olsr ad-hoc

8/13/2019 olsr ad-hoc

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Qamar A Tarar OLSR Protocol 1

Optimized Link State Routing

Protocol for Ad Hoc Networks

Qamar Abbas Tarar

Mobile ad-hoc networks based on wireless LAN


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Problems in MANETs

Scalabil i ty QoS

Secur i ty

Interoperat ion with the Internet

Lim ited Battery Life

Node Mob i l i ty

Unrel iable radio ch annelHidden terminal pro blem

Route maintenace

Unpredictable l ink propert ies


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Unicast-Routing Protocol for

MANET (Topology-based)

Table-Driven/

Proactive

Hybrid On-Demand-

driven/Reactive

Clusterbased/

Hierarchical

Distance-

Vector

Link-

State

ZRP DSR

AODV

TORA

LANMAR

CEDAR

DSDV OLSR

TBRPF

FSR

STARMANET: Mobile Ad hoc Network

(IETF working group)

Classification of Routing Protocols for

MANETS

CBRP


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Proactive vs Reactive Routing Protocols

Proactive Routing Protocols (DSDV, OLSR)+ Routes to all reachable nodes in the network available.

+ Minimal initial delay for application.

- Larger signalling traffic and power consumption.

Reactive Routing Protocols (DSR, CBR etc)

+ Smaller signalling traffic and power consumption.

- A long delay for application when no route to the

destination available


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Structure

OLSR

Overview

Multipoint relays

Neighbor sensing

MPR selection

MPR information declaration

Routing table calculation

Extensions in OLSR

Conclusions


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Overview

OLSR Developed by IETF

Table driven

Inherits Stability of

Link-state protocol

Selective Flooding

Periodic Link State

Information generated only by MPR

MPRs employed for optimization


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Link State Routing (eg, OSPF)

Each node periodically floods status of its links

Each node re-broadcasts link state

information received from its neighbour

Each node keeps track of link state

information received from other nodes

Each node uses above information to

determine next hope to each destination24 retransmissions to diffusea message up to 3 hops

Retransmission node


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OLSR Overview

In LSR

protocol a lot of control messages unnecessary duplicated In OLSR

onlyMPRretransmit control messages:

Reduce size of control message;

Minimize flooding

Other advantages (the same as for LSR): As stableas LSR protocol;

Proactiveprotocol(routes already known);

Does not depend upon any central entity;

Tolerates loss of control messages;

Supports nodes mobility.

Good for dense network


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Optimized Link state routing (OLSR)

24 retransmissions to diffusea message up to 3 hops

Retransmission node

11 retransmission to diffuse amessage up to 3 hops

Retransmission node


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Example of neighbor table

One-hop neighbors

Neighbors id State of Link

B Bidirectional

G UnidirectionalC MPR

Two-hop neighbors

Neighbors id Access though

E C

D C

Also every entry in the table has a timestamp, after which the

entry in not valid


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Multipoint Relays (MPR)

N

Reducere-transmission

in the same region Each node select a set

of MPR Selecto rs

MPR Selectors of node

N - MPR(N)- one-hop neighbors of N


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N

Reducere-transmission

in the same region Each node select a set

of MPR Selecto rs

MPR Selectors of node

N - MPR(N)- one-hop neighbors of N

MPR set of Node N

Set of MPRs is able to

transmit to all two-hop neighbors

Link between node and its MPR is

bidirectional.


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Every node keeps a table of routes to all knowndestination through its MPR nodes

Every node periodically broadcasts list of its MPR

Selectors (instead of the whole list of neighbors).

Upon receipt of MPR information each noderecalculates and updates routes to each known

destination



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MRP selection in OLSR

Node 1 Hop Neighbors 2 Hop Neighbors MPR(s)

B A,C,F,G D,E C

Available BW

OLSR: node B will select C as itsMPR So all the other nodes know

that they can reach B via C

30

10050110

25

60

10

40

510

D->B route is D-C-B, whosebottleneck BW is 3

3


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MRP selection in OLSR


B A,C,F,G D,E C

Available BW

OLSR: node B will select C as itsMPR So all the other nodes know

that they can reach B via C

30

10050110

25

60

10

40

510

D->B route is D-C-B, whosebottleneck BW is 3

3

Optimal route (i.e., path with

maximum bottleneck bandwidth:

D-F-B (bottleneck bandwidth of 10)


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Multi-Point Relays/routers

Passes Topology Information

Acts as router between hosts

Minimizes information retransmission

Forms a routing backbone


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Structure of an OLSR Network

MPRs form routing backbone

Other nodes act as hosts


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As devices move


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As devices moveTopological relationships change

Routes changeBackbone shape andcomposition changes


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MPR information declaration

TCTopology control message:

Sent periodically. Message might not be sent if there are no

updates and sent earlier if there are updates

Contains:

MPR Selector Table

Sequence number

Each node maintainsa Topology Tablebased on TC messages

Routing Tablesare calculated based on Topology tables


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Topology Table

Destination

address

Destinations

MPR

MPR Selector

sequencenumber

Holding time

MPR Selector in

the received TC

message

Last-hop node to the

destination.

Originator of TC

message


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Routing Table

Each nodemaintains a routing table to all known

destinations in the network Routing table is calculatedfrom Topological Table,

taking the connected pairs

Routing table: Destination address

Next Hop address

Distance

Routing Table is recalculatedafter every change inneighborhood table or in topological table


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Extensions in OLSR

QosOLSR

FastOLSR

Towards IPv6OLSR

Power saver mode

Change in the contents of TCpacket


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QoS Routing: Difficulties in QoS routing

Due to mobility

Availability and manageability of Link state metrics

Link quality changes quickly and continuously

Computational cost and protocol overhead affect

the performance of the QoS routing protocol

Protocol performance evaluation is complex


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Proactive QoS Routing

Advantages suitable for the unpredictable nature of Ad-Hoc networks

suitable for the requirement of quick reaction to QoS demands

makes call admission control possible

avoids the waste of network resources

Disadvantages

introduces additional protocol overhead

trade-off between the QoS performance and traditional protocol

performance

But..

Little work has been done to analyse the impact of the additional

overhead on pro-active QoS routing


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QoS Versions of OLSR

30

10050110

25

60

10

40

5

10

OLSR protocol does not guarantee

to find the best bandwidth route

3 heuristics are proposed to enhanceOLSR in bandwidth aspect

The heuristics select good bandwidth

neighbour as MPR

3


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QoS Versions of OLSR

OLSR_R1: similar to OLSR (i.e., choose 1-hop neighbours that cover

max. number of 2-hop neighbours), tie-breaker now max BWNode 1 Hop Neighbors 2 Hop Neighbors MPR(s)

B A,C,F,G D,E C

OLSR_R2: select the best BW neighbors as

MPRs until all the 2-hop neighbors are covered.


B A,C,F,G D,E F

OLSR_R3: selects the MPRs in a way such that

all the 2-hop neighbors have the max. bottleneckBW path through the MPRs to the current node.


B A,C,F,G D,E A,F

30

10050110

25

60

10

40

5103


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Evaluation of QoS OLSR

Simulation: generate networks, run OLSR algorithms, compare results

against paths calculated by Link-State algorithm (i.e. completeknowledge, all-pair shortest path)

Network area: 1000 M 1000 M

Number of nodes: 100

Transmission range: 100 M, 200 M, 300 M

Bandwidth: assigned randomly

Results are averaged over 100 randomly generated networks

f i


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Performance Metrics

Error rate:percentage of routes with non-optimal bandwidth

Average difference: for routes with non-optimal bandwidth,

how far off the optimal bandwidth are we

Overhead: the average number of control messages

transmitted per node

MPR count: average number of MPRs in the network

E i l R l


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Experimental Results

Algorithm Transmissi

on

Range

Performace Cost

Error

Rate

Average difference Over-

head

MPR

CountStandard

OLSR300M 28% 46% 12 65

200 M 41% 51% 24 68

100 M 12% 45% 5 42

OLSR_R1 300 M 14% 22% 12 65

200 M 21% 26% 24 68

100 M 8% 44% 5 42

OLSR_R2 300 M 0% 0% 18 70

200 M 0% 0% 33 72

100 M 0% 0% 5.7 45

OLSR_R3 300 M 0% 0% 26 71

200 M 0% 0% 38 73

100 M 0% 0% 5.7 44

Pure Link

State

Algorithm

300 M 0% 0% 1245 100

200 M 0% 0% 979 100

100 M 0% 0% 28 100


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N i hb Di i F OLSR


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Neighbor Discovery in Fast OLSR

3-procedures:

Switch to Fast-Moving/Default mode:

In Fast mode,send Fast-Hellos and vice versa.

A Fast-Hello is smaller than a Hello

Establishing fast Links:

A node in Fast-Moving mode sends Fast-Hello

messages at high frequency.

Refresh Fast links & Detect new broken links:

by sending periodic Fast-Hellos

T d IP 6 OLSR


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Towards IPv6 OLSR

OLSR operate well with both IPv4 and IPv6

To operate with IPv6, the only required change

is to replace the IPv4 addresses with IPv6 address.

The minimum packet and message sizes should be

adjusted accordingly, considering the greater size of

IPv6 addresses.

P d


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Power saver mode

A node can indicate if it agrees to keep the packets of its neighbors

Any node, who wants to go in sleep mode, will select ONLY that

neighbor as MPR who can keep its packets

TC packet will diffuse this info, and all data packets will be routed

through that power saver node

Ch i th t t f TC k t


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Change in the contents of TC packet

Instead of advertising its set of MPRs, a nodewill list its neighbors who has selected him as

an MPR

Many nodes (loosely connected, or at the

boundaries) will not be selected MPRany node. So they will not send any TC

(25% less overhead)

Less frequent changes in this set

Conclusions


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Advantages

Route immediately available

Reactivity to topological changes can be adjusted bysetting the time interval for HELLO messages

Minimize flooding by using MPR

Can be integrated into existing system as it requires nochange to IP format

Disadvantages

Bigger overhead

Need more power

Not all allgoritms pubically documented

Needs more operational experience to debug

Conclusions

R di


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Readings

G. Pei, M. Gerla, and X. Hong, "LANMAR: Landmark Routing for

Large Scale Wireless Ad Hoc Networks with Group Mobility," InProceedings of IEEE/ACM MobiHOC 2000, Boston, MA, Aug.

2000.

R. Ogier, F. Templin, M. Lewis, "Topology Dissemination Based on

Reverse-Path Forwarding (TBRPF) ," IETF Internet Draft , July 28

2003. Thomas Clausen, Philippe Jacquet, "Optimized Link State Routing

Protocol (OLSR) ," IETF Internet Draft , July 3 2003.

X. Hong, K. Xu, and M. Gerla, "Scalable Routing Protocols for

Mobile Ad Hoc Networks" IEEE Network Magazine, July-Aug,

2002, pp. 11-21 Thomas Kunz,Ying Ge, Louise Lamont, Quality of Service Routing

in Ad-Hoc Networks Using OLSR Carleton University, CRC,2002

M Benzaid, P Minet and K A Agha, Integrating fast mobility in the

OLSR routing protocol INRIA, LRI, France,September 2002.
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