A Study of MANET Routing Protocols: Joint Node Density, Packet Length and Mobility - SEMINAR

 

1. INTRODUCTION

            A mobile ad hoc network (MANET) is a collection of wireless mobile nodes that are communicating with each other using multi-hop wireless links without a centralized network infrastructure. Such networks are being deployed for many diverse applications, such as military network environments in the battle fields, disaster operations, search and rescue operations, conference rooms, and also in commercial applications such as vehicle ad hoc networks used in taxi service operation .Because the nodes in a MANET are mobile, the physical network topology changes frequently and unpredictably. In MANETs, there is no stationary infrastructure such as access points (APs), therefore each node has to act as router for forwarding packets to other nodes .Various MANET routing protocols have been developed by network researchers and designers primarily to improve the MANET performance with respect to establishing correct and efficient routes between a pair of nodes for packet delivery.

 

          In Mobile Ad Hoc Network (MANET), nodes communicate with one another through shared, limited radio channel in peer to peer fashion that makes MANET to be an infrastructure-less network shown in Fig.1. Moreover each mobile node or intermediate node in the network operates as routers forwarding packet to other nodes in order to establish end-to-end communication

 

            In a flat ad-hoc routing protocol, no node or address hierarchy exists and all nodes perform equivalent routing roles within the network, operating according to the same routing protocol. This category of protocols is further subdivided into reactive and proactive routing protocols.

 

Fig.1 A Mobile Adhoc Network

 

            Proactive protocols set up routing tables at each node and keep them updated regardless of the actual communication needs of the node. In other words, a proactive protocol will maintain routes to destinations that are not currently used for packets sent by the node. Link-state based algorithms are commonly used to implement proactive protocols. In this case, routing information is exchanged via broadcast with neighboring nodes periodically or as a result of network events. The primary advantage of proactive protocols is the fast connection setup. When a node needs to transmit a packet to a given destination node, there is a high probability that a route to that node already exists in the routing table. Thus, packets do not experience the higher delay that would be caused by an expensive route discovery process. Furthermore, if changes to the topology are infrequent, a node will have a fairly accurate view of the current network topology, including the costs (e.g. latency, bandwidth) associated with the paths it chooses. Unfortunately, their proactive nature represents an unnecessary overhead in lightly loaded networks, as routing table updates are exchanged regardless of existing communication needs.

            Given the mobile nature of nodes and their limited resources, additional traffic will further drain a node’s battery. It may be difficult to define an adequate trade-off between the frequency of routing table updates, in order to maintain an accurate view of the current topology, and preservation of already scarce resources. Prominent examples of proactive protocols for MANETs include DSDV and OLSR.

 

         Reactive protocols provide another alternative for flat ad-hoc routing. A reactive protocol avoids unnecessary maintenance traffic by discovering routes on demand. In other words, when a source node wishes to send a packet to a given destination node, the underlying reactive routing protocol will initiate a process to discover the path between both nodes. Discovered routes are cached at each node and removed from the routing table after a certain period of inactivity. The obvious advantage of reactive protocols is that they limit maintenance traffic to that which is required by currently used routes. This offers a scalable solution if a node tends to communicate with the same set of nodes and node mobility is limited, allowing a route to be discovered once and maintained for a long period of time. Additionally, nodes can better leverage power saving periods in lightly loaded networks given the lack of periodic route updates. Disadvantages include the time required to setup a route before a packet can be sent which will impact the latency of the first packet in a connection. The overhead incurred by route discovery may also make reactive protocols unsuitable if a node must communicate with an ever changing set of nodes. AODV and DSR are the most representative examples of reactive protocols.

 

            Examples of popular MANET routing protocols are: Optimized Link State Routing (OLSR).  Ad-Hoc On-Demand Distance Vector (AODV), Dynamic Source Routing (DSR), and Temporally Ordered   (TORA). AODV, DSR, are reactive routing protocols, share the on-demand behaviors and find the route only when packets to be transmitted. However, the routing mechanisms for these reactive protocols are quite different.

            For example, AODV uses table-driven approach and destination sequence.DSR uses a source initiated routing, whereas AODV, DSR  in Performance of a MANET routing protocol depends on various factors, including the complex interplay of protocol mechanisms and their specific settings with node density ,mobility, packet length (i.e. traffic intensity) and the behavior of wireless nodes used. A good understanding of the joint effect of node density, packet length and mobility on the performance of a typical IEEE 802.11 ("802.11") MANET is required for an efficient design and deployment of such systems. The combined effect of node density and packet length; node density and mobility on the performance of two different MANET routing protocols is investigated.

 

We address the following research question:

            What impact do different routing protocols (AODV, DSR) have on a typical 802.11 MANET for varying node density and packet length; node density and mobility concurrently? To answer the question posed we carry out a systematic performance analysis (by simulation) for two typical MANET routing protocols, which include two on-demand routing protocols, AODV, DSR. These routing protocols were selected based on their popularity, published results, and interesting characteristics and features.

 

 

2. LITERATURE SURVEY

 

 

            "Performance improvement of dynamic source routing protocol for multimedia services in mobile ad hoc network”.

            N. Taing, S. Thipchaksurat, R. Varakulsiripunth, and H. Ishii,

 

            Routing scheme for multimedia services called Modified Dynamic Source Routing (MDSR) protocol. The MDSR selects the shortest path by using power level. It provides better delays and number of hop paths hop paths from source to destination than DSR. The idea is to select a shortest path for delay-sensitive traffic using larger power level. For delay insensitive traffic, MDSR uses smaller power level.

 

Data transmissions is separated into two groups.

1. Priority transmission of real-time data stream which is delay sensitive data such as on-demand multimedia stream, videoconference etc. When this kind of traffic is applied and in order to reduce query response time, MDSR protocol uses larger transmission power level or in other words, the number of nodes in the range of the source is increased. Therefore,
2. Source node can select one fastest node to forward route request. It is non-real time data transmission, which allows delay while transmitting. When this kind of traffic is applied smaller transmission power level is used so that energy can be saved.

 

 

            "Study of distance vector routing protocols for mobile ad hoc networks,"

            L. Yi, W. Weichao, Z. Yuhui, and B. Bhargava

 

            A MANET routing protocol called Congestion Aware Distance Vector (CADV) to improve network performance in terms of packet delivery and routing load. CADV integrates congestion avoidance strategy into a proactive routing protocol such as Destination Sequence Distance Vector (DSDV).

            Four performance metrics are measured by varying the maximum speed of mobile hosts, the number of connections, and the network size. It is observed that network congestion is the dominant reason for packet drop for both AODV,DSR protocols. A new routing protocol, congestion-aware distance vector(CADV), to address the congestion issues. CADV out performs AODV in delivery ratio by about 5%, while introduces less protocol load. The result demonstrates that integrating congestion avoidance mechanisms with proactive routing protocols is a promising way to improve performance.

 

The following quantitative metrics are used to assess the performance:

• Packet Delivery Ratio: The ratio of the data delivered to the destinations (i.e., throughput) to the data sent out by the sources.
• Average End-to-end Delay: The average time it takes for a packet to reach the destination. It includes all possible delays in the source and each intermediate host, caused by routing discovery, queuing at the interface queue, transmission at the MAC layer, etc. Only successfully delivered packets are counted.
• Normalized Protocol Load: The routing load per unit data successfully delivered to the destination. The routing load is measured as the number of protocol messages transmitted hop-wise (i.e., the transmission on each hop is counted once). A unit data can be a byte or a packet.

 

            "HAODV: a New Routing Protocol to Support Interoperability in Heterogeneous MANET,"

            H. Safa, H. Artail, M. Karam, H. Ollaic, and R. Abdallah,

            Current AODV routing protocol becomes inefficient when used in a network formed of heterogeneous devices. Indeed AODV in its nature search the paths between homogeneous devices and ignore the ones between heterogeneous devices. A Routing protocol called Heterogeneous AODV (HAODV), optimizes existing AODV to support routing in heterogeneous networks (e.g. Wi-Fi and Bluetooth nodes). HAODV determines an optimum route not only based on path with the lowest hop-count but also with the low traffic and high stability.

            HAODV uses a method called Convert to delegate the conversion procedure to the interoperability model.

 

          "DOA:DSR over AODV routing for mobile ad hoc networks,"

          R. Bai and M. Singhal

 

            A lightweight hierarchical routing model, Way Point Routing (WPR), in which a number of intermediate nodes on a route are selected as waypoints and the route is divided into segments by the waypoints. Waypoints, including the source and the destination, run a high-level intersegment routing protocol, while the nodes on each segment run a low-level intra segment routing protocol. One distinct advantage of this model is that when a node on the route moves out or fails, instead of discarding the whole original route and discovering a new route from the source to the destination, only the two waypoint nodes of the broken segment have to find a new segment. This model is lightweight because it maintains a hierarchy only for nodes on active routes. Instantiation of WPR, is to use DSR as the intersegment routing protocol and AODV as the intra-segment routing protocol. This instantiation is termed DSR over AODV (DOA) routing protocol. Thus, DSR and AODV two well-known on-demand routing protocols for MANETs are combined into one hierarchical routing protocol and become two special cases of this protocol. The two novel techniques for DOA: one is an efficient loop detection method and the other is a multitarget route discovery.

 

            A Routing protocol called DOA (DSR over AODV), focusing on route maintenance. DOA implements two levels of route repair: intra-segment and inter segment .If a route fails, an intra-segment fixes it by using alternative routes within one segment

 

           

            "A review of current routing protocols for ad hoc mobile wireless networks,"

            E. M. Royer and C. K. Toh,

 

In MANET the  routing protocols may generally be categorized as:

1. Table-driven
2. Source-initiated (demand-driven)

 

Table-Driven Routing Protocols

            Table-driven routing protocols attempt to maintain consistent, up-to-date routing information from each node to every other node in the network. These protocols require each node to maintain one or more tables to store routing information, and they respond to changes in network topology by propagating updates throughout the network in order to maintain a consistent network view. The areas in which they differ are the number of necessary routing-related tables and the methods by which changes in network structure are broadcast. The following sections discuss some of the existing table-driven ad hoc routing protocols.

 

1.      Destination-Sequenced Distance-Vector Routing

2.      Cluster head Gateway Switch Routing

 

Source-Initiated On-Demand Routing

            A different approach from table-driven routing is source-initiated on-demand routing. This type of routing creates routes only when desired by the source node. When a node requires a route to a destination, it initiates a route discovery process within the network. This process is completed once a route is found or all possible route permutations have been examined. Once a route has been established, it is maintained by a route maintenance procedure until either the destination becomes inaccessible along every path from the source or until the route is no longer desired.

1.      Ad Hoc On-Demand Distance Vector Routing

2.      Dynamic Source Routing

 

            The table-driven ad hoc routing approach is similar to the connectionless approach of forwarding packets, with no regard to when and how frequently such routes are desired. It relies on an underlying routing table update mechanism that involves the constant propagation of routing information. This is not the case, however, for on-demand routing protocols. When a node using an on-demand protocol desires a route to a new destination, it will have to wait until such a route can be discovered. On the other hand, because routing information is constantly propagated and maintained in table-driven routing protocols, a route to every other node in the ad hoc network is always available, regardless of whether or not it is needed. This feature, although useful for datagram traffic, incurs substantial signaling traffic and power consumption. Since both bandwidth and battery power are scarce resources in mobile computers, this becomes a serious limitation.

 

 

3. PROBLEM STATEMENT

 

 

            The combined effect of node density, packet length and mobility is to be examined on   AODV and DSR for performance of a typical 802.11 MANET. combined node density and mobility has a significant effect on network throughput and packet delays for two routing protocols studied. Experimentation is done by simulation and through obtained results can give the effect of node density and mobility on network throughput and packet delays. And how packet length effects the network throughput and packet delay.

 

            Which protocol is suitable for different network scenarios can be known by simulation .Simulation is performed on two popularly used MANET routing protocols AODV (Adhoc on demand distance vector routing), DSR (Dynamic source routing).

 

4. PROPOSED METHODOLOGIES

                                                                                                                               

            Previous research on MANET routing protocols have focused on simulation study by varying network parameters, such as network size (node density), pause times ,hop count  independently still problem arises in measuring the effective performance of MANET routing protocols.

 

            Simulation model is used to analyze the performance of AODV, DSR. In this simulation considers

1. A small network with N <=10 nodes
2. A medium sized network with 10 >N<=50 nodes and
3. A denser network with 50> N <=100 nodes

 

The four performance metrics:

1.      End-to-end packet delay,

2.      Throughput,

3.      Routing load and

4.      Retransmission

were used for performance study of AODV and DSR.

 

            The end-to-end packet delay is defined as the average time (measured in seconds) required in sending a packet from source to a destination. This includes buffering during route discovery, queuing at the interface queue, retransmission at the medium access control (MAC), propagation and packet transmission time.

 

            The throughput (measured in bps) is the average rate of successful packet delivery.

 

            The routing load is the number of routing control packets transmitted for each data packet delivered at the destination.

 

            The retransmission is defined as the resending attempts of packets which have been lost or damaged due to link failure.

5. CONCLUSION

             The combined effect of node density, packet length and mobility for two routing protocols (AODV, DSR) on an 802.11 MANET. The performance of AODV and  DSR, for small, medium and large (dense) network scenarios with varying packet length and node mobility. Node density and mobility has a significant impact on underlying routing protocols. To provide an optimum MANET routing solution, we will currently implement an efficient MANET routing protocol.

 

 REFERENCES

 

[1]          N. Taing, S. Thipchaksurat, R. Varakulsiripunth, and H. Ishii, "Performance improvement of dynamic source routing protocol for multimedia services in mobile ad hoc network," presented at the 1st  International Symposium on Wireless Pervasive Computing, 2006, pp. 1- 5.

[2]        E. M. Royer and C. K. Toh, "A review of current routing protocols for ad hoc mobile wireless       networks," IEEE Personal Communications, vol. 6,no. 2, pp. 46- 55, 1999.

[3]        L. Yi, W. Weichao, Z. Yuhui, and B. Bhargava, "Study of distance vector routing protocols for mobile ad hoc networks," presented at the First IEEE International Conference on Pervasive Computing and Communications (PerCom 2003), March 23-26, 2003, pp. 187-194.

[4]        H. Safa, H. Artail, M. Karam, H. Ollaic, and R. Abdallah, "HAODV: a New Routing Protocol to Support Interoperability in Heterogeneous MANET," presented at the IEEE/ACS International Conference on Computer Systems and Applications (AICCSA ' 07), May 13-16 2007, pp. 893-9 00.

[5]        R. Bai and M. Singhal, "DOA:DSR over AODV routing for mobile ad hoc networks," IEEE Transactions on Mobile Computing, vol. 5, no. 10, pp. 14 03-1416, 2006.

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[9]        R. Bai and M. Singhal, "DOA: DSR over AODV routing for mobile ad hoc networks," IEEE  Transactions on Mobile Computing, no. 14 03- 1416,2006.

[10]      S. R. Das, C. E. Perkins, and E. M. Royer, "Performance comparison of  two on-demand routing protocols for ad hoc networks," presented at the Nineteenth Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM ' 00), Tel Aviv, Israel, March 2000, pp. 3-12

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