Fault Tolerant Routing in Tri-Sector Wireless Cellular Mesh Networks

1. Fault Tolerant Routing in Tri-Sector Wireless Cellular Mesh Networks Yasir Drabu and Hassan Peyravi Kent State University Kent, OH - 44240

2. Agenda • Introduction • Wireless Network Overview • Problem Definition • Proposed Solutions • Shortest Path Routing • Fault Tolerant Routing • Conclusion PDCS - 06

3. Intro - Wireless Network Architectures Point to Point Point to Multipoint Multipoint to Multipoint Dedicated links Our Focus Currently Most Common PDCS - 06

4. Wireless Mesh Networks (WMN) INTERNET • Structured, energy rich wireless multi-hop networks: • Wireless Client • Mobile, no routing, limited power • Wireless Router • Low mobility, routing and power rich • Wireless Gateway • Access to wired network. • Solves – “Last Mile Connectivity” PDCS - 06

5. Problem Definition • How do you route packets in a Wireless Mesh/Multi-Hop network? • Given: • Faulty wireless – multi path fading, selective fading, noise etc. • Shortest path may not be the best alternative. • Multiple hops/ multiple channel – radio limitations, channel allocation problem etc. PDCS - 06

6. Background • Many wireless routing algorithms: • Pro-active (DBF) , reactive (DSR, TORA) and hybrid (ZRP) • None are very fault tolerant and very focused on energy poor applications • Few provide fault tolerance • Agarwal 2004 (Stony Brook research lab) – build routing using spanning trees then re-associate to different root when link fails. • Slow, high message complexity, order of seconds. However not much work done on using topological properties of wireless network PDCS - 06

7. Proposed Honey Comb WMN Model Modified to Honey Comb • No wired backbone for each node • Place wireless elements on the edge instead of the center in a typical network • Uses more nodes with lower power for better coverage and higher throughput Proposed Honeycomb Model Typical Cellular Network PDCS - 06

8. Cellular Network: Central Base Station Omni-directional antenna Advantages Established Technologies Fewer Base Stations Limitations High power consumption Limited coverage Lower bandwidth No Fault tolerance Expensive to deploy and maintain due to wired back bone infrastructure. Honeycomb Network: BS as the edge Directional antennas Advantages Lower power per node Better coverage Higher throughput Fault tolerance Wireless interconnect, cheaper to deploy when wired infrastructure is factored in Limitations More complex hardware More nodes for same area Honey Comb Network Comparison PDCS - 06

9. Proposed Tri-Sector Node Model Wireless Router • Four Radios • Three directional antennas for communication with other routers • One omni-directional for wireless clients • The directional antenna can be on the same channel as they are spatially multiplexed. • Using different channels on different lobes will add to the complexity of the problem. • Omni-directional antenna is on a separate channel to minimize interference. N 1200 PDCS - 06

10. Earlier routing in Honeycomb Network • Honeycomb routing was introduced in [Stojmenovic:97] • Issues: • Uses (x, y, z) co-ordinates to route. • No consideration for link failure. Src: Stojmenovic:97 PDCS - 06

11. Honeycomb Brick Representation stretch • Two dimensional representation of honeycomb • Each node can be represented by a co-ordinate (x,y) • They have 25% smaller degree than regular grid meshes. Isomorphic pruned 2Dsquare mesh stretch PDCS - 06

12. Shortest Path Routing Algorithm PDCS - 06

13. Fault Tolerance In Brick Networks • Link faults common in wireless networks • How do we handle a fault in a mesh network? • Localized Temporal Routing • Temporal Routing Based on • Final direction of packet • Position of fault • Number of faults PDCS - 06

14. Fault Tolerant Routing Algorithm • Fault detection: Physical layer or the Medium Access Layer detects the fault. • Fault avoidance: Once a fault has been detected, the algorithm goes into recovery mode. Exploited topological properties to define alternate path. PDCS - 06

15. Fault Routing – Single and Multiple failures PDCS - 06

16. Limitations • Fault tolerance is a trade-off between delay and deliverability. • More hops introduce delay. • Model needs ground up deployment • Topological Rigidity • Cannot be deployed on all terrains PDCS - 06

17. Conclusions • Contributions: • Modeled fault tolerant network topology • Efficient addressing scheme • Shortest path routing algorithm • Developed fault tolerant routing which can handle multiple faults. • Future Work: • Gateway Placement • Resource allocation (channel assignment) PDCS - 06

18. Questions?

19. Wireless Multi-hop Networks • Type of multi-hop networks (Application Level Classification): • Ad hoc • Limited power, high mobility, relatively small. • Primary application – file sharing and collaboration. • Sensor Networks • Very low power, low bandwidth, large networks. • Primary application – Data accusation and sensing. • Wireless Mesh Networks (WMN) • Power rich, structured, high throughput • Primary application – access network to end users. PDCS - 06

20. Routing Challenges in WMN • Time varying link behavior • Shortest Path not always the best route • Using spanning trees do not exploit the natural robustness of a WMN. • Exploit alternate routes to make WMN fault tolerant • How to achieve load balancing. • How to maintain alternate routes? • How to choose one route over the other? On what basis/metrics? PDCS - 06