Highly Dynamic DestinationSequenced DistanceVector Routing DSDV for Mobile Computers Pravin Bhagwat Charles E Perkins Computer Science Department IBM TJ Watson ResearchCenter University of Maryland Hawthorne NY College Park MD Abstract users are free to move ab out at their convenience with out b eing constrained by wires An adhoc network is the co op erative engagementof This is a revolutionary development in p ersonal com a collection of Mobile Hosts without the required inter puting Battery p owered untethered computers are vention of anycentralized Access Point In this pap er likely to b ecome a p ervasive part of our computing in we present an innovative design for the op eration of such frastructure As p eople b egin to have mobile computers adho c networks The basic idea of the design is to op handy for whatever purp oses sharing information b e erate each Mobile Host as a sp ecialized router which tween the computers will b ecome a natural requirement p erio dically advertises its view of the interconnection Currently such sharing is made dicult by the need for top ology with other Mobile Hosts within the network users to p erform administrative tasks and set up static This amounts to a new sort of routing proto col We bidirectional links b etween their computers However haveinvestigated mo dications to the basic Bellman if the wireless communications systems in the mobile Ford routing mechanisms as sp ecied by RIP to computers supp ort a broadcast mechanism much more make it suitable for a dynamic and selfstarting network exible and useful ways of sharing information can b e mechanism as is required by users wishing to utilize ad imagined For instance anynumb er of p eople could ho c networks Our mo dications address some of the conceivably enter a conference ro om and agree to sup previous ob jections to the use of BellmanFord related p ort communications links b etween themselves with to the p o or lo oping prop erties of such algorithms in the out necessarily engaging the services of any preexisting face of broken links and the resulting time dep endent equipment in the ro om ie without requiring anypre nature of the interconnection top ology describing the existing communications infrastructure Thus one of links b etween the Mobile Hosts Finallywe describ e our primary motivations is to allow the construction of the ways in which the basic networklayer routing can temp orary networks with no wires and no administra b e mo died to provide MAClayer supp ort for adho c tiveintervention required In this pap er suchainter networks connection b etween the mobile computers will b e called an adhoc network in conformance with current usage Intro duction within the IEEE sub committee Recently there has b een tremendous growth in the Adho c networks dier signicantly from existing sales of laptop and p ortable computers These smaller networks First of all the top ology of interconnections computers nevertheless can b e equipp ed with hun may b e quite dynamic Secondly most users will not dreds of megabytes of disk storage high resolution color wish to p erform any administrative actions to set up displays p ointing devices and wireless communications suchanetwork In order to provide service in the most adapters Moreover since many of these small in size general situation we do not assume that every computer only computers op erate for hours with battery p ower is within communication range of every other computer This lack of complete connectivitywould certainly b e a reasonable characteristic of say a p opulation of mo bile computers in a large ro om which relied on infrared transceivers to eect their data communications Currently there is no metho d available which enables mobile computers with wireless data communications equipment to freely roam ab out while still maintaining metho d Eachnodemaintains a view of the network connections with each other unless sp ecial assumptions top ology with a cost for eachlinkTokeep these views are made ab out the way the computers are situated with consistent each no de p erio dically broadcasts the link resp ect to each other One mobile computer mayoften costs of its outgoing links to all other no des using a b e able to exchange data with two other mobile comput proto col such as o o ding As a no de receives this in ers which cannot themselves directly exchange data As formation it up dates its view of the network top ology a result computer users in a conference ro om maybe and applies a shortestpath algorithm to cho ose its next unable to predict which of their asso ciates computers hop for each destination Some of the link costs in a could b e relied up on to maintain network connection no des view can b e incorrect b ecause of long propaga esp ecially as the users moved from place to place within tion delays partitioned network etc Such inconsistent the ro om views of network top ologies might lead to formation of Routing proto cols for existing networks havenot routing lo ops These lo ops however are shortlived b een designed sp ecically to provide the kind of dy b ecause they disapp ear in the time it takes a message namic selfstarting b ehavior needed for adho c net to traverse the diameter of the network works Most proto cols exhibit their least desirable b e havior when presented with a highly dynamic inter connection top ology Although we thought that mo DistanceVector In distancevector algorithms bile computers could naturally b e mo deled as routers every no de i maintains for each destination x a set it was also clear that existing routing proto cols would x g where j ranges over the neighb ors of of distances fd ij place to o heavy a computational burden on each mobile iNodei treats neighbor k as a nexthop for a packet computer Moreover the convergence characteristics of x x destined for x if d equals min fd g The succession j ij ik existing routing proto cols did not seem go o d enough of next hops chosen in this manner lead to x along the to t the needs of adho c networks Lastly the wire shorest path In order to keep the distance estimates less medium diers in imp ortantways from wired me uptodate each no de monitors the cost of its outgo dia whichwould require that wemake mo dications to ing links and p erio dically broadcasts to each one its whichever routing proto col we mightcho ose to exp er neighb ors its current estimate of the shortest distance iment with For instance mobile computers maywell to every other no de in the network have only a single network interface adapter whereas The ab ove distancevector algorithm is the classical most existing routers havenetwork interfaces to connect Distributed BellmanFord DBF algorithm Com two separate networks together Besides wireless media pared to linkstate metho d it is computationally more are of limited and variable range in distinction to exist ecient easier to implement and requires muchless ing wired media Since we had to makelotsofchanges storage space However it is well known that this algo anywaywe decided to follow our adho c network mo del rithm can cause the formation of b oth shortlived and as far as we could and ended up with a substantially longlived lo ops The primary cause for formation new approach to the classic distancevector routing of routing lo ops is that no des cho ose their nexthops in a completely distributed fashion based on information Overview of Routing Metho ds which can p ossibly b e stale and therefore incorrect In our environment the problem of routing is essen Almost all prop osed mo dications to DBF algorithm tially the distributed version of the shortest path prob eliminate the lo oping problem by forcing all lem Eachnodeinthenetwork maintains for each no des in the network to participate in some form of in destination a preferred neighb or Each data packet con terno dal co ordination proto col Suchinterno dal co ordi tains a destination no de identier in its header When nation mechanisms might b e eective when top ological a no de receives a data packet it forwards the packet changes are rare However within an adho c mobile en to the preferred neighb or for its destination The for vironment enforcing anysuchinterno dal co ordination warding pro cess continues until the packet reaches its mechanism will b e dicult due to the rapidly changing destination The manner in which routing tables are top ology of the underlying routing network constructed maintained and up dated diers from one Simplicity is one of the primary attributes which routing metho d to another Popular routing metho ds makes any routing proto col preferred over others for however attempt to achieve the common ob jectiveof implementation within op erational networks RIP routing packets along the optimal path The nexthop is a classical example Despite the countingtoinnity routing metho ds can b e categorized into two primary problem it has proven to b e very successful within small classes linkstate and distancevector size internetworks The usefulness of RIP within adho c environment however is limited as it was not designed to handle rapid top ological changes Furthermore the LinkState The linkstate approach is closer to the techniques of splithorizon and poisonedreverse are centralized version of the shortest path computation tween arrival of the rst and the arrival of the best route not useful within the wireless environment due to the for each particular destination Based on this data a broadcast nature of the transmission medium Our de decision may b e made to delayadvertising routes