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

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

Presentation OutlineProject Overview and ObjectivesRelated WorksCBRP: MotivationsCBRP: the DetailsPerformance EvaluationConclusion and Future Work

Project OverviewMobile Ad hoc Networks (MANET), its

applications and challengesIETF working group MANET

Project OverviewMANET characteristics ( & the

difficulties for routing protocols) Dynamic Topology Limited Link Bandwidth Limited Power Supply for Mobile Node Need to scale to large networks

Project ObjectiveDesign 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?

DSRAODV, ABR,TORA

DSDV

OLSR

Related WorksProblems 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 WorksRe-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

52

6

7

910

11

Nbr ID Nbr status Link status7 member Bi-directional6 C_head Bi-directional4 member Bi-directional1 C_head Bi-directional

Adjacent Cluster Discovery

3

84

1

52

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 DiscoverySource S “floods” all clusterheads with Route Request

Packets (RREQ) to discover destination D

[3]

[3,1,8,11]

1

2

4

5 6 7

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.

1

2

4

5 6 7

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 6 7

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

1

2

4

5 6 7

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 CBRPObjective

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

Mechanism Spatial Locality

Local Route Repair

1

2

4

5 6 7

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]

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

Local Route Repair

1

2

4

5 6 7

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 6 7

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 linksCause 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 linksSelective use of Unilinks in CBRP

1 27

8 3

5

4

10

69

SuperclusterTaking advantage of hidden stability

from the changing topologyBetter support for natural mobility

patternsMerge stable clusters into

superclusterto 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 EnvironmentMobility 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 ParametersSimulator 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 30sNetwork interface buffer size 50Send 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

pack

et d

eliv

ery

ratio

CBRPCBRP-w/o repair

DSRDSDV

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

pack

et d

eliv

ery

ratio

CBRP

CBRP-w/o repair

DSR

2. Routing Overhead with respect to network sizeRouting 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

rout

ing

over

head

CBRP

CBRP-w/o repair

DSR

MilestonesAug 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

ConclusionCBRP is a robust/scalable routing

protocol superior to the existing proposals

Further study on Superclustering

QoS, Multicast support in CBRP