ShriRam College of Engineering & Management 1 A Review of Reactive, Proactive & Hybrid Routing Protocols for Mobile Ad Hoc Network M.Ramaiya Rohit Gupta Rachit Jain Head,Dept. Computer Science Dept. Computer Science Engineering, Dept. Electronics & Comm. Engineering, SRCEM,Gwalior SRCEM, Gwalior ITM Universe, Gwalior m.ramaiya@gmail.com rohitgupta09@in.com rachit2709@gmail.com Abstract-One of the most vibrant and active new fields today is that of ad hoc networks. Significant research in this area has been ongoing for nearly 35 years, also under the names packet radio or multi-hop networks. Mobile ad hoc network (MANET) is an autonomous system of mobile nodes connected by wireless links. Each node operates not only as an end system, but also as a router to forward packets. The nodes are free to move about and organize themselves into a network. These nodes change position frequently. Ad hoc networking allows portable devices to establish communication independent of a central infrastructure. However, the fact that there is no central Infrastructure and that the devices can move randomly gives rise to various kind of problems, such as routing and security. This paper discuss three routing protocols Destination Sequenced Distance vector (DSDV), Dynamic Source Routing (DSR) protocols and Ad hoc On Demand Distance Vector (AODV) which are used for efficient routing under different scenarios in Mobile Ad-hoc Network (MANET), which plays a critical role in places where wired network are neither available nor economical to deploy. Keywords- MANET, DSDV, AODV, DSR I. INTRODUCTION A mobile ad-hoc network (MANET) is a network composed of mobile nodes mainly characterized by the absence of any centralized coordination or fixed infrastructure, which makes any node in the network act as a potential router. MANETs are also characterized by a dynamic, random and rapidly changing topology. This makes the classical routing algorithms fail to perform correctly, since they are not robust enough to accommodate such a changing environment. Consequently, more and more research is being conducted to find optimal routing algorithms that would be able to accommodate for such networks [1]. II. MOBILE AD HOC NETWORK A. The Protocol Stack In this section the protocol stack for mobile ad hoc networks is described. This gives a comprehensive picture of, and helps to better understand, mobile ad hoc networks. Figure 1, shows the protocol stack, which consists of five layers: physical layer, data link layer, network layer, transport layer and application layer. It has similarities to the TCP/IP protocol suite. As can be seen the OSI layers for session, presentation and application are merged into one section, the application layer. On the left of Figure1, the OSI model is shown. It is a layered framework for the design of network systems that allows for communication across all types of computer systems. In the middle of the figure, the TCP/IP suite is illustrated. Because it was designed before the OSI model, the layers in the TCP/IP suite do not correspond exactly to the OSI layers. The lower four layers are the same but the fifth layer in the TCP/IP suite (the application layer) is equivalent to the combined session, presentation and application layers of the OSI model. On the right, the MANET protocol stack, which is similar to the TCP/IP suite, is shown. The main difference between these two protocols stacks lies in the network layer. Mobile nodes (which are both hosts and routers) use an ad hoc routing protocol to route packets. In the physical and data link layer, mobile nodes run protocols that have been designed for wireless channels. The network layer is divided into two parts: Network and Ad Hoc Routing. The protocol used in the network
ShriRam College of Engineering & Management 2 part is Internet Protocol (IP) and the protocols, which can be used in the ad hoc routing part, are Destination Sequenced Distance Vector (DSDV), or Dynamic Source Routing (DSR), Ad-Hoc on Demand Distance vector routing (AODV). Figure 1: The OSI Model, TCP/IP Suite, MANET Protocol Stack B. Proactive Algorithm All the proactive approach algorithms are based on traditional distance vector and link state protocols developed for use in wireless approach. The primary characteristic of proactive approach is that each node in the maintenance of network is to maintain a route to every other node in the network all the times regardless of whether or not these routes are needed [1]. In order to maintain correct route information, a node must periodically send control messages. Updates to route table are triggered or by certain events which caused in manipulation of other nodes (neighboring) route table. Link addition and removal can trigger an event-triggered updation of routing table. In proactive approach the main advantage is that the rout to each node is instantly found because the table contains all the nodal address. Source only need to check the routing table and transfer a packet. The major disadvantage of proactive approach is that each node is prone to rapid movement. So the overhead of maintaining a rout table is very high, and amount of routing state maintained at each node scales as order of o [n] where n is the number of nodes in the network. It becomes inefficient for a large network. C. Reactive Algorithm Reactive routing technique is also known as on-demand routing. It takes a different approach of routing, which overcomes the disadvantages of proactive routing. In reactive approaches those nodes, which require connectivity to the Internet reactively, find Internet gateways by means of broadcasting some kind of solicitation within the entire ad hoc network. This approach reduces the overhead of maintaining the route table as that of proactive. The node dynamically checks the route table, and if it does not find an entry for its destination or it finds an outdated entry it performs route discovery to find the path to its destination [1]. The signaling overhead is reduced in this method, particularly in networks with low to moderate traffic loads. However it has a drawback of route acquisition latency. That is when corresponding entry is not found the route discovery mechanism occurs which takes a very large amount of time, and for that time the packet waits for updation of the table. III. PROTOCOLS DESCRIPTION Destination-Sequenced Distance-Vector Routing (DSDV) is a table-driven routing scheme for ad hoc mobile networks based on the Bellman-Ford algorithm. The main contribution of the algorithm was to solve the Routing Loop problem. Each entry in the routing table contains a sequence number, the sequence numbers are generally even if a link is present; else, and an odd number is used. The number is generated by the destination, and the emitter needs to send out the next update with this number. Routing information is distributed between nodes by sending full dumps infrequently and smaller incremental updates more frequently. DSDV was one of the early algorithms available. It is quite suitable for creating ad hoc networks with small number of nodes. Since no formal specification of this algorithm is present there is no commercial implementation of this algorithm. Many improved forms of this algorithm have been suggested. DSDV requires a regular update of its routing tables, which uses up battery power and a small amount of bandwidth even when the network is idle [2]. Whenever the topology of the network changes, a new sequence number is necessary before the network re-
ShriRam College of Engineering & Management 3 converges; thus, DSDV is not suitable for highly dynamic networks. (As in all distancevector protocols, this does not perturb traffic in regions of the network that are not concerned by the topology change.) The list which is maintained is called routing table. The routing table contains the following: (1) All available destinations IP address (2) Next hop IP address (3) Number of hops to reach the destination (4) Sequence number assigned by the destination node (5) Install time table-driven routing framework and destination sequence numbers. DSR does not rely on any timer-based activities, while AODV does to a certain extent. Ad hoc On Demand Distance Vector AODV [3] shares DSR s on-demand characteristics in that it also discovers routes on an as needed basis via a similar route discovery process. However, AODV adopts a very different mechanism to maintain routing information. It uses traditional routing tables, one entry per destination. This is in contrast to DSR, which can maintain multiple route cache entries for each destination. Without source routing, AODV relies on routing table entries to propagate an RREP back to the source and, subsequently, to route data packets to the destination. AODV uses sequence numbers maintained at each destination to determine freshness of routing information and to prevent routing loops. All routing packets carry these sequence numbers. An important feature of AODV is the maintenance of timer-based states in each node, regarding utilization of individual routing table entries. A routing table entry is expired if not used recently. A set of predecessor nodes is maintained for each routing table entry, indicating the set of neighboring nodes which use that entry to route data packets. These nodes are notified with RERR packets when the next-hop link breaks. Each predecessor node, in turn, forwards the RERR to its own set of predecessors, thus effectively erasing all routes using the broken link. In contrast to DSR, RERR design of ondemand protocols is the reduction of the routing load. High routing load usually has a significant performance impact in low-bandwidth wireless links. While DSR and AODV share the ondemand behavior in that they initiate routing activities only in the presence of data packets in need of a route, many of their routing mechanics are very different. In particular, DSR uses source routing, whereas AODV uses a Figure 2: Route Request (RREQ) flooding Figure 3: Route Reply (RREP) propagation Dynamic Source Routing The key distinguishing feature of Dynamic Source Routing is the use of source routing. That is, the sender knows the complete hop-byhop route to the destination. These routes are stored in a route cache. The data packets carry the source route in the packet header. When a node in the ad hoc network attempts to send a data packet to a destination for which it does not already know the route, it uses a route discovery process to dynamically determine such a route. Route discovery works by flooding the network with route request (RREQ) packets. Each node receiving an RREQ rebroadcasts it, unless it is the destination or it has a route to the destination in its route cache. Such a node replies to the RREQ with a route reply (RREP) packet that is routed back to the original source. RREQ and RREP packets are also source routed. The RREQ builds up the path traversed across the network. The RREP routes itself back to the source by traversing this path backward. The route carried back by the RREP packet is cached at the source for future use. If any link
ShriRam College of Engineering & Management 4 on a source route is broken, the source node is notified using a route error (RERR) packet. The source removes any route using this link from its cache. A new route discovery process must be initiated by the source if this route is still needed [4]. Dynamic Source Routing (DSR) is a routing protocol for wireless mesh networks. It is similar to AODV in that it forms a route on-demand when a transmitting computer requests one. However, it uses source routing instead of relying on the routing table at each intermediate device. Many successive refinements have been made to DSR, including DSRFLOW. Determining source routes requires accumulating the address of each device between the source and destination during route discovery. Nodes processing the route discovery packets cache the accumulated path information. The learned paths are used to route packets. To accomplish source routing, the routed packets contain the address of each device the packet will traverse. This may result in high overhead for long paths or large addresses, like IPv6 [5]. To avoid using source routing, DSR optionally defines a flow id option that allows packets to be forwarded on a hop-by-hop basis. This protocol is truly based on source routing whereby all the routing information is maintained (continually updated) at mobile nodes. It has only two major phases, which are Route Discovery and Route Maintenance. Route Reply would only be generated if the message has reached the intended destination node (route record which is initially contained in Route Request would be inserted into the Route Reply). To return the Route Reply, the destination node must have a route to the source node. If the route were in the Destination Node's route cache, the route would be used. Otherwise, the node will reverse the route based on the route record in the Route Reply message header (symmetric links). In the event of fatal transmission, the Route Maintenance Phase is initiated whereby the Route Error packets are generated at a node. The erroneous hop will be removed from the node's route cache; all routes containing the hop are truncated at that point. Again, the Route Discovery Phase is initiated to determine the most viable route [5]. Zone Routing Protocol, ZRP, is a routing protocol that is designed for mobile ad hoc networks [6]. It is a hybrid protocol that is part proactive and part reactive. The proactive part, uses a modified distance vector scheme within the routing zone of each node. The routing zone is determined by a zone radius, which is the minimum number of hops it should take to get to any node. Thus, each node has a routing zone, which is composed of nodes within its local area. This proactive component is called Intrazone Routing Protocol (IARP). The reactive component is called Interzone Routing Protocol (IERP), and uses queries to get routes when a node is to send a packet to a node outside of its routing zone. ZRP uses a method called bordercasting in which a node asks all nodes on the border of its routing zone to look for the node outside of its routing zone. Intrazone Routing Protocol (IARP) The Intrazone Routing Protocol (IARP) proactively maintains routes to destinations within a local neighborhood, which is referred to as a routing zone. More precisely, a node s routing zone is defined as a collection of nodes whose minimum distance in hops from the node in question is no greater than a parameter referred to as the zone radius. Note that each node maintains its own routing zone. An important consequence is that the routing zones of neighboring nodes overlap. Interzone Routing Protocol (IERP) The operation of the reactive Interzone Routing Protocol (IERP) is quite similar to standard route discovery process of reactive routing protocols. An IERP route discovery is initiated when no route is locally available to the destination of an outgoing data packet. The source generates a route query message, which is uniquely identified by a combination of the source node s address and request number. The query is then relayed to a subset of neighbors as determined by the bordercast algorithm. Upon receipt of a route query message, a node checks if the destination lies in its zone or if a valid route to it is available in its route cache. If the destination is found, a route reply is sent back to the source. If not, the node bordercasts the query again. Hybrid Routing Protocol IV. CONCLUSION In this paper we have studied the hybrid, proactive and reactive routing approach for
ShriRam College of Engineering & Management 5 Mobile Ad Hoc network. We have also studied routing protocols that are Dynamic Source Routing (DSR), Ad hoc On Demand Distance Vector (AODV) and Destination-Sequenced Distance-Vector Routing (DSDV) Zone Routing Protocol (ZRP) of Mobile Ad-Hoc Networks. RERERENCES [1] C.E. Perkins and P. Bhagwat, Highly dynamic destination-sequenced distance vector routing (DSDV) for mobile computers, in Proc. ACM SIGCOMM 94, London, UK, Oct. 1994, pp.234-244. [2] Azizol Abdullah, Ahmad Faisal Amri Abidin, Nor Surayati Mohammad Usop, IJCSNS International Journal of Computer Science and Network Security, VOL.9 No.7, July 2009. [3] Charles E. Perkins, Elizabeth M. Royer, IEEE Personal Communications, February 2001. [4] D. Johnson, D. Maltz, and J. Broch. DSR: The Dynamic Source Routing Protocol for Multihop Wireless Ad Hoc Networks. In Ad Hoc Networking, C. Perkins (ed), Chapter 5, pages 139 172, 2001. [5] C. E. Perkins, E. M. Royer, and S. R. Das, Ad Hoc on Demand Distance Vector (AODV) Routing, http://www.ietf.org/internet- drafts/draftietfmanet-aodv-06.txt, IETF Internet Draft, July 2000. [6] Haas Z.J.; Pearlman M.R.; Samar P. The Zone Routing Protocol (ZRP) for Ad Hoc Networks, IETF Internet Draft, July 2002.Work in progress.