Fault Tolerant Routing in TriSector Wireless Cellular Mesh

Fault Tolerant Routing in Tri-Sector Wireless Cellular Mesh Networks Yasir Drabu and Hassan Peyravi Kent State University Kent, OH - 44240 Kent State University PDCS - 06

Agenda n Introduction q n n Problem Definition Proposed Solutions q q n Wireless Network Overview Shortest Path Routing Fault Tolerant Routing Conclusion Kent State University PDCS - 06 2

Intro - Wireless Network Architectures Point to Point Dedicated links Point to Multipoint Our Focus Currently Most Common Topology Reliability Adaptability Scalability Routing Complexity P to P High Low None P to M Low Moderate M to M High Kent State University PDCS - 06 3

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

Problem Definition n n How do you route packets in a Wireless Mesh/Multi-Hop network? Given: q q q 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. Kent State University PDCS - 06 5

Background n 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 n q n Few provide fault tolerance q Agarwal 2004 (Stony Brook research lab) – build routing using spanning trees then re-associate to different root when link fails. n Slow, high message complexity, order of seconds. However not much work done on using topological properties of wireless network Kent State University PDCS - 06 6

Proposed Honey Comb WMN Model Modified to Honey Comb Proposed Honeycomb Model Typical Cellular Network n n n 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 Kent State University PDCS - 06 7

Honey Comb Network Comparison Cellular Network: q q n n Honeycomb 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. Kent State University q q n n PDCS - 06 BS as the edge Directional antennas Advantages + + + Lower 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 8

Proposed Tri-Sector Node Model Wireless Router n Four Radios q q n N n Kent State University The directional antenna can be on the same channel as they are spatially multiplexed. q 1200 PDCS - 06 Three directional antennas for communication with other routers One omni-directional for wireless clients 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. 9

Earlier routing in Honeycomb Network n n Honeycomb routing was introduced in [Stojmenovic: 97] Issues: q q Uses (x, y, z) coordinates to route. No consideration for link failure. Src: Stojmenovic: 97 Kent State University PDCS - 06 10

Honeycomb Brick Representation stretch Isomorphic pruned 2 D square mesh stretch n n n 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. Kent State University PDCS - 06 11

Shortest Path Routing Algorithm Kent State University PDCS - 06 12

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

Fault Tolerant Routing Algorithm n n Kent State University PDCS - 06 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. 14

Fault Routing – Single and Multiple failures Kent State University PDCS - 06 15

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

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

Questions? Kent State University PDCS - 06

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

Routing Challenges in WMN n n n 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. q How to maintain alternate routes? q How to choose one route over the other? On what basis/metrics? Kent State University PDCS - 06 20