A Cluster-based Routing Protocol for Mobile Ad hoc Networks

1. A Cluster-based Routing Protocol for Mobile Ad hoc Networks Based on Mingliang Jiang, Jinyang Li, Y.C. Tay INTENET-DRAFT, July 1999 http://www.ietf.org/ 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: 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: • 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. 11 8 9 4 10 3 1 2 7 5 6 Cluster Formation (an example) • Variation of Min-ID • Minimal change • Define Undecided State • Aggressive Undecided -> Cluster head e.g. 2’s neighbor table

10. 11 8 9 4 10 3 1 2 7 5 6 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

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

12. 11 (D) 11 [11] [11,9] 9 [11,9,4] 8 4 10 3 3 (S) [11,9,4,3] 1 [11,9,4] the computed strict source route of 3->11 is: [11,9,4,3] 2 7 6 5 Route Reply • 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. the reversed loose source route of RREP: [11,8,1,3]

13. 11 (D) 11 9 8 4 10 3 (S) 3 1 2 7 6 5 Route Reply • 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. 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. 11 9 8 4 10 3 1 2 7 6 5 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->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. 11 9 8 4 10 3 1 2 7 6 5 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->11}

17. 11 9 8 4 10 3 1 2 7 6 5 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]

18. 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) 11 Source route header of data packet: [3,4,9,11] 9 8 4 10 3 3 (S) 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 802.11 RTS/CTS/Snd/Ack, ARP

20. Utilize Unidirectional links • Selective use of Unidirectional links in CBRP 5 6 7 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_timebefore 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 ratiowith 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