CBRP: A Cluster-based Routing Protocol for Mobile Ad hoc Networks

Presented by: Jiang MingliangSupervised by: Dr Y.C. Tay, Dr Philip Long

Presentation Outline

Project Overview and ObjectivesRelated WorksCBRP: MotivationsCBRP: the DetailsPerformance EvaluationConclusion and Future Work

Project Overview

Mobile Ad hoc Networks (MANET), its applications and challenges

IETF working group MANET

Project Overview

MANET characteristics ( & the difficulties for routing protocols) Dynamic Topology Limited Link Bandwidth Limited Power Supply for Mobile Node Need to scale to large networks

Project Objective

Design a routing protocol for MANET that is: efficient scalable distributed and simple to implement

Evaluate CBRP through simulation compare with different design alternatives compare against other MANET protocols

Related Works

Existing MANET protocols:

MANETrouting protocols

discover routes on-demand (re-active)

Maintain updated routes (pro-active)

Source routing

Table driven

Variation of distant vector?

Variations of link state routing?

DSR

AODV, ABR,TORA

DSDV

OLSR

Related Works

Problems with pro-active routing protocols high overhead in

periodic/triggered routing table updates

low convergence rate waste in maintaining routes that are not

going to be used!! Simulating results have shown RIP, OSPF, DSDV

fails to converge in highly dynamic MANET.

Related Works

Re-active Routing Protocols prohibitive flooding traffic in route discovery route acquisition delay

every route breakage causes a new route discovery

Works in trying to reduce flooding traffic LAR (GPS for every mobile node?) DSR (aggressive caching)

CBRP: Motivations

Design Objective:a distributed, efficient, scalable protocol

Major design decisions: use clustering approach to minimize on-

demand route discovery traffic use “local repair” to reduce route acquisition

delay and new route discovery traffic suggest a solution to use uni-directional links

CBRP: Protocol Overview

Cluster Formation

Mechanism: Variations of “min-id” cluster formation algorithm.Nodes periodically exchange HELLO pkts to

maintain a neighbor tableneighbor status (C_HEAD, C_MEMBER, C_UNDECIDED)link status (uni-directional link, bi-directional link)

maintain a 2-hop-topology link state table

Objective:Form small, stable clusters with only local information

Node ID Node StatusNeighbor ID Neighbor status Link status

… … …Adjacent cluster ID…

HELLO message format:

Cluster Formation (an example)

Variation of Min-ID Minimal change Define Undecided State Aggressive Undecided ->

Clusterhead

e.g. 2’s neighbor table3

84

1

5

2

6

7

910

11

Nbr ID Nbr status Link status

7 member Bi-directional

6 C_head Bi-directional

4 member Bi-directional

1 C_head Bi-directional

Adjacent Cluster Discovery

3

84

1

5

2

6

7

910

11

Objective:For clusterheads 3 hops away to discover each other

Mechanism:Cluster Adjacency Table exchanged in HELLO message

e.g. 4’s Cluster Adjacency Table

Adj cluster ID Gateway8 96 2

Route Discovery

Source S “floods” all clusterheads with Route Request Packets (RREQ) to discover destination D

[3]

[3,1,8,11]

1

2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

[3,1]

[3,1,6]

[3,1,8]

Route Reply Route reply packet (RREP) is sent back to source along

reversed “loose source route” of clusterheads. Each clusterhead along the way incrementally compute a

hop-by-hop strict source route.

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2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

the reversed loose source route of RREP: [11,8,1,3]

[11][11,9]

[11,9,4]

[11,9,4,3]

the computedstrict source route of3->11 is: [11,9,4,3]

[11,9,4]

Route Reply Route reply packet (RREP) is sent back to source along

reversed “loose source route” of clusterheads. Each clusterhead along the way incrementally compute a

hop-by-hop strict source route.

1

2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

the reversed loose source route of RREP: [11,8,1,3]

the computedstrict source route of3->11 is: [11,9,4,3]

Route Error Detection

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2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

Use source routing for actual packet forwarding A forwarding node sends a Route Error Message (ERR) to

packet source if the next hop in source route is unreachable

Source route header of datapacket: [3,4,9,11]

Route error (ERR)down link: {9->11}

Local Route Repair in CBRP

Objective Increase Packet Delivery Ratio Save Route Rediscovery flooding traffic Reduce overall route acquisition delay

Mechanism Spatial Locality

Local Route Repair

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3

11

3 (S)

11 (D)

A forwarding node repairs a broken route using its 2-hop-topology information and modifies source route header accordingly.

Destination node sends a gratuitous route reply to inform source of the modified route

Source route header of datapacket: [3,4,9,11]

Route error (ERR)down link: {9->11}

Local Route Repair

1

2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

A forwarding node repairs a broken route using its 2-hop-topology information and modifies source route header accordingly.

Destination node sends a gratuitous route reply to inform source of the modified route

Source route header of datapacket: [3,4,9,11]

Modified source route [3,4,9,8,11]

Local Route Repair

1

2

4

5 67

8

9

10

3

11

3 (S)

11 (D)

A forwarding node repairs a broken route using its 2-hop-topology information and modifies source route header accordingly.

Destination node sends a gratuitous route reply to inform source of the modified route

Source route header of datapacket: [3,4,9,11]

Gratuitous route reply[3,4,9,8,11]

Utilize Unidirectional links

Cause of unidirectional links Hidden Terminal Difference in transmitter power or

receiver sensitivity.Pitfalls with unilinks

Discovery of (dead) unilinks Problems with 802.11

RTS/CTS/Snd/Ack, ARP

Utilize Unidirectional links

Selective use of Unilinks in CBRP

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8 3

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Supercluster

Taking advantage of hidden stability from the changing topology

Better support for natural mobility patterns

Merge stable clusters into supercluster

to be further studied

Performance EvaluationGoals

show the robustness of CBRP’s packet delivery with reduced overhead.

evaluate how CBRP scales to larger networks compare different design alternatives (with/without local

repair) compare CBRP with other MANET routing protocols

Tools ns (network simulator) with wireless extension. features

models Lucent WaveLAN DSSS radio with signal attenuation, collision and capture.

implements IEEE 802.11 link layer

Simulation Environment

Mobility Model (random way-point) Nodes move within a fixed rectangular area m x n Each node chooses a random destination and move

toward it at a speed uniformly distributed between 0 and max_speed

When reaching its destination, a node pauses for pause_time before start moving again.

Traffic Model A node creates a session with a randomly selected

destination node. Packets of fixed size 128 byte are sent with constant

sending rate of 4 pkts/sec

Simulation Parameters

Simulator parameters

CBRP implementation parameters

channel bandwidth 2Mbps transmission range 250mmax_speed 20m/s simulated time 600s

Route Request Retransmit Interval(exponential backoff)

500ms

Timeout for packets without a route 30s

Network interface buffer size 50

Send buffer size at the packet originator 50

1. Packet delivery ratio with respect to network mobility

Network mobility is directly affected by pause_time. pause_time has value {0, 30s, 60s, 120s, 300s, 600s} with 0

representing constant mobility and 600s signifying a stationary network.

Packet Delivery Ratio for 50-node network (30 CBR sources, 128-byte packets)

0.7

0.75

0.8

0.85

0.9

0.95

1

0 150 300 450 600pause time

pa

cke

t d

eli

very

ra

tio

CBRP

CBRP-w/o repair

DSR

DSDV

2. Packet delivery ratio with respect to network size

Simulated network of nodes {25, 50, 75, 100, 150} with constant mobility, 60% of nodes have active CBR sessions.

Packet Delivery Ratio with increasing number of nodes

0.5

0.6

0.7

0.8

0.9

1

25 50 75 100 125 150number of nodes

pa

ck

et

de

live

ry r

ati

o

CBRP

CBRP-w/o repair

DSR

2. Routing Overhead with respect to network size

Routing overhead(normalized) = #routing pkts sent/ #data pkts delivered.

Routing Overhead with increasing number of nodes

0

2

4

6

8

25 50 75 100 125 150number of nodes

rou

tin

g o

ve

rhe

ad

CBRP

CBRP-w/o repair

DSR

Milestones

Aug 98, CBRP as Internet DraftAug 98, in Chicago Presentation to the

IETFOct 98, presentation to MMlab, EE, NUSNov 98, Presentation to IETF in OrlandoMar 99, paper submitted to Globecom99

Limitations of CBRP

Source Routing, overhead bytes per packet

Clusters small, 2 levels of hierarchy, scalable to an extend

Conclusion

CBRP is a robust/scalable routing protocol superior to the existing proposals

Further study on Superclustering

QoS, Multicast support in CBRP