Transcript of "Backbone nodes based stable routing for mobile ad hoc networks"
Backbone Nodes Based Stable Routing for Mobile Ad Hoc Networks Vinay Rishiwal 1, A. Kush 2, S. Verma 3 M.J.P. Rohilkhand University, Bareilly1, Kurushetra University, Kurushetra2, IIITM, Gwalior3, India. email@example.com, firstname.lastname@example.org, email@example.com ABSTRACT The recent trend in ad hoc network routing is the reactive on-demand philosophy where routes are established only when required. Most of the protocols in this category, however, use single route and do not utilize multiple alternate paths. This paper proposes a scheme to improve existing on-demand routing protocols by introducing the concept of stable backbone based node scheme in network topologies scenario. The scheme establishes the multi paths without transmitting any extra control message. It offers quick adaptation to distributed processing, dynamic linking, less memory overhead and loop freedom at all times. The Scheme has been incorporated with the AODV and DSR protocols. The extensive simulation has been done for the performance evaluation; it clearly shows that the scheme performs very well with increasing packet delivery for different network scenarios. Keywords: Ad hoc networks, Routing protocols, Backbone nodes, AODV, DSR.1. INTRODUCTION proposed scheme is discussed. Section 4 providesA mobile ad hoc network (MANET) is a collection simulation details and results. Section 5 concludes theof autonomous nodes, which communicate using paper.wireless links without any fixed network infrastructureand centralized administrative support. The main 2. PREVIOUS STUDYapplication of mobile ad hoc network is in emergency The primary goal of routing protocol is to establish arescue operations and battle fields. correct and efficient route between a pair of nodes so that messages may be delivered in a timely manner.This paper addresses the problem of routing in mobile Routing protocols in Mobile ad hoc networks can bead hoc network. Since mobile nodes in mobile ad hoc classified in to two broad categories asnetwork can move randomly the topology may change 1 Proactive or Table drivenarbitrarily and frequently at unpredictable times. 2. Reactive or On demandTransmission and reception parameters may alsoimpact the topology. So it is very difficult to find and The proactive or table driven protocols attempt to findmaintain an optimal route. The routing algorithm must a route continuously and maintain routing informationreact quickly to topological changes. Due to dynamic from each node to every other node within the network,nature of MANETs, the problem of broken path so that whenever data is needed to be transmittedbecomes prominent. Most of the existing protocols between two nodes, the route is already there. Themaintain single routing path and rediscover the new nodes are required to maintain consistent up-to-datepath whenever a link fails. A scheme has been routing information in one or more tables. DSDV,proposed here which takes the advantage of stable WRP, CGSR etc are the protocols of thisbackbone nodes to provide the alternate path in case of category.a link failure. This scheme can be incorporated in anyexisting on demand routing protocol to improve the In Reactive approach routes are created only whenperformance. The efforts in this paper has been made desired by the source node. When a node requires ato incorporate the scheme on AODV and DSR. route to other node, it initiates a route discovery process with in the network. All permutations areRest of the paper is organized as follows. The Section 2 examined and best possible route is established. Thedeals with study on existing protocols. In section 3 the route is maintained by some route maintenance 1
procedure until either the destination becomes the backbone nodes can be 6, 8 and 9. These nodes areinaccessible or until the route is no longer desired. nearer to the routing path nodes and can join theAODV, DSR, LMR, TORA, and ABR process any time.etc are reactive protocols. 9There is another category of routing protocols known 1 3as hybrid routing which is a compromised approach Sbetween proactive and reactive approaches. Zone 2Routing Protocol (ZRP)  is one of the mostimportant protocols under this category. This protocol 4limits the scope of table driven procedure to a small Darea called zone. Outside the zone area reactive 6approach is followed. Surveys of routing protocols for 5 8ad hoc networks have been discussed in [1,11] 73. PROPOSED STUDY:The proposed scheme takes care of on demand Figure 1: Stable route using Backbone Nodes.routing along with a new concept of backbone nodes.These backbone nodes help in reconstruction phase in AODV: For AODV the protocol description has beenthe fast selection of new routes. Selection of backbone explained as: the protocol is divided into three phases.nodes is made upon availability of nodes. Each route Route Request (REQ), Route Repair (REP) and Errortable has an entry for number of backbone nodes Phase (ERR).attached to it. Whenever need for a new route arises incase of route break, check for backbone nodes are 3.1 Route Construction (REQ) Phasemade, and a new route is established. Same process is This scheme can be incorporated with reactive routingrepeated in route repair phase. Route tables are updated protocols that build routes on demand via a query andat each hello interval as in AODV with added entries reply procedure. The scheme does not require anyfor backbone nodes. Backbone nodes are nodes at the modification to the AODVs RREQ (route request)one hop distance from its neighbor. Backbone nodes propagation process. In the scheme with Backboneare those nodes which are not participating in route nodes, when a source needs to initiate a data session toprocess currently or nodes which enter the range of a destination but does not have any route information,transmission during routing process. As nodes are in it searches a route by flooding a ROUTE REQUESTrandom motion for a scenario, so there is every (REQ) packet. Each REQ packet has a unique identifierpossibility that some nodes are idle and are in the so that nodes can detect and drop duplicate packets. Anvicinity of the routing nodes. Whenever a break in the Intermediate node with an active route, upon receivingroute phase occurs due to movement of participant a no duplicate REQ, records the previous hop and thenode, node damage or for other reasons; theses idle source node information in its route table. It thennodes which have been termed as backbone nodes take broadcasts the packet or sends back a ROUTE REPLYcare of the process and start routing. The whole process (REP) packet to the source if it has an active route tobecomes fast and more packet delivery is assured. The the destination. The destination node sends a REP viachanges in the existing protocol are required at route the selected route when it receives the first REQ orreply and route recovery phases. In these phases the subsequent REQs that traversed a better active route.route table is updated with entries of backbone nodes. Nodes monitor the link status of next hops in activeEach route table has an entry for number of backbone routes. When a link break in an active route is detected,nodes surrounding it and their hop distance form the an ERR message is used to notify that the loss of linknode. For simplicity of the protocol the distance has has occurred to its one hop neighbor. Here ERRbeen assumed to be one hop. message indicates those destinations which are noAs it has been described in Figure 1, the Route longer reachable by way of the broken link. Takingselection from S (source) to D (destination) is made via advantage of the broadcast nature of wireless1-2-3-4 using shortest path routing. In case any of the communications, a node promiscuously overhearsparticipating nodes damages or move out of the range, packets that are transmitted by their neighboring nodes. 2
When a node that is not part of the route overhears a sender (originator) of the currently undeliverableREP packet not directed to itself transmit by a neighbor packet. BN attached is number of backbone nodes.(on the primary route), it records that neighbor as the This factor is transmitted as weight factor to all nodesnext hop to the destination in its alternate route table. to select best available path. Addition of backboneFrom these packets, a node obtains alternate path nodes help in selecting stable routes.information and makes entries of these backbone nodes(BN) in its route table. If route breaks occurs it just DSR:starts route construction phase from that node. The The key feature of DSR is the use of source routing.protocol updates list of BNs periodically in the route That is, the sender knows the complete hop-by-hoptable. route to the destination. These routes are stored in a route cache. The data packets carry the source route in3.2 Route Error & Maintenance (REP) Phase the packet header. When a node in the ad hoc network attempts to send a data packet to a destination forData packets are delivered through the primary route which it does not already know the route, it uses aunless there is a route disconnection. When a node route discovery process to dynamically determine suchdetects a link break (for example, receives a link layer a route. Route discovery works by flooding thefeedback signal from the MAC protocol, node1 does network with route request (RREQ) packets. Each nodenot receive passive acknowledgments, node2 does not receiving a RREQ, rebroadcasts it, unless it is thereceive hello packets for a certain period of time, etc.), destination or it has a route to the destination in itsit performs a one hop data broadcast to its immediate route cache. Such a node replies to the RREQ with aneighbors. The node specifies in the data header that route reply (RREP) packet that is routed back to thethe link is disconnected and thus the packet is original source. RREQ and RREP packets are alsocandidate for alternate routing. Upon receiving this source routed. The RREQ builds up the path traversedpacket, previous one hop neighbor starts route so far. The RREP routes itself back to the source bymaintenance phase and constructs an alternate route traversing this path backwards. The route carried backthrough backbone nodes by checking their stability. by the RREP packet is cached at the source for futureNodes those have an entry for the destination in their use. If any link on a source route is broken, the sourcealternate route table; transmit the packet to their next node is notified using a route error (RERR) packet. Thehop node. Data packets therefore can be delivered source removes any route using this link from itsthrough one or more alternate routes and are not cache. A new route discovery process must be initiateddropped when route breaks occur. To prevent packets by the source, if this route is still needed. DSR makesfrom tracing a loop, these mesh nodes forward the data very aggressive use of source routing and routepacket only if the packet is not received from their next caching. No special mechanism to detect routing loopshop to the destination and is not a duplicate. When a is needed. Also, any forwarding node caches the sourcenode of the primary route receives the data packet from route in a packet it forwards for possible future use.alternate routes, it operates normally and forwards the Some additional optimizations have been proposedpacket to its next hop when the packet is not a here for DSR as (i) Selection: In DSR route requestduplicate. All this route maintenance occurs under have been modified by changing cache settings. Alocal repair scheme. value is set at some minimum level and route reply is checked, If route reply does not occur in that time then3..3 Local Repair backbone nodes are used. Backbone nodes have been entered at random level for DSR for better results. AnWhen a link break in an active route occurs, the node intermediate node can use an alternate route from itsupstream of that break may choose to repair the link own cache, when a data packet meets a failed link onlocally if the destination was no farther and there exists its source route. (ii) route repair: A source nodeBackbone Nodes that are active. The Time to live receiving a RERR packet piggybacks the RERR in the(TTL) of the REQ should initially be set to the following RREQ. This helps clean up the caches offollowing value: other nodes in the network that may have the failedTTL = max (MIN_Repair_TTL+ BN, 0.5* #hops) link in one of the cached source routes. (iii) Duplicate routes: When a node overhears a packet not addressedWhere MIN_Repair_TTL is the known hop count to to itself, it checks whether the packet could be routedthe destination. #hops is the number of hops to the 3
via itself to gain a shorter route. If so, the node sends a Pause time of 0 means maximum mobility and 300 isRREP to the source of the route with this new, better minimum mobility. Speed has been kept constant at 15route. Aside from this, promiscuous listening helps a meter per second.node to learn different routes without directlyparticipating in the routing process. Packet delivery ratio4. Simulation and Results 98Simulation study has been carried out to study the 96performance study of proposed scheme with existing 94 AODVdifferent protocols. Simulation Environment used is 92 Refined AODV ra tioNS-2 (network simulator).The version NS 2.28 has 90 DSRbeen used to carry out the process. Simulation resultshave been compared with AODV and DSR and their 88 Refined DSRmodified versions. The metrics used in the simulation 86study to perform evaluations have been discussed 84below. 1 2 5 10 15 20Packet Delivery Ratio: The fraction of successfully speed m/sreceived packets, which survive while finding theirdestination. This performance measure also determinesthe completeness and correctness of the routingprotocol. Figure 3 : Packet delivery at different speedsEnd-to-End Delay: Average end-to-end delay is thedelay experienced by the successfully delivered An approximate increase of 16-20 % have been seenpackets in reaching their destinations. This is a good in packet delivery of AODV and DSR modifiedmetric for comparing protocols. This denotes how versions. AODV gets stable even at higher pause timeefficient the underlying routing algorithm is, because as shown in figure 2. This trend is more evident withdelay primarily depends on optimality of path chosen. use of stable backbone nodes. The scenario has been changed in figure 3 for 50 nodes moving at different speeds. Speed has been varied from 1 meter per second Packet delivery ratio to 20 meters per second. 1 End to end delay 0.95 AODV 0.8 refined AODVratio 0.9 DSR 0.7 REF DSR 0.6 AODV d e la y (m s ) 0.85 Refined AODV 0.5 0.8 DSR 0 20 50 100 150 200 250 300 0.4 Refined DSR Pause time 0.3 0.2Figure 2 : Packet delivery at pause times 0 0.5 1 1.5 2 2.5 3 3.5In simulation study 50 nodes have been taken in a speed m/srandom scenario with 1000 × 750 areas. The areaselected is rectangular instead of square as in earlier Figure 4: End to end delay at different speedssimulations. This relates it better to real life scenarios.The study has been conducted at different pause times. 4
The trend clearly indicate more packet delivery for Special Issue on Routing in Mobile Communicationrefined versions of protocols. Refined ADOV has Networks, pp. 183-197, Oct. 1996.better delivery at faster speeds. It gets stabilized at fast  C. C. Chiang, H. K. Wu, W. Liu, and M.speeds. The initial fall can be attributed to time Gerla,”Routing in Clustered Multihop, Mobilerequired for more calculations involved in better Wireless Networks with fading channels”, Proc. ofselection of stable route. IEEE SICON’97, pp. 197-211, April 1997. C. Perkins, et al , “Ad Hoc On Demand DistanceOne more parameter has been used as End to end Vector (AODV) Routing”, draft-ietf-manet-aodv-delay. It is expected that initially delay is more for 10.txt, Jan 19, 2002.refined versions. This is because all initial calculations D. Johnson, “The Dynamic Source Routing Protocoltake more time. It takes more time in initial selection of for Mobile Ad Hoc Networks (DSR)”, draft-ietf-manet-Route and when it stabilizes then the delay decreases as dsr-07.txt, Feb 21, 2002.shown in figure 4. DSR is better in all cases as it uses Yong-Bae Ko and Nitin H. Vaidya,” Locationcache Added Routing (LAR) in Mobile Ad Hoc Networks”, ACM/IEEE International Conference on Mobile5. CONCLUSION Computing and Networking, pp. 66-75, Oct. 1998.A new scheme has been presented that utilizes a mesh V. D. Park and M. S. Corsion, “A Highly Adaptivestructure and alternate paths. The scheme can be Distributed Routing Algorithm for Mobile Wirelessincorporated into any ad hoc on-demand unicast Network”, IEEE Sixteenth Annual Joint Conference ofrouting protocol to improve reliable packet delivery in the IEEE Computer and Communication Societies,the face of node movements and route breaks. INFOCOM’97, pp 1405-1413, vol. 3 April 1997.Alternate routes are utilized only when data packets  C. K. Toh, “A Novel Distributed Routing Protocolcannot be delivered through the primary route. As a to Support Ad Hoc Mobile Computing”, Proceedingscase study, the proposed scheme has been applied to of the 1996 IEEE Fifteenth Annual InternationalAODV and DSR and it was observed that the Phoenix Conference on Computers andperformance improved. Simulation results indicated Communications, pp. 480-486, March 1996.that the technique provides robustness to mobility and  Z. J. Hass, “A New Routing Protocol for theenhances protocol performance. Average increase in Reconfigurable Wireless Network,” IEEE 6thpacket delivery occurs for both protocols. The International Conference on Universal PersonalBackbone based node Routing gives a better approach Communication Record 1997, Vol. 2, pp. 562-566,for on demand routing protocols for route selection and Oct. 1997.maintenance. It caused a bit more end to end delay.  S. Ramanathan and M. Steenstrup, “A survey ofThe process of checking the protocol scheme is on for routing techniques for mobile communicationsmore sparse mediums and real life scenarios and also networks”, Mobile Networks and Applications, pp. 89–for other metrics like Path optimality, Link layer 104, 1996.overhead. Additionally, the plan is to further evaluate  NS Notes and Documentation, available atthe proposed scheme by using factor of power and www.isi.edu/vint.quality of service.6. REFERENCES: E. M. Royer and Chai Keong Toh, “A Review ofCurrent Routing Protocols for Ad Hoc Mobile WirelessNetworks”, IEEE Personal Communications, Vol. 6,No. 2, April 1999, pp 46-55. C. Perkins and P. Bhagwat, “Highly DynamicDestination Sequenced Distance Vector Routing(DSDV) for Mobile Computers,” ComputerCommunication Reviews, pp. 234-244, Oct. 1994. S. Murthy and J. J. Gracia-Luna-Aceves,”AnEfficient Routing Protocol for Wireless Networks”,ACM Mobile Networks and Applications Journal, 5