A Review of Curren t Routing Proto cols for Ad-Ho c Mobile Wireless Net w orks Elizab eth M. Ro y er C-K T oh Dept. of Electrical & Computer Engineering Dept. of Electrical & Computer Engineering Univ ersit y of California, San ta Barbara Georgia Institute of T ec hnology , A tlan ta er oyer@alpha.e c e.ucsb.e du cktoh@e e.gate ch.e du Abstract An ad-ho c mobile net w ork is a collection of mobile no des that are dynamically and arbitrarily lo cated in suc h a manner that the in terconnections b et w een no des are capable of c hanging on a con tin ual basis. In order to facilitate comm unicatio n within the net w ork, a routing proto col is used to disco v er routes b et w een no des. The primary goal of suc h an ad-ho c net w ork routing proto col is correct and e�cien t route establishmen t b et w een a pair of no des so that messages ma y b e deliv ered in a timely manner. Route construction should b e done with a minim um of o v erhead and bandwidth consumption. This pap er examines routing proto cols for ad-ho c net w orks and ev aluates these proto cols based on a giv en set of parameters. The pap er pro vides an o v erview of eigh t di�eren t proto cols b y presen ting their c haracteristics and functionalit y , and then pro vides a comparison and discussion of their resp ectiv e merits and dra wbac ks. 1 In tro duction Since their emergence in the 1970s, wireless net w orks ha v e b ecome increasingly p opular in the com- puting industry . This is particularly true within the past decade whic h has seen wireless net w orks b eing adapted to enable mobilit y . There are curren tly t w o v ariations of mobile wireless net w orks. The �rst is kno wn as infrastructured net w orks, i.e., those net w orks with �xed and wired gatew a ys. The bridges for these net w orks are kno wn as base stations. A mobile unit within these net w orks con- nects to, and comm unicates with, the nearest base station that is within its comm unication radius. As the mobile tra v els out of range of one base station and in to the range of another, a \hando� " o ccurs from the old base station to the new, and the mobile is able to con tin ue comm unication seam- lessly throughout the net w ork. T ypical applications of this t yp e of net w ork include o�ce wireless lo cal area net w orks (WLANs). The second t yp e of mobile wireless net w ork is the infrastructureless mobile net w ork, commonly kno wn as an ad-ho c net w ork. Infrastructureless net w orks ha v e no �xed routers; all no des are capable of mo v emen t and can b e connected dynamically in an arbitrary manner. No des of these net w orks function as routers whic h disco v er and main tain routes to other no des in the net w ork. Example applications of ad-ho c net w orks are emergency searc h-and-rescue op erations, meetings or con v en tions in whic h p ersons wish to quic kly share information, and data acquisition op erations in inhospitable terrains. This pap er examines routing proto cols designed for these ad-ho c net w orks b y �rst describing the op eration of eac h of the proto cols and then comparing their v arious c haracteristics. The remainder of the pap er is organized as follo ws: Section 2 presen ts a discussion of t w o sub divisions of ad-ho c routing proto cols. Subsection 2.1 discusses curren t table-driv en proto cols, while Subsection 2.2 describ es 1
Ad-Hoc Routing Protocols Source-initiated Table Driven On-Demand Driven DSDV WRP AODV DSR LMR ABR CGSR TORA SSR Figure 1: Categorization of Ad-Ho c Routing Proto cols. those proto cols whic h are classi�ed as on-demand. Section 3 presen ts qualitativ e comparisons of table-driv en proto cols, follo w ed b y on-demand-driv en proto cols, and �nally a general comparison of table-driv en and on-demand proto cols. Applications and c hallenges facing ad-ho c mobile wireless net w orks are discussed in Section 4. Finally , Section 5 concludes the pap er. 2 Existing Ad-Ho c Routing Proto cols Since the adv en t of D ARP A pac k et radio net w orks in the early 1970s [11 ], n umerous proto cols ha v e b een dev elop ed for ad-ho c mobile net w orks. Suc h proto cols m ust deal with the t ypical limitations of these net w orks, whic h include high p o w er consumption, lo w bandwidth, and high error rates. As sho wn in Figure 1, these routing proto cols ma y generally b e categorized as: (a) table-driv en and (b) source-initiated on-demand driv en. Solid lines in this �gure represen t direct descendan ts while dotted lines depict logical descendan ts. Despite b eing designed for the same t yp e of underlying net w ork, the c haracteristics of eac h of these proto cols are quite distinct. The follo wing sections describ e the proto cols and categorize them according to their c haracteristics. 2.1 T able-Driv en Routing Proto cols The table-driv en routing proto cols attempt to main tain consisten t, up-to-date routing information from eac h no de to ev ery other no de in the net w ork. These proto cols require eac h no de to main tain one or more tables to store routing information, and they resp ond to c hanges in net w ork top ology b y propagating up dates throughout the net w ork in order to main tain a consisten t net w ork view. The areas where they di�er are the n um b er of necessary routing-related tables and the metho ds b y whic h c hanges in net w ork structure are broadcast. The follo wing sections discuss some of the existing table-driv en ad-ho c routing proto cols. 2.1.1 Destination-Sequenced Distance-V ector Routing (DSD V) The Destination-Sequenced Distance-V ector Routing proto col (DSD V) describ ed in [17 ] is a table- driv en algorithm based on the classical Bellman-F ord routing mec hanism [7 ]. The impro v emen ts made to the Bellman-F ord algorithm include freedom from lo ops in routing tables. Ev ery mobile no de in the net w ork main tains a routing table in whic h all of the p ossible desti- nations within the net w ork and the n um b er of hops to eac h destination are recorded. Eac h en try is mark ed with a sequence n um b er assigned b y the destination no de. The sequence n um b ers enable the 2
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