Adaptive backup routing for ad-hoc networks

Adviser: Ho-Ting Wu

Speaker: Zen-De Liu

Date:05/14/2007

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Outline

Introduction Related work Adaptive backup routing

AODV-ABR AODV-ABL

Simulation and analysis Conclusion Reference

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Introduction

Ad-hoc network is a self-organized,dynamically changing multi-hop network.

All mobile nodes in an ad-hoc network are capable of communicating with each other without the aid of any established infrastructure or centralized controller.

An ad-hoc network.

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Introduction(2) Many routing protocols have been proposed for ad-hoc networks.These r

outing protocols can be divided roughly into two types, table-driven and demand routing protocol.

Table-driven routing protocols: keep a global picture of network topology and respond to topological changes by propagating update messages throughout the wireless network. such as Destination-Sequenced Distance-Vector routing.

On-demand routing protocols:The route is created only when it is desired by the source node in the on-demand routing protocols. such as Ad-hoc On-Demand Distance-Vector.

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Introduction(3)

The on-demand routing protocol in ad-hoc network have high route discovery latency and reliable problems.

AODV- BR (backup route) improved on-demand routing protocols by creating a mesh and providing multiple alternate routes without transmitting any extra control message.

AODV-BR has to pay extra efforts in the maintenance of alternate route tables and in route recovery.

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Related Work

AODV:AODV can be simply divided into three parts: route request, route reply and route maintenance.

RREQ : When a source node desires a route to a destination for which it does not alread

y have a route, it broadcasts a route request (RREQ) packet across the network . Nodes receiving this packet update their information for the source node and set

up backwards pointers to the source node in the route tables . In addition to the source node's IP address, current sequence number, and broad

cast ID, the RREQ also contains the most recent sequence number for the destination of which the source node is aware

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Related Work(2) A node receiving the RREQ may send a route reply (RREP) if it is either the d

estination or if it has a route to the destination with corresponding sequence number greater than or equal to that contained in the RREQ .

Nodes keep track of the RREQ's source IP address and broadcast ID. If they receive a RREQ which they have already processed, they discard the RREQ and do not forward it.

RREP:Once the source node receives the RREP, it may begin to forward data packets to the destination.

If the source later receives a RREP containing a greater sequence number or contains the same sequence number with a smaller hop count, it may update its routing information for that destination and begin using the better route .

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Related Work(3)

Route maintenance: A route is considered active as long as there are data packets periodically travelling from the source to the destination along that path.

Once the source stops sending data packets, the links will time out and eventually be deleted from the intermediate node routing tables.

If a link break occurs while the route is active, the node upstream of the break propagates a route error (RERR) message to the source node to inform it of th

e now unreachable destination(s). After receiving the RERR, if the source node still desires the route, it can reini

tiate route discovery .

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Related Work(4) AODV-BR: When establishing the mesh and looking for multi-p

ath routes, the algorithm takes advantage of the RREPs (Route Replies) messages of AODV without generating additional control messages.

Each neighboring node overhears the RREP packets and records the source of one of RREP packets as the next hop to the destination into its alternate route table.

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Related Work(5)

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Related Work(6)

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Related Work(7)

AODV–LR: tries to repair the link error without informing the source node and without the disruption in the data delivery.

performance can be improved because of that no data retransmissions from the source are required if link failures can be repaired locally.

the local link repairs might increase the hop counts of the data path and then enlarge the end-to-end delays.

a threshold can be used to decide which policy should betaken – to start a local repair process or to conduct a new route discovery process.

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AODV-Adaptive backup routing (ABR)

AODV-ABR In AODV-BR, It’s appropriate to construct the alternat

e paths during the route reply phase.

When the topology changes more dramatically, alternate paths which were constructed during the reply phase may also be broken.

Adaptive to the topology variations

=>AODV-ABR

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AODV-ABR

Constructing alternate routes by overhearing RREP packet, the mesh structure also can be created by overhearing the data packets transmitted from neighbor nodes.

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AODV-ABR(2) Establishment of the primary andalternate routes when the RREP reaches the source node.

Keeps the informationof hop count in the routing table and alternateroute table.

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AODV-ABR(3)

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Broken link repair When a node detects a link failure in

AODV-BR, it will perform a one-hop data broadcast to its neighbors which forwards those packets to destination via alternate route.

The ‘‘one-hop data broadcast’’ will result in poor effectiveness under heavy traffic networks because it will create some unnecessary and duplicated data packets delivered through the alternate routes.

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Broken link repair(2)

When a node detects a link failure in AODV-ABR, it will perform a handshake process with its immediate neighbors to repair the broken route. The handshake process is accomplished by two one-hop control signals: BRRQ and BRRP.

according to the hop count, the upstream node of the broken link (originator) can select a shorter alternate route.

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Re-route in AODV-ABR

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Re-route in AODV-ABR(2)

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Algorithm : Procedure for Handling Link Break in AODV-ABR. Procedure for link-break handling { Broadcast BRRQ to neighbors with TTL=1; Wait for receiving BRRP packets; If (BRRP packet received before timeout) { Compare the hop count fields of all received BRRP packets; Choose the BRRP with the smallest hop count; Update the next-hop field in the routing table with the neighbor which transmitted the BRRP with the smallest hop count; Update the hop count field in the routing table with the smallest hop count; Relay data packets to the next hop; } Else Send RERR back to the source; }

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Algorithm : Procedure for Receiving BRRQ in AODV-ABR. Procedure for receiving BRRQ { If (There exists an entry to the destination in its alternate route table) If (BRRQ packet is not received from the next hop to the destination) { Reply BRRP packet to the initiator of BRRQ; Copy the routing information from the alternate route table to the routing table; } }

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AODV-ABL

Combination of ABR and Local repair.

When the distance between the broken link and the destination is not farther than MAX_REPAIR_TTL hops, try to repair the link by broadcasting a RREQ control signal,just as AODV-LR.

if the broken link is far away from the destination ,repair the link by a handshake process with immediate neighbors.

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Algorithm 4. Procedure for Handling Link Break in AODV-ABL. Procedure for link-break handling in AODV-ABL { If (The destination is not farther than MAX_REPAIR_ TTL hops away) Start local repair; Else { Broadcast BRRQ to neighbors with TTL=1; Wait for receiving BRRP packet;

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If (BRRP packet received before timeout) { Compare the hop count fields of all received BRRP packets; Choose the BRRP with the smallest hop count; Update the next-hop field in the routing table with the neighbor which transmitted the BRRP with the smallest hop count; Update the hop count field in the routing table with the smallest hop count; Relay data packets to the next hop; } Else Send RERR back to the source; } }

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Simulation and analysis Simulation environment

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Simulation and analysis

Compare the five schemes: AODV, AODV-BR (Backup Route), AODV-ABR (Adaptive Backup Route), AODV–LR (Local repair), and AODV-ABL (combination of ABR and LR) in different pause time.

Longer pause time implies less mobility.

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Simulation and analysis

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Simulation and analysis

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Simulation and analysis

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Simulation and analysis

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Simulation and analysisThe impact of traffic load :transmission rate of 6

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Simulation and analysisThe impact of traffic load :transmission rate of 8

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Simulation and analysisunder heavy loads by doubling the traffic to 20 session

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Conclusion AODV-ABL has the highest throughput ,followed by AODV-LR or AODV-

ABR and then AODV or AODV-BR. AODV-LR is more suitable for high loads. AODV-BR performs better in light loads and decreases in heavy traffic situat

ion because of the increase in packet collisions when there are more and more traffic.

AODV-ABR utilizes the alternative routes of AODV-BR and the concept of AODV–LR. It can repair the failing route by only inquiring the immediate neighbor nodes that have alternate routes.

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Conclusion AODV-ABR is not only adaptive to the variations of net

work topology ,but also has small control overhead then AODV-LR.

AODV-ABL provide more stability for connections and retain highest performance under a high node mobility ad-hoc network.

In the future, will improve the proposed schemes by taking the Qos issues into account.

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Reference

Wei Kuang Lai,Sheng-Yu Hsiao,Yuh-Chung Lin ， "Adaptive backup routing for ad-hoc networks" ， ScienceDirect Computer Communications 30 (2007) 453–464.

Sung-Ju Lee ,Mario Gerla ，“ AODV-BR: Backup Routing in Ad hoc Networks”, Proceedings of IEEE WCNC 2000.

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Q&A