1 Introduction to Wireless Ad-Hoc Networks Routing Michalis Faloutsos Some slides borrowed From Guor-Huar Lu

2 Outline Challenges Design Goals Specified by MANET (for now…) Types of Routing Protocols in Detail Conclusion

3 Challenges Dynamic Topologies Bandwidth-constrained, variable capacity links Energy-constrained Limited Physical security Scalability

4 Types of routing Flat Proactive Routing Link state Fish-Eye Routing, GSR, OLSR. Table driven: Destination-Sequenced Distance Vector ( DSDV), WRP) On-Demand or Reactive Routing Ad hoc On-demand Distant Vector (AODV) Dynamic Source Routing (DSR) Hybrid Schemes Zone Routing ZRP, SHARP (proactive near, reactive long distance) Safari (reactive near, proactive long distance) Geographical Routing Hierarchical: One or many levels of hierarchy Routing with dynamic address Dynamic Address RouTing (DART), L+

5 Proactive Protocols Proactive: maintain routing information independently of need for communication Update messages send throughout the network periodically or when network topology changes. Low latency, suitable for real-time traffic Bandwidth might get wasted due to periodic updates They maintain O(N) state per node, N = #nodes

6 On-Demand or Reactive Routing Reactive: discover route only when you need it Saves energy and bandwidth during inactivity Can be bursty -> congestion during high activity Significant delay might occur as a result of route discovery Good for light loads, collapse in large loads

7 Hybrid Routing Proactive for neighborhood, Reactive for far away (Zone Routing Protocol, Haas group) Proactive for long distance, Reactive for neighborhood (Safari) Attempts to strike balance between the two

8 Hierarchical Routing Nodes are organized in clusters Cluster head “controls” cluster Trade off Overhead and confusion for leader election Scalability: intra-cluster vs intercluster One or Multiple levels of hierarchy

9 Geographical Routing Nodes know their geo coordinates (GPS) Route to move packet closer to end point Protocols DREAM, GPSR, LAR Propagate geo info by flooding (decrease frequency for long distances)

10 Dynamic Routing: a new approach DART Ericsson et al., L+ Morris et al Goal: can we enforce address aggregation But: nodes are moving Then: address should change

11 Dynamic Routing: general idea Separation of identity and address Identity is who you are Address is where you are Rule for enforcing “structure” in addresses: near by nodes should have nearby addresses Using the Rule, we can “aggregate” information

12 DART: in more detail Basic idea: permanent nodeID =/= transient address The address reflects network location It is a proactive routing scheme, distance vector Consequences: Routing is simplified: address tell me where you are Nodes with similar addresses are “near” each other Challenges: Address allocation: When I move, change my address ID to Address mapping: Given an ID, find the address

13 Some more theoretical issues

14 Network Capacity The capacity of a wireless network is Where N nodes, and C channel capacity Explanation: N nodes in the field Destinations are random On average N^0.5 hops per path Each node has N^0.5 paths go through Gupta Kumar paper

15 Mobility increases capacity Grossglausser and Tse (infocom 2001) Statement: if nodes move they will eventually carry the info where you want Protocol: sender send one copy to receiver or one neighbor Sender and relay will at some run into destination and send the packet All paths are at most two hops They show that the capacity of the network does not go to zero Tradeoff?

16 Hierarchical routing: bounds Cluster nodes, and route between and within clusters Location management: finding where Routing finding how to get there Multiple levels: log(N) levels Location Mgm: Each nodes stores O(N) locations Routing overhead: O(log^3N) Dominating factor: location management and not the routing Location mgmt handoff: O(log^2N) See Susec Marsic, infocom 02

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18 Types of routing Flat Proactive Routing Link state Fish-Eye Routing, GSR, OLSR. Table driven: Destination-Sequenced Distance Vector ( DSDV), WRP) On-Demand or Reactive Routing Ad hoc On-demand Distant Vector (AODV) Dynamic Source Routing (DSR) Hybrid Schemes Zone Routing ZRP, SHARP (proactive near, reactive long distance) Safari (reactive near, proactive long distance) Geographical Routing Hierarchical: One or many levels of hierarchy Routing with dynamic address Dynamic Address RouTing (DART)

19 Proactive: DSDV - Destination-Sequenced Distance Vector Algorithm By Perkins and Bhagvat Based on Bellman Ford algorithm Exchange of routing tables Routing table: the way to the destination, cost Every node knows “where” everybody else is Thus routing table O(N) Each node advertises its position Sequence number to avoid loops Maintain fresh routes

20 DSDV details Routes are broadcasted from the “receiver” Nodes announce their presence: advertisements Each broadcast has Destination address: originator No of hops Sequence number of broadcast The route with the most recent sequence is used

21 Reactive: Ad-Hoc On-demand Distance Vector Routing (AODV) By Perkins and Royer Sender tries to find destination: broadcasts a Route Request Packet (RREQ). Nodes maintain route cache and use destination sequence number for each route entry State is installed at nodes per destination Does nothing when connection between end points is still valid When route fails Local recovery Sender repeats a Route Discovery

22 Route Discovery in AODV 1 Propagation of Route Request (RREQ) packet

23 Route Discovery in AODV 2 Path taken by Route Reply (RREP) packet

24 In case of broken links… Node monitors the link status of next hop in active routes Route Error packets (RERR) is used to notify other nodes if link is broken Nodes remove corresponding route entry after hearing RERR

25 Dynamic Source Routing (DSR) Two mechanisms: Route Maintenance and Route Discovery Route Discovery mechanism is similar to the one in AODV but with source routing instead Nodes maintain route caches Entries in route caches are updated as nodes learn new routes. Packet send carries complete, ordered list of nodes through which packet will pass

26 When Sending Packets Sender checks its route cache, if route exists, sender constructs a source route in the packet’s header If route expires or does not exist, sender initiates the Route Discovery Mechanism

27 Route Discovery 1 (DSR) Building Record Route during Route Discovery

28 Route Discovery 2 (DSR) Propagation of Route Reply with the Route Record

29 Route Maintenance Two types of packets used: Route Error Packet and Acknowledgement If transmission error is detected at data link layer, Route Error Packet is generated and send to the original sender of the packet. The node removes the hop is error from its route cache when a Route Error packet is received ACKs are used to verify the correction of the route links.

30 The Zone Routing Protocol (ZRP) Hybrid Scheme Proactively maintains routes within a local region (routing zone) Also a globally reactive route query/reply mechanism available Consists of 3 separate protocols Protocols patented by Cornell University!

31 Intrazone Routing Protocol Intrazone Routing Protocol (IARP) used to proactively maintain routes in the zone. Each node maintains its own routing zone Neighbors are discovered by either MAC protocols or Neighbor Discovery Protocol (NDP) When global search is needed, route queries are guided by IARP via bordercasting

32 Interzone Routing Protocol Adapts existing reactive routing protocols Route Query packet uniquely identified by source’s address and request number. Query relayed to a subset of neighbors by the bordercast algorithm

33 Comparisons 1 Things in common: IP based operation Distributed operation Loop-free routing Very little or no support for sleep period operation and security

34 Comparisons 2 FSRAODVDSRZPR Source Routing No YesNo Periodic message YesNo Yes (Locally) Functioning Proactively YesNo Yes (Locally) Functioning Reactively NoYes Yes (Globally) DSDV

35 Conclusion On-demand routing protocols (AODV and DSR) are gaining momentum. More analysis and features are needed (Performance comparison between protocols, QoS extension and analysis, multicast, security issues etc…) Good paper (though old): A review of current routing protocols for ad-hoc mobile wireless networks, E. Royer, C.K. Toh

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37 Performance? End-to-end data throughput and delay Route acquisition time Percentage of out-of-order delivery Efficiency: Average number of data bits transmitted/data bits delivered Average number of control bits transmitted/data bits delivered Average number of control and data packets transmitted/data packet delivered

38 Parameters Network Size Connectivity (average degree of a node) Topology rate of change Link capacity (bps) Fraction of unidirectional links Traffic patterns Mobility Fraction/frequency of sleeping nodes

39 References Mobile Ad hoc Networking (MANET): Routing Protocol Performance Issues and Evalution Considerations (RFC 2501) P. Misra., “Routing Protocols for Ad Hoc Mobile Wireless Networks”, The Zone Routing Protocol (ZRP) for Ad Hoc Networks Fisheye State Routing Protocol (FSR) for Ad Hoc Networks Ad hoc On-demand Distance Vector (AODV) Routing The Dynamic Source Routing Protocol for Mobile Ad Hoc Networks (DSR)

40 Fisheye State Routing (FSR) Node stores the Link State for every destination in the network Node periodically broadcast update messages to its neighbors Updates correspond to closer nodes propagate more frequently

41 Multi-Level Scope (FSR) Central node (red dot) has the most accurate information about nodes in white area and so on. Parameters: Scope level/radius size

42 ZPR architecture

43 Design Goals Peer-to-peer mobile routing capability in mobile, wireless domain. Intra-domain unicast routing protocol: Effective operation over a wide range of mobile networking scenarios and environments Supports traditional, connectionless IP services Efficiently manages topologies changes and traffic demands

44 Desired properties Distributed operation Loop freedom Demand-based operation Proactive operation Security “Sleep” period operation Unidirectional link support