[ieee 2010 international conference on computer and information application (iccia) - tianjin, china...

A Distributed Truthful Routing Protocol for Mobile Ad Hoc Networks

Fatemeh Shirzad#1, Ali Movaghar#2, Eslam Shirzadeh*3 # Department of Computer Engineering

Sharif University of Technology Tehran, Iran

[email protected] [email protected]

* Shahab Danesh Institute Qom, Iran

[email protected]

Abstract— In Mobile Ad hoc Networks (MANETs), nodes depend on each other for routing and forwarding their packets. However, to save power and other resources, nodes belonging to independent authorities may behave selfishly, and not cooperate in network activities. Such selfish behaviour poses a real threat to the proper functioning of MANETs. To cope with this situation, a motivation stimulation mechanism is required to provide sufficient incentives for nodes to forward other nodes’ packets. One appropriate approach is to have network nodes pay in order to motivate them to cooperate with the protocol. To achieve truthfulness, the payment should be based on the cost of transmission of packets. Since the mentioned costs are private to the nodes, a suitable mechanism is needed to collect the real values. In this paper, we propose a distributed truthful routing protocol utilizing the game theoretic notion of the mechanism design to solve the problem. To the best of our knowledge, our proposed protocol is the first protocol attaining the message complexity of d)O(n + , in which n is the number of nodes in the network, and d is an upper bound on the length of the path. The proof of the protocol’s properties is provided and its performance is evaluated through simulation. Experimental results confirm that the proposed protocol has a considerably low overhead and outperforms the previously proposed protocol TMRP which has the best performance between truthful routing protocols in ad hoc networks, in terms of overhead and end-to-end delay with a slight decrease in delivery ratio. Instead, our protocol finds optimal paths that can save energy consumption and decrease the payments to the intermediate nodes.

Keywords-Mobile Ad hoc Networks;Selfish Node;Cooperation;Truthful Protocol;Game Theory

I. INTRODUCTION During the last few years mobile ad hoc networks have

received much attention. This is due to their potential application and the increasing growth in using mobile devices. These networks are rapidly deployable, self-configuring, and infrastructure-less networks where nodes are connected by wireless links. Due to the limited transmission range of wireless network interfaces, a node has to rely on other nodes to forward packets to its intended destinations. Routing is a key issue in ad hoc networks that has been the topic of extensive research in the last few years.

Most of existing routing protocols in ad hoc networks [1], [2], [3], [4] assume that all nodes follow the prescribed protocol. In general, all network functions namely route discovery, packets transfer, and network control messages transfer are dependent on the cooperation between nodes. The validity of this assumption is challenged when nodes may not belong to the same authority and may not pursue a common goal. For example, if battery-powered nodes relay packets for others, their energy will decrease, that is undesirable from a selfish standpoint. Since later, they may have insufficient energy for their own packets they won’t relay any messages at all. If every node argues in this fashion, then the throughput that each node receives will drop dramatically. Thus, a motivation stimulation mechanism is required to encourage nodes to provide service to other nodes.

The power consumed to forward other nodes’ packets can be regarded as the node’s cost. A naive method to stimulate cooperation is to give nodes some incentive for data forwarding. Since different nodes spend different costs on forwarding same amount of data, it is desirable to reimburse the forwarding nodes according to their costs so that those nodes can get incentives. However, to maximize the payoff, selfish nodes may not reveal their true costs. Thus, we need truthful protocols for preventing this scenario. A protocol is called truthful or strategy-proof if it maximizes the payoff to the nodes only when they reveal their true cost. Up to now, VCG mechanism [5], [6], [7] is the only truthful mechanism for finding least cost path in the network [8].

Control overhead and energy consumption are two important performance metrics. On-demand routing establishes paths to respective destinations only when necessary. Therefore, it reduces energy consumption and control overhead. But on-demand protocols suffer from considerable route discovery latencies under intermittent data applications when a new route is requested in large networks and high populated scenarios. Decreasing control overhead has a large effect on performance of protocols. Truthfulness in conjunction with loop-free routing results in increased complexity of protocol design, and consequently the related control overhead increases too. Thus, many of truthful routing protocols have high control overhead and low packet delivery ratio. TMRP [9] is one of the proposed protocols

International Conference on Computer and Information Application（ICCIA 2010）

133C978-1-4244-8598-7 /10/$26.00 2010 IEEE

that achieves high packet delivery ratio, incurs low end-to-end delay, and low overhead. Therefore this protocol has not shortcomings of other truthful protocols, but to achieve such good network performance it sacrifices cost optimality of selected path.

In this paper we propose a distributed truthful routing protocol in wireless ad hoc networks setting where every wireless node has a private cost of transmitting the data packet. Our main contribution is reducing control message overhead, because this metric has large effect on other performance metrics such as packet delivery ratio and average end to end delay. In the proposed protocol every rational selfish wireless node will follow the protocol without any deviation. Also computational burden is distributed over all intermediate and destinations nodes. The main features of our proposed protocol is truthfulness, cost optimality, low control overhead, low computational complexity, high packet delivery ratio, and low average end to end delay. To the best of our knowledge it is the first truthful protocol that achieves good network performance and path optimality simultaneously.

The remainder of this paper is organized as follows. Section II reviews the related work and section III presents the problem model and preliminaries. Section IV presents our proposed protocol. In section V, we analysis the proposed protocol and we show truthfulness of the protocol. Simulation results are discussed in section VI. Section VII concludes the paper and discusses possible future works.

II. RELATED WORK In recent years, mechanism design [10] is introduced to

solve the problem of nodes cooperation. The first routing protocol that used VCG mechanism to solve selfishness problem in wireless ad hoc networks is Ad hoc-VCG [11]. The main properties of this protocol are truthfulness and cost efficiency. It needs )O(n3 control messages for a route discovery, where n is the number of network nodes. CORSAC [12] is a truthful routing protocol which combines VCG mechanism with cryptography. The control overhead of this protocol is O(�.E.n), where � is the number of power levels, and E is the number of edges. Overhead of CORSAC is also very high. COMMIT [13] is another VCG-based protocol. It uses underlying topology control protocols. Its control overhead is in the order of )log.O(n2 n . SLTC [14] is a truthful, cost efficient and stable path routing protocol. In this protocol, nodes use State Cache to store their one-hop neighbour information and send this information to the source. Each route request message is rebroadcasted only once by each node of the network, and SLTC attains to a O(n.d) complexity, where d is the diameter of the network. LOTTO [15] and LSTOP [16] are two other truthful routing protocols. LOTTO incurs an overhead of )O(n2 , while LSTOP incurs an even lower overhead of O(n) on the average, and )O(n2 in the worst case. One problem in LSTOP is that in a network with insufficient high density, the sub graph that source constructs may not be biconnected, and it needs to invoke a new route discovery. Another truthful routing protocol with control overhead of )O(n2 is

LOTER [17]. We can see advances in reducing control overhead in these works but it is still high and it is desirable to reduce control overhead to achieve better network performance such as higher packet delivery ratio and lower average end to end delay. TMRP [9] is a multipath routing protocol in ad hoc networks with selfish nodes. In this protocol VCG is used in packet forwarding. It reduces overhead to 2n-2 packets per route discovery. This is good advance in truthful routing protocols, but this protocol does not find the cost efficient path.

III. SYSTEM MODEL AND PRELIMINARIES In finding a solution for truthful routing problem, we are

given a graph N=(V,E,c) that describes the network. The set of nodes }v,...,v,{v=V n21 corresponds to n (|V|=n) mobile devices distributed in a two dimensional plane. V×VE , is a set of directed edges )v,v( ji , and :c V → for each node

iv indicates private cost of transmitting unit of data. Each node has a unique identification number (for our purposes, this will be the index i of node iv ), but it is not a priori known which nodes are currently in the network, nor edge set E or cost function c is known. We use the well-known UDG (unit disk graph) model for ad hoc networks. In this model each node has the same and constant transmission range. All nodes in the network use omni-directional antennas.

It is assumed that network is bi-connected and also network density is enough that each two neighbours have a common neighbour. All nodes are assumed to be selfish and are not malicious. We assume that there is no collusion between the nodes.

The problem is to find the least cost path and compute the payments to the nodes on it between the source and the destination. To enforce nodes to act truthfully and reveal their true cost VCG mechanism is used. This mechanism is a result in the mechanism design. According to VCG, first the least cost path from the source to the destination must be computed, Say LCP. To compute payment ipay to each node

iv on the LCP, (1) must be applied:

i-ii c+|LCP|-|LCP|=pay (1) where |LCP| -i is the total cost of least cost path without considering iv , and |LCP| is the total cost of the least cost path. To be familiar to the mechanism design and VCG mechanism see [10].

IV. DISTRIBUTED TRUTHFUL ROUTING PROTOCOL Our proposed protocol is a distributed and low-overhead

truthful routing protocol. It provides cost-efficiency that means the least cost path is selected. Control overhead of our proposed protocol is O(n+d), in which n is the number of nodes in the network, and d is an upper bound on the length of the path. This is significant reduce in control overhead of truthful routing protocols in ad hoc networks. Packet delivery ratio of our protocol is very high. Also computations of the least cost path and payments to the nodes on it are


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distributed, so that computational complexity has been reduced in each node.

Our truthful routing protocol consists of two main phases; Route discovery and Data transmission. Route discovery includes least cost path selection and payment computation; the payments to the intermediate nodes are done in the data transmission phase. We now present the phases in detail.

Route Discovery Whenever a source node 0v=S wants to communicate

with a destination node nv=D and does not know any route to D, it broadcasts a ROUTE REQUEST (RREQ) packet and sets a timer. This packet contains the unique identifier 0 of the source node, the unique identifier n of the destination node, and a sequence number n,0sn .

When the timer times out, if the source still does not know any route to the destination, it should initiate a new route discovery.

Every node jv except D that receives the RREQ directly from S, appends the packet by adding the identification j, and the cost jc of relaying a data packet; rebroadcasts the packet, and inserts the identification number of S and n,0sn into its SENT TABLE.

Assume w.l.o.g. that a RREQ packet from S that is received by iv and contain least cost path among all RREQ packets that is received by this node, passes through intermediate nodes 1-i21 v,...,v,v .The RREQ packet that

iv broadcasts is as:

>ic i, |,1-iiLCP| ,1-ic 1,-i ..., |,-1

iLCP| ,1c 1, ,n0,sn n, ,0 ,RREQ< :*iv

where 0 and n are the identification numbers of the source and the destination; n,0sn is the sequence number of the RREQ; 1,…, i-1 are the identification numbers of intermediate nodes; i is the identification number of iv .

i1 c ..., ,c are the cost of relaying a data packet by nodes

i1 v..., ,v ; 1}-i {1,...,k |,LCP| -ki is the cost of least cost path

without node kv that is computed by iv . The cost of relaying a data packet by the source node is omitted in all of the RREQ packets, because it is the same in all the paths and has no effect in the LCP and payments computations. �

Each node jv except S and D that receives RREQ packet directly from an intermediate node iv , checks if the packet’s source identification number and n,0sn has been inserted into SENT TABLE or not. The packet will be dropped if so, Otherwise jv stores the information embedded in the packet in its WAIT TABLE, i.e., stores this:

>ic i, |,1-iiLCP| ,1-ic 1,-i ..., |,-1

iLCP| ,1c 1, ,n0,sn n, ,0 <

jv sets a timer if it is the first RREQ packet with the same source identification number and n,0sn . Information of any RREQ packet that is received before timer times out, is stored in jv ’s WAIT TABLE. Such waiting method to get information has been used in [14], [15]. When the timer

times out, jv selects least cost path among paths received by it, using information in its WAIT TABLE. For each node

kv on the selected LCP, |LCP| -kj is computed using the

routes and |LCP| -ki ’s stored in WAIT TABLE, where iv is a

neighbour node of jv . |LCP| -kj is computed as:

(2) .c+TABLE} WAIT in the storedbeen has that vodirectly t

RREQ asent has that v v | TABLE WAITin the storedbeen has that ut vpath withocost least ofcost |,LCPmin{|=|LCP|

j

j

ii

k-ki

k-j

If there is no least cost path without kv , and there is no |LCP| -k

i in the WAIT TABLE, |LCP| -kj is set to infinity.

After theses computations, jv broadcasts a RREQ packet that contains the source and destination identification numbers, sequence number n,0sn , identification numbers and cost of relaying a data packet by nodes on selected LCP, and

|LCP| -kj for each node kv on the selected LCP. Also, jv

inserts the identification number of S and n,0sn into its SENT TABLE to drop later RREQ packets with the same source identification number and n,0sn . It also stores the identification number of the last node on the selected LCP in its PREVIOUS TABLE. This node is one of the jv 's neighbours and is sender of the selected LCP.

Upon receiving RREQ packet, the destination node D acts same as intermediate nodes. The difference is the computation of the payments to the nodes on the LCP. Let |LCP| denote the total cost of the least cost path. The VCG-payment kpay for intermediate node kv on the LCP is computed by (3):

k-knk c+|LCP|-|LCP|=pay (3) Equation (3) is composed of two parts: the first part is the

bonus that node kv receives |)LCP|-|LCP(| -kn , and the second part is the cost of relaying a data packet by )(c v kk . To compute |LCP| -kn , (4) is used:

(4) .TABLE} WAIT in the storedbeen has that D odirectly t

RREQ asent has that v v | TABLE WAITin the storedbeen has that ut vpath withocost least ofcost |,LCPmin{|=|LCP|

ii

k-kik-n

later, it will be shown that the scheme is strategy-proof. After computing LCP and the payments to each node on

it, the destination node sends a RREP packet to the source node along LCP. We assume w.l.o.g. that the least cost path computed by D is in the order of D , v..., , v, v,S k21 . The RREP packet is as:

>pay ..., ,pay ,pay ,sn n, ,0 ,RREP< k21n0, In order to prevent intermediate nodes from altering

payments, the destination node signs RREP packet with a digital signature. Upon receiving RREP packet in each intermediate node, it inserts a new entry in ROUTE TABLE. This entry includes the source and destination identification


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numbers, and the next hop identification number from which RREP is received.

The RREP packet is sent back along the reverse order of LCP until it is received in the source node. After receiving RREP packet in the source node, a route entry in ROUTE TABLE is built and data transmission is started.

Consider that, upon receiving any type of control packets in each node, it deletes all entries with lower n,0sn for intended source within its tables. Also if received control packets have lower n,0sn than an entry in any table, it is dropped. Indeed sequence number is very important in this protocol.

Now we consider an example. Suppose that network graph is as Fig. 1. S is the source node and D is the destination node. Let 0 and 7 be the identification numbers of S and D, respectively. The identification number of each intermediate node iv is i. The number beside each node indicates the cost incurred by that node to relay a data packet. At first, S broadcasts a RREQ packet (packet 1).

>0 7, 0, RREQ,< :*S :1 Packet First two numbers are the identification numbers of S and

D, and the last number is sequence number of the packet. This packet is received by , v,v 21 and 3v . These three nodes are neighbours of S, and rebroadcast RREQ packet immediately and drop any RREQ packet that they receive later. Also they record 0 as the identification number of previous node in their PREVIOUS TABLE. The packets are as:

>3 1, 0, 7, 0, RREQ,< :* v:2 Packet 1 >4 2, 0, 7, 0, RREQ,< :* v:3 Packet 2 >2 3, 0, 7, 0, RREQ,< :* v:4 Packet 3

in these three packets, the last two numbers are nodes' identification numbers and the cost of relaying a data packet, respectively.

In the next stage nodes , v,v 54 and 6v receive RREQ packets and upon receiving the first packet in each node, that node sets a timer. We assume that the timers time out in order of , v,v 54 and 6v . When the timer of 4v times out, only the packets 2 and 3 have been received and saved in 4v 's WAIT TABLE. Since packet 2 has lower path cost, 4v

broadcasts a RREQ packet using information of packet 2: >6 4, 6),+(4 3, 1, 0, 7, 0, RREQ,< :* v:5 Packet 4

Figure 1. An example of a network with selfish nodes, numbers beside

each node is its cost of relaying a data packet.

In this packet, 1 and 4 are the identification numbers of 1v and 4v , respectively, 3 and 6 are the costs of relaying a data packet by this two nodes, and 4+6=10 is |LCP| -1

4 . Node 4v records 1 as the identification number of the previous node in its PREVIOUS TABLE.

When 5v 's timer times out, packets 2, 3, 4, and 5 have been received in 5v . Packet 4 has lower total path cost, therefore 5v creates and broadcasts a RREQ packet as: >5 5, 5),+(3 2, 3, 0, 7, 0, RREQ,< :* v:6 Packet 5

Node 5v records 3 in its PREVIOUS TABLE. When 6v 's timer times out, packets 3, 4, and 6 have been received

in 6v . Packet 4 has lower total path cost, therefore 6v creates and broadcasts a RREQ packet as:

>3 6, 3),+(4 2, 3, 0, 7, 0, RREQ,< :* v:7 Packet 6 6v records 3 in its PREVIOUS TABLE. Three RREQ

packets 5, 6, and 7 are received by D. The LCP from S to D is D, , v, v,S 63 that is get from packet 7. In order to compute 3pay and 6pay , |LCP| 3-

7 and |LCP| 6-7 must be

computed. These computations are done by D as:

7.=9} 7, ,8 ,min{=}contain vnot doespath that any ofcost total|,LCP| |,LCP| |,LCPmin{|=|LCP|

3

-36

-35

-34

3-7

4.=2+5-7=pay3

7.=7} 9, , , ,min{=}contain vnot doespath that any ofcost total|,LCP| |,LCP| |,LCPmin{|=|LCP|

6

-66

-65

-64

6-7

5.=3+5-7=pay6 D creates a RREP packet and sends it back to the source:

.>5 4, 0, 0, RREP,< :vD 6 Upon receiving RREP in 6v , it sends RREP without any

change to 3v . Node 6v knows 3v from PREVIOUS TABLE. Also it creates a route entry in its route table. This route entry contains identification numbers of S,D, and the next hop to D that is D.

.>5 4, 0, 0, RREP,< :vv 36 Node 3v sends RREP to S and creates a route entry with

next hop 6v . .>5 4, 0, 0, RREP,< :Sv3

Data Transmission In the data transmission phase the data packets are

relayed through the LCP found in the route discovery phase. Each node that receives the data packet sends it to the next hop using ROUTE TABLE. To make the payment to each relay node, a central server can be employed [18]; it is a central trusted entity that is responsible for nodes accountings.

Route Recovery During the data transmission phase, intermediate nodes

may move or fail or an intermediate node may know that the previous payment is not valid any more. In such cases, the corresponding intermediate node sends a ROUTE ERROR


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(RERR) packet to the source along the reverse path. After receiving the RRER packet, the source node initiates a new route discovery phase.

V. ANALYSIS In this section we show that the proposed protocol finds

the least cost path, is truthful and has low overhead. Also its computational complexity is discussed.

A. Path Optimality Our proposed protocol selects the least cost path. This is

Obvious from the protocol description. Because each intermediate node selects most cost efficient path between received paths and sends it to its neighbours. The wait time in each node must be set appropriately so that the destination node can get enough information to compute the least cost path and the payments to nodes on it.

B. Truthfulness In this subsection we prove that each node reveals its true

cost and doesn’t modify or drop any packet. We assume that there is no collusion between nodes. To show truthfulness, we prove two lemmas.

Lemma 1: Each node jv declares its true cost of relaying a data packet jc .

Proof. We consider two cases. In the first case jv under-declares jc and in the second case over-declares it.

Case of under-declaration. There are two cases. In the first case, jv is on the LCP. By under-declaring jc , jv is still on the LCP, and according to (3), this does not increase the utility of jv . In the second case, jv is not on the LCP. In this case, if under-declaration of jc causes jv to be put on the LCP, the utility of jv reduces to a negative utility as it will incurs costs that are higher than the payment it gets. Therefore, we conclude that under-declaring jc by jv has no advantage to it.

Case of over-declaration. Alternatively, there are two cases. In the first case, jv is on the LCP. Over-declaring jc may leave the LCP unchanged. This does not increase the utility of jv , since the payment is independent of jv 's reported cost. But if by over-declaring its cost, jv is no longer on the LCP, jv 's positive utility reduces to zero. In the second case, jv is not on the LCP. Over-declaring its cost can not put it on the LCP, thus it leaves jv 's zero utility unchanged. Therefore, we conclude that over-declaring jc is unattractive to jv .

From these two cases, we conclude that every node declares its cost of transmission of data unit truthfully.

Lemma 2: Every node jv in the network do not modify information of other node iv .

Proof. We consider four cases:

• If both the iv and jv are on the LCP, increasing ic by jv may result either in jv no longer being on the LCP or it still remaining on the LCP. The former, reduces jv 's positive utility to zero, while the later may reduces jv 's utility or leave it unchanged. If jv decreases ic , it can be beneficial to it. To solve this problem, we can use a simple listening and reporting mechanism. Thus, if jv decreases ic , other nodes will know this alteration and send a message to the destination. Upon receiving this message, the destination will connect to iv and get true value of

ic from a secure connection. Therefore, increasing or decreasing ic , has no advantage to jv . Consider, the listening and reporting mechanism that is used is a simple mechanism and only can prevent nodes from altering other nodes’ information and it can not prevent nodes from lying their own private cost, the only way to this purpose is using mechanism design and VCG as it has been proved in [8].

• If iv is on the LCP, but jv is not, alteration of ic will be detected, because all nodes on the LCP forward their packets truthfully. Any inconsistency in reported values by different nodes will cause the destination to get information from iv via a secure connection.

• If iv is not on the LCP and jv is on it, altering ic by

jv will not be beneficial to it, because similar to second case, ic will be received by the destination via another paths other than LCP and lying about it can be detected.

• If both nodes are not on the LCP, increasing ic can not put jv on the LCP, and decreasing ic will lead to negative utility for iv , and it will not forward data packets. Therefore, jv has no advantage in altering

ic in this case. By these four cases, we showed that modifying cost of

other nodes is not attractive to any node. It is obvious that also alteration of |LCP| -k

i is not in favour of jv , because this value is used only for computation of payments for iv and has not any effect on jv 's utility.

Also dropping any information is not in favour of jv , because this information either has not any effect on jv 's utility or increases cost of paths that jv is on them, thus its utility will decrease or not change.

We proved that nodes have no advantage in modifying or dropping information of other nodes.

From lemma 1 and lemma 2 we have theorem 1. Theorem 1: Proposed protocol is truthful.


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C. Message Complexity Every node except the destination broadcasts a RREQ

packet, resulting in a total of n-1 packets, where n is the number of nodes. RREP packets are sent on the LCP. As the hop count of the LCP is at most d hops (we bound this amount using timer mechanism in each node), at most, d RREP packets are sent. Therefore, number of control packets in a route discovery phase is n+d-1. Thus a route discovery in the proposed protocol incurs O(n+d) overhead. TMRP as a truthful multipath protocol incurs 2n-2 control packets. TMRP has the lowest control overhead between truthful routing protocols. Our proposed protocol has lower overhead than TMRP.

Another feature of the proposed protocol is that, there is no need to record the LCP in the data packets and route reply packets. Each intermediate node on the LCP knows previous and next node on the LCP. Therefore, by this feature, header size of data packets and also size of RREP packets can be reduced.

Also we used a listening and reporting mechanism to prevent altering other nodes’ information. This mechanism has no control overhead in the network. Indeed if a node acts selfishly and alters other nodes’ information to increase its utility, it will be detected and reported by this mechanism. Therefore, this node can not increase its utility and thus, it has no incentive to alter other nodes’ information. In this way, the node never alters the other nodes’ information and the mechanism will not report and no reporting packet will be exchanged. Indeed this is an interesting feature that this mechanism prevents altering information without any extra control packet.

D. Computational Complexity In the proposed protocol, the least cost path selection in

each intermediate node and destination node is a linear search between paths that received from some neighbours. If we show maximum number of nodes’ neighbor by h, the least cost path selection in each node is in the order of O(h). Also each intermediate node jv computes |LCP| -k

j for every node kv on the selected least cost path and sends it to its neighbours, This computation in each intermediate and destination node is in the order of )d.h(O 2 . In other proposed truthful routing protocols that compute least cost path, burden of the LCP and payments computations is centralized on one node, the source or destination node. This node must have topology information of entire network and then can calculate LCP using Bellman-Ford or Dijkstra algorithms and also to calculate payment to each node on the LCP, these algorithms are used. For example if Dijkstra algorithm is used, the computations is in the order of )n(O 3 . Indeed our proposed protocol distributes the burden of the computations in the network, therefore computational complexity is reduced.

VI. PERFORMANCE EVALUATION In this section, we evaluate and compare the performance

of our proposed protocol with TMRP. The proposed protocol

is not compared with generic routing protocols such as DSR and AODV because those protocols have different model that nodes are willing to cooperate, however our protocol is based on the assumption that nodes may act selfishly. Also we don’t compare the proposed protocol with popular truthful routing protocols such as Ad hoc-VCG because model of network that used in our proposed protocol is Unit Disk Graph (UDG) but those protocols don’t use this model. TMRP uses UDG and its performance such as control overhead is better than other proposed truthful routing protocols. Therefore we compare our proposed protocol with TMRP.

We use a simulation model based on Glomosim [19]. Unless specified otherwise, the following parameters are used in the simulations. 60 nodes are placed uniformly in a field with dimensions 600m×600m. We used the IEEE 802.11 Distributed Coordination Function (DCF) as the MAC protocol. All nodes in the network follow the Random waypoint mobility model. The maximum speed is set to 0m/s-10m/s, and the pause time is set to 50s. All nodes have the same radio range of 250m. Each simulation is executed for 900s. 10 CBR flows are simulated each with the rate of 4 512-byte packets per second, started at 120s and ended at 880s. Data points represented in the graphs are averaged over 10 simulation runs, each with a different seed.

In the simulation study, we consider the following metrics:

• Control overhead: The control overhead is defined as the total number of routing control packets exchanged by the nodes in the network.

• Average end-to-end delay: It is the average end-to-end delay over all surviving data packets from the sources to the destinations.

• Packet delivery ratio: This is the percentage of the total number of data packets received by the destinations to the overall number of data packets originated by all nodes.

We assume that nodes do not change their packet forwarding cost during the simulation.

A. Effect of Node Mobility We first evaluate effect of node mobility on performance

of two protocols. Control overhead: Fig. 2 shows the control overhead

with respect to the maximum speed of the network’s node. We observe that the proposed protocol’s overhead is much lower than that of TMRP. This has numerous reasons; First, as discussed in Section V, the proposed protocol incurs

1-d+n control overhead per route discovery while TMRP results in a total control overhead of 2n-2. Second, in TMRP each node sends hello message every two seconds. Third, Although in TMRP nodes have multiple paths in their route table that makes it fault tolerant to link breakage, but to establish second price auction, if a node has less than two routes to the destination it sends a route error message resulting in increased route discoveries. Therefore, TMRP’s overhead is higher than that of the proposed protocol resulting in higher radio interference and longer output


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queues. Thus, more route discoveries will be initiated, and more control overhead will be resulted that worsens the situation. As the maximum speed increases, link breakage increases, RERR packets increases, more route discovery is requested and thus the overhead of both the protocols increases too.

Average end to end delay: Fig. 3 shows the average end to end delay with respect to the maximum node speed. Proposed protocol has lower average end to end delay than that of TMRP. This is an indirect result of TMRP’s higher control overhead that results in longer output queues and more route discoveries and thus, source nodes need more time to find paths to the destinations. As the maximum speed increases, route discoveries slow down and output queues become longer. Therefore, end to end delay increases in both the protocols.

Packet delivery ratio: Fig. 4 shows the packet delivery ratio with respect to the maximum speed of the network’s node. We observe that packet delivery ratio for both the protocols lays above 94%. TMRP’s packet delivery ratio is very high. The reason is that each node has multiple paths to the destinations and this provides better resistance to link breakage, and also to achieve this high ratio, TMRP don’t select minimum cost path because selecting such a path need higher control overhead that results in lower packet delivery ratio. Although the proposed protocol is a single path routing protocol but it achieves high packet delivery ratio that is very close to that of TMRP and has slight difference.

We observe that the proposed protocol achieves very good network performance. It is true that TMRP‘s packet delivery ratio is higher than that of the proposed protocol, but this is negligible and also TMRP does not select minimum cost paths. Our proposed protocol selects minimum cost path and also achieves high performance.

B. Effect of Network Size The simulations are conducted with maximum node

Figure 2. Control overhead with respect to maximum speed

Figure 3. Average end to end delay with respect to maximum speed

Figure 4. Packet delivery ratio with respect to maximum speed

speed of 10m/s, and the number of nodes are varies between 50 and 90 nodes. 8 CBR flows are simulated.

Control overhead: From Fig. 5 we observe that as the number of nodes increases, control overhead in both the protocols increases. In TMRP the network size has high effect on the control overhead, while in the proposed protocol effect of network size is very low. Thus the proposed protocol is scalable with respect to the network size.

Average end to end delay: Fig. 6 shows that as the number of nodes increases, the delay increases for both the protocols. The proposed protocol incurs lower delay than TMRP.

Packet delivery ratio: From Fig. 7 we observe that as the number of nodes increases, more packet drops take place.

We see that the packet delivery ratio in both the protocols is very high.

VII. CONCLUSION AND FUTURE WORK In this paper we presented a distributed truthful routing

protocol for mobile ad hoc networks. This protocol applies VCG mechanism to stimulate cooperation in the network. The protocol overcomes the shortcomings of previously proposed truthful routing protocols. We compared our

Figure 5. Control overhead with respect to network size

Figure 6. Average end to end delay with respect to network size


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Figure 7. Packet delivery ratio with respect to network size

protocol with TMRP which is a truthful multipath routing protocol and to the best of our knowledge it has the lowest control overhead between truthful routing protocols that have been presented until now. We observed that our proposed protocol has even lower control overhead than TMRP.

A prominent feature of our proposed protocol is that it incurs only n+d-1 control packets for a route discovery. It can achieve more than 90% packet delivery ratio that is close to packet delivery ratio of TMRP. Also we can see a reduction in end-to-end delay. Another feature of our protocol over TMRP is that it computes the most cost efficient path.

In this paper, we assumed that every node has the same constant transmission power. We leave designing a protocol with a comparable performance which has relaxed this assumption for the future work. Designing multipath version of the proposed protocol to achieve fault tolerance and load distribution in the network is another line of extending the work.

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