Introduction to Ad Hoc Mobile Wireless Networks cctsengjwit

Introduction to Ad Hoc Mobile Wireless Networks 電機學院電信研究所 曾志成 cctseng@jwit. edu. tw Jan 10, 2000 電信研究所 曾志成

Jan 10, 2000 2 Outline n n n Introduction Features Network architectures MAC protocols Routing protocols Conclusions 電信研究所 曾志成

Jan 10, 2000 3 Introduction n What is Ad Hoc Network? n n An Ad Hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration. Example: n n n Rescue Missions Exhibitions Conferences 電信研究所 曾志成

Jan 10, 2000 4 Features n n n 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

Jan 10, 2000 5 Network Architectures Hierarchical n n n Nodes are partitioned into clusters Some nodes are chosen as cluster heads Properties: n n easy to manage mobility sub-optimal routing 電信研究所 曾志成

Jan 10, 2000 6 Network Architectures Flat Topology n n All nodes are equal Each node is considered as a router n n n existence of multiple paths no “single-point-failure” flow control congestion control power efficiency 電信研究所 曾志成

Jan 10, 2000 7 MAC Protocols n Contention-based n CSMA-family n n n efficient under low load, unstable under heavy load users sense the channel at the transmitter but collisions occur at the receiver Contention-free n Reservation, Polling, Token passing n not efficient under light load, stable under heavy load 電信研究所 曾志成

Jan 10, 2000 MAC Protocols To 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 8

Jan 10, 2000 9 MAC Protocols MACA Protocol n n 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

Jan 10, 2000 10 Challenges of Routing Protocol n The topology may changes quite often. n n n n n 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

Jan 10, 2000 Characterization of Ad Hoc Routing Protocols 電信研究所 曾志成 11

Jan 10, 2000 n n n 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 12

Jan 10, 2000 13 Distance Vector Routing n n Distributed Bellman-Ford Each router n n n 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

Jan 10, 2000 Distance Vector Routing Counting-to-Infinity n Router A is “down” A B C D E 1 3 3 5 5 7 7. . 2 2 4 4 6 6 8. . 3 3 3 5 5 7 7. . 4 4 6 6 8. . n Router A is “up” A 電信研究所 曾志成 B C D E 1 1 2 2 2 3 3 4 14

Jan 10, 2000 15 Link State Routing n Who are my neighbors? n n Computes the cost between my neighbors. Builds up a link-state packet. Broadcasts the link-state packet. n n HELLO packet Flooding Computes a new path. n Dijkstra algorithm 電信研究所 曾志成

Jan 10, 2000 n n 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 16

Jan 10, 2000 Destination-Sequenced Distance-Vector Routing (2) 4 3 2 1 Des Next Metric SEQ NO. 1 2 2 S 406_MH 1 2 2 1 S 128_MH 2 3 2 2 S 564_MH 3 4 4 0 S 710_MH 4 5 6 2 S 392_MH 5 6 6 1 S 076_MH 6 7 6 2 S 128_MH 7 8 6 3 S 050_MH 8 5 8 6 7 1 電信研究所 曾志成 Des Next Metric SEQ NO. 1 6 3 S 516_MH 1 2 2 1 S 238_MH 2 3 2 2 S 674_MH 3 4 4 0 S 820_MH 4 2 S 502_MH 5 6 6 1 S 186_MH 6 7 6 2 S 238_MH 7 S 160_MH 8 8 6 3 17

Jan 10, 2000 Clusterhead Gateway Switch Routing (CGSR) (1) 5 4 3 1 Node Gateway Cluster Head 6 8 7 2 電信研究所 曾志成 18

Jan 10, 2000 n n n 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 19

Jan 10, 2000 20 The Wireless Routing Protocol (WRP) (1) (0, J) J 1 10 10 (2, K) B 5 1 K (1, K) (0, J) J I (2, K) (0, J) J J (10, B) B B I (10, I) 電信研究所 曾志成 K (11, B) I (2, K) K (infinity, -) (0, J) K (infinity, -) (2, K) B I (10, I)

Jan 10, 2000 n The Wireless Routing Protocol (WRP)(2) Each node responsible for maintaining four table: n n n n Distance table predecessor) (distance to each node from each neighbor and 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 21

Comparison (Table-Driven) Jan 10, 2000 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. 電信研究所 曾志成 22

Jan 10, 2000 Source-Initiated On-Demand Routing Protocols (1) n n n Create routes only when desired by the source node. Route discovery process. Route maintenance process. 電信研究所 曾志成 23

Jan 10, 2000 Ad Hoc On-Demand Distance Vector Routing (1) N 2 destination N 5 N 8 source N 1 N 7 N 4 N 3 N 2 N 5 N 8 N 1 source N 7 N 4 N 6 Propagation of RREQ destination N 3 N 6 Path of the RREP to the source 電信研究所 曾志成 24

Jan 10, 2000 n n n n Ad Hoc On-Demand Distance 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 25

Jan 10, 2000 26 Dynamic Source Routing (DSR) (1) N 2 N 1 source N 1 destination N 1 -N 2 N 5 N 1 -N 3 -N 4 N 1 -N 2 -N 5 N 1 -N 3 -N 4 N 1 -N 3 -N 4 -N 7 N 4 N 1 N 8 N 1 -N 3 -N 4 -N 6 N 2 N 1 -N 2 -N 5 -N 8 destination N 1 -N 2 -N 5 -N 8 N 5 N 1 -N 2 -N 5 -N 8 N 1 source N 7 N 4 N 6 N 3 Building of the route record during route discovery N 1 Propagation of the route reply with the route record 電信研究所 曾志成

Jan 10, 2000 n n 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 27

Jan 10, 2000 Temporally Ordered Routing Algorithm (TORA) (1) B A C A D C D G E B G E F F Assume G is the destination B A C A D E B C D G E F 電信研究所 曾志成 G F 28

Jan 10, 2000 n n Provide multiple routes. Three basic function: n n n Temporally Ordered Routing Algorithm (TORA) (2) 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 29

Jan 10, 2000 Associativity-Based Routing (ABR) (1) DEST BQ SRC RN[1] SRC LQ[H] RN[0] DEST 電信研究所 曾志成 30

Jan 10, 2000 n n 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: n n n Route discovery: broadcast query and await-reply, metric by association stability. Route reconstruction (RRC) Route Deletion 電信研究所 曾志成 31

Jan 10, 2000 Associativity-Based Routing (ABR) (3) n RRC in ABR: n n n SRC Node Movement DEST Node Movement Intermediate Nodes (Ins) Movement n n 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 32

Jan 10, 2000 n n Signal Stability Routing (SSR) (1) Route base on the signal strength between nodes and a node’s location stability. Cooperative protocols: n Dynamic Routing Protocol n n n 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 33

Jan 10, 2000 Comparison of Source-Initiated On-Demand Routing Protocols 電信研究所 曾志成 34

Jan 10, 2000 n n n 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 35

Proactive/Table-Driven Protocols Jan 10, 2000 n n n 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 36

Jan 10, 2000 n n n 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 37

Jan 10, 2000 38 Zone Routing Protocol n n A routing zone is defined to includes the nodes whose distance is at most some predefined number r. ZONE. 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

Signal Stability-Based Adaptive Routing Jan 10, 2000 n n Dynamic Routing Protocol (DRP) Forwarding Protocol (FP) Signal Stability Table (SST) Routing Table (RT) 電信研究所 曾志成 39

Jan 10, 2000 40 Cluster-Based Routing n n 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

Jan 10, 2000 41 Conclusions n n 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. Qo. S guaranteed needs to be addressed if multimedia application is considered. 電信研究所 曾志成