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Introduction to Ad Hoc Mobile Wireless Networks

Introduction to Ad Hoc Mobile Wireless Networks. 電機學院電信研究所 曾志成 cctseng@jwit.edu.tw. Outline. Introduction Features Network architectures MAC protocols Routing protocols Conclusions. Introduction. What is Ad Hoc Network?

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Introduction to Ad Hoc Mobile Wireless Networks

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  1. Introduction to Ad Hoc Mobile Wireless Networks 電機學院電信研究所 曾志成 cctseng@jwit.edu.tw

  2. Outline • Introduction • Features • Network architectures • MAC protocols • Routing protocols • Conclusions 電信研究所 曾志成

  3. Introduction • What is Ad Hoc Network? • An Ad Hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration. • Example: • Rescue Missions • Exhibitions • Conferences 電信研究所 曾志成

  4. Features • Lack of a centralized entity • All the communication is carried over the wireless medium • Rapid mobile host movements • Limited wireless bandwidth • Limited battery power • Multi-hop routing 電信研究所 曾志成

  5. Network ArchitecturesHierarchical • Nodes are partitioned into clusters • Some nodes are chosen as cluster heads • Properties: • easy to manage mobility • sub-optimal routing 電信研究所 曾志成

  6. Network ArchitecturesFlat Topology • All nodes are equal • Each node is considered as a router • existence of multiple paths • no “single-point-failure” • flow control • congestion control • power efficiency 電信研究所 曾志成

  7. MAC Protocols • Contention-based • CSMA-family • efficient under low load, unstable under heavy load • users sense the channel at the transmitter but collisions occur at the receiver • Contention-free • Reservation, Polling, Token passing • not efficient under light load, stable under heavy load 電信研究所 曾志成

  8. MAC ProtocolsTo Sense Or Not To Sense? Hidden terminal problem 1. A transmits to B 2. C wants to transmit to B. It does not hear A’s transmission, accesses the channel and collides. • Exposed terminal problem • 1. B transmits to A • 2. C wants to transmits to D. • It hears B’s transmission • and unnecessarily defers. 電信研究所 曾志成

  9. MAC ProtocolsMACA Protocol • RTS(Request To Send), CTS(Clear To Send) • Transmitter driven • Three-way handshake • Hidden terminal problem still exists 電信研究所 曾志成

  10. Challenges of Routing Protocol • The topology may changes quite often. • The router moves around dynamically. • The life time of a link decreases. • Lots of routing information are useless. • Hard to determine a route to the destination. • Network bandwidth • Power consumption • Convergence issues • Storage overhead • Computational overhead • Loop free 電信研究所 曾志成

  11. Characterization of Ad Hoc Routing Protocols 電信研究所 曾志成

  12. Table-Driven Routing Protocols • Each node respond to changes in network topology by propagating updates throughout the network. • Always a ready path for any O-D pair. • Low route delay, Bandwidth inefficiency 電信研究所 曾志成

  13. Distance Vector Routing • Distributed Bellman-Ford • Each router • contains a routing table. • periodically broadcasts to each of its neighbor routers its view of the distance to all hosts. • computes the shortest path to each host based on the information advertised by each of its neighbors. 電信研究所 曾志成

  14. Distance Vector Routing Counting-to-Infinity • Router A is “up” • Router A is “down” A B C D E A B C D E 2 2 4 4 6 6 8 . .  3 3 3 5 5 7 7 . .  4 4 4 4 6 6 8 . .  1 3 3 5 5 7 7 . .    2 2 2    3 3     4  1 1 1 1 電信研究所 曾志成

  15. Link State Routing • Who are my neighbors? • HELLO packet • Computes the cost between my neighbors. • Builds up a link-state packet. • Broadcasts the link-state packet. • Flooding • Computes a new path. • Dijkstra algorithm 電信研究所 曾志成

  16. Destination-Sequenced Distance-Vector Routing (1) • Each entry of routing table is marked with a sequence number assigned by destination nodes. • Freedom from loops in routing table. • Two possible types of packet: full dump and incremental. • The route labeled with the most recent sequence number is used, if ties, the one with the smallest metric is used. 電信研究所 曾志成

  17. Destination-Sequenced Distance-Vector Routing (2) Des Next Metric SEQ NO. 1 2 2 S406_MH1 2 2 1 S128_MH2 3 2 2 S564_MH3 4 4 0 S710_MH4 5 6 2 S392_MH5 6 6 1 S076_MH6 7 6 2 S128_MH7 8 6 3 S050_MH8 Des Next Metric SEQ NO. 1 6 3 S516_MH1 2 2 1 S238_MH2 3 2 2 S674_MH3 4 4 0 S820_MH4 2 S502_MH5 6 5 6 6 1 S186_MH6 7 6 2 S238_MH7 S160_MH8 8 6 3 4 5 3 2 8 6 1 7 1 電信研究所 曾志成

  18. Clusterhead Gateway Switch Routing (CGSR) (1) 5 4 3 6 8 1 7 2 Node Gateway Cluster Head 電信研究所 曾志成

  19. Clusterhead Gateway Switch Routing (CGSR) (2) • Hierarchical architecture. • Cluster head selection algorithm. • Least Cluster Change(LCC) clustering algorithm. • Use DSDV as underlying routing scheme with heuristic cluster-head-to-gateway routing approach. • Routing table and cluster member table. 電信研究所 曾志成

  20. The Wireless Routing Protocol (WRP) (1) (0,J) (0,J) J 10 J (2,K) 10 (2,K) 1 5 B I B I 1 (2,K) (2,K) K K (1,K) (infinity,-) (0,J) (0,J) J J (10,B) B I B I (10,I) (10,I) K K (11,B) (infinity,-) 電信研究所 曾志成

  21. The Wireless Routing Protocol (WRP)(2) • Each node responsible for maintaining four table: • Distance table (distance to each node from each neighbor and predecessor) • Routing Table (shortest distance and predecessor to each node) • Link-Cost Table • Message retransmission list(MRL) table • MRL records which updates in an update message need to be retransmitted and which neighbor should acknowledge the retransmission. • Hello Message required. • Avoid “count-to-infinity”. • Path-Finding Algorithm. 電信研究所 曾志成

  22. Comparison (Table-Driven) N =number or nodes in the network. D =diameter. h =height of routing tree x =number of nodes affected by topological change *WRP can use hierarchically. ** There is a separate protocol can support multicast.

  23. Source-Initiated On-Demand Routing Protocols (1) • Create routes only when desired by the source node. • Route discovery process. • Route maintenance process. 電信研究所 曾志成

  24. Ad Hoc On-Demand Distance Vector Routing (1) N2 destination N2 destination N5 N8 N5 N8 source N1 N1 N7 N4 N7 source N4 N3 N6 N3 N6 Propagation of RREQ Path of the RREP to the source 電信研究所 曾志成

  25. Ad Hoc On-DemandDistance Vector Routing (2) • Build on DSDV. • Pure on-demand route acquisition system. • Path recovery process: broadcast RREQ packet with sequence number. • The destination or intermediate node responds by unicasting a RREP packet back to the neighbor from which it first receive RREQ. • Only supports symmetric link. • Route maintenance: link failure notification is propagated. • Hello message can be used, but not required. 電信研究所 曾志成

  26. Dynamic Source Routing (DSR) (1) N2 destination N1-N2 N1-N2-N5 N1 N5 N8 N2 destination N1-N2-N5-N8 N1-N2-N5-N8 N1-N3-N4 N1-N3-N4-N7 N1-N2-N5-N8 N5 N8 source N1 N1-N3-N4 N7 N4 N1 N1-N3-N4 N1-N3-N4-N6 N1 N1-N3 N7 source N4 N3 N6 N3 N1 Building of the route record during route discovery Propagation of the route reply with the route record 電信研究所 曾志成

  27. Dynamic Source Routing (DSR) (2) • Each node maintain a route cache. • Route discovery: broadcast route request packet. Route reply is generated when reach either the destination or intermediate node. • Piggyback if no symmetric links. • Route maintenance: route error packet are generated when data link layer report, and route cache contained the hop are truncated. 電信研究所 曾志成

  28. Temporally Ordered Routing Algorithm (TORA) (1) B C B C A A D D G G E E F F Assume G is the destination B C B C A A D D G G E E F F 電信研究所 曾志成

  29. Temporally Ordered Routing Algorithm (TORA) (2) • Provide multiple routes. • Three basic function: • Route creation • Route maintenance: concept of link reversal. • Route erasure: using clear packet. • Establish Directed Acyclic Graph (DAG) similar to Lightweight Mobile Routing (LMR). • Require synchronized clocks. • Similar to the “count-to-infinity” problem. 電信研究所 曾志成

  30. Associativity-Based Routing (ABR) (1) DEST BQ SRC SRC RN[1] DEST LQ[H] SRC RN[0] DEST 電信研究所 曾志成

  31. Associativity-Based Routing (ABR) (2) • New routing metric: degree of association stability - connection stability of one node with respect to another node over time and space. • Three phase: • Route discovery: broadcast query and await-reply, metric by association stability. • Route reconstruction (RRC) • Route Deletion 電信研究所 曾志成

  32. Associativity-Based Routing (ABR) (3) • RRC in ABR: • SRC Node Movement • DEST Node Movement • Intermediate Nodes (Ins) Movement • Upper Arm IN’s Moves • Lower Arm IN’s Moves • Subnet-Bridging MH Movement • Concurrent Nodes Movement: 7 cases... 電信研究所 曾志成

  33. Signal Stability Routing (SSR) (1) • Route base on the signal strength between nodes and a node’s location stability. • Cooperative protocols: • Dynamic Routing Protocol • Signal Stability Table • Routing Table • Static Routing Protocol: passing packet up the stack if it is receiver or looking up in RT. 電信研究所 曾志成

  34. Comparison of Source-Initiated On-Demand Routing Protocols

  35. Comparison Between AODV and DSR • The communication overhead of DSR is larger. • The memory overhead of DSR is larger. • AODV require symmetric link. • DSR not using periodic routing advertisements. • DSR allow multiple routes to destination. 電信研究所 曾志成

  36. Proactive/Table-Driven Protocols • Attempts to continuously evaluate the routes within the network • Always a ready path for any O-D pair. • Distance vector: Each router maintains a table giving the distance from itself to all possible destination. • Link state: Each router maintains a complete picture of the topology of the entire network. • Low route delay, Bandwidth inefficiency 電信研究所 曾志成

  37. Reactive/On-Demand Protocols • Invoke a route determination procedure on demand only • Route construction/discovery • Route maintenance • Route optimization • Long route discovery delay • Not applicable for real-time communication 電信研究所 曾志成

  38. Zone Routing Protocol • A routing zone is defined to includes the nodes whose distance is at most some predefined number rZONE. • Inside the zone: proactive • Outside the zone: reactive • Only nodes at the boundary of zone are queried 電信研究所 曾志成

  39. Signal Stability-Based Adaptive Routing • Dynamic Routing Protocol (DRP) • Forwarding Protocol (FP) • Signal Stability Table (SST) • Routing Table (RT) 電信研究所 曾志成

  40. Cluster-Based Routing • Dividing the topology into a number of overlapping clusters. • Using broadcast routing and connectionless packet forwarding approach. 電信研究所 曾志成

  41. Conclusions • Some issues in the design of ad hoc networks are pointed out. • The MAC protocols need to solve the hidden terminal problem. • The routing protocols have to be able to adapt to the dynamic topology changes. • QoS guaranteed needs to be addressed if multimedia application is considered. 電信研究所 曾志成

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