Ad-hoc On-Demand Distance Vector Routing (AODV) and simulation in network simulator

Content Introduction to ad-hoc networks AODV : Concept AODV : Mechanism Simulation in Network Simulator Conclusions

Introduction to ad-hoc networks Network of mobile wireless nodes  No infrastructure (e.g., base stations, fixed routers, centralized servers)  Dynamic topology Routing infrastructure created dynamically at intermediate node  Data can be relayed by intermediate nodes  Limited battery power and transmission range resources in the nodes Usage:  Military environments, emergency and rescue operations, meeting rooms, etc

AODV : Concept Reactive routing  Pure on-demand route acquisition system  The routes are created when needed, so called “on-demand” A broadcast route discovery mechanism  RREQ (Route Request packet) broadcasting to find a route  RREP (Route Reply packet) is used to set up forward path Dynamic establishment of route table entries  Nodes lie on active paths only maintain routing information Destination sequence number  Prevention of routing loops  Avoidance of old and broken routes Maintenance of timer-based states  A routing table entry is expired if not used recently

AODV : Mechanism Path discovery Every node maintains two separate counters Sequence number Broadcast-id (increments whenever the suorce issues a new RREQ)  The source requests using RREQ broadcasting Destination number of RREQ is the last known number to the source  The destination replies using RREP (Route Reply) unicasting The sequence number is first incremented if it is equal to the number in the request RREP contains the current sequence number, hop count = 0, full lifetime  Intermediate nodes Discard duplicate requests Replies if it has an active route with higher destination sequence number Otherwise broadcasts the request on all interfaces

AODV : Mechanism Path discovery  Intermediate nodes Setup reverse path  A node records the address of the neighbor who send RREQ Keep track of some information  Destination IP address, Source Ip address, Broadcast_id, Expiration time for reverse path route entry, Source node’s sequence number Setup forward path  Unicast RREP (Route reply) back to the reverse path  Each node along the path sets up a forward pointer to the node from which the RREP came  Update its routing table entry  Propagate the first RREP or the RREP if contains a greater destination sequence# or the same sequence# with a smaller hop count then contained in RREQ  Nodes that are not along the path determined by the RREP will timeout and will delete the reverse pointers

Example B S E C G F A H D Y I K P L J T Z RREQ

Example B S E C G F A H D Y I K P L J T Z Reverse Path Setup

Example B S E C G F A H D Y I K P L J T Z

B S E C G F A H D Y I K P L J T Z

B S E C G F A H D Y I K P L J T Z RREP

Example B S E C G F A H D Y I K P L J T Z Forward path setup

Example B S E C G F A H D Y I K P L J T Z

B S E C G F A H D Y I K P L J T Z

B S E C G F A H D Y I K P L J T Z

Route table management  Soft-state associated with the entry (useful information stored in route table management): Route request expiration time (purpose of this timer is to erase reverse path routing entries from those nodes that do not lie on the path) Route caching timeout (or the time after which the route is considered to be invalid) Active route timeout (this information is maintained so that all active source nodes can be notified when a link breaks) A neighbor is considered active if it originates or relays at least one packet to the destination

Path maintenance  Neighboring nodes with active routes periodically exchange hello messages  If a next hop link in the routing table fails, the active neighbors are informed  The RERR (unsolicited RREP) indicates the unreachable destinations  The source performs a new route request when it receives a RERR

Simulation in network simulator Now we are going to start simulation in Network Simulator This example contains 30 nodes which are moving and use AODV routing protocol

Conclusion  AODV -- efficient algorithm for ad-hoc networks  Need for broadcast is minimized  Quick response to link breakage in active routes  Loop free routes

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