- Email: [email protected]
Gathering-based routing protocol in mobile ad hoc networks
Computer Communications 30 (2006) 202–206 www.elsevier.com/locate/comcom
Short communication
Gathering-based routing protocol in mobile ad hoc networks Chang Wook Ahn
*
Communication Laboratory, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Republic of Korea Received 10 June 2005; received in revised form 17 July 2006; accepted 27 July 2006 Available online 22 August 2006
Abstract A gathering-based routing protocol (GRP) for mobile ad hoc networks is presented. The idea is to rapidly collect network information at a source node at an expense of a small amount of control overheads. The source node can equip promising routes on the basis of the collected information, thereby continuously transmitting data packets even if the current route is disconnected. It results in achieving fast (packet) transfer delay without unduly compromising on (control) overhead performance. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Mobile ad hoc networks; Routing protocol; Network information
1. Introduction Since all nodes in the mobile ad hoc networks can be mobile and communicate with one another either directly or through intermediate nodes with no fixed infrastructure, it is necessary to design an efficient routing protocol [1]. Proactive routing protocol (PRP) requires every node to maintain full routing information, while reactive routing protocol (RRP) typically relies on the flooding of queries to discover a destination [1]. PRP is, therefore, suitable for supporting the delay sensitive services such as voice and video [1–3]. However, it consumes a significant portion of the network capacity in order to keep the routing information current. The class of distance-vector based protocols such as destination-sequenced distance-vector routing protocol (DSDV) [2] and wireless routing protocol (WRP) [3] are representative examples of PRP. Although RRP may not be suited for real-time communication, it does not generally incur significant control overheads [1,4,5]. The query-reply handshake assisted protocols such as ad hoc on-demand distance-vector routing protocol (AODV) [4], dynamic source routing protocol (DSR) [5],
*
Tel.: +82 31 280 9654; fax: +82 31 280 9555. E-mail address: [email protected]
0140-3664/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2006.07.017
and temporally ordered routing algorithm (TORA) [6] belong to the RRP. Naturally, an approach for simultaneously taking the strengths of PRP and RRP has attracted due attention of late. This approach is widely known as hybrid routing protocol. Cluster-based routing protocol [7], zone routing protocol [8], and fisheye state routing protocol [9] are representative examples. However, the genuine objective has not been effectuated. In other words, they fall within the purview of a compromise between PRP and RRP. In this regard, this paper proposes a simple, but efficient routing protocol in the mobile ad hoc networks. This is the gathering-based routing protocol (GRP). The aim is to somehow garner the benefits accruing from the short transfer delay of PRP and the small overheads of RRP. 2. Gathering-based routing protocol A mobile ad hoc network is modeled as an undirected graph where a set of nodes and a set of (full-duplex) links are time-varying sets. We assume the use of a MAC protocol which resolves the problem of hidden/expose nodes. A representative instance is given in [10]. It is also assumed that all the nodes can enable a promiscuous receive mode. There is another assumption that every node recognizes its own neighbors (by incorporating a neighbor discovering
C.W. Ahn / Computer Communications 30 (2006) 202–206
protocol) and thus all the information associated with them are available. The goal of the proposed routing protocol (i.e., GRP) is to rapidly gather network information at a source node without spending a large amount of overheads. It offers an efficient framework that can simultaneously draw on the strengths of PRP and RRP. The procedures of GRP are described below. A source node broadcasts a destination query (DQ) packet to its neighbors. The DQ packet is continuously forwarded into each node’s neighbors until the destination is reached. It is simply implemented by the conventional flooding process of RRP (as in DSR or AODV). That is, the DQ packet plays the same role of route request (RREQ) packet of RRP so that it consists of the address of the source, the destination node’s address, and the sequence number. When the DQ packet reaches the destination, the destination node broadcasts a network information gathering (NIG) packet to its neighbors. The structure of NIG packet is similar to that of DQ packet, but it additionally contains
203
link reversal flag (LRF) for resolving deadlock and variable-length payload for recording/gathering the network information. The NIG packet propagates over the entire network by a gathering process. It is given as follows. When nodes receive the NIG packet with a new sequence number for the first time, they attach all the known information (without any redundancy) and then forward the newly updated NIG packet along their effective outgoing links (EOLs). The EOLs are defined by the links over which the NIG packets are not received or not eavesdropped. If there is no EOL in case that the eavesdropping for all the NIG packets received at the node does not occur, viz., deadlock, the corresponding node sets the LRF (of the NIG packet) to ‘1’ and forwards the NIG packet along its latest incoming link. It is similar to the link reversal procedure of temporally ordered routing algorithm (TORA) [6]. Once the NIG packet arrives at the source, the source node computes the best route on the basis of the collected information and then immediately starts to transmit data packets. The first NIG packet is delivered according to
a
b
Fig. 1. Pseudo-code of route establishment procedures. (a) At the source node. (b) At the destination node. (c) At intermediate nodes.
204
C.W. Ahn / Computer Communications 30 (2006) 202–206
c
Fig. 1 (continued )
the similar procedure of route reply packet (RREP) of RRP. In the route computation, there are many factors which consist of route cost. (A detailed description is given in experiments.) In the course of data packet transmission, if another NIG packet having the same sequence number arrives, then the information gathered by the packet is reflected – the source computes the best route again and replaces the old route with the new one. Fig. 1 minutely describes the above route establishment procedures as a pseudo-code. It is natural that a question on correctness of the route establishment process (of GRP) be brought up. In this regard, the following theorem clears up the question. Theorem. The route establishment process always furnishes a feasible route without fault. Proof. Assume that the number of nodes in the network is finite. It is also assumed that the network topology varies slowly so that the information collected at the source node is not stale. Although the rate of network topology change generally affects the information validity, it does not harm the validity of route establishment process itself.
DQ packet generated from the source node propagates over the network according to the conventional route query process (as in RRP). Note that validity of the query process has already been proved in a theoretical or empirical manner [4,5]. It denotes that the DQ packet surely reaches the destination node. Upon receiving the DQ packet, the destination node broadcasts an NIG packet with a view to gathering the network information. That is, a gathering process is invoked. Thus, the NIG packet traverses the entire network such a manner that each node forwards (newly updated) NIG packets towards its own EOLs. Note that the gathering process can get stuck only when any eavesdropping event corresponding to all the received NIG packets does not take place. But this case can be resolved by invoking the link reversal process (as in TORA) at the problematic node. The link reversal process has already been justified [6]. It ensures that the NIG packet traverses the entire network without undergoing any deadlock. In the gathering process, moreover, all the links are closed to the receiving or eavesdropping event because the NIG packet is invoked when any EOL exists. It indicates
C.W. Ahn / Computer Communications 30 (2006) 202–206
that the NIG packet generated by the destination node surely conveys all the network information to the source node within a finite time. Since the source node gets the network knowledge, a feasible route can always be established by exploiting any route computation algorithm. Therefore, it attests to the validity of the route establishment process of GRP. h It is noted that the source node always manages the second best route as a backup route in order to quickly cope with the link failure situation (i.e., route disconnection), thereby further promoting short transfer delay. If the source does not find any promising backup route, it sends an invoke message to the destination with a view to recollecting the (up-to-date) network information. Auxiliary procedures required for maintaining the present route and deleting the obsolete route are straightforward. Although any (route) repair mechanism can readily be incorporated with GRP, it is not required in essence. As the GRP constantly offers high quality routes by the above procedures, it achieves fast transfer delay without much compromising on overhead performance. In other words, it benefits from PRP and RRP schemes simultaneously (not just hybridize them).
RREQ packet, and GRP uses 400 bits for the NIG packet. In addition, all protocols employ a common control packet for checking and notifying the route validity at every 2 s. Each control packet amounts to 50 bits and the size is determined after taking into consideration enough length of each protocol on the basis of the given network scale for fair comparison. Data traffic is generated at 14.4k bps and routes are computed by Dijkstra’s algorithm [12]. The following cost function is employed for the route computation: cij ¼ a qij þ ð1 aÞ vij ; where cij is a cost as node i transmits data packets to node j, qij and vij are (normalized) queue length and mobile speed from node i to node j, respectively, and a is a weighting constant (in the experiments, a = 0.5). Fig. 2 shows the average (packet) transfer delay as a function of mobility. It is obvious that DSDV highly outperforms AODV. In the figure, GRP exhibits the best delay performance. This is because it can transfer data packets along the best route found after quickly gathering the net-
3. Experimental results Since GRP makes an attempt to incorporate the strengths of PRP and RRP, the reference instances are taken from DSDV [2] and AODV [4]. In this experiment, average (packet) transfer delay and control overhead are chosen as performance measures. This is because DSDV and AODV can be of great benefit for packet transfer and control overhead, respectively. An analogous idea in route establishment has been introduced in [11]. But there is an important difference in discovering network knowledge. That is, it tries to collect the network information at the side of destination. In order to reduce the overheads, it is necessary that the destination node must postpone the route computation/report for a specified time. As the time period increases, the overhead performance improves while the transfer delay grows. For shorter intervals, reverse results are obtained. It denotes that a tradeoff between delay and overhead performances is inevitable. Meanwhile, the GRP gathers network knowledge and compute feasible routes at the source node. Thus, it does not compromise on delay and overhead performances. It is obvious that the performance of GRP is superior to that of [11]. However, a comparative study between two protocols is not provided as our focus is to test how well the GRP garners the benefits of PRP and RRP. The network consists of 40 nodes moving randomly in all directions at a given average speed (over a 1000 m2). Radio transmission range is 120 m. Meanwhile, the length of control packet is fixed (for simplicity) that DSDV uses 2k bits for exchanging a ‘full dump’ (and variable bits for an ‘incremental’) message, AODV uses 200 bits for the
205
Fig. 2. Average packet transfer delay versus mobile speed.
Fig. 3. Control overhead versus mobile speed.
206
C.W. Ahn / Computer Communications 30 (2006) 202–206
work information. It is noted that the best delay performance does not necessarily mean the highest data throughput. Although the result is not illustrated, it is obvious that the throughput of PRP (i.e., DSDV) degrades faster than that of RRP (i.e., AODV) as the mobile speed increases. In addition, GRP can continuously transmit data packets (by means of the backup route) even if the best route is disconnected. With regard to DSDV, the probability that the network topology alters before updating all the routing tables increases as the mobility grows. This is the reason that the GRP is much superior to the DSDV in the case of high mobility. Fig. 3 depicts the control overheads as a function of mobile speed. Since DSDV should update routing tables of all the nodes when the network topology changes, it consumes the largest overheads. On the contrary, AODV exhibits the best overhead performance since it needs the control packet for just searching, maintaining, and repairing route(s). With regard to the overhead performance, GRP lies between DSDV and AODV. This is because it has an operating procedure that is similar to AODV (i.e., flooding) except that it incorporates a little larger NIG packet, and uses additional overheads for managing the backup route. 4. Conclusion An efficient routing protocol for mobile ad hoc networks has been proposed. It rapidly collects network information at the source node using a small amount of control overheads. Since the source node effectively manages promising routes based on the gathered information, it can speedily transfer data packets without unduly wasting control overheads. It means that the proposed protocol simultaneously gets the best of both PRP and RRP. References [1] E.M. Royer, C.K. Toh, A review of current routing protocols for ad hoc mobile wireless networks, IEEE Personal Communications (1999) 46–55.
[2] C.E. Perkins, Highly dynamic destination-sequenced distance-vector routing (DSDV) for mobile computers, Computer Communications Review (1994) 234–244. [3] S. Murth, J.J. Garcia-Luna, An efficient routing protocol for wireless networks, ACM Mobile Networks and Application Journal – Special Issue on Routing in Mobile Communication Networks (1996) 183– 197. [4] C.E. Perkins, E.M. Royer, S.R. Das, Ad hoc on-demand distance vector (AODV) routing, IETF Mobile Ad Hoc Networks Working Group, IETF RFC 3561. [5] D.B. Johnson, D.A. Maltz, Dynamic source routing in ad hoc wirless networks, in: T. Imielinski, H. Korth (Eds.), Mobile Computing, Kluwer Academic Publishers, Norwell, MA, 1996, pp. 153–181 (chapter 5). [6] V.D. Park, M.S. Corson, A highly adaptive distributed routing algorithm for mobile wireless networks, in: Proceedings of IEEE INFOCOM’97, 1997, pp. 1405–1413. [7] Y.T.M. Jiang, J. Li, Cluster based routing protocol, IETF Internet Draft, draft-ietf-manet-cbrp-spec-01.txt (1999). [Online]. Available from:
Chang Wook Ahn recevied his Ph.D. degree in the department of Information and Communication, Gwangju Institute of Science and Technology (GIST), Korea, in 2005. Currently, he is working in the Samsung Advanced Institute of Technology (SAIT). His research interests include the design and analysis of MAC protocols and QoSoriented routing for broadband radio access networks and mobile ad-hoc networks. In particular, he has focused on developing intelligent wireless networks using evolutionary computing and machine-learning techniques.
Short communication
Gathering-based routing protocol in mobile ad hoc networks Chang Wook Ahn
*
Communication Laboratory, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Republic of Korea Received 10 June 2005; received in revised form 17 July 2006; accepted 27 July 2006 Available online 22 August 2006
Abstract A gathering-based routing protocol (GRP) for mobile ad hoc networks is presented. The idea is to rapidly collect network information at a source node at an expense of a small amount of control overheads. The source node can equip promising routes on the basis of the collected information, thereby continuously transmitting data packets even if the current route is disconnected. It results in achieving fast (packet) transfer delay without unduly compromising on (control) overhead performance. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Mobile ad hoc networks; Routing protocol; Network information
1. Introduction Since all nodes in the mobile ad hoc networks can be mobile and communicate with one another either directly or through intermediate nodes with no fixed infrastructure, it is necessary to design an efficient routing protocol [1]. Proactive routing protocol (PRP) requires every node to maintain full routing information, while reactive routing protocol (RRP) typically relies on the flooding of queries to discover a destination [1]. PRP is, therefore, suitable for supporting the delay sensitive services such as voice and video [1–3]. However, it consumes a significant portion of the network capacity in order to keep the routing information current. The class of distance-vector based protocols such as destination-sequenced distance-vector routing protocol (DSDV) [2] and wireless routing protocol (WRP) [3] are representative examples of PRP. Although RRP may not be suited for real-time communication, it does not generally incur significant control overheads [1,4,5]. The query-reply handshake assisted protocols such as ad hoc on-demand distance-vector routing protocol (AODV) [4], dynamic source routing protocol (DSR) [5],
*
Tel.: +82 31 280 9654; fax: +82 31 280 9555. E-mail address: [email protected]
0140-3664/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2006.07.017
and temporally ordered routing algorithm (TORA) [6] belong to the RRP. Naturally, an approach for simultaneously taking the strengths of PRP and RRP has attracted due attention of late. This approach is widely known as hybrid routing protocol. Cluster-based routing protocol [7], zone routing protocol [8], and fisheye state routing protocol [9] are representative examples. However, the genuine objective has not been effectuated. In other words, they fall within the purview of a compromise between PRP and RRP. In this regard, this paper proposes a simple, but efficient routing protocol in the mobile ad hoc networks. This is the gathering-based routing protocol (GRP). The aim is to somehow garner the benefits accruing from the short transfer delay of PRP and the small overheads of RRP. 2. Gathering-based routing protocol A mobile ad hoc network is modeled as an undirected graph where a set of nodes and a set of (full-duplex) links are time-varying sets. We assume the use of a MAC protocol which resolves the problem of hidden/expose nodes. A representative instance is given in [10]. It is also assumed that all the nodes can enable a promiscuous receive mode. There is another assumption that every node recognizes its own neighbors (by incorporating a neighbor discovering
C.W. Ahn / Computer Communications 30 (2006) 202–206
protocol) and thus all the information associated with them are available. The goal of the proposed routing protocol (i.e., GRP) is to rapidly gather network information at a source node without spending a large amount of overheads. It offers an efficient framework that can simultaneously draw on the strengths of PRP and RRP. The procedures of GRP are described below. A source node broadcasts a destination query (DQ) packet to its neighbors. The DQ packet is continuously forwarded into each node’s neighbors until the destination is reached. It is simply implemented by the conventional flooding process of RRP (as in DSR or AODV). That is, the DQ packet plays the same role of route request (RREQ) packet of RRP so that it consists of the address of the source, the destination node’s address, and the sequence number. When the DQ packet reaches the destination, the destination node broadcasts a network information gathering (NIG) packet to its neighbors. The structure of NIG packet is similar to that of DQ packet, but it additionally contains
203
link reversal flag (LRF) for resolving deadlock and variable-length payload for recording/gathering the network information. The NIG packet propagates over the entire network by a gathering process. It is given as follows. When nodes receive the NIG packet with a new sequence number for the first time, they attach all the known information (without any redundancy) and then forward the newly updated NIG packet along their effective outgoing links (EOLs). The EOLs are defined by the links over which the NIG packets are not received or not eavesdropped. If there is no EOL in case that the eavesdropping for all the NIG packets received at the node does not occur, viz., deadlock, the corresponding node sets the LRF (of the NIG packet) to ‘1’ and forwards the NIG packet along its latest incoming link. It is similar to the link reversal procedure of temporally ordered routing algorithm (TORA) [6]. Once the NIG packet arrives at the source, the source node computes the best route on the basis of the collected information and then immediately starts to transmit data packets. The first NIG packet is delivered according to
a
b
Fig. 1. Pseudo-code of route establishment procedures. (a) At the source node. (b) At the destination node. (c) At intermediate nodes.
204
C.W. Ahn / Computer Communications 30 (2006) 202–206
c
Fig. 1 (continued )
the similar procedure of route reply packet (RREP) of RRP. In the route computation, there are many factors which consist of route cost. (A detailed description is given in experiments.) In the course of data packet transmission, if another NIG packet having the same sequence number arrives, then the information gathered by the packet is reflected – the source computes the best route again and replaces the old route with the new one. Fig. 1 minutely describes the above route establishment procedures as a pseudo-code. It is natural that a question on correctness of the route establishment process (of GRP) be brought up. In this regard, the following theorem clears up the question. Theorem. The route establishment process always furnishes a feasible route without fault. Proof. Assume that the number of nodes in the network is finite. It is also assumed that the network topology varies slowly so that the information collected at the source node is not stale. Although the rate of network topology change generally affects the information validity, it does not harm the validity of route establishment process itself.
DQ packet generated from the source node propagates over the network according to the conventional route query process (as in RRP). Note that validity of the query process has already been proved in a theoretical or empirical manner [4,5]. It denotes that the DQ packet surely reaches the destination node. Upon receiving the DQ packet, the destination node broadcasts an NIG packet with a view to gathering the network information. That is, a gathering process is invoked. Thus, the NIG packet traverses the entire network such a manner that each node forwards (newly updated) NIG packets towards its own EOLs. Note that the gathering process can get stuck only when any eavesdropping event corresponding to all the received NIG packets does not take place. But this case can be resolved by invoking the link reversal process (as in TORA) at the problematic node. The link reversal process has already been justified [6]. It ensures that the NIG packet traverses the entire network without undergoing any deadlock. In the gathering process, moreover, all the links are closed to the receiving or eavesdropping event because the NIG packet is invoked when any EOL exists. It indicates
C.W. Ahn / Computer Communications 30 (2006) 202–206
that the NIG packet generated by the destination node surely conveys all the network information to the source node within a finite time. Since the source node gets the network knowledge, a feasible route can always be established by exploiting any route computation algorithm. Therefore, it attests to the validity of the route establishment process of GRP. h It is noted that the source node always manages the second best route as a backup route in order to quickly cope with the link failure situation (i.e., route disconnection), thereby further promoting short transfer delay. If the source does not find any promising backup route, it sends an invoke message to the destination with a view to recollecting the (up-to-date) network information. Auxiliary procedures required for maintaining the present route and deleting the obsolete route are straightforward. Although any (route) repair mechanism can readily be incorporated with GRP, it is not required in essence. As the GRP constantly offers high quality routes by the above procedures, it achieves fast transfer delay without much compromising on overhead performance. In other words, it benefits from PRP and RRP schemes simultaneously (not just hybridize them).
RREQ packet, and GRP uses 400 bits for the NIG packet. In addition, all protocols employ a common control packet for checking and notifying the route validity at every 2 s. Each control packet amounts to 50 bits and the size is determined after taking into consideration enough length of each protocol on the basis of the given network scale for fair comparison. Data traffic is generated at 14.4k bps and routes are computed by Dijkstra’s algorithm [12]. The following cost function is employed for the route computation: cij ¼ a qij þ ð1 aÞ vij ; where cij is a cost as node i transmits data packets to node j, qij and vij are (normalized) queue length and mobile speed from node i to node j, respectively, and a is a weighting constant (in the experiments, a = 0.5). Fig. 2 shows the average (packet) transfer delay as a function of mobility. It is obvious that DSDV highly outperforms AODV. In the figure, GRP exhibits the best delay performance. This is because it can transfer data packets along the best route found after quickly gathering the net-
3. Experimental results Since GRP makes an attempt to incorporate the strengths of PRP and RRP, the reference instances are taken from DSDV [2] and AODV [4]. In this experiment, average (packet) transfer delay and control overhead are chosen as performance measures. This is because DSDV and AODV can be of great benefit for packet transfer and control overhead, respectively. An analogous idea in route establishment has been introduced in [11]. But there is an important difference in discovering network knowledge. That is, it tries to collect the network information at the side of destination. In order to reduce the overheads, it is necessary that the destination node must postpone the route computation/report for a specified time. As the time period increases, the overhead performance improves while the transfer delay grows. For shorter intervals, reverse results are obtained. It denotes that a tradeoff between delay and overhead performances is inevitable. Meanwhile, the GRP gathers network knowledge and compute feasible routes at the source node. Thus, it does not compromise on delay and overhead performances. It is obvious that the performance of GRP is superior to that of [11]. However, a comparative study between two protocols is not provided as our focus is to test how well the GRP garners the benefits of PRP and RRP. The network consists of 40 nodes moving randomly in all directions at a given average speed (over a 1000 m2). Radio transmission range is 120 m. Meanwhile, the length of control packet is fixed (for simplicity) that DSDV uses 2k bits for exchanging a ‘full dump’ (and variable bits for an ‘incremental’) message, AODV uses 200 bits for the
205
Fig. 2. Average packet transfer delay versus mobile speed.
Fig. 3. Control overhead versus mobile speed.
206
C.W. Ahn / Computer Communications 30 (2006) 202–206
work information. It is noted that the best delay performance does not necessarily mean the highest data throughput. Although the result is not illustrated, it is obvious that the throughput of PRP (i.e., DSDV) degrades faster than that of RRP (i.e., AODV) as the mobile speed increases. In addition, GRP can continuously transmit data packets (by means of the backup route) even if the best route is disconnected. With regard to DSDV, the probability that the network topology alters before updating all the routing tables increases as the mobility grows. This is the reason that the GRP is much superior to the DSDV in the case of high mobility. Fig. 3 depicts the control overheads as a function of mobile speed. Since DSDV should update routing tables of all the nodes when the network topology changes, it consumes the largest overheads. On the contrary, AODV exhibits the best overhead performance since it needs the control packet for just searching, maintaining, and repairing route(s). With regard to the overhead performance, GRP lies between DSDV and AODV. This is because it has an operating procedure that is similar to AODV (i.e., flooding) except that it incorporates a little larger NIG packet, and uses additional overheads for managing the backup route. 4. Conclusion An efficient routing protocol for mobile ad hoc networks has been proposed. It rapidly collects network information at the source node using a small amount of control overheads. Since the source node effectively manages promising routes based on the gathered information, it can speedily transfer data packets without unduly wasting control overheads. It means that the proposed protocol simultaneously gets the best of both PRP and RRP. References [1] E.M. Royer, C.K. Toh, A review of current routing protocols for ad hoc mobile wireless networks, IEEE Personal Communications (1999) 46–55.
[2] C.E. Perkins, Highly dynamic destination-sequenced distance-vector routing (DSDV) for mobile computers, Computer Communications Review (1994) 234–244. [3] S. Murth, J.J. Garcia-Luna, An efficient routing protocol for wireless networks, ACM Mobile Networks and Application Journal – Special Issue on Routing in Mobile Communication Networks (1996) 183– 197. [4] C.E. Perkins, E.M. Royer, S.R. Das, Ad hoc on-demand distance vector (AODV) routing, IETF Mobile Ad Hoc Networks Working Group, IETF RFC 3561. [5] D.B. Johnson, D.A. Maltz, Dynamic source routing in ad hoc wirless networks, in: T. Imielinski, H. Korth (Eds.), Mobile Computing, Kluwer Academic Publishers, Norwell, MA, 1996, pp. 153–181 (chapter 5). [6] V.D. Park, M.S. Corson, A highly adaptive distributed routing algorithm for mobile wireless networks, in: Proceedings of IEEE INFOCOM’97, 1997, pp. 1405–1413. [7] Y.T.M. Jiang, J. Li, Cluster based routing protocol, IETF Internet Draft, draft-ietf-manet-cbrp-spec-01.txt (1999). [Online]. Available from:
Chang Wook Ahn recevied his Ph.D. degree in the department of Information and Communication, Gwangju Institute of Science and Technology (GIST), Korea, in 2005. Currently, he is working in the Samsung Advanced Institute of Technology (SAIT). His research interests include the design and analysis of MAC protocols and QoSoriented routing for broadband radio access networks and mobile ad-hoc networks. In particular, he has focused on developing intelligent wireless networks using evolutionary computing and machine-learning techniques.