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High Performance Mobile Ad hoc Networking Herbert Rubens Baruch Awerbuch [email protected] [email protected] Johns Hopkins University Department of Computer Science Wireless Communication Lab wireless.cs.jhu.edu Presentation Overview Mobile Ad hoc Networking Overview Research Contributions Related Work The Pulse Protocol The Medium Time Metric Wave Relay System Feel free to ask questions throughout the presentation! Mobile Ad hoc Network A self configuring network of mobile routers connected by wireless links The routers may move freely, creating arbitrary network topologies The network topology can change rapidly and unpredictably Nodes communicate by wirelessly forwarding or relaying data through intermediate nodes The network can be connected to the larger Internet or operate independently http://en.wikipedia.org/wiki/Mobile_ad-hoc_network JHU Wave Relay Network Node Locations Determine Topology Mobile Ad hoc Networking Timeline Destination Sequenced Distance Vector (DSDV) Functions and Structure of a Packet Radio Station CD Player Apple Founded 1975 Microsoft Founded Herbert Benjamin Rubens 1979 Apple IIgs 1985 DARPA Packet Radio Networks Intel 486 Windows 3.0 1991 www Ad hoc On-demand Distance Vector (AODV) Y2K 1995 Dynamic Source Routing (DSR) Today Optimized Link-State Routing Protocol (OLSR) Burchfiel, J., Tomlinson, R., Beeler, M. (1975). "Functions and structure of a packet radio station". AFIPS: 245. Kahn, R. E. (January 1977). "The Organization of Computer Resources into a Packet Radio Network". IEEE Transactions on Communications COM-25 (1): 169–178. Kahn, R. E., Gronemeyer, S. A., Burchfiel, J., Kunzelman, R. C. (November 1978). "Advances in Packet Radio Technology". Proceedings of IEEE 66 (11): 1468–1496. Jubin, J., and Tornow, J. D. (January 1987). "The DARPA Packet Radio Network Protocols". Proceedings of the IEEE 75 (1). Fundamental Challenges Complex dynamics of a wireless link Continuously fluctuating RF environment (without mobility!) Bit Error Rate Modulation Different modulations work better in different RF environments Multi-path, channel fading, delay spread Link Capacity Mobility Further increases wireless link dynamics Creates hard transitions = small packets more reliable then large packets walk around a corner and everything changes If all of the links are continuously changing, how do you select a set of links to form a path? Research Objectives Scalability Design routing algorithms which scale to thousands of devices while minimizing control overhead Routing algorithm must perform under vehicular mobility, urban channel fading, and arbitrary communication patterns Efficiency Selected routes must: Maximize individual path capacity Minimize network resource consumption Continuously adapt to changes Research Contributions Medium Time Metric (MTM) Pulse Protocol First route selection metric to consider multi-rate radios Provably optimal route selection in small to medium sized networks Experimental results and simulated results validate approach Extremely scalable routing protocol designed for mobile networks Optimized for infrastructure access and peer-to-peer traffic patterns Protocol extensions provide integrated time synchronization and power saving Sensor Network Pulse Protocol Directly trades route activation delay for power saving efficiency Optimized for infrequently changing sensor network topologies Optimized for sensor to collector traffic model Publications Relevant to Thesis MONET Journal – “The Medium Time Other work Algorithms for the On-Demand Secure Byzantine Routing Protocol” Metric: High Throughput Route Selection in Multi-rate Wireless Networks” WONS 2005 – “The Pulse Protocol: ESAS 2006 – “Dynamics of Learning SECURECOM 2005 – “On the Survivability of Routing Protocols in Ad Hoc Wireless Networks” Mobile Ad hoc Network Performance Evaluation” MILCOM 2004 – “The Pulse Protocol: NDSS 2005 – “Secure Multi-hop INFOCOM 2004 – “The Pulse Protocol: INFOCOM 2005 – “Provably Competitive WONS 2004 – “High Throughput Route IZS 2004 – “Swarm Intelligence Routing WiSE 2002 – “An On-Demand Secure Sensor Network Routing and Power Saving” Energy Efficient Infrastructure Access” Selection in Multi-rate Wireless Networks” Infrastructure Access” Adaptive Routing” Resilient to Byzantine Adversaries” Routing Protocol Resilient to Byzantine Failures” Existing Approaches Receivers Urban Channel Environment 10 5 • Multi-path fading & shadowing 0 -5 • Rapidly changing channel conditions -10 -15 -20 0 200 400 600 800 1000 1200 1400 1600 1800 2000 Reactive On-Demand Protocols (AODV, DSR) 10 5 • On-demand protocols have no prior knowledge of channels conditions 0 -5 -10 • A RREQ packet provides only a single sample of a complex distribution -15 -20 0 200 400 600 800 1000 1200 1400 1600 1800 2000 10 5 0 -5 -10 Destination -15 Source -20 -25 • Channel is continuously changing -30 -35 -40 Proactive Link State Protocols (OLSR, TBRPF) 0 200 400 600 800 1000 1200 1400 1600 1800 2000 • Continuous flooding from every node in the network 10 5 0 -5 • Hello Protocol – detects link changes -10 -15 -20 -25 -30 -35 -40 0 200 400 600 800 1000 1200 1400 1600 1800 2000 You can not accurately track channel with control packets! How Often Does Connectivity Change? 10% of min-hop paths fail within 1.3 seconds After 5 seconds 25% of min-hop paths have failed On-Demand routes may only work for a short period of time Link State Protocols need to flood every time a link changes These simulations only consider changes from connected not connected (in free space) What about changes in link speed? Reliability? Hard transitions in a real environment? Fast-fading and urban channel effects? Connectivity is continuously changing at an extremely fast rate! Simulation: • 100 Nodes • 1000m x 1000m area • Random Waypoint Mobility (Max Speed=20m/s) • Calculate All-to-All shortest path initially, then track how long until the route fails Pulse Protocol Outline Pulse Protocol Overview Scalable multi-hop ad hoc routing protocol Based on Tree Routing Tree Routing vs. Direct Routing The Pulse Protocol Proactive Component Tracks minimum amount of information to avoid flooding for route establishment and maintenance Periodic flood operation (similar to Hello Protocol) Proactively rebuilds spanning tree Estimates neighbors, density, SNR, loss rates, capabilities, number of radios, MTM metric On-Demand Component Route establishment Using only UNICASTS! Gratuitous mechanism Neighbors promiscuously monitor packets Metric tracked at the speed of data packets NOT control packets! Path switches as metrics change Local changes in connectivity only generate local traffic Unlike BOTH on-demand and link state protocols Ad hoc Nodes Network Connectivity Pulse Flood Spanning Tree Source and Destination Need to Establish a Path Pulse Response Sent to Root Destination Paged on Next Pulse Destination Sends Pulse Response Path Option 1: Through the Root Through the Root Path 9 Hops Shortest Path 2 Hops This option is inefficient! It is not necessary to go to the root. Better routes already exist! Path Option 2: Tree Traversal Tree Traversal Path 5 Hops Shortest Path 2 Hops Path Option 3: Tree Shortcut Tree Shortcut Path 3 Hops Shortest Path This is the initially selected path of the Pulse protocol. 2 Hops Path Optimization: Gratuitous Reply Selected Path 2 Hops Shortest Path 2 Hops Node sends gratuitous reply Proactive Route Maintenance Proactive Route Maintenance Tree Routing vs. Direct Routing Direct Routing Attempts to initially discover the shortest path Link state tracks every link in the network regardless of whether it is used a shortest path spanning tree for every node in the network On-Demand Requires large overhead floods the network to establish a route re-floods when ever the path breaks a shortest path spanning tree for all nodes transferring data Tree Routing Proactively rebuilds a single spanning tree on top of the network Boot straps communication off of the tree route Route are not initially the direct shortest path, but routing mechanism allows the path to converge towards the shortest path Active destinations can be reached without flooding the network Efficient operation for realistic traffic patterns Pulse Protocol Concepts Aggregation – for scalability Spanning tree represents a compressed view of the network topology Pro-active component maintains the minimum amount of information to allow efficient route establishment De-Aggregation – for efficiency The routing metric is tracked at the speed of the data flow Changes to the metric are only reported locally Routes are continuously adjusted as the metrics change High speed accurate route tracking is essentially an on-demand decompression of the topology However, it occurs ONLY in areas of the network with active data flows Result: a scalable routing structure which tracks paths at the speed of the data flow Internet Gateway Example • All nodes routing to centrally located internet gateway • Best possible case for Pulse Protocol • Pulse source is designated as the centrally located gateway • Representative of Pulse internet access deployment at JHU • Similar to DoD “Reach Back” model Representative of most common real-world communication model Delivery Ratio Simulations DSR Pulse • Pure peer-to-peer communication pattern • Pulse source is an arbitrary mobile node SNS Scalability Simulation 10 km Size: 10 km x 10 km Nodes: 5,000 Speed: 1 m/s Traffic: 5 Mbps Delivery Ratio: 97.2% 10 km Links: 50,000 on average • 100 stationary backbone nodes were arranged in a 10 by 10 grid • 5000 nodes were randomly placed and moved randomly • Exponential random traffic pattern was used • A network of 5,000 nodes could contain up to 25 million wireless links. Medium Time Metric Outline Why do wireless radios operate at multiple rates? Minimum Hop Metric shortcomings Medium Time Metric Advantage of Multi-Rate? 1 Mbps 2 Mbps 5.5 Mbps 11 Mbps • 802.11g • 1,2,5,6,11,12,18,24,36,48,54 Mbps • 802.11n (draft) • A lot more! Up to 300 Mbps. Direct relationship between communication rate and the channel quality required for that rate As distance increases, channel quality decreases Therefore: tradeoff between communication range and link speed Multi-rate provides flexibility Challenge to the Routing Protocol Must select a path from Source to Destination Links operate at different speeds Fundamental Tradeoff Fast/Short links = low range = many hops/transmissions to get to destination Slow/Long links = long range = few hops/transmissions Minimum Hop Metric (Traditional Technique) Not designed for multi-rate networks A small number of long slow hops provide the minimum hop path These slow transmissions occupy the medium for long times, blocking adjacent senders Selecting nodes on the fringe of the communication range results in reduced reliability New Approach: Medium Time Metric (MTM) Assigns a weight to each link proportional to the amount of medium time consumed by transmitting a packet on the link Enables the Pulse protocol to discover the path that minimizes total transmission time MTM Example Medium Time Usage Destination Link Throughput 11 Mbps 2.5ms 4.55 Mbps 5.5 Mbps 3.7ms 3.17 Mbps 2 Mbps 7.6ms 1.54 Mbps 1 Mbps 13.9ms 0.85 Mbps Source Path Medium Time Metric (MTM) Path Throughput 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps 1 13.9ms = 13.9 ms 0.85 Mbps MTM Example Medium Time Usage Destination Link Throughput 11 Mbps 2.5ms 4.55 Mbps 5.5 Mbps 3.7ms 3.17 Mbps 2 Mbps 7.6ms 1.54 Mbps 1 Mbps 13.9ms 0.85 Mbps Source Path Medium Time Metric (MTM) 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps 5.5 + 2 1 3.7ms 13.9ms 7.6ms Path Throughput = 11.3 ms = 13.9 ms 1.04 Mbps 0.85 Mbps MTM Example Medium Time Usage Destination Link Throughput 11 Mbps 2.5ms 4.55 Mbps 5.5 Mbps 3.7ms 3.17 Mbps 2 Mbps 7.6ms 1.54 Mbps 1 Mbps 13.9ms 0.85 Mbps Source Path Medium Time Metric (MTM) 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps 11 + 2 2.5ms 7.6ms 5.5 + 2 3.7ms 1 13.9ms 7.6ms Path Throughput 1.15 Mbps = 10.1 ms = 11.3 ms = 13.9 ms 1.04 Mbps 0.85 Mbps MTM Example Medium Time Usage Destination Link Throughput 11 Mbps 2.5ms 4.55 Mbps 5.5 Mbps 3.7ms 3.17 Mbps 2 Mbps 7.6ms 1.54 Mbps 1 Mbps 13.9ms 0.85 Mbps Source Path Medium Time Metric (MTM) 11 + 11 11 Mbps 5.5 Mbps 2 Mbps 1 Mbps 2.5ms 2.5ms = 5.0 ms 11 + 2 2.5ms 7.6ms 5.5 + 2 3.7ms 1 Path Throughput 13.9ms 7.6ms 2.38 Mbps 1.15 Mbps = 10.1 ms = 11.3 ms = 13.9 ms 1.04 Mbps 0.85 Mbps MTM Advantages Paths which minimize network utilization, maximize network capacity Avoiding low speed links inherently provides increased route stability Global optimum under complete interference Excellent heuristic in even larger networks High speed links operate with greater margin and are more elastic under changes Experimental results show up to 17 times greater throughput using MTM in 802.11g networks Wave Relay System and Test-bed Wave Relay Test-bed Over 50 Wave Relay Routers deployed across JHU Campus Urban City Environment Internet Access, Ad hoc Access Points, Voice over IP Mobility testing from automobiles Over 100 JHU students simultaneously use network each day for Internet Access System tested at Holcim Industrial Plant (Chicago, IL) Complex propagation environment Enabled real-time industrial process control Currently Deployed Custom Applications Military Distributed Battlefield Mapping GPS based interactive map Eventual reliability Locality Specific Messaging System GPS based messaging system Messages targeted to any user at a specific location Wave Relay Device Software Pulse Protocol [Infocom’04, Milcom’04, WONS’05] Scalable ad hoc routing protocol Active path tracking Based on Tree Routing strategy Medium Time Metric [MONET,WONS’04] High Throughput Path Selection Increased Path Elasticity Efficient Multi-rate Operation Hardware Handles merge, partition, failure Embedded Linux Distribution Leader Election Algorithm Embedded Single Board Computer Less then 8 MB storage requirement Linux Kernel Module 2.4 and 2.6 compatibility Operates at layer 2 Distributed virtual switch architecture provides seamless bridging Intel IXP425 Network Processor On-chip Cryptographic Accelerator 64 Mb Ram onboard 4 mini-PCI interfaces Dual 10/100 Ethernet Compact flash interface Serial port / JTAG / GPIO Hardware Watchdog Power over Ethernet +9V to +48V DC Input Atheros 802.11g/b Wireless Card 16 MB Intel Strata Flash Garmin GPS 16 receiver Li-Ion Battery Pack Industrial NEMA 67 Enclosure 400 mW (26 dBm) output power Stores OS & Wave Relay software ~20 hours continuous runtime 4 N-type antenna mounts 2 Ethernet Ports (6) protection against dust (7) water submersible Wireless Shuttle Bus Project http://wireless.cs.jhu.edu/mobile/ Conclusion The Pulse Protocol provides scalable routing under high levels of mobility The Medium Time Metric selects high throughput routes and minimizes consumption of the shared wireless medium The Wave Relay test-bed demonstrates the effectiveness of the Pulse + MTM protocols in a real-world urban environment Thank You! Questions?