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

1
CBRP A Cluster-based Routing Protocol for
Mobile Ad hoc Networks

• Presented by Jiang Mingliang
• Supervised by Dr Y.C. Tay, Dr Philip Long

2
Presentation Outline

• Project Overview and Objectives
• Related Works
• CBRP Motivations
• CBRP the Details
• Performance Evaluation
• Conclusion and Future Work

3
Project Overview

• Mobile Ad hoc Networks (MANET), its applications
  and challenges
• IETF working group MANET

4
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

5
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

6
Related Works

• Existing MANET protocols

discover routes on-demand (re-active)
Source routing
DSR
Table driven
AODV, ABR, TORA
MANET routing protocols
Variation of distant vector?
DSDV
Maintain updated routes (pro-active)
OLSR
Variations of link state routing?
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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.

8
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)

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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

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CBRP Protocol Overview
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Cluster Formation
Objective Form small, stable clusters with only
local information

• Mechanism
• Variations of min-id cluster formation
  algorithm.
• Nodes periodically exchange HELLO pkts to
• maintain a neighbor table
• neighbor status (C_HEAD, C_MEMBER, C_UNDECIDED)
• link status (uni-directional link, bi-directional
  link)
• maintain a 2-hop-topology link state table

HELLO message format
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Cluster Formation (an example)

• Variation of Min-ID
• Minimal change
• Define Undecided State
• Aggressive Undecided -gt Clusterhead
• e.g. 2s neighbor table

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Adjacent Cluster Discovery
Objective For clusterheads 3 hops away to
discover each other Mechanism Cluster Adjacency
Table exchanged in HELLO message e.g. 4s
Cluster Adjacency Table
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Route Discovery

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

3
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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.

the reversed loose source route of RREP
11,8,1,3
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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.

the reversed loose source route of RREP
11,8,1,3
the computed strict source route of 3-gt11 is
11,9,4,3
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Route Error Detection

• 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

11 (D)
Source route header of data packet 3,4,9,11
3 (S)
Route error (ERR) down link 9-gt11
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Local Route Repair in CBRP

• Objective
• Increase Packet Delivery Ratio
• Save Route Rediscovery flooding traffic
• Reduce overall route acquisition delay
• Mechanism
• Spatial Locality

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Local Route Repair

• 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

11 (D)
Source route header of data packet 3,4,9,11
3 (S)
Route error (ERR) down link 9-gt11
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Local Route Repair

• 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

11 (D)
Source route header of data packet 3,4,9,11
3 (S)
Modified source route 3,4,9,8,11
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Local Route Repair

• 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

11
11 (D)
Source route header of data packet 3,4,9,11
9
8
4
10
3
3 (S)
1
2
Gratuitous route reply 3,4,9,8,11
7
6
5
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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

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Utilize Unidirectional links

• Selective use of Unilinks in CBRP

5
6
7
9
2
1
4
8
3
10
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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

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Performance Evaluation

• Goals
• show the robustness of CBRPs 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

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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

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Simulation Parameters

• Simulator parameters
• CBRP implementation parameters

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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.

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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.

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2. Routing Overhead with respect to network size

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

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Milestones

• Aug 98, CBRP as Internet Draft
• Aug 98, in Chicago Presentation to the IETF
• Oct 98, presentation to MMlab, EE, NUS
• Nov 98, Presentation to IETF in Orlando
• Mar 99, paper submitted to Globecom99

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Limitations of CBRP

• Source Routing, overhead bytes per packet
• Clusters small, 2 levels of hierarchy, scalable
  to an extend

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Conclusion

• CBRP is a robust/scalable routing protocol
  superior to the existing proposals
• Further study on Superclustering
• QoS, Multicast support in CBRP