Analysis of Routing Protocol Performance on Multi-Hop Wireless Ad Hoc Networks

Multi-Hop Wireless Ad-Hoc Networks are characterized by dynamic and frequently changing topologies, bandwidth constrained variable capacity ~ links and energy-constrained operation. Nodes in such a network are usually laptops or hand held personal digital assistants (PDA), which have limited resources like battery power, CPU power, storage capacity, and transmission range. Internet Protocol (IP) based routing protocols are not suitable for these types of networks as they rely either on periodic updates or require stable topologiesfor efficient routing. The objectivefor this paper is to evaluate proposed routing protocols for MH-WANET based on peiformance. This evaluation should be done theoretically and through simulation. The goal of this paper is to present useful insight in proposed routing protocols for Multi-Hop Wireless Ad-Hoc Networks through the means of theoretical and simulation based study. The simulation environment is based on a Network Simulator 2 from Berkeley with wireless extensi0!l provided by Monarch group at Carnegie Mellon University (CMU). Terms: QoS, Multi-Hop Wireless Networks, Routing l.Introduction: Wireless communication between mobile users is becoming more popular than ever before. This is due to recent technological advances in laptop computers and wireless data communication device, such as wireless modems and wireless LANs. This has lead to lower prices and higher data rates. There are three distinct approaches for enabling wireless communication between two hosts. The first approach is to let the existing cellular network infrastructure carry data as well as voice. The second approach is to form a Simple Wireless Ad-Hoc Network (SWANET), which allows a mobile node related to its fixed station Angkul Kongmunvattana Department of Computer Science University of Nevada, Reno, NV 89577 to roam in its neighborhood even if it is outside of its host station [7]. The third approach is to allow communication among all users wanting to communicate with each other utilizing more than one hop (Multi-Hop). These networks are known as Multi-Hop Wireless Ad-Hoc Networks (MH-WANET). MH-WANET has several advantages compared to traditional cellular systems and SWANET, which includes on demand setup, fault tolerance and unconstrained connectivity. MH-WANET does not rely on any pre-established infrastructures and can therefore be deployed in places with no infrastructure [2]. Nodes act as a host as well as router; therefore a routing protocol is necessary to make the routing decisions. Currently a standard routing protocol for MH-WANET does not exist; however; establishments of the same protocol are in progress. Many problems remain to be solved before any standards can be determined. This paper looks at some of these problems and tries to evaluate some of the currently proposed protocols. Many routing protocols have been proposed, but few comparisons between different protocols have been made. Of the work that has been done in this field, only the work done by monarch project at Carnegie Mellon University (CMU) has compared some of the different proposed routing protocols and evaluated them based on some quantitative metrics [2]. Other simulation results do exist [3] that have been done on individual protocols. However, these simulations have not used the same metrics and therefore are not comparable with each other. Our simulations have confirmed that Dynamic Source Routing protocol (DSR) [4] and Ad-Hoc Distance ~-,r=i '01Internatwnal Conference 1885 ,eclor (AODV) [5] protocol for MH-WANET ~orms better on less mobile conditions and : SR outperforms AODV on less source .:;.:--=sity. AODV protocol demonstrated a stable -..jng overhead; network routing load and rate _ hich link breakages are reported at high ~~ and high source density. It; however, :-. e a better packet delivery ratio in sharp -~ra.stto DSR whose performance was 30% r ~'tanAODV. ':~Iulti-Hop Wireless Ad-Hoc 'tt\vorks: A new kind of wireless network :oroposedby Internet Engineering Task Force a"" which is known as "Multi-Hop Wireless _-Hoc Networks" (MH-WANET). In MH..,;Tf each node is capable of dynamically _~ -,'italinformation with respect to changing .:..Uons,and variable topology on energy and . .:.:.~ldth constrained links. Each node has a ~ ess interface of limited range and they ~icate with each other over radio or ~ media. Nodes in the MH-WANET are mobile, but can also consist of stationary such as access points to the Internet. In '":9Ulationswe have used Lucent Wave ~el, which gives a range o,f 250 m to -::Dbilenode. A Multi-Hop Wireless Ad:\etwork (MH-WANET) uses no __~ administration. This is to ensure that -~ork won't collapse when one of the :=~es moves out of transmitter range of -as. Nodes should be able to enter/leave ~rk at any time. Since the range of the :=3I1smitteris limited, multiple hops may -_0:)00 to reach other nodes. Every node ~~ng in an MH-WANET must be able to .:~ packets for other nodes. Hence each _ ... _ as a host and as a router. A router is an !:ich, among other functions runs a .~ f!"otocol. MH-WANET is also capable _-~.::'g topologychanges and malfunctions '.:6. It is fixed through network .f"_-;!tion.For instance, if a node leaves .::!k and causes link breakages, affected ~ easily request new routes and the . ":','ill be solved. This will slightly _, ~ delay but the networkwill still be u.-_ -~ The radioenvironmentas an access media has special properties that must be considered when designing protocols for MHWANET. Multi-Hop in a radio environment may result in an overall transmit capacity gain and power gain due to the squared relation between' coverage and required output power. By using Multi-Hops, nodes can transmit the packets with a much lower output power. However, usage of Multi-Hop Wireless Ad-Hoc Networks also introduces problems unique to itself. For example the nodes are always energy constrained and links are bandwidth constrained where the messaging is usually performed using broadcast messages, hence there is emphasis on to find ways to limit the exchange of information between nodes. 3.Routing Protocols for Ad Hoc mobile networks: Since routing requires multiple hops through the network, a routing protocol is needed. A routing protocol is a service protocol that is'used (by routers, but not by hosts) to maintain routing tables. The link state and distance vector protocols are avoided in Multi-Hop Wireless Ad-Hoc Networks, due to frequently changing topologies and requirement to make dynamic routing decisions. Another characteristic of conventional protocol is that they assume bi-directional links; in the wireless radio environment this is not always true. Routing algorithms in a MH-WANET can be classified as either proactive or reactive. Proactive protocols attempt to continuously evaluate the routes within the network so that when a packet needs to be forwarded, the route is already known and can be immediately used. Proactive schemes have the advantage that when a route is needed, the delay before actual packets can be sent is very small. On the other hand proactive schemes needs time to converge to a steady state. This can cause problems if the topology is changing frequently. Since the conventional routing protocols do not meet the demands for Multi-Hop Wireless Networks, new protocols like table driven protocols or on demand driven protocols have been proposed. Table driven routing protocols attempt to maintain consistent, up-to-date routing information from each node to every other node 1886 PDPTA '01 International Conference in the network whereas Source initiated ondemand routing protocol takes a different approach by creating a route only when desired by the source node. An ideal routing protocol has distributed operation, loop free, demand based operation, multiple routes, unidirectional link support, security, power Conservation and QoS support. Dynamic Source Routing protocol: The Dynamic source routing [4] is a source initiated on-demand routing protocol based on the concept of source routing. DSR uses no periodic routing messages, thereby reducing network bandwidth overhead, conserving battery power and avoiding large routing updates throughout the MH-WANET. Instead, DSR relies on support from the Media Access Layer (MAC), which should inform the routing protocol about link failures. The basic advantages of DSR protocol are that nodes do not require maintaining routing information, and routes are often predetermined even before transmission takes place. Secondly, DSR is on demand in nature, so there is minimal routing overhead over the mobile nodes and it also works in symmetric as well as in asymmetric conditions. However, each packet carries a slight overhead containing the source route of the packet. Th,is overhead grows when the packet has to go through more hops to reach the destination. So the packets sent will be slightly bigger because of the overhead. The DSR protocol is composed of two mechanisms that work together to allow the discovery and maintenance of source routes in the Multi-Hop Wireless Ad-Hoc Network. In particular, unlike other protocols, DSR requires no periodic packets of any kind at any level within the network. Ad hoc on Demand Distance Vector (AODV) Routing protocol: AODV [5] is actually an on-demand version of DSDV protocol, which is a table-dri ven routing protocol. The main difference between the DSDV and the AODV routing protocol is that the routing table in ,AODV protocol is required to be updated only when desired by the source node. In AODV protocol, when a source node wants to send information to the destination node, it first cheeks the routing to see the availability to the route destination. If the route is not available in its routing table, or the previous valid route has expired then it initiates a route discovery process. The AODV protocol uses hello messages that are broadcasted periodically to the intermediate neighbors. The DSR protocol has the advantage of supporting both symmetric and asymmetric links, where as AODV protocol only support symmetric links. 4. Simulation Setup: We have used network simulator 2(ns-2) [I], which is a discrete event simulator, targeted at networking research. It provides substantial support for simulation of TCP, routing, and multicast protocols. The current version of the network simulator does not support wireless networks. The network simulator alone is only intended for stationary networks with wired links. The monarch group at CMU has developed a model to simulate multi-hop wireless network, complete with physical, data link and MAC layer models on ns-2. Lucent Wave LAN is used as a radio propagation model in the simulator. Wave LAN is a shared media radio with a nominal bit-rate of 2Mb/see and a nominal radio range of 250 meters. ,Traffic and mobility models: The traffic source is CBR (continuous bit-rate). The sourcedestination pairs are usually spread randomly over the network. The size of data packet is 512 bytes. The packets are sent at the rate of 4 packets per second. The mobility uses random way point model [2], which states that, a group of nodes, which pause for a specific duration of time during their motion. We use the configurations used by many other researchers i.e. 1500m x 300m field with 50 Nodes. In this field a node begins its journey from a random source to a random destination with a randomly chosen speed (uniformly distributed between 020m/sec). The pause time is varied which also affects the relative speeds of the mobiles. Simulations are done for 900 sec. Each data point represents an average of two runs with identical traffic models, but different randomly "~! '01 International Conference 1887 ;merated mobility scenarios. For maintaining TJ1esswe use identical mobility and traffic .:enarios for DSR and AODV Protocols. A 1'ical simulation with ns and the mobility .:.:nsion consists a scenario file, which .xscribes the movement pattern of the nodes, _-.1 a communication file that describes the ffic in the network. Ietries: Four key performance metrics: -~ket delivery ratio, routing overhead. error =~l-ets transmitted and normalized routing =-f'. These metrics are evaluated to examine AIlOUS aspects of the routing protocols. Packet .ery ratio is the ratio of the data packets ..c ered to the destination to those generated by ~ Constant Bit Rate (CBR) sources. Routing rlzeadis the total number of routing packets :..::.smittedduring the simulation where each =smission of the packet (each hop) counts as -~ mmsmission. Error packets transmitted is t: wtal number of error packets transmitted ~g a simulation. During a simulation, each -..enlink is reported by a single transmission error packet. Normalized routing load ~res the total number of routing packets _-.:>nUttedfor each data packet deliyered at the _"'1ation. Simulation Results: As noted in _,;),'14.1, simulations were performed using ~ different node speeds: a maximum speed ~ _ of 20m/s, 30m/s and 40m/s respectively. a comparison was conducted for the "'Colwith 10 sources and max set speeds of r..30m/s and 40m/s. These speed values are ""1:'.~, maximum speed limits set in the ~ion scenario files. The speed by which _~ move is generated randomly by the ~ which is usually falls in the range of 0 :s: max speed limit set by the user during ::..rio generation. For all the simulations, the -:mication pattern is peer-to-peer, with . ~.lI1having either 10 or 20 sources sending .,;".:,...ets per second. In my simulations I not ~d pause time as a base to calculate the =:: of my performance metrics but also ;ued the performance metrics with base as changing speed of mobile node. The maximum speed limit of the mobile nodes is changed from 20m/s to 40m/s. The performance of the DSR and AODV protocols can also be measured on the basis of each individual pause time. We would like to clearly state that we used the performance metrics and parameters similar to that of the Johnson's [2] paper at Mobicom'98 to verify accuracy of our simulations. I have taken in consideration some new parameters to explore new aspects of routing protocols performance. Routing Overhead Details: Figures 6,8 and 9 show the performance of DSR and AODV protocols respectively, over multi hop wireless ad hoc networks. The performance metric in consideration is "routing overhead" occurred during the simulation. "Routing Overhead' is the total number of routing packets transmitted during the simulation. [2]. Each curve represents the routing overhead with various sources and variable speeds. The results clearly show that for lower speeds, DSR protocol performs better than AODV by a factor of 6. However as the speed is increased the DSR continues to out perform AODV by at factor of 10 at 40m/s speed. Figure 9 shows the routing overhead for DSR protocol with various sources as a function of speed in Multi-Hop Wireless Ad-Hoc Networks (MHWANET). The results show that for DSR protocol with 20 sources and a pause time of 0 (constant mobility), the routing overhead increases by 900% when the speed of mobile node is doubled to 40m/s. In similar situation the Routing Overhead in AODV protocol increases by only 200%. However, the Routing Overhead by AODV protocol is at least two times to that of DSR protocol. But it does manage to highlight that change in Routing Overhead in AODV protocol is at least 50% less drastic as DSR protocol. Hence overall, DSR protocol has less routing overhead compared to AODV protocol. The routing overhead in DSR protocol could be kept low if a higher pause time is chosen for the mobile nodes, when movement at high speed becomes necessary 1888 PDPTA '01 International Conferena