Node-Disjoint Alternative Dual-Path Routing for Data ... - CiteSeerX

2008 Ninth International Conference on Parallel and Distributed Computing, Applications and Technologies

Node-disjoint Alternative Dual-path Routing for Data Salvation in Mobile Ad hoc Networks Chu-Hsing Lin1, Fuu-Cheng Jiang2, Jen-Chieh Chang3 Department of Computer Science and Information Engineering, Tunghai University, Taichung, Taiwan {1chlin, 2admor}@thu.edu.tw , [email protected] Frode Eika Sandnes4 Faculty of Engineering, Oslo University College P.O. Box 4, St. Olavs Plass, N-0130 Oslo, Norway 4 [email protected]

characterized by high mobility, low power, limited storage, and limited transmission range. Mobile nodes communicate through bi-directional radio links and data transmission is a key challenge. MANET communication events are called sessions. The two communicating parties, namely the source node and the destination node comprise a session pair (or sourcedestination pair). A mobile can communicate directly with other nodes if such a link exists within the radio transmission range. If the distance between a session pair is too large to establish direct contact, then the data must be sent via intermediate nodes connecting the two parties. At least one valid routing path must be established before the source node of a session pair can send data to its destination node. MANET routing protocols can be roughly categorized into three categories [1], namely table-driven routing, source-initiated ondemand routing, and hybrid routing. Well known source-initiated on demand routing protocols include AODV [2] and DSR [3]. These protocols are based on the strategy of only find valid routes once they are needed by the source node. This procedure is known as route discovery. Route discovery involves the route request phase (RREQ) and the route reply phase (RREP). These protocols all construct a single-path route between a source node and a destination node. Backup routing protocols [4-7] are usually designed to provide data salvation capabilities for the previously mentioned protocols, and they are classified as a special type of single-path routing protocols. A multipath routing protocol usually establishes several valid paths for a session pair during a successful protocol run. A backup routing protocol mainly establishes one valid primary path together with several other

Abstract This study elaborates the influence patterns of different backup strategies on AODV-based routing protocols. Although some backup routing strategies yield good data delivery rates, they suffer from low efficiency. To make the process of data salvation more efficiently in case of link failure, we explore the possibility of combining the AODV-BR strategy and on-demand node-disjoint multi-path routing protocols. This article proposes an improved approach named NDAMR (Node-Disjoint Alternative Multiple Path), a routing protocol that maintains the only two shortest backup paths in the source and destination nodes. The NDAMR can alleviate the redundancy-frames overhead during the process of data salvation by the neighboring intermediate nodes. Our simulation results have demonstrated that NDAMR delivers good data delivery performance while restricting the impacts of transmission collision and contention. Keywords: Multi-path routing, node-disjoint multi-path, alternative path, data salvation, transmission collision and contention, mobile ad-hoc network, simulation.

1. Introduction A mobile ad hoc network (MANET) is a wireless network model without the need of central base stations. MANETs can be applied in medical emergencies, during natural catastrophes, for military applications and to conduct geographic exploration. Mobile and wireless devices belonging to a MANET are usually called mobile nodes. These nodes are

978-0-7695-3443-5/08 $25.00 © 2008 IEEE DOI 10.1109/PDCAT.2008.50

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alternative paths during a successful protocol run. After the backup structure (or alternative paths) of the primary path is established, it can be used for data salvation when a mobile node on the primary path encounters a link failure. Backup routing protocols may need to face the problem of transmission collision and contention, which is caused by the additional traffic incurred by the backup strategy. Figure 1 depicts several well-known AODV-based backup routing protocols. This study addresses AODV-based backup routing protocols, in particular AODV-BR [4]. The performance characteristics of backup routing protocols are analyzed and a novel backup routing strategy based on the concept of extra node-disjoint multi-paths [14-18] is proposed to overcome the shortcomings of existing protocols. The proposed routing strategy is coined the term: Node-Disjoint and Alternative Multi-path Routing (NDAMR). Furthermore, a series of simulation experiments to demonstrate the reliability and efficiency of NDAMR. The results also show that NDAMR can improve the data delivery performance and reduce the frequency of transmission collision and contention.

2.1 AODV-BR (AODV-Backup Routing) AODV-BR [4] establishes one primary path together with alternative paths during its route reply phase. Intermediate nodes overhear radio broadcasted RREP packets and set up alternative paths in their routing tables. Once a mobile node of the primary path encounters a link failure, it adopts a one hop data broadcast of data packets that need to be saved. The one hop data broadcast operation changes the headers of the data packets such that it contains the routing information of the node suffering from link failure, the disconnected hop, and the destination. Neighboring nodes overhear the one hop data broadcast and adopt the pre-defined backup strategy to salvage the data packets. Figure 2 illustrates the AODV-BR backup structure and data salvation strategy.

Primary path

Alternate path

Fig. 2.(a) AODV-BR backup structure.

Fig. 1. The backup structure of (a) AODV-BR, (b) 2HBR, and (c) AODV-MM.

2. Background In this section, the relevant AODV-backup routing protocols are addressed. The technical background regarding the backup structure and the data salvation scenario are in detail explored before proposing our approach. And the critical defect embedded in the AODV-backup routing protocols , due to the spread of salvaged data packets , is also described in the following paragraphs.

Data salvation Fig. 2.(b) AODV-BR data salvation.

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enhances the rate of data delivery and prevents the spread of salvaged data packets which again lead to an increase in transmission collisions and contention. AODV-BR 1 will hereafter be referred to simply as AODV-BR for simplicity. One obvious drawback of the AODV-BR fixed next hop policy is that there is only one alternative path, i.e., the disconnected next hop. Although this policy prevents the spread of salvaged data packets, it results in resources being consumed by neighboring nodes. To resolve these problems and improve performance additional node-disjoint paths are employed.

AODV-BR can be further categorized into AODVBR 1 based on a fixed next hop policy, and AODV-BR 2 based on an any next hop policy. The backup structure and the characteristic of the one hop data broadcast of AODV-BR 1 and 2 are identical. The only difference is the choice of alternative paths, which are used to salvage data packets broadcasted by nodes neighboring the node with link failure. AODV-BR 1 salvages broadcasted data packets if there is an alternative path to the destination node and the next hop of its alternative path is exactly same node as the one pointed to by the broken link. Neighboring nodes in AODV-BR 2 salvages broadcasted data packets as long as there is an alternative path to the destination node, and the next hop can be any node.

3.2 The Proposed Routing Protocol The route discovery is performed through the route request phase and the route reply phase. Data salvation is initiated when a mobile node encounters a link failure. The route request mechanism described in [9] is adopted for creating multiple node-disjoint paths, i.e., several paths which have no intermediate nodes in common. However, only one additional node-disjoint primary path is created in addition to the first primary path for the session pair. This strategy was chosen as the route independence property of node-disjoint multipath allows data transmissions on different paths of the session pair without affecting each other. Moreover, this route discovery mechanism has been shown to have small routing costs and transmission delays. Next, the two node-disjoint multiple paths of a session pair are established by the destination node at the same routing protocol run and are therefore both guaranteed suitable for data transmission. Finally, load balancing can easily be incorporated into the scheme such that larger part of the network can be utilized under heavy traffic conditions. NDAMR is illustrated in Figure 3.

2.2 Backup routing transmission collision and contention One problem to consider when designing backup routing protocols is that of transmission collision and network contention in case of link failure [4]. Backup routing is based on first creating a backup structure, that later can be used to salvage data packets that passes through nodes with link failures. Since the alternative path usually is longer than the primary path, it typically takes longer for the message to reach its destination. Moreover, if the data packets fail to arrive at their destination then resources such as, bandwidth, routing costs, and power of the mobile nodes are unnecessarily wasted. Furthermore, if a mobile node broadcasts data packets to be salvaged to its neighbors, and there are a large number of neighboring nodes then there may be a dramatic increase in wireless traffic due to the assistance provided by these neighboring nodes. If many nodes help forwarding the data packets, then there will be many copies of the same data packets spread across the network. This situation is termed as spread of salvaged data packets. Unwise selection of next hop nodes will magnify the problem. For example, any next hop policy spreads data packets in such a manner that the problem of transmission collision and network contention is increased.

3. The Proposed Routing Protocol 3.1 AODV-BR 1 vs. AODV-BR 2 The backup routing protocol proposed herein is derived from AODV-BR. AODV-BR creates only one hop alternative paths to form its backup structure in the route reply phase, and it doesn’t use extra routing packets during the route reply or data salvation phase. AODV-BR 1 is based on a fixed next hop policy which

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Route request phase 1. Adopt the route request mechanism described herein and accumulate route information. 2. A source node without a valid path to the destination node originates a RREQ packet, appends its own address in the route record before broadcasting it. 3. Algorithm 1 is applied by intermediate node that receives the RREQ packet. Algorithm 1: Recording the shortest hop count. 1 2 3 4 5 6 7 8 9 10 11 12

if (duplicated RREQ packet) and (the path is longer) then drop it; else if (the shortest path to the source) then Shortest_Hop:= RREQ_Hop_Count; Previous_Hop_to_Source:= RREQ_Previous_Hop; Route_Record.append(My_Address); RREQ_Hop_Count += 1; re-broadcast the RREQ packet; else drop it; endif Definitions: RREQ_Hop_Count : the RREQ packet hop count. RREQ_Previous_Hop : the previous hop that sent the RREQ packet. Shortest_Hop : the shortest hop count of the same RREQ packet. Previous_Hop_to_Source : next hop of the reverse path. Route_Record : RREQ packet accumulated address list.

3.2.2 Route Reply Rhase The destination node receives several identical RREQ packets with different accumulated paths. These paths are then assessed. Only the two shortest paths that are node-disjoint are stored in the route tables of the source and destination nodes. The steps regarding the route reply phase are listed as follows:

Fig. 3. NDAMR route discovery and maintenance phases.

3.2.1 Route Request Phase

Route request phase

NDAMR establishes two node-disjoint primary paths for a session pair. Node-disjoint paths are route independent which means that they do not have any common intermediate nodes and they will therefore not affect each other during data transmission. The steps regarding the route request phase are listed as follows:

1. The first RREQ packet received by the destination node is recorded in the route table before a RREP packet is returned to the source node.

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WaveLAN is used as the radio model. WaveLAN supports a nominal bit rate of 2 Mb/s and a radio range of 250 m. The simulations are based on constant bit rate (CBR) traffic sources and 64 packet send buffers. The data packet payload is 512 bytes. Packets are dropped if they remain in the send buffer for more than 30 seconds. All packets sent by the routing layer are queued in the interface queue which has a maximum capacity of 50 packets. Routing packets have higher priority than data packets. A total of 50 mobile nodes were placed into a square area of 1000 X 1000 m2. Each simulation was run for 180 seconds. Each data point on the simulation curves in the figures represents an mean of five protocol runs with identical traffic/mobility scenarios. Identical mobility or traffic scenarios are used across the protocols discussed herein. During the simulations the following performance measures were used [10-16]. The packet delivery rate defines the ratio of data packets successfully delivered to the destination nodes to those generated by the CBR sources.

2. Duplicate RREQ packets are compared with the one stored in the route table. Only the one that is both shortest and node-disjoint is kept. Next, a RREP packet is returned to the source node. 3. Algorithm 1 is applied by intermediate node that receives the RREQ packet.

3.2.3 Data Salvation Once a mobile node on the primary path faces a link failure a one-hop data broadcast is transmitted to its neighbors that then use the following Algorithm 2. The neighbors have at least two choices, namely to use the second primary path or the alternative paths. Algorithm 2: NDAMR data salvation backup strategy (action performed by neighboring nodes) 1 2 3 4 5 6 7 8 9 10 11 12 13 14

if (active alternative path to destination) then if (condition 1) and (condition 2) then DataPkt_Next_Hop:=Alternative_Next_Hop; forward data packets; break; endif else if (active primary path to destination) then if (condition 1) then DataPkt_Next_Hop : = Primary_Next_Hop; forward data packets; break; endif else drop it; endif Definitions: DataPkt : the broadcasted data packet sent by the node with a link failure. DataPkt_Next_Hop : the next hop of the broadcasted data packet. Alternative_Next_Hop : next hop along the alternative path. Primary_Next_Hop : next hop along the primary path. Conditions: 1. My active path’s next hop is not the hop that needs help. 2. My alternative path’s next hop is exactly the disconnected hop.

Packet delivery rate =

received data packets sent data packets

(1)

The mean end-to-end delay of data packets includes all possible delays caused by buffering during route discovery latency, queuing at the interface queue, retransmission delays at the MAC, data salvation latency, and propagation and transfer times. It is defined as

Average delay =

total latency received data packets

(2)

The normalized routing load defines the number of routing packets transmitted per data packet delivered at the destination node. Each hop-wise transmission of a routing packet is counted as one transmission. It is given by.

4. Simulation Environment

Normalized routing load =

routing packets received data packets

This study employs NS-2 [8] software tools for network simulations, Distributed Coordination Function (DCF) of IEEE 802.11 for wireless LANs is used as the MAC layer protocol, and Lucent’s

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(3)

5. Performance Evaluation Simulation 1 varies the maximum speed of mobile nodes to simulate different degree of network mobility. Simulation 2 varies the transmission rate of traffic sources to simulate different traffic loads. Figures 4 and 5 show the packet delivery rate for simulation 1 and 2, respectively. According to Figure 4, the data delivery rate of NDAMR is higher than that of both AODV and AODV-BR. NDAMR therefore has better data delivery efficiency than the other strategies, even under high mobility conditions. Figure 5 shows that NDAMR has a higher data delivery rate than AODV-BR. This improvement is mainly due to the improved node selection policy of NDAMR. Figures 6 and 7 depict the mean delays for simulation 1 and 2, respectively. NDAMR has a consistently shorter mean delay than AODV-BR. Figures 8 and 9 demonstrate the normalized routing load of the two simulations, respectively. Here, NDAMR has a lower routing load compared to the other strategies. This observation reveals that NDAMR efficiently reduces the amount of transmission collisions and contention. The mean delay of NDAMR is smaller because salvaged data packets have less chance of passing through an alternative path which is too far off the path to their destination. Routing costs are reduced due to the efficient AODV-BR one-hop radio broadcast and by avoiding interference through multiple node-disjoint paths. NDAMR can improve the data delivery rate without the need for more routing packets or larger routing tables. Unnecessary transmission collisions and network contention are effectively avoided.

Fig. 5. Packet delivery rate (Simulation 2)

Fig. 6. Mean delay time (Simulation 1)

Fig. 4. Packet delivery rate (Simulation 1)

Fig. 7. Mean delay time (Simulation 2)

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7. Acknowledgements This work was supported in part by Taiwan Information Security Center (TWISC), National Science Council under the grants NSC 95-2218-E-001001, NSC95-2218-E-011-015, and NSC95-2221-E029020 -MY3.

8. References [1] E. M. Royer, C. K. Toh, A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks, IEEE Personal Communications Magazine, Vol. 6, No. 2, April 1999, pp. 46-55.

Fig. 8. Normalized routing load (Simulation 1)

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Fig. 9. Normalized routing load (Simulation 2)

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6. Conclusions This study addresses the characteristics of AODVbased routing protocols, and how different backup strategies affect network performance. In particular, the study addresses how to design a backup strategy and node choice policy to prevent transmission collisions and contention. Although AODV-BR delivers an acceptable data delivery rate, its backup policy limits the choices during data salvation. In order to improve the data delivery ratio without increasing the spread of salvaged data packets, which leads to transmission collisions and network contention, nodedisjoint multi-path are employed. Simulation experiments confirm that NDAMR improves the data delivery rate and limits the amount of transmission collisions and network contention.

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