Interference-Aware QoS OLSRfor Mobile Ad-hoc Network Routing

SAWN 2005, May 24

P. Minet & D-Q. Nguyen

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Outline

1. Introduction2. QoS framework for ad-hoc networks3. Interference-aware QoS OLSR4. Performance evaluation5. Conclusion

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1. Introduction

Transmissions and receptions in ad-hoc networks are subject to radio interference.=> Bandwidth resource is affected.

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1. Introduction

Ad-hoc networks have scarce resources.=> QoS management in ad-hoc networks is more difficult than

in wired networks. Admission control is needed.

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2. QoS framework

Class 2

Bandwidth Controland Reservation

Application(Bandwidth)

Path Computation

MAC layer metrics

QoS Advertisements

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2. QoS frameworkApplication(Bandwidth)

Routing on theReserved Path

Class 2 Marking

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3. Interference-aware QoS OLSR

QoS signalisation

Measure local available bandwidth (LAB) At each node. Based on values obtained from MAC layer.

LAB dissemination Any node broadcasts in Hello message : its LAB and

the LAB of each neighbor. Any MPR (multipoint relay) broadcasts in TC message

the LAB of each MPR selector.

MPR selection based on LAB Any node selects its MPRs so that it can reach any

two-hop neighbor by a largest path; i.e. path with maximum bandwidth.

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3. Interference-aware QoS OLSR

i

m n

x y z

5 1

N1(i) = {m, n}N2(i) = {x, y, z}

OLSR native MPR selection MPR selection with bandwidth

MPR selection example :

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3. Interference-aware QoS OLSR

Interference-aware admission control

Accept a new flow iff: QoS required by this flow can be met. QoS of already accepted flows must not be altered.

Perform in 2 steps: Step 1: Selection of an acceptable path

Any node on the path must provide the amount of bandwidth required by the new flow.Can be checked locally by the source node.

Step 2: Path feasibility with interferencesAny node in the interference zone of a node on the path must have enough bandwidth to support this new flow.A message is sent from source to destination.

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3. Interference-aware QoS OLSR

Admission control example :

S

DS

D

This path forthe Yellow flow

is not acceptable!

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3. Interference-aware QoS OLSR

Interference-aware QoS routing algorithm

The shortest routes tend to minimize network resources required for transmission of each packet from its source to destination in a wireless multihop environment. => Minimize the number of hops as first criterion.

Some flows require bandwidth as QoS parameter.=> Consider local available bandwidth at each node as second criterion.

Route computation is called upon any topology change.=> Complexity must be similar to Dijkstra algorithm.

Network resources is scarce.=> Algorithm is based on partial knowledge of topology.

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3. Interference-aware QoS OLSR

Interference-aware QoS routing algorithm

Algorithm 1: Default algorithm used to compute routing table. Unconstrained, widest-shortest path. Called upon any change in the one-hop neighborhood,

two-hop neighborhood or topology table.

Algorithm 2: Constrained by a bandwidth request. Used to compute a route offering the requested

bandwidth from a source to a destination if the default route, from algorithm 1, cannot provide that bandwidth.

Called by the admission control for a new flow with bandwidth demand.

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3. Interference-aware QoS OLSR

Admission control example with routing algorithm 2 :

S

DS

D

Flow Yellowacceptable!

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4. Performance evaluation

Simulation plan 250 static nodes uniformly located on a 2500x2500m2 square. 7 CBR flows, each requires 175Kbps at application level. MAC 802.11b, no RTS/CTS. Native OLSR and Interference-aware QoS OLSR routing.

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4. Performance evaluation

Results obtained with native OLSR

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4. Performance evaluation

Results obtained with Inteference-aware QoS OLSR routing

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4. Performance evaluation

Loss rate comparison

FlowNative OLSR (with 4 flows)

(%)

Native OLSR (with 7 flows)

(%)

Interference-Aware (with 7

flows) (%)

1 23.56 41.56 0.982 7.91 50.44 1.343 1.65 38.58 2.054 28.81 66.99 1.645 - 66.06 3.466 - 39.07 1.957 - 68.86 1.55

Average 15.48 53.08 1.85

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5. Conclusion

Interference-aware routing can accept more flows into the network.

It offers better stability to the accepted flows, better bandwidth guarantee to the applications than native OLSR.

If it cannot find a route meeting the bandwidth requested,then such a route does not exist.

Main drawback: more MPRs selected => more control overhead, broadcasting using MPR becomes less efficient.

Perspective: Reduce control overhead, improve broadcasting.