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Mobile Ad-hoc Networks (MANET)

Mobile Ad-hoc Networks (MANET). Ad-hoc network: A collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. Significant differences to existing wired networks: Wireless Self-starting No administrator

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Mobile Ad-hoc Networks (MANET)

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  1. Mobile Ad-hoc Networks (MANET) • Ad-hoc network: • A collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. • Significant differences to existing wired networks: • Wireless • Self-starting • No administrator • Cannot assume that every computer is within communication range of every other computer • Possibly quite dynamic topology of interconnections • Traffic types: unicast/multicast/anycast/geocast Wireless Networking

  2. Routing in MANET • Routing assumptions for unicast traffic • Flat topology assumption • Proactive: DSDV, TORA, WRP • Reactive: AODV, DSR, STAR • Hierarchical topology assumption • Clustering: CBRP, PATM • Geographic assumption • Location aided routing: LAR, GeoCast Wireless Networking

  3. Unicast-Routing Protocol for MANET (Topology-based) Table-Driven/ Proactive Hybrid On-Demand /Reactive Clusterbased/ Hierarchical Distance Vector Link- State ZRP DSR AODV TORA LANMAR CEDAR DSDV OLSR TBRPF FSR STAR MANET: Mobile Ad hoc Network (IETF working group) Classification of Routing Protocols for MANETS Wireless Networking

  4. Desired Properties of Ad Hoc Routing Protocols • Distributed • Bandwidth efficient • Reduce control traffic/overhead • Battery efficient • Fast route convergence • Correct: loop free • Reduce overhead • Unidirectional Link Support Wireless Networking

  5. Performance Metrics of Ad Hoc Routing Protocols • Maximize • end-to-end throughput • delivery ratio • Minimize • Congestion (load-balancing) • end-to-end delay • packet loss • shortest path/minimum hop (route length) • overhead (bandwidth) • energy consumption Wireless Networking

  6. Mobile Ad hoc Networks (MANET) vs. Sensor Networks Wireless Networking

  7. source 2 source 1 source 2 source 1 source 2 Address Centric Routing (AC) Temperature Reading (source 2) Temperature Reading (source 1) Z B Give Me The Average Temperature? ( sink ) Wireless Networking

  8. source 2 source 1 source 2 source 1 & 2 Data Centric Routing (DC) Temperature Reading (source 2) Temperature Reading (source 1) Z B Give Me The Average Temperature? ( sink ) Wireless Networking

  9. Dynamic Source Routing (DSR) [Johnson96] • When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery using Route Request (RREQ) • Each node appends own identifier when forwarding RREQ • Promiscuous mode Wireless Networking

  10. Route Discovery in DSR Y Z S E F B C M L J A G H D K I N Represents a node that has received RREQ for D from S Wireless Networking

  11. Route Discovery in DSR Y Broadcast transmission Z [S] S E F B C M L J A G H D K I N Represents transmission of RREQ [X,Y] Represents list of identifiers appended to RREQ Wireless Networking

  12. Route Discovery in DSR Y Z S [S,E] E F B C M L J A G [S,C] H D K I N • Node H receives packet RREQ from two neighbors: • potential for collision Wireless Networking

  13. Route Discovery in DSR Y Z S E F [S,E,F] B C M L J A G H D K [S,C,G] I N • Node C receives RREQ from G and H, but does not forward • it again, because node C has already forwarded RREQ once Wireless Networking

  14. Route Discovery in DSR Y Z S E F [S,E,F,J] B C M L J A G H D K I N [S,C,G,K] • Nodes J and K both broadcast RREQ to node D • Caveat: Since nodes J and K are hidden from each other, their • transmissions may collide Wireless Networking

  15. Route Discovery in DSR • Broadcast storm prevention • Drop previously seen messages • Loop prevention • Host drops messages with its address in route record (like BGP) Wireless Networking

  16. Route Discovery in DSR • Destination D on receiving the first RREQ, sends a Route Reply (RREP) • RREP is sent on a route obtained by reversing the route appended to received RREQ • Not always the case, sometimes need new route request • RREP includes the route from S to D on which RREQ was received by node D Wireless Networking

  17. Route Reply in DSR Y Z S RREP [S,E,F,J,D] E F B C M L J A G H D K I N Represents RREP control message Wireless Networking

  18. Dynamic Source Routing (DSR) • Node S on receiving RREP, caches the route included in the RREP • When node S sends a data packet to D, the entire route is included in the packet header • hence the name source routing • Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded Wireless Networking

  19. Data Delivery in DSR Y Z DATA [S,E,F,J,D] S E F B C M L J A G H D K I N Packet header size grows with route length Wireless Networking

  20. Data Delivery in DSR • Send route error packet if next hop cannot be reached • Delete route from the cache when receiving error packet • Passive acknowledgement: • When node overhears next hop forwarding message. Wireless Networking

  21. DSR Optimization: Route Caching • Each node caches a new route it learns by any means • Through Route Request (RREQ) • When node K receives RREQ [S,C,G] destined for node D, node K learns route [K,G,C,S] to node S • Through Route Reply (RREP) • When node S finds RREP [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F • When node F forwards RREP[S,E,F,J,D], node F learns route [F,J,D] to node D Wireless Networking

  22. DSR Optimization: Route Caching • Through DATA packet’s source routes • When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D • A node may also learn a route when it overhears Data • Problem: Stale caches may increase overheads • Splicing of cached routes • Example: know [A,H,I] overheard [I,G,F] Wireless Networking

  23. DSR Optimization: Piggybacking • Possible to piggyback route reply on new route requests • Also small data • TCP handshake • Host must forward piggybacked data when replying to request with cached routes Wireless Networking

  24. DSR Optimization: Error Handling • Disconnected network leads to repeated route requests • Addressed through exponential backoff • Eavesdropping on route error packets • Temporarily mark invalid route • Other nodes may reply with invalid cached routes Wireless Networking

  25. Dynamic Source Routing: Advantages • Routes maintained only between nodes who need to communicate • reduces overhead of route table maintenance • Routing cache can further reduce route discovery overhead • A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches Wireless Networking

  26. Dynamic Source Routing: Disadvantages • Packet header size grows with route length due to source routing • Flooding of route requests may potentially reach all nodes in the network • Stale caches will lead to increased overhead Wireless Networking

  27. Distance-Vector routing • Each node maintains a routing table containing • Number of hops to each destination • Next hop to reach each destination • list of all destinations • The succession of next hops leads to a destination • Each node periodically broadcasts its current estimate of the shortest distance to each available destination to all of its neighbors • Typical representative: Distributed Bellman-Ford (DBF) Wireless Networking

  28. AODV (Ad Hoc On-Demand Distance Vector) • AODV is based on the DSDV (Destination-Sequenced Distance Vector) algorithm • Distance vector • Different sequence numbers for each destination. • Creation of routes on a demand basis – traffic reactive • Nodes that are not on a selected path do not maintain routing information or participate in routing table exchanges! • Goal: Minimize broadcast overhead and transmission latency Wireless Networking

  29. Route Sequence Numbers • Unique counter for each destination • Symbolizes the “freshness” of a route • Source specifies the most recently known route during route establishment • Updated occasionally • Link failure • Destination moves • Intermediate nodes move Wireless Networking

  30. Route Requests from S to D in AODV Y Z S E F B C M L J A G H D K I N Represents a node that has received RREQ for D from S Wireless Networking

  31. Route Requests from S to D in AODV Y Broadcast transmission Z S E F B C M L J A G H D K I N Represents transmission of RREQ Wireless Networking

  32. Route Requests from S to D in AODV Y Z S E F B C M L J A G H D K I N Represents links on Reverse Path Wireless Networking

  33. Reverse Path Setup from S to D in AODV Y Z S E F B C M L J A G H D K I N • Node C receives RREQ from G and H, but does not forward • it again, because node C has already forwarded RREQ once Wireless Networking

  34. Reverse Path Setup from S to D in AODV Y Z S E F B C M L J A G H D K I N Wireless Networking

  35. Reverse Path Setup in AODV Y • Node D does not forward RREQ, because node D • is the intended targetof the RREQ Z S E F B C M L J A G H D K I N Wireless Networking

  36. Route Reply from D to S in AODV Y Z S E F B C M L J A G H D K I N Represents links on path taken by RREP Wireless Networking

  37. Route Reply in AODV • Intermediate node may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender S • Recent path means higher sequence number • The likelihood that an intermediate node will send a RREP not as high as DSR • An intermediate node which knows a route, but with a smaller sequence number, cannot send Route Reply Wireless Networking

  38. Forward Path Setup in AODV Y Z S E F B C M L J A G H D K I N Forward links are setup when RREP travels along the reverse path Represents a link on the forward path Wireless Networking

  39. Data Delivery in AODV Routing table entries used to forward data packet. Route is not included in packet header. Y DATA Z S E F B C M L J A G H D K I N Wireless Networking

  40. Local Link Maintenance • Periodic “hello” messages broadcast to immediate neighbors • Failing to receive hello messages indicates a link failure • Link failure notifications sent to source nodes • Sources rediscover new route to destination Wireless Networking

  41. AODV Key Advantages • “Partial” routing tables are constructed reactively • Entries are updated only when a node sends to an unreachable node • No periodic global updates • Node not on active paths maintain no routing entries  Reduce packet overhead • Routing table • No source routing needed  reduce bit overhead • “Route caching”  reduce establishment latency • Sequence number  override stale routes • source based broadcast id loop freedom • Push link failure to relevant nodes  Reduce establishment latency Wireless Networking

  42. AODV and DSR : Disadvantages • Common problems for both AODV and DSR • Potential collisions between route requests propagated by neighboring nodes • Insertion of random delays before forwarding RREQ • Increased contention if too many route replies come back due to nodes replying using their local cache - Route Reply Storm problem • Random delays + carrier sensing Wireless Networking

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