Properties – Are signal impulse Do not contain any coded information – Are robust Several simultaneous burst can still be identified as one burst – They are shorter that a normal ACK • Utilization In transmission to the gateway Multicast: Bursts identify correct receptions BACK MERLIN: Integrating energy-efficient MAC and Routing In local broadcast Broadcast: Bursts identify reception errors BNACK Asynchronous transmission Mechanism Tc Tc CCA Tx1 Preamble CCA Packet Sleep Tc Rando m CCA Preamble CCA Packet Sleep Tx2 Rando m Sleep Listen Sleep Transmit CCA Rx1 Burst* Listen Sleep Sleep Burst* CCA Rx2 Listen Sleep Sleep Slot length Rx1 * burstACK if local broadcast, burst NACK if multicast Rx1 Tx1 Tx1 Tx2 Rx2 Rx2 MERLIN: Integrating energy-efficient MAC and Routing Tx2 Disadvantages 1)MERLIN does not address a specific receiving node Zone 1 Zone 2 Zone 3 A multiple copy of the same msg sent can be generated B increase overhead! 2) Some collisions due to the Hidden Terminal Problem (HTP) Zone 3 A ? B MERLIN: Integrating energy-efficient MAC and Routing Zone 4 Zone 5 Routing characteristics (I) Controlled multipath • 3 small buffers of upstream, downstream and local broadcast are provided • Packets organised in multiple msgs of the same data traffic type; • Packets contain a msg-ID index of included msgs; • Nodes, which lose the contention, keep on listening to the beginning of the transmitted packet then go into sleep; • Nodes discard from their buffer the msgs already fowarded. P Msg-index a c k e Channel contention t messages Pro : Reduce overhead in transmission! Con : Small increase of node activity; Increase complexity. MERLIN: Integrating energy-efficient MAC and Routing Discard msgs already forwarded from their queue Listen to the packet index Routing characteristics (II) Timezone maintenance • Timezone update are sent periodically; • Failed reception of timezone update from zone N-1 node to zone N node triggers a upstream multicast of Timezone Update request (TUR) – • N-1 failed local broadcast TUR – • N-1 node/s reply Connection reestablished At least one reply change of zoen to N+1 N failed downstream broadcast TUR 2 1 2 1 1 3 3 2 1 3 4 2 2 3 4 4 4 6 TUR 4 3 MERLIN: Integrating energy-efficient MAC and Routing TUR 5 Assessment Simulation tool: OmNet++ Framework: EU EYES project Evaluation against SMAC+ESR In Progress: Philips Sand node implementation MERLIN: Integrating energy-efficient MAC and Routing Scenario and Setup •Scenarios •Metrics: •Energy consumption per RX packet •Network lifetime •E-to-E latency •Total packet overhead •% sleeping time •5 nodes two-hops Forwarder Sources Destinations •Parameters: •70 nodes Random multihop MERLIN: Integrating energy-efficient MAC and Routing •Duty cycle (acting on CW and frametime size) •Low traffic conditions (12 packet/min) •High traffic conditions (60 packet/min) Low traffic 2-hops scenario MERLIN: Integrating energy-efficient MAC and Routing High traffic 2-hops scenario MERLIN: Integrating energy-efficient MAC and Routing Multihop scenario: Lifetime Note: These graphs have little relevance if not related to the EtoE latency MERLIN: Integrating energy-efficient MAC and Routing Multihop scenario: Latency/energy Given a certain sustainable latency, MERLIN consumes between 2 and 2.5 times less energy than SMAC+ESR MERLIN: Integrating energy-efficient MAC and Routing Total packet overhead The MAC routing integrated nature MERLIN results in a smaller packet overhead than SMAC+ ESR. MERLIN: Integrating energy-efficient MAC and Routing Conclusion • Description and simulated results of MERLIN have been presented; • MERLIN is suitable for large scale sensor networks with energy consumption as main goal; • MERLIN is suitable for communication to a from the gateway • The multicast mechanism with burst ACK showed large improvement on the communication reliability • The integrated nature and the absence of handshake mechanisms help reducing the EtoE packet delay • EtoE delay can be traded-off for a longer network lifetime Results showed lifetime being extended by a factor of 2.5 of MERLIN with respect to SMAC MERLIN: Integrating energy-efficient MAC and Routing Thank you for your kind attention MERLIN: Integrating energy-efficient MAC and Routing