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