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

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

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

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

CBRP: Protocol Overview

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

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.

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:

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

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

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]

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]

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]

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}

Local Route Repair in CBRP Objective 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 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}

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]

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

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

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

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

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

Simulation Parameters Simulator parameters CBRP implementation parameters

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.

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.

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

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

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