Drahtlose Kommunikation. Infrastrukturlose Netze

Transkript

1 Drahtlose Kommunikation Infrastrukturlose Netze

2 Übersicht Untersuchte Netzstruktur und Problemstellungen Topologie-basierte Routingprotokolle Geographische Routingprotokolle 2

3 Large Scale Wireless Networks On board powered devices Wireless communication No network infrastructure 3

4 Large Scale Wireless Networks Example: sensor networks 4

5 Large Scale Wireless Networks Example: ad hoc networks 5

6 Large Scale Wireless Networks Example: robotic networks 6

7 Large Scale Wireless Networks Limited comm. range Regulatory constraints Implied network graph 7

8 Large Scale Wireless Networks Data communication: unicast, multicast, broadcast, anycast, geocast, 8

9 Large Scale Wireless Networks Topology control: neighbor elimination, backbone construction, virtual overlays, relocation, 9

10 Localized and Non-Localized Protocol Design Request neighbors? Localized: achieve a network wide objective with local decisions only 10

11 Localized and Non-Localized Protocol Design Inform network General hope that localized protocols: save resources, support arbitrary network scale, deal better with dynamics, still work when full network view is not possible Localized: achieve a network wide objective with local decisions only Non-localized: Local change may require a network wide decision 11

12 Routing Protocol classification d-hoc Routing Protocols non-localized Topology-based Geographic localized Proactive Reactive Remark 1: Topology control is typically achieved by a localized algorithm. Remark 2: In this lecture we do not consider topology control so much; just a few examples while explaining routing. asic Greedy Partial Flooding DFS-based Stateless Energy aware 12

13 Übersicht Untersuchte Netzstruktur und Problemstellungen Topologie-basierte Routingprotokolle Destination-Sequenced Distance-Vector Routing (DSDV) Optimized Link State Routing (OLSR) d-hoc On-Demand Distance Vector Routing (ODV) Dynamic Source Routing (DSR) Geographische Routingprotokolle 13

14 Topology-ased Routing Overview Topology-ased Routing Protocols Proactive (Table-driven) Reactive (Source-initiated on-demand) DSDV OLSR ODV DSR TOR 14

15 DSDV: Main Idea 15

16 DSDV: Table Maintenance? D E E E D E D D E D E D D E D E D E E E 16

17 DSDV: Shortest Paths D E F? D D E E F D E D E D E E E F E F F => or? D D E E F D E D E E E F E 17

18 DSDV: Shortest Paths F E D 0 1 E 2 D E 3 E E 1 F E D D D 1 E E 1 F D 2 E 2 F => F,? d = 2?

19 DSDV: Topology hanges inf D 2 2? 1 0 D D D 3 0 inf D 3? 2 1 D D 0 inf D inf 19

20 DSDV: Topology hanges inf D 2 D inf D D D D 0 inf D inf 3 inf D inf 2 D inf D D inf 1 20 D inf 1 2

21 DSDV: Sequence Numbers => D => D or => D? D => D 21

22 DSDV: Sequence Numbers => D, S = 42 = > D! D S = => D, S = 43 22

24 Proactive protocols OLSR ombine link-state protocol & topology control Optimized Link State Routing (OLSR) Topology control component: Each node selects a minimal dominating set for its two-hop neighborhood alled the multipoint relays Only these nodes are used for packet forwarding llows for efficient flooding Link-state component: Essentially a standard link-state algorithm on this reduced topology Observation: Key idea is to reduce flooding overhead (here by modifying topology) 24

25 Multipoint Relays MPR oncept Subset M of neighbors of given node S which covers all 2-hop neighbors of S Node is covered if it can receive message from S either directly or via 1-hop neighbor Nodes in subset M are called relay point Minimum-size multipoint relay is of interest for energy efficient broadcasting Reduce number of broadcast relays but over all nodes by the broadcast U Example for node S 1-hop neighbors:,,, D, E, F F X 2-hop neighbors: U, V, W, X multipoint relay: {,, D, E} S minimum-size multipoint relay: {, F} V E W Fact: Finding a minimum-size multipoint relay is NP complete pproximations required! Example greedy approximation D 25

26 Multipoint Relays Greedy approximation Repeat selecting node which maximizes set of not so far covered nodes Example (1) Maximum provided either by or F; select (2) Maximum provided then by F (3) ll nodes covered; result {, F} U F X V S E D W 26

28 ODV: Main Idea RREQ RREQ S RREQ D RREQ RREQ RREQ RREQ RREQ RREQ 28

29 ODV: Main Idea RREQ RREP D S 29

30 ODV: Main Idea D S 30

31 ODV: Node Mobility D RREQ S 31

33 DSR route discovery procedure Search for route from 1 to 5 [1] 1 [1] [1,7] 6 7 [1,7] [1,4] 4 1 [1,4,6] [1,7,2] 5 [1,7,3] [5,3,7,1] Node 5 uses route information recorded in RREQ to send back, via source routing, a route reply 33

34 Übersicht Untersuchte Netzstruktur und Problemstellungen Topologie-basierte Routingprotokolle Geographische Routingprotokolle Greedy-Routing und Planar-Graph-Routing Konstruktion von planaren Graphen Lokales Multicasting eispiel MSTEM 34

35 Localized Geographic Unicast Forwarding destination node source node ssumptions: Localization system Nodes know position of Themselves Their neighbors The destination 35

36 Geographic Greedy Routing (a) E D S T (b) G F S? T F E Strategy: select from nodes closer to the destination the one which minimizes a local cost metric D Problem: greedy routing failure 36

37 Recovery based on Planar-Graph Routing destination node source node 37

38 Planar Graph Routing Example P S T F 38

39 Planar Graph Routing Example P Q S T F 39

43 We need a Planar Graph W U V U V V Gabriel Graph (GG) Relative Neighborhood Graph (RNG) U Delaunay Triangulation (DT) 43

44 We need a UDG or QUDG r max U V r min U Unit disk graph (UDG) Quasi unit disk graph (QUDG) UDG: Localized GG and RNG versions based on 1-hop neighbors UDG: Localized DT version based on 2-hop neighbors (and less) QUDG: Sort of localized GG (possibly the same for RNG) 44

45 Problems and Limitations Locally constructing a planar graph in arbitrary networks is impossible u y x Even worse: localized unicast routing is impossible in arbitrary graphs v Localized single path algorithms deviation from shortest paths Let k be the hop/euclidean length of the shortest path connecting s and t Localized single path algorithms may produce paths of length O(k 2 ) Some even worse but some exist which are upper bounded by O(k 2 ) s t 45

46 Localized Unicast Routing in Practice! arbitrary graph wireless network graph Wireless network graph has structure! im at localized unicast approaches with high delivery rate Method of choice: sorts of clustering 46

47 Geographic lustering 47

51 K-Hop lustering 51

56 Localized Multicast Forwarding Problem destination node destination node destination node source node destination node ssumptions: Location system Nodes know position of Themselves Their neighbors The destinations 56

57 uilding locks T1 D S T2 T3 57

58 uilding locks Message Split T1 D S T2 T3 58

59 uilding locks Next Hop Selection T1 D S? T2 T3 59

60 uilding locks Recovery T1 D S? T2? T3 60

62 EMST ackbone ssisted Localized Routing T9 T1 T8 T7 S T1,,T9 T2 T3 T6 T5 T4 62

63 EMST ackbone ssisted Localized Routing T9 T1 T8 T7 T2 S T3 T6 T5 EMST(S,T1,,T9) T4 63

64 EMST ackbone ssisted Localized Routing T9 T1 T8 T7 D3 D1 T2 S T3 T6 T5 D2 T4 64

65 EMST ackbone ssisted Localized Routing T9 T1 T8 T7 T7,T8,T9 T2 S T4,T5,T6 T1,T2,T3 T3 T6 T5 T4 65

66 The ost over Progress Framework Which one is the better next hop node? V T1 T2 S T1,T2,T3 W T3 66

67 The ost over Progress Framework T1 V T2 S W T3 pproximate expected number of hops H(S,V) H(S,V) EMST(S,T1,T2,T3) / ( EMST(S,T1,T2,T3) - EMST(V,T1,T2,T3) ) pproximate expected cost (S,V) = cost(s,v) * H(S,V) Select node X which provides progress and minimizes (S,X) 67

68 MSTEM & MFE T6 T1 T5 F1 F2 S T2 T4 T3 68

69 MSTEM & MFE T6 T1 T5 F1 F2 S T2 T4 T3 69

70 MSTEM & MFE F1 V F2 W T3 S T1 F3 U T2 70

73 MSTEM & MFE S F1 V F2 T1 W p T3 F3 U T2 73

74 MSTEM & MFE F1 V F2 W S T1 F3 U T2 74

75 MSTEM & MFE F1 V F2 W S F3 U T2 75

76 Zusammenfassung Untersuchte Netzstruktur und Problemstellungen Topologie-basierte Routingprotokolle Geographische Routingprotokolle 76

77 Zusammenfassung Wir betrachteten hier: drahtlose Vernetzung ohne aufwendige (und kostenpflichtige) Infrastruktur bdeckung größerer Gebiete trotz limitierter Kommunikationsreichweite Multihop-Kommunikation Wir haben es hier somit hauptsächlich mit einem Netzwerkproblem zu tun Wesentliche Probleme: Routing und Topologiekontrolle npassung traditioneller Routing-Verfahren: Topologie-basiertes Routing Neuer Routing-nsatz auf der asis von Knotenkoordinaten Dieser nsatz erlaubt ganz neue Formen der Datenkommunikation und generell ganz neue Formen von Netzorganisation Generelles Paradigma, um mit der Dynamik solcher infrastrukturlosen Multihop- Netze umzugehen: lokale lgorithmen/verfahren Dieses Paradigma ist auch zur eherrschung von komplexen und dynamischen Internet-Overlay-Topologien anwendbar Mit den hier behandelten lokalen Verfahren wurde nur ein kleiner usschnitt eines interessanten Forschungsfeldes betrachtet Mehr in der Vorlesung Lokale Netzstrukturen 77