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    Mobile adhoc Mobile adhoc Document Transcript

    • A Paper Presentation on ROUTING PROTOCOLS IN MOBILE AD HOC NETWORKS (MANETS) Prepared For SAMYAK’09 K L E F UNIVERSITY Vijaywada. Presented by, M.Pavan K.Hari Prasad gettopavan@gmail.com hari1219@gmail.com IVth IT IVth IT Ph.No:9490017034 Ph.No:9492757194 MALINENI LAKSHMAIAH ENGINEERING COLLEGE (Affiliated to JNTU, Kakinada and Approved by AICTE) (Accredited by NBA) Singarayakonda, PRAKASAM Dt. - 523101
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs Abstract: A mobile ad hoc network (MANET) is a wireless network that uses multi-hop peer-to-peer routing instead of static network infrastructure to provide network connectivity. Ad-Hoc networks are mobile wireless networks that have no fixed infrastructure. There are no fixed routers- instead each node acts as router and forwards traffic from other nodes. MANET is a type of ad-hoc network with rapidly changing topology. Since the nodes in a MANET are highly mobile, the topology changes frequently and the nodes are dynamically connected in an arbitrary manner. In order To facilitate communication with the network, a routing protocol is used to discover the routes between nodes. Efficient routing of packet is a primary MANET challenge. Today, there exist various routing protocols for this environment. Mobile Ad Hoc Networks (MANETs) consist of nodes that change position frequently. To accommodate the changing topology special routing algorithms are needed. For relatively small networks flat routing protocols may be sufficient. However, in larger networks either hierarchical or geographic routing protocols are needed. There is no single protocol that fits all networks perfectly. The protocols have to be chosen according to network characteristics, such as density, size and the mobility of the nodes. MANETs have applications in rapidly deployed and dynamic military and civilian systems. The network topology in a MANET usually changes with time. Therefore, there are new challenges for routing protocols in MANETs since traditional routing protocols may not be suitable for MANETs. For example, some assumptions used by these protocols are not valid in MANETs or some protocols cannot efficiently handle topology changes. Current research on routing protocols for Mobile Ad-hoc Network (MANET) has converged to several dominating routing protocols, including Optimized Link State Routing (OLSR), Ad-hoc On-demand Distance Vector (AODV) and Dynamic Source Routing (DSR). At the same time, classic routing protocols such as Open Shortest Path First (OSPF) and Destination Sequenced Distance Vector (DSDV) are improved for the MANET context. Research efforts also focus on issues such as Quality of Service (QoS), energy efficiency, and security, which already exist in the wired networks and are worsened in MANET. This paper gives brief description on what are Mobile Ad Hoc NETworks, what are their uses, routing protocols in MANETs, and various types of protocols that are available for the MANETS. Finally after a brief description of the protocols there is a comparison simulation that describes which protocol is suited under which circumstances. 2
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs Introduction: The Internet Engineering Task Force has defined a Mobile Ad hoc Network (MANET) as: “An autonomous system of mobile routers (and associated hosts) connected by wireless links--the union of which form an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet”. Simply put, a MANET is a wireless mobile network that is self-forming, self maintained, and self-healing. Nodes stay connected even as the network topology changes. The Mobile Ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. In order to make that work, typically each node needs to act as a router to relay packets to nodes out of direct communication range. Under these circumstances, routing is much more complex than in conventional (static) networks. Many of the possible solutions are determined by the characteristics of the media, the behavior of nodes and the data flow. Since research in Ad Hoc Networking has resulted in such a large amount of routing algorithms and protocols, it has become more and more difficult to decide, which algorithms are superior to others under what conditions. For a successful deployment, this is an important problem, since a wrong choice may have a severe impact on the performance, and consequently on the acceptance of the new technology. Also, providing just any protocol is not feasible, due to the different requirements on hardware and lower network layers. What are Mobile Ad-Hoc Networks? Mobile Ad-Hoc Networks (MANETs) are collections of mobile nodes, dynamically forming a temporary network without preexisting network infrastructure or centralized administration. • Mobile nodes can be arbitrarely located and are free to move randomly at any given time. • No dedicated routers, each node in a MANET network acts as a router and is responsible for discovering and maintaining routes to other nodes. • The primary goal of the MANET routing protocol is correct and efficient route establishment to facilitate communication within the network between arbitrary nodes. Where MANETs are used? • For military and rescue use. • Information distribution for meetings, seminars etc. • Internet / intranet hot spots in public transportation. • Localized advertising and shopping. • New mobile devices are invented constantly and used various ways. Characteristics of MANET 3
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs networks: • Dynamic topology: Nodes are free to move arbitrarely within the network (or leave and join the network) causing random topology changes which can happen rapidly at unpredictable times. • Variable capacity links: Significantly lower link capacities compared to traditional hardwired links. • Energy-constrained mobile nodes: Nodes usually operate on batteries a all operations must be optimized for energy conservation. • Weakened physical security: More prone to physical threats than hardwired networks. Why traditional routing protocols are not suitable for MANETs? • MANETs are usually highly dynamic and heterogeneous mobile networks. • No pre-existing infrastructure. • No centralized administration. • Dynamic topologies. • Variable capacity links. • Energy-constrained nodes. • Limited physical security. MANET Protocols: Some of the better known MANET protocols are AODV, TORA, DSR, TBRPF and OLSR. Each protocol has evolved over time to better suit the particular requirements of various types of mobile ad hoc networks. These protocols are classified broadly into two categories. 1) Proactive 2) Reactive. These two protocols suffer from some problems under some situations. So there are new types of protocols developed which combine the features of both the proactive and reactive types ]Reactive vs. proactive ad-hoc routing protocols: Proactive Protocols: Periodic topology updates a node always possesses the latest routing information. Proactive MANET protocols update routing information in a proactive manner by exchanging route information at periodic intervals. The exchange of table- based route information is evenly distributed across the wireless network. As a result, routes are established prior to being needed, providing a wireless network that is low in latency, at the expense of increased overhead. The well known proactive routing protocols are TBRPF, DSDV. Reactive protocols: Rather than distribute all route information across the entire network, On- demand MANET protocols perform route maintenance only when required. On- demand protocols create fewer networks overhead since the exchange of routing information is localized rather than evenly distributed. The result is a network with less overhead, at the expense of increased latency due to the route discovery process The well-known reactive protocols are AODV, DSR. DSR AODV TBRPF DSDV 4 Ad-Hoc Routing Protocols ProactiveReactive
    • A Routing Protocols in Mobile Ad Hoc Networks – MANETs Now let us know about each of these MANET protocols. Reactive Routing Protocol-DSR: The acronym for DSR is Dynamic Source Routing.  The DSR is a simple and efficient on-demand source routing protocol designed for multihop wireless ad- hoc networks.  Two major phases: route discovery and route maintenance.  Route discovery = used to discover new source routes across multiple network hops to arbitrary destinations in an ad-hoc network.  Route maintenance = responsible for detecting network topology changes and keeping up-to-date information of already discovered source routes.  Route discovery and route maintenance rely on source route caches and they can contain several routes to the same destination node.  Designed to work up to 200 nodes.  Supports both unidirectional and bidirectional links. Route Discovery: Route Req. “A” “A, B” “A, B, C” id=2 id=2 id=2 Initiator Target Route Reply “A, B, C” id=2  If source route to the target node is not found from the cache node A initiates route discovery.  Route-Request packet contains: - Information about initiator (A) - The target of Route-Request (E) - Unique request identifier (2) - List of node addresses through which the particular Route- reqest has been forwarded.  It is highly possible that some nodes receive the same Route- Request packet more than once duplicate packets are discarded.  When returning Route-Reply, node E must take into account that some links in source route might be unidirectional (MAC).  If node E doesn’t have a route to node A, it must it turn send a Route-Request to the node A. In that case, Route-Reply packet is piggybacked in a Route-Request packet to avoid infinite recursion. Route Maintainance:  Each node is responsible for confirming that the next hop in a source route receives the packet.  The packet is retransmitted up to some maximum number of times until the confirmation is received from the next hop.  Route-Error packet contains information which link has failed so the initiator can remove that source route from its cache.  When a node receives a Route- Request, it first searches its route cache for the target node. If route is found, the node can send a Route- Reply to the initiator. 5 B C D
    • A A Routing Protocols in Mobile Ad Hoc Networks – MANETs Preventing Route-Reply storms:  Cache lookups allow nodes to quickly reply to Route-Requests but can result Route-Reply storms.  To avoid storms, the DSR uses a random delay before a node can send a Route-Reply.  d = H * (h – 1 + r) - H, small const. Delay - h, number of hops is source route - r, 0 or 1 Longest source routes are send last. HOP Limits:  A Route-Request packet contains a hop limit which can be used to limit the number of intermediate nodes participating in the route discovery.  The hop limit can be used to implement an expanding ring type of route discovery technique. Packet salvaging: Initiator Target  When a route error is detected and the Route-Error packet has been sent, a node may attempt to salvage data packet instead of discarding it.  If the node which sent the Route- Error packet finds a new route to the target node from its route cache, it can replace the original source route with the new one.  After replacing the original source route, the data packet is marked as salvaged to prevent the packet being salvaged multiple times which might result routing loop. Automatic Route Shortening:  Source routes in use may be automatically shortened if one or more intermediate nodes are no longer needed.  The node which notices that there are redundant intermediate nodes in path, sends a Route-Reply to the initiator which contains shortened route to the target node. Use of Route-Error Messages:  When an initiator node receives a Route-Error packet, it piggybacks this error message to the next Route-Request and broadcasts it to the local network.  In this way, the route caches of adjacent nodes will be cleaned up from invalid routes. Multicast routing:  DSR does not support true multicasting but provides some means to simulate it.  When a DSR node wants to send a multicast data packet, it piggybacks it inside a Route- Request packet which target address is set to some specified multicast address.  The Route-Request packet is then broadcasted normally within the specified hop count.  Different hop count values allow nodes to use controlled ring like flooding. Reactive Protocol-AODV : The Ad hoc On-Demand Distance Vector (AODV) is an embedded MANET protocol that works dynamically to 6 B C D B C D
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs establish and maintain routes, adapting quickly to changing link conditions. The Ad hoc On-Demand Distance Vector (AODV) algorithm enables dynamic, self- starting, multihop routing between participating mobile nodes wishing to establish and maintain an ad hoc network. AODV allows mobile nodes to obtain routes quickly for new destinations, and does not require nodes to maintain routes to destinations that are not in active communication. AODV allows mobile nodes to respond to link breakages and changes in network topology in a timely manner. The operation of AODV is loop- free, and by avoiding the Bellman-Ford "counting to infinity" problem offers quick convergence when the ad hoc network topology changes (typically, when a node moves in the network). When links break, AODV causes the affected set of nodes to be notified so that they are able to invalidate the routes using the lost link. One distinguishing feature of AODV is its use of a destination sequence number for each route entry. The destination sequence number is created by the destination to be included along with any route information it sends to requesting nodes.Using destination sequence numbers ensures loop freedom and is simple to program. Given the choice between two routes to a destination, a requesting node is required to select the one with the greatest sequence number. Messages for route discovery: Route Requests (RREQs), Route Replies (RREPs), and Route Errors (RERRs) are the message types defined by AODV. These message types are received via UDP, and normal IP header processing applies. The messages are not blindly forwarded. However, AODV operation does require certain messages (e.g., RREQ) to be disseminated widely, perhaps throughout the ad hoc network. The range of dissemination of such RREQs is indicated by the TTL in the IP header. Fragmentation is typically not required. Route Creation: When a source node does not have a route for a required destination, AODV initiates a route request/route reply cycle by broadcasting a route request (RREQ) packet across the wireless network. Upon receiving the RREQ, nodes must determine whether or not they are the destination node. If a node is not the destination and does not have a route to the destination, it will rebroadcast the RREQ to its neighbors and update its route table to include a reverse pointer to the source node. This process will continue until a route to the destination node is found, or the If a node is the destination node, or has a route to the destination node, it will respond by sending a route reply (RREP) to the source node. Intermediate nodes update their route information about the source and destination nodes. Upon receiving the RREP, the source node can forward data to the destination node using the newly created route. If the RREP is not received within a certain time frame, the source node will retry the RREQ. route request process times out. Route Deletion: A route will remain active as long as data continues to travel across the route. If a route becomes inactive for a period of time, the route will be deleted. A userdefined timeout value determines the time period for which a route must be inactive in order to be deleted from the route table. Each time a packet is sent across a route, the timer is reset. Any time a link breakage occurs, a route error 7
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs (RERR) is propagated to mark the unusable route as invalid. Upon detecting a broken link, a node will send a RERR to any neighbors that had been using the node as the next hop for the route. After receiving the RERR, each node deletes the invalid route from its route table. If a route to the destination is still required, the source node will reinitiate the route discovery process. ERR packets are not sent if the route timeout expires, as all intermediate routers will have timed out as well. Sequence Numbers: AODV uses sequence numbers to avoid routing loops and to measure the “freshness” of route information. Prior to broadcasting RREQ, RREP, and RERR packets, AODV must increment its sequence number. Each route maintains a sequence number, with higher sequence numbers indicating “fresher” routes. When multiple routes are available to a destination node, the route with the greatest sequence number is used. Packets with lower sequence numbers are ignored and dropped. Stationary Wireless Infrastructure: While many mobile ad hoc networks do not rely on any stationary infrastructure, many applications require the use of towers/repeaters to extend the range of the wireless network. While using stationary infrastructure provides a more cellular like wireless network, this type of infrastructure can create issues that MANET protocols do not typically take into account. The network uses towers to extend the range of wireless network. The towers have strong signals between them. All application data from the mobile vehicles is sent to the wired network connected at tower. At some point, the signal to Tower A has become too weak for application data to successfully traverse the network. The signal between the vehicle and Tower A is barely strong enough for the AODV control messages to reach Tower A. If enough control messages are received between the vehicle and the tower, Tower A may remain listed as a viable route to the network to which it is connected. The vehicle now has a strong link to Tower B, which in turn has a strong link to Tower A. Tower A will remain listed as a viable gateway to the network as long as the vehicle receives the minimum amount of control messages required to keep a route in the route table. Once the vehicle gets completely out of range from Tower A, Tower B will become the intermediate node. This issue is commonly known as “Gray Zone.” To combat the Gray Zone issue it accounts for control packet signal strength information when making routing decisions. Embedded within each control packet is a signal strength measurement. The control packet contains a user-defined signal strength threshold. If the control packet signal strength from Tower A falls below the user-defined threshold, the vehicle’s direct route to Tower A will be dropped, forcing the vehicle data to find a new route. As a result, the vehicle would route data to Tower A by using Tower B as an intermediate node. Even though this creates an extra hop for the route, the route is more efficient since the signal remains strong. Proactive Routing Protocol-DSDV The acronym for DSDV is Distance Vector Destination Sequenced Routing. This routing protocol was developed at the IBM, in 1996. The protocol is a distance vector protocol, which uses the modified Bellman-Ford algorithm. This is a 8
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs Proactive Routing protocol, where the route is always available. However, the protocol has some limitations as well. It maintains routing info among all the nodes, it uses periodic update messages, there is a route settling time and routes may not converge. The DSDV protocol operates in the following way: Mobile nodes maintain routes to all possible destinations and exchange routing information between each other. Hop counts are used as routing metrics, and in order to ensure that the routing information is up to date, sequence numbers are used. A given node keeps track of its own time and the sequence of events that happen. Thus, the node assigns sequence numbers to distance vector updates, which updates contain information about the neighbors. Proactive Routing Protocol- TBRPF: Topology Dissemination Based on Reverse-Path Forwarding (TBRPF) is a proactive, link-state routing protocol designed for mobile ad-hoc networks (MANETs), which provides hop-by-hop routing along shortest paths to each destination. Each node running TBRPF computes a source tree (providing shortest paths to all reachable nodes) based on partial topology information stored in its topology table, using a modification of Dijkstra's algorithm. To minimize overhead, each node reports only part of its source tree to neighbors. TBRPF uses a combination of periodic and differential updates to keep all neighbors informed of the reported part of its source tree. Each node also has the option to report addition topology information (up to the full topology), to provide improved robustness in highly mobile networks TBRPF performs neighbor discovery using "differential" HELLO messages which report only changes in the status of neighbors. This results in HELLO messages that are much smaller than those of other link-state routing protocols such as OSPF. TBRPF consists of two main modules: the neighbor discovery module, and the routing module which performs topology discovery and route computation. Neighbor Discovery: The TBRPF Neighbor Discovery (TND) protocol allows each node i to quickly detect the neighbor nodes j such that a bidirectional link (I,J) exists between an interface I of node i and an interface J of node j. The protocol also quickly detects when a bidirectional link breaks or becomes unidirectional. TND is designed to be fully modular and independent of the routing module. TND performs ONLY neighbor sensing, i.e., it determines which nodes are (1-hop) neighbors. As a result, TND can be used by other routing protocols, and TBRPF can use another neighbor discovery protocol in place of TND, e.g., one provided by the link layer. Nodes with multiple interfaces run TND separately on each interface, similar to OSPF. Thus, a neighbor table is maintained for each local interface, and a HELLO sent on a particular interface contains only information regarding neighbors heard on that interface. Advantages of modular neighbor sensing: • If a network performs neighbor sensing in the link/mac layer, then TBRPF can be used without HELLOs, thus eliminating redundancy. 9
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs • TBRPF neighbor sensing can be used with other routing protocols, and conversely, other neighbor sensing protocols can be used with TBRPF. • In OLSR, since HELLOs (which report neighbor interface addresses) are used to discover 2- hop neighbors, MPRs cover all 2- hop interfaces, which is redundant. • In TBRPF, 2-hop neighbors are discovered using Topology Updates (not HELLOs), so parent selection is based only on Router IDs thus avoiding this redundancy. Routing Module: Each node running TBRPF maintains a source tree, denoted T, which provides shortest paths to all reachable nodes. Each node computes and updates its source tree based on partial topology information stored in its topology table, using a modification of Dijkstra's algorithm. To minimize overhead, each node reports only part of its source tree to neighbors. The main idea behind the current version of TBRPF came from PTSP, another protocol in which each node reports only part of its source tree. The part of T that a node reports to neighbors is called the "reported subtree" and is denoted RT. Each node reports RT to neighbors in periodic topology updates (e.g., every 5 seconds), and reports changes (additions and deletions) to RT in more frequent differential updates (e.g., every 1 second). Periodic updates inform new neighbors of RT, and ensure that each neighbor eventually learns RT even if it does not receive all updates. Differential updates ensure the fast propagation of each topology update to all nodes that are affected by the update. A received topology update is not forwarded, but may result in a change to RT, which will be reported in the next differential or periodic update. Comparison Simulations: Features of protocols: AODV DSR TBRPF Loop-freedom Yes Yes No Multiple routes No Yes Possible Unidirectional link support Possible Yes No Multicast Possible No No Periodic Broadcast Possible No Yes Maximum No. of nodes <100 200 <200 Expiration of routing info. Yes No Yes Category Reactive Reactive Proactive Metrics used in the studies: _ Packet delivery ratio: Ratio between the amount of incoming and actually received application data packets _ Routing overhead: Total number of routing control packets transmitted during the simulation _ Control byte overhead: Total number of routing control bytes used in the control packets _ Path optimality: Difference between the actually taken and the best possible path for a packet to reach its destination Summarizing the results: Low mobility, low traffic AODV DSR TBRPF Packet delivery ratio High High High End to end delay Middle Middle Middle Routing Low Low Middle 10
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs overhead Path optimality Middle Middle Very good High mobility, High traffic AODV DSR TBRPF Packet delivery ratio Middle Middle High End to end delay Middle Middle Middle Routing overhead Very High Middle Middle Path optimality Middle Low Good _ The routing overhead for the two on- demand protocols heavily depends on node mobility _ In general, AODV sends many small routing control packets, while DSR sends less, but bigger control packets (this also depends on the used data packet size) _ Some of the authors consider DSR more useful in smaller networks with less mobility and the usage of AODV more appropriate in ad-hoc networks with a higher mobility and data transfer rate. _ TBRPF has a constant routing overhead (proactive) _ All protocols do quite well concerning delivery ratio Problems of the particular protocols: _ AODV uses more, but smaller routing control packets  critical concerning wireless medium properties (e.g. interference). This becomes worse for a higher load, as neighbors have to be rediscovered (congestion causes link failures). _ DSR has some problems concerning the cache usage: The advantage of multiple routes becomes a disadvantage with high mobility (lack of good criteria for choosing one particular of the possible routes). In bigger networks, the source- routing principle can also become a problem. _ TBRPF is a proactive protocol. Therefore it may not be suitable for networks with low mobility (e.g. stationary battery powered sensor networks). The lack of loop-freedom causes packet loss, waste of bandwidth and causes other problems. Conclusion: To improve efficiency, it is essential to model the performance of existing protocols. In order to do so, we have compared the performance of Proactive (TBRPF) and Reactive (ADOV and DSR) routing protocols for mobile ad hoc networks in terms of Throughput and End to End Delay. It was observed from simulation that DSDV gives maximum throughput in small sized networks, DSR for Medium sized networks and ADOV for large networks. Although hardware integration and wireless communication devices have improved in the last few years, .the. Ad- hoc routing protocol has not yet been found. - The recent activities of the MANET working group show that there are still fundamental questions to answer. . Scalability? . Energy efficiency? . Security? . Combination of physical, data-link and network layer? - MANET hopes that experiences made with third-party experimental implementations helps solving them. - Additionally, more fundamental research is done by the IRTF. References: Websites: -- http://www.ietf.org/rfc/rfc3561.txt 11
    • Routing Protocols in Mobile Ad Hoc Networks – MANETs -- http://www.isi.edu/ -- http://www.cs.technion.ac.il/ Books: -- Bertsekas, D. and R. Gallager, "Data Networks, Prentice-Hall", 1987 . 12