The Mobile Multihop Solution in Ad hoc Networks

The Mobile Multi-hop Solution in Ad hoc Networks Speaker : Yu-Che Lin Adviser : Prof. Jian-Jiun Ding National Taiwan University Institute of Communication Engineering May 2007 1

Outlines n n n Preview of Development on Wireless Network Properties for Mobile Ad hoc Networks (MANET) Access in MANET n n n Routing in MANET n n The Unfairness Conditions in typical CSMA Topology-Aware Fair Access (TAFA) Broadcast – Efficiently Flooding Unicast – Routing Protocols n Proactive Routing n Reactive Routing (On-Demand) Conclusions & Future Works References 2

Preview of Development on Wireless Network (1) n Wireless Wide Area Network & Wireless Local Area Network n n n Large coverage Large power consume Complex distributed system Long bit address Personal Area Network n n Low coverage Low power consume TDMA or FH-SS Short bit address Ad hoc networks exist in those two modes 3

Preview of Development on Wireless Network (2) n Ad hoc n n n Cellular n n n Wireless local area network (WLAN) PAN - Bluetooth Packet radio Infrastructure-free GSM WAP GPRS 3 G Satellite n n Low Earth Orbit (LEO) Geostationary Earth Orbit (GEO) 4

Standards or Protocols n Mobile Ad hoc Networks (MANET) n n WLAN - 802. 11 Standards n n Protocols in physical layer and MAC layer PAN - 802. 15 Standards n n Protocols in MAC layer and IP layer (routing) Protocols in physical layer and MAC layer MANET Maintain the Physical and MAC Layers in 802. 11 or 802. 15 ! 5

Properties for Mobile Ad hoc Networks (MANET) n n n Dynamic Topologies Bandwidth-Constrained ; Variable Capacity Links Energy-Constrained Limited Physical Security Sparse Density 6

Access in MANET 7

The Unfairness Conditions in typical CSMA n The Near-Far problem n n n Square law under radio intensity Consequently collisions occurs n Solutions n Adaptively adjust the mobiles’ powers n Adaptively configure the mobiles’ contention windows Original or Derivative Flows 8

Four Targets in Topology. Aware Fair Access (TAFA) n n Exchange and Maintenance of Flow Information Adaptive Backoff Algorithm Switching Sender-Initiated and Receiver-Initiated Scheme as Appropriate Dealing with Two-Way Flows (TCP) 9

1. Exchange and Maintenance of Flow Information n The Service Tag n n The Direct Flag n n n The measurement for channel resource on the flow n Updated by the sender after receiving ACK Directly listening to channel Indirectly listening to channel The position Flag n n Original flows (data streams) Derivative flows (ACKs) 2 a c 1 b d In d’s flow table : 1 - Directly listening to b. 2 - Indirectly known by the b’s advertisement. 10

2. Flow-Aware Adaptive backoff algorithm n Among the Two Flags n n The service tag The direct flag 11

3. Switching Sender-Initiated (SI) and Receiver-Initiated (RI) Scheme n The Hybrid Scheme Alternate in Two Modes n n Sender-initiated (SI) n Typically RTS – CTS – data - ACK Receiver-initiated (RI) n Consequently fail in RTS n Sender invite the receiver to start next transmission n CTS – data – ACK 12

Routing in MANET 13

Broadcast – Efficiently Flooding n Distributed Heuristic n n n Find a dominating set (DS) in a heuristic way Partial nodes in DS, partial nodes connect to DS Multiple Relaying n n n 2 -hop neighbors n The neighbor of the neighbor Multipoint relays (MPRs) n Nodes that rebroadcast datagram n Decided by its 1 -hop neighbors n Contain all the 2 -hop neighbors MPR selector MPR nodes 2 -hop nodes s s MPR selector 14

Unicast – Routing Protocols n Proactive Routing n n All nodes maintain the routing table and have the topology information before transmitting Reactive Routing (On-Demand) n Discover the present route by transmitter querying instead maintain the huge information 15

Proactive Routing (1) n Distance Vector Protocols (Local Algorithm) n Destination-Sequenced Distance-Vector (DSDV) n Routing table n Using destination sequence numbers n Wireless Routing Protocol (WRP) n Routing table n Sequence numbers on next hop and next-to-last hop 16

Proactive Routing (2) n Link State Protocols (Global Algorithm) n n Optimized Link State Routing (OLSR) n Routing table n Using multipoint relays (MPRs) n Routing table exists in links between MPRs and their MPR-selectors n Suitable for large and dense networks Topology Broadcast Based on Reverse-Path Forwarding (TBRPF) n Routing table RT Reject n hop-by-hop routing along shortest paths forwarding n Source Tree based on topology table n Reported Tree (RT) n Path of each node to its shortest neighbor(s) n Nodes maintain only RTs 17

Reactive Routing (On-Demand) n Dynamic Source Routing (DSR) n n n Route request (RREQ) Route Reply (RREP) The intermediate nodes record a route through RREP (route cache) Path establish after RREP Ad hoc On-demand Distance Vector (AODV) n n n Route request (RREQ) Route Reply (RREP) Using sequence numbers Maintain the latest sequence number Ad hoc On-demand Multipath Distance Vector (AOMDV) offer multipath 18

Conclusions & Future Works n n Demand-based routing offers quick adaptation to dynamic link conditions, low processing and memory overhead, low network utilization, and determines unicast routes to destinations within the ad hoc network. proactive routing is desirable in a few of situations that only the bandwidth and the energy resources permission. It seams that the bounded improvement are in the result without the physical handling. Future work about antenna diversity is put in the next discussion. 19

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