Routing Protocols for Mobile Ad-Hoc Networks By : Neha Durwas For: Professor U.T. Nguyen COSC 6590

09/19/062 Outline of the Presentation  What are Mobile Ad-Hoc networks ?  Different types of Routing Protocols  Table Driven Protocols DSDV  On-Demand Protocols AODV DSR  Comparison between the Protocols  Recap

09/19/063 What are Mobile Ad-Hoc networks?  An autonomous collection of mobile users  Communicate over relatively constrained bandwidth  The network topology may change rapidly and unpredictably over time  The network is decentralized  Therefore, routing functionality will be incorporated into mobile nodes

09/19/064 Types of Routing Protocols

09/19/065 Table Driven Routing Protocols  Already existing protocols available and in use for wired networks  Routing information is periodically advertised to all nodes  All nodes have an up-to-date view of the network  When needed, a route is immediately available from the routing table

09/19/066 Destination Sequence Distance Vector (DSDV) Routing Protocol  Table driven protocol based on the Bellman- Ford algorithm  Has freedom from the looping problem and the count-to-infinity problem Looping Problem 321 DCB Count-To-Infinity Problem

09/19/067 DSDV: How it works  Every entry in the routing table has a sequence number with updates having increasing sequence numbers  Each node maintains the shortest distance and  The first node on the shortest path for each node in the network

09/19/068 DSDV: Showing sequence numbers For node H6

09/19/069 DSDV: Transmitting Route Information  Routing information is broadcast on the network  Tables are exchanged between nodes at regular intervals (or significant change in local topology)  Two types of updates Incremental Updates – single NDPU Full Dumps – Multiple NDPUs

09/19/0610 DSDV: Transmitting Route Information  Updates initiated by destination with a new sequence number > previous sequence number  Node receives and updates this information automatically  The node may also wait for some time to ensure it has a route with lowest number of hops

09/19/0611 DSDV : Reconfiguration  If a broken link is detected, the end node of the broken link sets the weight to ∞  An update with an odd sequence number is assigned

09/19/0612 DSDV: Reconfiguration  Each node on receiving the update with weight ∞ quickly disseminates it to its neighbors  Therefore a single broken link propagates throughout the network

09/19/0613 Route Establishment in DSDV

09/19/0614 Route Maintenance in DSDV

09/19/0615 DSDV: Numerical Example  Assume that (1/5)th of the nodes change location in every 60 second intervals.  Every node must maintain the full routing table for all nodes.  Every time a mobile node changes location, it must a transmit a message to every other mobile node so they can change the routing table.  How many routing messages per minute are generated if the network contains 10 mobile nodes ? 100 mobile nodes ? 1000 mobile nodes ? ‘k’ mobile nodes assuming B is the fraction of nodes change location per minute ? *This example was taken from Prof. Andrew Eckford’s notes in Mobile Communications.

09/19/0616 DSDV: Advantages and Disadvantages  Advantages Routing information available immediately from the routing table  Disadvantages Uses up too much BW just to send messages Uses control overhead proportional to the square of the number of nodes in the network ~ O(k2) Is not scalable in Ad-Hoc networks Results in stale routing information at nodes

09/19/0617 Source-Initiated On Demand Protocols  Also called Reactive Protocols  Discovers a new route only when required by a node to communicate with a destination  A node initiates a route discovery process  This process is completed once a route is found or all possible route permutations have been examined  More suited for Ad-Hoc networks

09/19/0618 Ad-Hoc On Demand Distance Vector (AODV) Routing  Pure on-demand route acquisition  “Flat” protocol i.e. all network devices are treated the same way  Uses a ‘Destination Sequence Number’ (DestSeqNum) to identify most recent path  Source node floods a “Route Request” packet

09/19/0619 Route Requests in AODV B A S E F H C G I Represents a node that has received RREQ for D from S D

09/19/0620 Route Requests in AODV B A S E F H C G I Represents transmission of RREQ Broadcast transmission D

09/19/0621 Route Requests in AODV B A S E F H C G I Represents links on Reverse Path D

09/19/0622 Reverse Path Setup in AODV B A S E F H D C G I Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

09/19/0623 Route Reply in AODV B A S E F H D C G I Represents links on path taken by RREP

09/19/0624 AODV: How it works  A node updates its path information only if DestSeqNum of current packet > last DestSeqNum stored at the node

09/19/0625 AODV: Route Establishment  When a node receives a RREQ, it Either forwards it to the neighbours Prepares a RREP  Validity of route at intermediate node is determined by comparing sequence number at intermediate node with DestSeqNum in the RREQ  If RREQ is received many times, then duplicates are discarded

09/19/0626 AODV: Route Establishment  All intermediate nodes with valid routes can send a RREP  Before forwarding a RREQ, each node adds its BcastID and the previous node address  A timer is used to determine how long one waits for a RREQ

09/19/0627 Route Establishment in AODV

09/19/0628 Route Maintenance in AODV

09/19/0629 AODV: Another Example RREQ RREP 3 Sends RREP because it has an active route to 5 Route Discovery Data RERR Route Maintenance

09/19/0630 AODV: Advantages and Disadvantages  Advantages Establishes routes on demand Uses DestSeqNums to find latest route to destination Requires less time in setting up a connection  Disadvantages Periodic beaconing leads to unnecessary BW consumption Multiple RREPs in response to a single RREQ can lead to heavy control overhead Intermediate nodes have stale entries

09/19/0631 Dynamic Source Routing (DSR) Protocol  Designed specifically for use in multi-hop wireless ad hoc networks  Composed of the two main mechanisms Route Discovery Route Maintenance

09/19/0632 DSR: How it works  Sending to other hosts Sender puts source route in header If a recipient is not destination, it keeps forwarding  Route Discovery Broadcast RREQ with destination Receive RREP with sequence of hops to target

09/19/0633 DSR: How it works  Route record Sequence of hops taken by route request packet  Request ID Used for duplicate detection

09/19/0634 DSR: How it works (2)  Receiving a route request packet If (init_addr, req_id) in list of recent requests, stop If this host is in route record, stop If host is the target, return copy of route record in the route reply to the initiator Else, append host address to the route record and re-broadcast

09/19/0635 DSR: How it works  Piggybacking When sending route reply, cannot just reverse route record  Unless there is an entry in cache Must piggyback route reply on a route request targeted at initiator

09/19/0636 DSR: How it works  Route Maintenance Monitors the correct operation of routes If data link layer reports problems, send a route error packet to sender Else, use passive acknowledgement

09/19/0637 Optimizations on DSR  Optimization Add entries to cache anytime a new route is learned  Route Cache Store of source routes

09/19/0638 Route Establishment in DSR

09/19/0639 Route Maintenance in DSR

09/19/0640 DSR: Another Example

09/19/0641 DSR: Example 2 continued

09/19/0642 DSR: Advantages and Disadvantages  Advantages Route cache improves the performance of the protocol Faster routing possible for real time application having low to-end delay  Disadvantages Route maintenance mechanism does not locally repair a broken link Stale route cache information can result in delays Performance degrades in highly mobile environments

09/19/0643 Comparison between AODV and DSR Performance degradesBetter performanceNode Movement The source node and the intermediate node store next hop information Source routing in which a data packet carries the complete path to be traversed Packet Transmission NoYesRequires beaconing (Hello packet) DSRAODV

09/19/0644 Comparisons between Table Driven and On Demand Protocols After a route discovery Immediately from route table Availability of Routing Information When requestedPeriodic Advertisements Route Updates Proportional to the number of communicating nodes and increases with increased node mobility Proportional to the size of the network regardless of network traffic Routing Overhead On-demand Table-driven

09/19/0645 Performance of Ad-Hoc Routing Protocols  Based on the paper, J. Broach et al., “A Performance Comparison of Multi-Hop Wireless Ad Hoc Wireless Networks”, Proc. 4th Annual ACM/IEEE Int. Conf. Mobile Computing and Networking, MOBICOM ’98, Dallas, Texas, 1998, pp

09/19/0646 Performance of Ad-Hoc Routing Protocols: Simulation Model  Used the ns-2 simulator  Considered Routing protocols: DSDV, AODV, TORA, DSR  Simulation model: 50 wireless mobile node moving in a 1500m x 300 square each node can buffer up to 50 packets waiting for transmission routing protocols evaluated on the same 210 scenarios nodes move between random points with a speed chosen uniformly within [0,maxspeed] the node is then stationary for a certain pause time a number of traffic sources (10,20,30) generates packets at a constant bit rate

09/19/0647 Application Data Packet Delivery DSDV slow in responding to link breaks (propagate from destination) AODV and DSR allows local repair and multiple routes

09/19/0648 Routing Overhead Routing overhead large in AODV due to flooding DSR allows routes to be learned by overheard packets

09/19/0649 Recap  Two main types of protocols Table driven  DSDV Too much BW consumption, therefore not good for Ad Hoc Networks Source initiated On Demand  AODV RREQ sent and RREP received from intermediate nodes Beaconing required, Stale information possible at nodes  DSR Route cache information used efficiently to control overhead

09/19/0650 References    Ad-Hoc Wireless Networks: Architectures and Protocols     

09/19/0651 Thank you for your patience. Any questions / comments ?