comparison between aodv and olsr protocol

Comparison Between AODVand OLSR

Prepared By

Md. Al-Amin-Al-Mehedi Sr.System Engineer

Contact: [email protected] +8801718161615

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Content What is AODV ?

Advantage Disadvantage

What is OLSR ? Advantage Disadvantage

Comparison Performance and scalability Resource usage Security consideration

Conclusion

What is AODV ?

Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol for mobile ad hoc networks (MANETs) and other wireless ad-hoc networks . AODV is capable of both unicast and multicast routing. It is a reactive routing protocol, meaning that it establishes a route to a destination only on demand. AODV is, as the name indicates, a distance-vector routing protocol. AODV avoids the counting to infinity problem of other distance-vector protocols by using sequence numbers on route updates.

Advantages of AODV

AODV protocol is a flat routing protocol it does not need any central administrative system to handle the routing process.

The AODV protocol is a loop free and avoids the counting to infinity problem.

AODV has higher bandwidth share.

Advantages of AODV (Cont..)

AODV tries to keep the overhead of the messages small. If host has the route information in the Routing Table about active routes in the network, then the overhead of the routing process will be minimal.

The AODV has great advantage in overhead over simple protocols which need to keep the entire route from the source host to the destination host in their messages.

Disadvantage of AODV

AODV has higher processing demand.

AODV consumes more share of the bandwidth.

AODV takes more time to build the routing table.

What is OLSR ?

The Optimized Link State Routing protocol (OLSR) is a routing protocol that is optimised for mobile ad-hoc networks but can also be used on other wireless ad-hoc networks. It is a proactive link-state routing protocol that floods a topology table of it's neighbors to all nodes in the network which then compute optimal forwarding paths locally.

Advantage of OLSR OLSR has less average end to end delay.

The OLSR implementation is more user-friendly and worked with less headaches

OLSR is also a flat routing protocol, it does not need central administrative system to handle its routing process.

It increases the protocols suitability for ad hoc network with the rapid changes of the source and destinations pairs.

Advantage of OLSR (Cont..)

OLSR protocol does not require that the link is reliable for the control messages, since the messages are sent periodically and the delivery does not have to be sequential.

The OLSR routing protocol simplicity in using interfaces, it is easy to integrate the routing protocol in the existing operating systems, without changing the format of the header of the IP messages. The protocol only interacts with the host’s Routing Table.

OLSR protocol is well suited for the application which does not allow the long delays in the transmission of the data packets.

Disadvantage of OLSR

OLSR needs more time re-discovering a broken link.

wider delay distribution.

OLSR requires more processing power when discovering an alternate route.

Comparison between AODV and OLSR

Performance and scalability: As proactive protocol, OLSR reduces

the control overhead forcing the MPR to propagate the updates of the link state, also the efficiency is gained compared to classical link state protocol when the selected MPR set is as small as possible. But the drawback of this is that it must maintain the routing table for all the possible routes, so there is no difference in small networks, but when the number of the mobile hosts increase, then the overhead from the control messages is also increasing. This constrains the scalability of the OLSR protocol. The OLSR protocol work most efficiently in the dense networks.

The overhead of reactive protocols like AODV is related mostly to the discovery of the new route and from the updates of the usable routes. So in the network with light traffic and low mobility the reactive protocols scales perfectly to the larger networks with low bandwidth and storage overhead. As the undesirable environment for reactive protocols is the network with heavy traffic with large number of destinations with high mobility. This situation will result that a big number of routes will break resulting repeated route discoveries and error reports in the network .

Comparison between AODV and OLSR (cont..)


From the information above it is obvious that proactive protocols produce higher routing efficiency than reactive protocols in the network with scattered traffic. Because the updates come from periodic updates and no additional overhead occurs for finding new routes, but then the proactive protocols use more bandwidth and resources than reactive protocols.


The AODV protocol need to discover the route first in order to send the actual data , so the search latency affects of the AODV protocol , OLSR does not need to do the extra work for the discovery of the route so it provides low single packet transmission latency. The reactivity of the detecting topological changes in OLSR can be improved by shortening the time interval of periodic control messages. The OLSR drawback is that it use constantly the bandwidth but AODV is trying to keep the bandwidth usage low for the maintaining of the routes.


Resource Usage:The storage complexity of the OLSR protocols is related on how much hosts are in the network, but the storage complexity of AODV is related to the number of the communication pairs. It is because the OLSR has to have all possible routes in Routing Table, while for AODV active routes are necessary. In the addition, the OLSR must keep the topology information in the topology set, MPR information in MPR selector set and also update the state information about the links and neighbors . So the OLSR must maintain the information about the hosts that it does not need.


Security Considerations :The main points in the AODV and OLSR protocols is that the control messages must be protected, that the malicious information sent by some attacking host could not affect the routing processes in the network. Both protocols should use the IPsec authentication headers for the authentication of the hosts. The AODV needs less protection of the control messages it is enough to protect the RREP and RRER messages in order for the protocol to be secured, but in the case of OLSR all the control messages are needed to be secured.


If the OLSR includes gateways hosts, then they have to be statically configured in order to advertise the routes to the valid addresses into the ad hoc network. Based on this information it is obvious that the AODV is more flexible to security solutions, because not all the AODV control messages are in need of the protection, so it can save the resource usage of the AODV protocol compared to OLSR.

Operation of AODVRoute Discovery: Whenever a source node has to send information to a destination, but doesn’t have a valid route to it, it initiates a route discovery process. The source creates an AODV RREQ (Route Request) packet. This packet contains the source node’s IP address, current (source) sequence number, destination IP address, last known destination sequence number (set to zero if no prior route exists), a broadcast ID , which is incremented with each RREQ and a Hop Count field set to zero.

Operation of AODV (cont..)

This RREQ packet is broadcasted by the source to its neighbors. The neighboring nodes first check to see if they have already seen the RREQ. If it has already seen the RREQ then it’s discarded, otherwise it checks to see if it has a fresher route to the destination in question . If yes, then it sends a RREP (Route Reply) back to the source and a gratuitous reply to the destination informing it about the source node details.


If no, then it forms a reverse route entry, for the source node in its route table noting the source node’s IP address and sequence number as well as the number of hops to the source node and the IP address of the neighbor from which the RREQ was received. This is used to forward the RREP back to the source node.


The node then increments the hop count and broadcasts it to its neighbors. This goes on until either the destination is reached or a node with a valid route to the destination is reached. In case the RREQ is lost or the destination is unreachable where Node Traversal Time is the time taken to travel the distance between two neighboring nodes and the Timeout buffer is used to account for congestion delays the source node reinitiates the route discovery process as specified by the RREQ retries parameter.


The RREP from the destination contains the destination IP address, its current sequence number, the source IP address and a lifetime field in addition to the hop count field which is set to zero. If an intermediate node sends the RREP, it contains the destination sequence number, hop count value equal to its distance from the destination and the lifetime value set to the amount of time for which its route table entry for the destination will still be valid.


The RREP is unicasted back to the source node. Any intermediate node receiving the RREP, sets up a forward route having the IP address of the destination and the neighbor from which the RREP arrived, the hop count value is incremented and then added and the lifetime of this entry is set to the lifetime in the RREP. Each time the route is used it lifetime is extended. There is also a delete period before actually deleting the route information to prevent any routing loops.


When the source node receives the RREP, it also performs similar actions to update it route table. In case of multiple RREPs, the one with the highest sequence number or the minimum hop count is selected. Fig.2 shows the route discovery process. Here S is the source and D is the destination. The figure illustrates the reverse path formed during route discovery and consequent forward path to the destination.


Reverse Path Setup Forward Path Setup

Fig. 2 Paths formed during the route discovery


Fig. 4.2.1 Propagation of RREQ Fig. 4.3.1 Route Maintenanceand route determination


When the RERR message is received by a neighbor it also marks its route table entry for the destination as invalid and sends again RERR messages to its precursors. In figure 4.3.1.I, the node N4 moves to N4’ and so node N3 can not communicate with it anymore, connectivity is lost. N3 creates a RERR message to N2, there the route is marked invalid and unicasts the message to N1. The message is unicast since we have only route passing through each node.


N1 does the same thing and unicasts the message to the source node. When the RERR is received at the source node and it still needs the route to the destination it reinitiates a route discovery. Figure 4.3.1 shows the new route from the source to the destination through node N5. Also if a node receives a data packet for a node which it does not have an active route to, it creates a RERR message and broadcasts it as described above.


If no broadcast has been send within, by default,

one second, each node broadcasts Hell message

to its neighbors in order to keep connectivity up to

date. These messages contain the node’s IP

address and its current sequence number. So that

these messages are not forwarded from the node’s

neighbors to third parties the Hello message has a

TTL value of one.


Route Maintenance: If any destination or intermediate node moves outside of an active communication path, the node upstream of the break initiates, a RERR (Route ERRor) message listing the unreachable destinations. The RERR is broadcast so as to reach all precursor nodes as maintained by the individual nodes. Once it reaches the source node it may initiate a new route discovery process if required.


Local Connectivity Management: Neighborhood information is obtained by having the nodes send HELLO packets to each other. A hello message is an unsolicited RREP. If a node does not receive any hello message from its neighbor during a specific hello interval then it assumes its neighbor is either inactive or out of range and updates it connectivity information with regards to this particular node.

Operation of OLSRIn OLSR protocol, there are four main stepsto creating a route table: neighbor sensing,MPR selection, MPR information declarationand route table calculation. During theneighbor sensing, each node periodicallybroadcasts the HELLO message containinginformation about its one-hop neighbors andtheir link status. The HELLO messages arereceived by all the one-hop neighbors, butthey are not retransmitted tofurther nodes.

Operation of OLSR (cont..)Upon receipt of the HELLO messages, eachNode can update its knowledge of its onehop neighbors and two-hop neighbors. Thisinformation about One hop and two-hopneighbors is recorded in a neighbor table.On the basis of this information, each nodeperforms the selection of its MPR set .Duringthe MPR selection, each node independentlyselects its MPR set according to the MPRselection scheme.

Operation of OLSR (cont..)

As a result, all of the two-hop neighbors ofeach node are contained in the union of theneighbor sets of its MPRs. Then, each nodedeclares its MPRs in the subsequent HELLOmessages. From the HELLO messages,whichContain the MPRs, each node can inform itsMPR Selectors and construct its MPR Selectortable.


During the MPR information declaration, each node broadcasts specific control messages called Topology Control messages to declare its MPR Selector set. The TC messages are forwarded through MPR nodes and transmitted to all nodes in the MANET. According to the MPR selectors

and the information in TC messages, a node maintains a network topology table to record

the MPRs of other nodes. The topology table is a base of calculating the route table.

Operation of OLSR (cont..) During the route table calculation, a node

calculates the route table based on the information contained in the neighbor table and the topology table. To find a path from a source (S) to a destination (D), an intermediate node (I1) one hop away to D has to be found and the connection pair [I1, D] obtained; then, a node (I2) one hop away to I1 has to be found and the connection pair [I2, I1] obtained; and so forth, until a node In is found in the MPR sets of S. Based on this process, the route table is built by tracking the connection pairs included in the topology entries in a topology table.


To attain the optimal routing path, the connection pairs on the minimal path are selected. In OLSR draft version 5 [9], associated networks and host support are added. A node may act as a gateway between the MANET and a subnet not running OLSR. In order to inject the routing information describing the associated subnets into a MANET, a gateway periodically broadcasts its existence and its associated subnet address in the MANET using Network Association (HNA) messages.


The HNA messages indicate which network is reachable through this gateway. The HNA messages are propagated in an optimal way so that only MPR nodes retransmit the broadcast messages. Each node in the MANET maintains information concerning which node acts as a gateway and its associated network address. When a packet is destined for an address in a

subnet indicated by a gateway and there is not a host entry in the route table, a MANET node will forward it according to the gateway entry in its route table.


To achieve the integration of a MANET with the Internet based IPv6, three main tasks need to be accomplished: gateway discovery, address auto configuration, and routing and addressing in a heterogeneous environment. The first step is the gateway discovery. To achieve the hybrid network connection, the installation of gateways that understand the protocols of MANET and the IP suite is needed. From the point of view of MANET, these gateways act as ARs to the Internet.


An MN should discover the existence of gateways and then select one gateway as an AR to the Internet. The basic IP-based mechanism for access router discovery only supports those systems with one-hop connection between MNs and access routers. The MANET in the multi-hop environment makes the discovery mechanism more complex. The second step is address auto configuration. In order to be able to communicate with Internet hosts, each MN must configure an IP address with the prefix of a gateway.


With this address, the MN can send packets to and receive packets from hosts in the Internet. The third step is routing and addressing in the heterogeneous environment. In a heterogeneous environment, when an MN arriving in a MANET sends packets to a host on the Internet, the packets are first transferred to a MANET gateway by MANET routing and then sent to the destination by IPv6 routing; when a host on the Internet sends packets to an MN arriving in a MANET, the packets are first transferred to a MANET gateway by IPv6 routing and then sent to the MN by MANET routing.

Conclusion

The AODV protocol will perform better in the networks with static traffic with the number of source and destination pairs is relatively small for each host. It uses fewer resources than OLSR, because the control messages size is kept small requiring less bandwidth for maintaining the routes and the route table is kept small reducing the computational power. The AODV protocol can be used in resource critical environments.

Conclusion (Cont..)

The OLSR protocol is more efficient in networks with high density and highly sporadic traffic. But the best situation is when the between a large number of hosts. The quality metrics are easy to expand to the current protocol. OLSR requires that it continuously have some bandwidth in order to receive the topology updates messages.

comparison between aodv and olsr protocol

Education

olsr protocol

disadvantageof aodv

disadvantage of olsr

reactive routing protocol

flat routing protocol

olsr performance

headaches olsr

olsr implementation