Papers. Ad Hoc Routing. Outline. Motivation

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1 CS E: Wireless Networks (Spring 2006) Ad Hoc Routing Discussion Leads: Abhijit Deshmukh Sai Vinayak Srinivasan Seshan Dave Andersen Papers Outdoor Experimental Comparison of Four Ad Hoc Routing Algorithms Gray, Dubrovsky, Masone, Kotz, Fiske, McGrath, Newport, Liu, Yuan A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols Broch, Maltz, Johnson, Hu, Jetcheva Link-level Measurements from an b Mesh Network Aguayo, Bicket, Biswas, Judd, Morris Outline Motivation Outdoor Experimental Comparison APRL ODMRP AODV STARA Performance Comparison DSDV TORA DSR AODV Link-level Measurements, Mesh Networks RoofNet Temporal and Spatial Variation Take Aways Q & A Motivation Infrastructureless Networks Ad Hoc Routing Algorithms? Issues coupled with Wireless Ad Hoc? Dynamic Nature Limited Transmission Range Node as a router No Maintenance Tradeoff: Link state maintenance & Messaging complexity 1

2 Ad Hoc Network Routing Protocols AdHoc Routing Algorithms (1) APRL STARA AODV ODMRP Proactive Reactive APRL STARA AODV ODMRP APRL Proactive Routing Periodic Beaconing Ping Destination Via Neighbor (PDVN) Features Loopless routing Any path (not necessarily the shortest) STARA Proactive Scheme Periodic broadcast of neighborhood probe packets NP and NP_ACKs Probabilistically chooses neighbor thru which to route packet First uniform, then based on end to end latency Sends dummy data packets (DDPS) to update latency information of alternate routes 2

3 AODV Reactive Scheme Route request (RREQ) packet to explore route to destination Route response (RREP) along reverse route Link failure detection? Periodic Hello messages Link layer detection ODMRP Reactive routing protocol Route establishment Similar to AODV Sender broadcasts JoinQuery Interested parties respond with JoinReplies Sender piggybacks data packet along with JoinQuery Outdoor Evaluation-Experimental Setup Analysis All 4 algos implemented at the user level Apps use virtual interface, Routing algos use physical interface UDP Traffic + Multicast IP Traffic Generator Packet Number + sizes 2 Gaussian Distributions Delay b/w packet streams 2 Exponential Distributions Destination Laptops 1 Uniform Distribution Message Delivery Ratio Communication Efficiency Hop Count 3

4 Analysis (Contd.) Zero Hop Failures Stara-S 88% APRL 63% AODV 25% Final Verdict AODV Good in limited bandwidth or energy resources OMDRP If bandwidth and energy resources are plentiful & data packets are small and reliability is crucial Reactive is better than proactive Tradeoff in AD-HOC algorithms Efficiency vs. Reliability DSDV (Destination-Sequenced Distance Vector) Distance Vector Routing Protocol Tag Route with Sequence Number Updates Periodically Infinite-metric route DSDV vs. DSDV-SQ Change == new metric Triggered update == New sequence number Overhead vs. packet delivery ratio DSDV (Destination-Sequenced Distance Vector) Advantages loop-free fewest-hop path Disadvantages Periodic updates Maintaining routes in the presence of mobility Route info. may be expensive and unnecessary 4

5 TORA (Temporally Ordered Routing Algorithm) Highly adaptive, loop-free distributed algorithm Link-reversal Maintain a mesh Local Adaptation Key Design Concept localization of control messages to a very small set of nodes near the occurrence of a topological change. Three basic steps Route creation Route maintenance Route erasure A Link Reversal B F C E G Any node, other than the destination, that has no outgoing links reverses all its incoming links. Node G has no outgoing links D Represents a link that was reversed recently Link Reversal A B F C E G TORA QUERY packet propagation UPDATE packet subsequent height increase of neighbors CLEAR packet Incase of a network partition D Now all nodes (other than destination D) have an outgoing link 5

6 TORA Advantages Loop free paths Establish routes quickly, before topology changes Able to detect network partitions very quickly Disadvantages Temporary oscillations (count to infinity type) Needs synchronization DSR (Dynamic Source Routing) Source Routing On-demand Two mechanisms Route Discovery ROUTE REQUEST (propagating, non-propagating) Route Maintenance DSR (Dynamic Source Routing) DSR (Dynamic Source Routing) Advantages Reactive: only active routes Route caching : reduce route discovery overhead Disadvantages Packet header size Collisions between route requests and route reply? Route Request Reply 6

7 Evaluation DSR vs. AODV-LL Similar shape, yet AODV has greater overhead? Propagation of route discovery packets to all nodes 2200 route discoveries DSR: 950 non-propagating propagating DSDV-LL : 110,000 ROUTE REQUEST TORA Congestive Collapse Positive feedback loop MAC-layer collisions Evaluation Evaluation DSDV-SQ Constant Overhead Periodic update with new sequence number Link Level Measurements in Mesh Networks Analyze cause of packet loss Neighbor Abstraction Ability to hear control packets or No Interference Strong correlation between BER and S/N RoofNet pairs communicate At intermediate loss rates Temporal Variation Spatial Variation 7

8 Roofnet Node Map Typical Rooftop View 1 kilometer A Roofnet Self-Installation Kit RoofNet Antenna ($65) 8dBi, 20 degree vertical 50 ft. Cable ($40) Low loss (3dB/100ft) Computer ($340) 533 MHz PC, hard disk, CDROM Miscellaneous ($75) Chimney Mount, Lightning Arrestor, etc b card ($155) Engenius Prism 2.5, 200mW Software ( free ) Our networking software based on Click Total: $685 Takes a user about 45 minutes to install on a flat roof Implies failure of Neighbor Abstraction 8

9 RoofNet (Spatial Distribution of Loss Rates) RoofNet (Effect of Signal-to-Noise Ratio) High S/N == high delivery probabilities Range of S/N values > 3 db Reasons for Differences? Different Antenna Heights Multi-path fading RoofNet (Effect of Power Level) milliwatts doubles delivery RoofNet (Effect of Multi-Path) Significant losses inter-node distance Reflected signal delayed by a microsecond Approx 300 meters 9

10 Q & A 10