A Simulation Analysis on reactive Route Repair techniques for QoS sensitive applications in Mobile Ad Hoc networks

George N. Aggelou, Rahim Tafazolli Centre for Mobile Communications Systems Research (CCSR)

University of Surrey U.K.

{ G.Aggelou, R.Tafazolli} @eim.surrey.ac.uk

Abstmct - One of the main challenges in mobile ad hoc networks (MANETS) is the routing of calls to mobile users moving frequently. The major tasks of routing are to fmd a route to a terminal quickly, a process often called ROUTE DISCOVERY, and to maintain and repair the active routes, a process often called ROUTE MAINTENANC~PAIR. ROUTE MAINTENANC~PAIR is a vital process as it deals with the salvage of calls when a link failure along a data route occurs. Data losses or failures in turn impact the end-to- end perceived quality of the application. In this paper we analyse through simulations various ROUTE REPAIR techniques tailored for operation in MANETS and demonstrate the effects of relative node velocity, node density and communication range on the communication cost and scalability of a routing protocol.

I. PRESENT MANET ROUTE REPAIR SCHEMES When a data source node wishes to send a data packet to some destination node, it first examines if a route to this destination exists. If so, it proceeds and transmits the packet over its network interface to the next hop identified in its routing table. Each intermediate node upon reception of the data packet, first acknowledges its correct reception to the previous hop and attempts to forward it to the next hop, if a path to destination is available. If the link to next hop has failed such that an intermediate node is unable to forward the packet, the node initiates the ROUTE REPAIR phase. In RDMAR [l], an efficient distributed two-level ROUTE REPAIR algorithm which adaptively subdivides the task of maintaining and re-establishing active routes to mobile destinations, has been presented. In brief, when a failure along an active route occurs the ROUTE REPAIR algorithm, at the node that detects the failure, examines its relative distance to the calling and called nodes, and accordingly two heuristics are considered:

if its relative distance from the called node is smaller or equal to this from the calling node, then Relative Distance Micro-discovery (RDM) is applied to localise the repair of the failed route on the region of the network where the failure occurs; otherwise, the node proceeds and informs the calling node about the failure to deliver the call through this path, this is called, the Failure Notification (FN) phase.

Due to the localisation property, the ROUTE REPAIR phase in RDMAR is bandwidth efficient in large networks because the flooding rate is much smaller and thus control messages do not have to propagate globally throughout the network. The later property ensures also that scalability does not get worse when the number of nodes increases. The purpose of this paper is to study two classes of ROUTE REPAIR techniques that broadly used in present ETF candidate MANET routing schemes [l] and determine their performance measures under various mobility and communication scenarios. In the first class, which used in RDMAR protocol, RDM and FN are used interchangeably as illustrated above, while in the second error messages (similar to FN phase) are always sent to the source(s) of the failed data. Results illustrate the importance and significance of the ROUTE REPAIR process when a call is routed through a MANET, as optimally configured ROUTE REPAIR functions result to a significant decrease of network resources for route re- establishment when route failures occur as well as to the perceived quality of the call.

11. SIMULATION EXPERIMENTS The graphs in Fig 1 show the packet delivery ratio (PDR) and routing packet overhead for the all-opt RDMAR protocol which utilizes the two classes of ROUTE REPAIR (RR) schemes. In all the three mobility models considered in this paper, the numerical results obtained show that the difference in PDR between the two RR schemes is small and vanishes as the communication range increases. The control overhead, however, is significantly lower when FN/RDM is used together compared to when FN is used alone. The results show the significant effect of the RDWFN algorithm due to localisation property on the overall communication cost.

Furthermore, we increased the number of participating nodes to examine the scalability of the routing protocol in terms of average communication cost when the two ROUTE REPAIR schemes are used. As expected, communication overhead in FN-based scheme increases because flooding rate increases since the number of

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nodes that initiate a ROUTE DISCOVERY becomes bigger. Note, however, the satisfactory behaviour of the ROUTE REPAIR algorithm in RDMAR protocol ou>M/FN) in resource utilisation as the number of nodes increases (Fige 2b), whereas PDR remains in the same levels. See also (Fige 2a) that because of the increased path availability, due to larger node density (50 nodes), the protocol achieves higher PDR ratios for small T, values (100-200m) compared to small-to-medium (30 nodes) populations. The later observation is true since for large populations the virtual links do not break because the network is so dense that the breakage of physical links caused by node movement is compensated by the creation of other physical links due to node movement.

111. CONCLUSIONS AND FUTURE WORK In this paper we examined the performance of two on- demand ROUTE REPAIR algorithms used in IETF

MANET routing schemes. Specifically, an F ” M - based ROUTE REPMR scheme, first presented by the authors in [l], is analysed in this paper and its performance is compared with that of an FN-based ROUTE REPAIR scheme. We conclude that when the FN phase is combined with a properly configured RDM mechanism can provide an extremely robust and responsive protocol to keep the control overhead low for establishing (or re-establishing) and maintaining communications, which otherwise would be considerably more if the FAILURE NOTIFICATION messages were solely forwarded to the source of the data packet.

REFERENCES [l] IETF MANET Working Group.

http://www.ietf.org/html.charters/manet- charter.html

Fig 1 a) Protocol Efficiency (PDR) and b) Communication Cost Prol~col Enkiemy (FOR) mot

Velocity = 14 4 [KnVh]. MchIlty Panem = Random An- C+”ummMn Cod n Tx

V*“ I 4 4 4 K” w w P.”. R.n”

- Nob. - 30 ( R O M - F W )

TI (m)

( 4 (b) Fige 2 a) PDR and b) Communication Cost Plots for varying node populations

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