Recently, the demands on wireless sensor networks have switched from low trafﬁc rate and static topology to more challenging requirements in order to meet the rapid expansion of WSN into various domain applications. This paper proposes a seamless cross layer solution that integrates network layer and medium access control to accommodate some of the new challenges. This new solution allows routing paths being generated dynamically to meet the requirement of potential mobile nodes. Higher data throughput and ﬂow control are part of the new demands required to be addressed urgently. The proposed solution integrates a priority based MAC to handle congestion and packet loss problems which commonly happened in WSN when an occurrence of event spread into wide are

Andonovic, Ivan

Andrae, Christian

Kwong, Kae

Michie, Craig

English

Name not available

A priority based routing protocol for wireless sensor networks

University of Strathclyde Institutional Repository

Strathprints Institutional RepositoryAndrae, Christian and Kwong, Kae and Michie, Craig and Andonovic, Ivan (2009) A priority basedrouting protocol for wireless sensor networks. In: Proceedings of the 10th Annual PostgraduateSymposium on The Convergence of Telecommunications, Networking and Broadcasting (PGNET2009), 1900-01-01.Strathprints is designed to allow users to access the research output of the University of Strathclyde.Copyright c© and Moral Rights for the papers on this site are retained by the individual authorsand/or other copyright owners. You may not engage in further distribution of the material for anyprofitmaking activities or any commercial gain. You may freely distribute both the url (http://strathprints.strath.ac.uk/) and the content of this paper for research or study, educational, ornot-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to Strathprints administrator:mailto:strathprints@strath.ac.ukhttp://strathprints.strath.ac.uk/A Priority Based Routing Protcol forWireless Sensor NetworksChristian Andra¨, Kae Hsiang Kwong, Craig Michie and Ivan AndonovicDepartment of Electronic and Electrical Engineering, University of Strathclyde,204 George Street, G1 1XW Glasgow, United Kingdomemail: { christian.andrae, kwong, c.michie, i.andonovic} @eee.strath.ac.ukAbstract—Recently, the demands on wireless sensor networkshave switched from low trafﬁc rate and static topology to morechallenging requirements in order to meet the rapid expansionof WSN into various domain applications. This paper proposesa seamless cross layer solution that integrates network layerand medium access control to accommodate some of the newchallenges. This new solution allows routing paths being gener-ated dynamically to meet the requirement of potential mobilenodes. Higher data throughput and ﬂow control are part of thenew demands required to be addressed urgently. The proposedsolution integrates a priority based MAC to handle congestionand packet loss problems which commonly happened in WSNwhen an occurrence of event spread into wide area.I. INTRODUCTIONA Wireless sensor network (WSN) is a network systemthat is formed autonomously by a group of sensor nodeswhich are commonly fabricated by using low cost/speciﬁcationhardware. The development of wireless sensor networks hasevolved from its original initiative and found its way intobroader applications. Some of the new applications pose higherdemands than conventional WSNs and exceed its originaldesign spaces. For instance, in [1] the design principle hasmoved from the conventional low data volume to information-rich data applications in which data volume is dramaticallydistinguished from conventional WSNs. In [2], the WSNtechnology has been applied into farming industry, whereindividual animals are mounted with a sensor node that isfabricated into a collar. The location of the sensor nodeis mobile and it will change whenever the animal moves.Therefore, this new application has broken one of the commonassumptions of WSN, where the location of sensor nodes issaid to be static.Cross layer implementation is a common way of efﬁcientprotocol implementation, where different layers of the protocolstack exchange information. In the case under consideration,network layer and medium access layer (MAC) are imple-mented in such a way. MAC and routing layer exchanginginformation about the nodes status and the message type that isgoing to be send. This way of implementation looses the strictway of the layered structure of the OSI deﬁnition. It makesit easier for the applications to gather information directlyfrom the physical layer (PHY), [3]. As a result, a light-weightprotocol referred to as PriBaR is developed. In order to allowthis protocol to run and survive in challenging environmentduring the development process a few principles are followedrigorously:i Small in size. The code size has to be in the region ofa few, less than 100 kBytes. That was achieved, the totalsize of the transfered code image of the proposed protocolwas 43.6 kBytes.ii Low memory usage. The hardware restriction of the MI-CAz nodes just allow 512K byte of data, [4] . Therefore,a routing table that records all neighbouring nodes mightnot be advisable.iii Low power consumption. Hand-shaking, neighbour dis-covery, network congestion and packet retransmission allcost power. All these should be kept to minimum.iv Autonomous and independent operation. Data transmis-sion tasks (i.e. packet relay, link establishment, routing)should run independently and should not impact the sensoractuation. Each sensor node should be able to operateautonomously as well as part of a WSN. Protocols shouldnot be over-complex and require frequent hand-shaking toestablish new links.The paper is structured as follows. Section II gives anoverview of related work. In section III, the PriBaR cross layerprotocol is introduced and the experimental setup is described.Following this, section V presents the results of this work.Finally, section VI summarizes the ﬁndings of this paper andgives an outlook to future work.II. RELATED WORKA depth survey in [5] has outlined that WSNs can effectivelyconduct some of the networking tasks that require co-operativeaction from neighbouring nodes (i.e. resource sharing andautonomously networking). WSNs are still lacking capabilityto perform an integrate network management such as networkresource allocation and data loss recovery in which will adaptto current network condition. For example, in [6], [7], [8]novels resource management and channel access schemes havebeen studied. Whereas, issues related to congestion avoidanceand packet loss recovery have been discussed in [9], [10].Generally, researchers look into these problems in isolation.With a single layer of routing and networking scheme it mightnot work well when the environment changes. A WSN is de-ployed commonly in challenging and complex environments.Such environments might be unmanned, impossible to retrievefor manual reconﬁguration or simply hazardous.ISBN: 978-1-902560-22-9 © 2009 PGNet Figure 1. A typical network topology conﬁguration by PriBaR protocolTo the best knowledge of the authors there was no suchwork, combining the prioritised medium access with a au-tonomous zone set up. The used AIMRP routing protocolhas been studied extensively in [11]. The P-MAC mediumaccess was implemented before at Strathclyde University. Theexpertise following from this can be used to implement thecombination of these both protocols. The expected advantagesof a lightweight implementation and prioritised medium accesswill be explained in more detail in the following section III.III. PRIORITY BASED ROUTING PROTOCOL, PRIBARThe proposed PriBaR protocol is the ﬁrst step to developinga fully integrated protocol that equips WSN with trafﬁcengineering module that allows it to perform dynamic routingand network congestion management. This PriBaR protocol iscomprised with two parts:i. the dynamic routing module andii. the congestion management moduleA unique network topological structure, which dissects thesensor nodes into a number of zones according to their positionis required by the PriBaR protocol. The zones are extended,starting from the base station outwards to the farther remotesensor nodes. These zones are organised and identiﬁed byusing the (hop-)distance between sensor node and base station.This information is recorded by each individual sensor nodein a unique ﬁeld - TIER ID. The base station is set to zone 1.If the sensor node is one hop away from the base station it issaid that this particular sensor node is located in zone 2 andfor all the sensor nodes that are one hop away from the basestation the value for their TIER ID is equal to 2. Whereas,if a node needed to forward a packet to the base station andthis packet requires assistance of 3 sensor nodes performingmulti-hop relays then this sensor node is said to be in zone 5(TIER ID=5). The number of zones is limited by the variabletype it was assigned to, uint8_t which allows 256 valuesstarting from zero.To establish the network topology conﬁguration, a simplepassing through mechanism is used. The base station broad-casts a network conﬁguration packet which contains BS ID= 0 and TIER ID = 1. When this packet is received by asensor node located in vicinity to BS it will know that it isone hop away from BS and set its TIER ID = 2. All othernodes that received the message will do the same. The nodesthat received the ﬁrst broadcast will continue the networkconﬁguration process by issuing a conﬁguration packet withTIER ID = 2. This message will be received by other nodeswhich will set their TIER ID to 3 accordingly. This processthen continues until all the nodes are reached and assignedwith a corresponding TIER ID. As soon as the conﬁgurationpacket has been successfully passed through the networktopology, the PriBaR protocol can start to route packets backto the BS.The second part of PriBaR protocol is network congestionmanagement module. In TCP/IP network, congestion manage-ment is based on:i comparison of historical trafﬁc volume [12],ii response time [12], andiii packet loss [13]These approaches not only require large amount of memoryand computing power but also reside on top of TCP/IP layer,which associate with an overhead that is not possible to applyin WSN. To mitigate the network congestion, the PriBaRprotocol relies on the CSMA/CA medium access control withpriority packet support. This module works like this:i when the channel is too busy random delay kicks in,the nodes have to wait for x amount of time before re-transmissionii prioritised packets are associated with important or criticaldata, therefore they will access the channel with higherpriority.Message generatedNOYES isprioritised~~~~set backoffto 2.4 msset backoffto 10 mscompete forChannelsend MessageFigure 2. Flow chart; setting initial backoff when competing for the channelNodes can distinguish between three types of messages.First message type is TIER message. A node that did notreceive a TIER message does not know its position in thenetwork, and therefore is not going to take over any forwardingjobs and does not generate trafﬁc itself. This type of message isrecognised by the MAC layer since it has a different messagetype ID and therefore triggers a different function. The ﬂowchart of the triggered function is displayed in Fig. 3. Secondtype of message is the data message. Initially white-spacedwith zeros, the only information in this message is the originnode ID and TIER zone ID, the time of departure from theorigin node, the buffer utilisation and dropped messages countat the origin node and whether it is a prioritised message ornot. Each intermediate node is ﬁlling its information aboutID, TIER zone ID, buffer utilisation and number of droppedpackets at the ﬁrst white space it ﬁnds next to the informationfrom the previous node. A data message usually is acknowl-edged on reception. Therefore, the MAC acknowledgement(ACK) is turned on and indicates that the sent message isreceived from the relay node or base station. On receptionof an ACK the transmission is ﬁnished. It is prompting thebuffer pointer to be increased and therefore sending the nextmessage, if there is one. Furthermore, the resend-counter isreset. The reset counter is used to limit the retries before amessages is going to be dropped. The ﬂow chart of PriBaR’smedium access is illustrated in Fig. 2.received TIERset up messageﬀ	NOYESalreadyset upYESownTIER ID> rx TIERIDNOﬀupdate TIERID infoforwardTIER msgﬁnished TIERzone set upﬀ	Figure 3. TIER set up ﬂow chartIV. EXPERIMENT CONFIGURATIONMain goal of the experimental set up was to create 4 zoneseach hosting 5 nodes. In order to set up a non-overlappedmulti-tier environment, it was impossible within the givenenvironment to set up more than 4 zones, where each zonegot a LoS (line of sight) to the next upper and lower zone andevery node can receive the time base signal. The experimentrequired a careful conﬁguration so that the nodes in xth-TIERzone could only communicate to nodes in (x+1)th and (x−1)thtiers but no others. This was done by separating the nodesin different screened areas within the lab; concrete walls areutilised to provide necessary partitioning allowing a numberof TIERs being setup in a conﬁned area. Fig. 4 illustrates theexperiment conﬁguration. With this set up there was no zonex that had a line of sight (LoS) with neither x − 2 nor x + 2.In the experiment, 20 nodes, always 5 node in one of the4 zones, were used and one base station node, all based onMICAz [xbow] hardware.Time BasisWall1mBSZone 2Zone 3Zone 4Zone 5LaboratoryCorridorLegend:Single nodeZone of 5 nodesTime Signal BasisFigure 4. Dimensions of the experimental set upAfter the zone conﬁguration was completed, the nodes onlyperformed forwarding task to those nodes that were locatedin the previous zone, which have a higher TIER ID. Thismeans that, for example, nodes in zone two would not accepta message from nodes in zone four. In the experiment, thesensor nodes did not only act as a relay node, but also astrafﬁc sources. Each node is programmed with an exponentialtrafﬁc generator, which will generate 23 normal packets persecond and 1 priority packet every 60 seconds.The measurement with this set up will be presented in thefollowing section. The presented ﬁgures will all be organisedin the same way that they x-axis represents the zone IDs, they-axes the measured physical quantity, and the different greyscales represent a different node in the corresponding zone.If the value drops to zero in a certain zone and rises abovezero in the following zone, this simply means that the physicalquantity could not be measured at this speciﬁc node.V. RESULTSThe measurements that were carried out within the exper-iment include the total delay of both, normal and prioritisedmessages, the amount of dropped messages at each node, againfor both kinds of messages. Furthermore, each node that for-warded a message was stamping its buffer utilisation of normalmessages, if the message was a non-prioritised message, orthe prioritised buffer utilisation was stamped, if the forwardedmessage was a prioritised message. Additionally, each nodewas putting its ID and its TIER zone ID into the message.Based on that information it can be shown that no messagethat arrived at the base station was taking an unnecessary turnor was looping between zones at all.   																Figure 5. Generated packets at nodes over the network   		Figure 6. Buffer utilisation over the networkThe ﬁrst graph that is presented in Fig. 5 shows the amountof generated messages at each node that arrived at the basestation, which does not mean that every message arrived atthe base station. This graph shows that messages from TIERzones further away from the base station suffer from higherlikelihood of packet loss and therefore fewer packets arrivedfrom there. In an ideal network, including an ideal channelwith zero loss, unlimited bandwidth and unlimited buffercapacity, one would expect a uniform distribution of generatedmessages. The message counter at each node, which includesalso the dropped messages, suggest such a distribution. Thereason for this is increased buffer utilisation towards thebase station and hence the resulting higher contention for thechannel. Fig. 6 shows the corresponding buffer utilisation.One important issue of the experiment was to show thatprioritised messages are travelling through the network fasterthan others. As it can be seen from Tab. I, prioritised messagestravelled faster through the network than not prioritised ones.Table IDELAY TIMESDelay [ms] zone 2 zone 3 zone 4 zone 5p messages 1753.2 3627.8 4630.9 6859.9non-p messages 3475.1 6255.0 8365.1 5493.7VI. CONCLUSION AND FUTURE WORKIn this paper, a cross layer solution has been proposed tofulﬁl the latest evolution trends of WSN in which data loadincreases from its conventional low volume to a moderate load.Instead of using static topology, here, the network topologyis dynamic which changes frequently. This evolution hasoffered new challenges in WSN research and development,contradicting current WSN design spaces.From the values in Tab. I the prioritised message handlingwas proven. Decreasing the initial back off time and alwayshandling prioritised messages ﬁrst, increases the likelihoodto win the channel for the transmission and hence fasterforwarding is achieved. Also the routing scheme of PriBaRis proven, since not a single message that arrived at the basestation took an unecessary hop or looped between zones.This scheme of straight forward routing will be adjusted inthe future to guarantee delivery even if there is no nexthop directly available. Therefore, the experimental set upneeds to be reconﬁgured and the implementation of furtherfunctionality is required.REFERENCES[1] I. F. Akyildiz, T. Melodia, and K. R. Chowdury, “Wireless multimediasensor networks: A survey,” IEEE Wireless Communications, 2007.[2] M. Radenkovic and B. Wietrzyk, “Wireless mobile ad-hoc sensornetwork for very large scale cattle monitoring,” in Proc. IEEE SixthInternational Conference on Networking (ICE’07), 2007.[3] H. Karl and A. Willig, Protocols and Architectures for Wireless SensorNetworks. The Atrium, Southern Gate, Chichester, West Sussex PO198SQ, England: John Wiley & Sons Ltd., 2005.[4] C. Technology, MICAz Datasheet. [Online]. Available: http://www.xbow.com/Products/Product pdf ﬁles/Wireless pdf/MICAz Datasheet.pdf[5] C. Wang, K. Sohraby, B. Li, M. Daneshmand, and Y. Hu, “A surveyof transport protocols for wireless sensor networks,” Networking, IEEE,vol. 20, no. 3, 2006.[6] K. H. Kwong, H. G. Goh, C. Michie, and I. 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A lightweight medium access protocol (lmac) for wireless sensor networks,”

A new transport layer sensor network protocol,” in

A survey of transport protocols for wireless sensor networks,”

A trafﬁc aware, energy efﬁcient mac protocol for wireless sensor networks,” Circuits and Systems,

An address-light, integrated mac and routing protocol for wireless sensor networks,”

Available: http://www.xbow. com/Products/Product pdf ﬁles/Wireless pdf/MICAz Datasheet.pdf

Predictive congestion control protocol for wireless sensor networks,”

Priority medium access control for wireless sensor network,” Communication Systems and Networks,

Protocols and Architectures for Wireless Sensor Networks. The Atrium,

Pump-slowly, fetchquickly (psfq): A reliable transport protocol for sensor networks,”

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Wireless multimedia sensor networks: A survey,”

http://www.cms.livjm.ac.uk/pgnet2009/Proceedings/Papers/2009044.pdf

A priority based routing protocol for wireless sensor networks

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