1. A Cluster-based Routing Protocol for Mobile Ad hoc Networks
Based on
Mingliang Jiang, Jinyang Li, Y.C. Tay
INTENET-DRAFT, July 1999
Draft-ietf-manet-cbrp-spec-01.txt

2. Presentation Outline Introduction
Terminology & conceptual data structures
Cluster formation
Adjacent cluster discovery
Routing discovery
Routing details
Conclusion

3. Introduction
MANET (Mobile Ad hoc Networks) characteristics ( & the difficulties for routing protocols)
Dynamic Topology
Limited Link Bandwidth
Limited Power Supply for Mobile Node
Need to scale to large networks
Design a routing protocol for MANET that is:
efficient
scalable
distributed and simple to implement

4. CBRP: Motivations Design Objective: Major design decisions:
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

5. CBRP: Protocol Overview

6. CBRP Terminology Node ID: unique, using IP address
Cluster: a group of nodes with one cluster head, cluster are overlapping or disjoint.
Host cluster: a node regards itself in cluster X if it has a bi-directional link to cluster head of X.
Cluster head: elected, only one in cluster
Gateway: any node a cluster use to communicate with adjacent cluster
HELLO message: all nodes broadcast HEELO message periodically every interval time, includes: Neighbor Table and Cluster Adjacent Table

7. Conceptual Data Structure
Neighbor Table: neighbor info, each entry has
1. ID of neighbor
2. Role of neighbor
3. Status of link ( bi- or uni-directional)
Cluster Adjacency Table: adjacent cluster info, each entry has
1. ID of neighbor cluster
2. Gateway node
3. Status from gateway to neighbor cluster head
Two-hop topology Database: By examining neighbor table, ‘complete’ info about network topology that is at most two-hops away from itself.

8. Cluster Formation Objective: Mechanism:
Form small, stable clusters with only local information
Mechanism:
Variations of “min-id” cluster formation algorithm.
Nodes periodically exchange HELLO packets 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:

9. Cluster Formation (an example)
Variation of Min-ID
Minimal change
Define Undecided State
Aggressive Undecided -> Cluster head
e.g. 2’s neighbor table 3 8 4 1 5 2 6 7 9 10 11

10. Adjacent Cluster Discovery
Objective:
For cluster heads 3 hops away to discover each other
Mechanism:
Cluster Adjacency Table exchanged
in HELLO message
e.g. 4’s Cluster Adjacency Table 3 8 4 1 5 2 6 7 9 10 11

11. Route Discovery
Source S “floods” all cluster heads with Route Request Packets (RREQ) to discover destination D
3 (S)
11 (D) 1 2 4 5 6 7 8 9 10 3 11
[3,1,8,11]
[3,1,8]
[3]
[3,1]
[3,1,6]

12. Route Reply 3 (S) 11 (D) 1 2 4 5 6 7 8 9 10 3 11 the reversed
Route reply packet (RREP) is sent back to source along reversed “loose source route” of cluster heads.
Each cluster head along the way incrementally compute a hop-by-hop strict source route.
3 (S)
11 (D) 1 2 4 5 6 7 8 9 10 3 11
the reversed
loose source route of RREP: [11,8,1,3]
[11,9]
[11]
[11,9,4]
[11,9,4,3]
the computed
strict source route of
3->11 is: [11,9,4,3]
[11,9,4]

13. Route Reply 3 (S) 11 (D) 1 2 4 5 6 7 8 9 10 3 11 the reversed
Route reply packet (RREP) is sent back to source along reversed “loose source route” of cluster heads.
Each cluster head along the way incrementally compute a hop-by-hop strict source route.
3 (S)
11 (D) 1 2 4 5 6 7 8 9 10 3 11
the reversed
loose source route of RREP: [11,8,1,3]
the computed
strict source route of
3->11 is: [11,9,4,3]

14. Route Error Detection 1 2 4 5 6 7 8 9 10 3 11 11 (D) 3 (S)
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 1 2 4 5 6 7 8 9 10 3 11
11 (D)
Source route header of data
packet: [3,4,9,11]
3 (S)
Route error (ERR)
down link: {9->11}

15. Local Route Repair in CBRP
Objective
Increase Packet Delivery Ratio
Save Route Rediscovery flooding traffic
Reduce overall route acquisition delay
Mechanism
Spatial Locality

16. Local Route Repair 1 2 4 5 6 7 8 9 10 3 11 11 (D) 3 (S)
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 1 2 4 5 6 7 8 9 10 3 11
11 (D)
Source route header of data
packet: [3,4,9,11]
3 (S)
Route error (ERR)
down link: {9->11}

17. Local Route Repair 1 2 4 5 6 7 8 9 10 3 11 11 (D) 3 (S)
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 1 2 4 5 6 7 8 9 10 3 11
11 (D)
Source route header of data
packet: [3,4,9,11]
3 (S)
Modified source route
[3,4,9,8,11]

18. Local Route Repair 11 11 (D) 9 8 4 10 3 (S) 3 1 2 7 6 5
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 (S) 3 1
Gratuitous route reply
[3,4,9,8,11] 2 7 6 5

19. 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 RTS/CTS/Snd/Ack, ARP

20. Utilize Unidirectional links
Selective use of Unidirectional links in CBRP 5 7 6 9 2 1 4 8 3 10

21. Supercluster
Taking advantage of hidden stability from the changing topology
Better support for natural mobility patterns
Merge stable clusters into supercluster

22. 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

23. Simulation Parameters
Simulator parameters
CBRP implementation parameters

24. 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.

25. 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.

26. 2. Routing Overhead with respect to network size
Routing overhead(normalized) = #routing pkts sent/ #data pkts delivered.

27. Limitations of CBRP Source Routing, overhead bytes per packet
Clusters small, 2 levels of hierarchy, scalable to an extend

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