CSC344 Wireless and Mobile Computing

1. CSC344Wireless and Mobile Computing COMSATS Institute of Information Technology, Lahore Muhammad Sharjeel

2. Routing in Wireless Ad-Hoc Networks Lecture No 16

3. Ad-Hoc Networks • “The art of networking without a network” [Frodigh et al.] • Ad-Hoc is Latin word means "for this purpose"

4. Ad-Hoc Networks Why do we need ad-hoc networks? • More laptop users, more smartphones users • More devices with Wi-Fi-support (e.g.televisions, home-theaters, media servers) • Moving users, vehicles, etc. • Outdoors places • In all these occasions there is no centralized infrastructure (such as APs) • So ad-hoc network is a necessity

5. Ad-Hoc Networks: Features and Characteristics • No fixed infrastructure, Decentralized mobility-adaptive operation • Self organizing network without the need of fixed network infrastructure • Dynamic topology (Mobility) • Each node participates in routing by forwarding data to neighbor nodes • Fast network topology changes due to nodes movement • Scalability up to thousands of nodes, Security is limited • Bandwidth constrained: Congestion is a norm • Multi-hopping: Obstacles, spectrum reuse, energy conservation • Self-Organization: Addressing, routing, clustering, location, power control

6. Ad-Hoc Networks vs Cellular Networks

7. Ad-Hoc Networks: Applications • Can be used in many scenarios where deployment of a wired network is impractical or impossible • Emergency, Disasters • Wearable computing • Battlefield, Military environment • Unmanned ground/airborne/underwater vehicles • Hybrid: Multi-hop cellular • Wireless Mesh Networks • Sensor Networks

8. Ad-Hoc Networks VANETs and MANETs

9. MANETs • Mobile Ad-Hoc Networkis a self-configuring infrastructure-less network of mobile devices connected by wireless • Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently • Each must forward traffic unrelated to its own use, and therefore be a router • Such networks may operate by themselves or may be connected to the larger network

10. VANETs • Every participating car in the network is a wireless router or node, allowing cars approximately 100 to 300 meters of each other to connect and, in turn, create a network with a wide range • VANET can be considered a subset of MANET • Nodes do not move in any random direction • Nodes are powered (energy is not an issue) • Node contact time is limited • Intermittent connectivity might occur • Node speed is bounded • Mostly high speed, but occasionally stop and slow moving

11. VANETs

12. VANETs What are in a vehicular network (VANET) • On Board Unit (Vehicles) • Road Side Unit • GPS (optional) • Back-end system (Network infrastructure)

13. VANETs • The Connected Car Scenario

14. VANETs • Difference of communications between inter-vehicle and vehicle-to-infrastructure communication • V2V • Dynamic routing • Ad-Hoc network • Short to medium range • V2I • Fixed routing • Fixed network • Medium to long range

15. VANETs - Applications • Safety • Intersection warning • Vehicle probe • Travel time estimation • Environmental/Road surface data collection • Emergency vehicle • preemptive traffic control • Navigation • Telematics • The integrated use of telecommunications and informatics within road vehicles • Intelligent Transportation System(ITS) • Add information and communications technology to transport infrastructure and vehicles

16. Ad-Hoc Networks: Issues • Medium Access: Distributed, no time sync, directional antennas • Routing: Route acquisition delay, quick reconfiguration, loop free • Multicasting: Common in Ad-Hoc, emergency/military • Transport Layer: Frequent path breaks • QoS: End-to-end quality of service • Self-organization: Neighbor discovery, report link failures • Security: DoS, jamming, energy depletion • Energy Management: Transmission Power, battery monitoring, processor power • Addressing and Service Discovery: Global • Pricing Scheme: Incentives for relaying

17. Ad-Hoc Networks: Routing Requirements • Fully distributed • Localized • Global state (all nodes-all time) maintenance is expensive • Loop-Free routing • Minimize route acquisition delay: Proactive/Reactive • Quick route reconfiguration: Adaptive to Frequent changes • Changes in unrelated parts should not impact a node • Energy conservation: Sleep periods • Unidirectional Link Support • Minimize: • Bits Transmitted/Bits Delivered = Average hops • Control bits/data bits = Overhead

18. Classification of Routing Protocols • Routing Updates: • Proactive: Before needed (table-driven) • Reactive: When required (on-demand) • Hybrid: Combined, know neighbors, others on-demand • Temporal Information: • Based on node lifetime, location • Past temporal information (Past History) • Future temporal information (Prediction) • Topology Organization: • Flat: Global addresses • Hierarchical: Geographical or hop distance • Resource Optimization: • Power-Aware: Local or global battery power • Geographical info based • Efficient Flooding

19. Classification of Routing Protocols Distance Vector: • Each node sends its complete table (distances to all nodes in the network) to its neighbors • Large vectors to small number of nodes • Use Bellman-Ford algorithm to compute the shortest path • Routing Information Protocol (RIP) is a distance vector protocol Link State: • Each nodes sends its link information (distances to its neighbors) to all nodes in the network • Small vectors to large number of nodes • Use Dijkstra’sto compute the shortest path • Open Shorted Path First (OSPF) is a link state routing protocol

20. DSDV Destination Sequenced Distance-Vector Routing Protocol • Enhanced version of the distributed Bellman-Ford algorithm • Each node maintains a table that contains • Shortest distance to every other node in the network • First node on the shortest path • Incorporates updates with sequence number to prevent loops and count-to-infinity problem

21. DSDV • Routes to all destinations are readily available at all times • Tables are exchanged between neighbors at regular intervals to keep an up-to-date view of the network topology • Table updates are of two types: • Incremental updates: These are used when a node does not observe significant changes • Full dumps: It is done when changes are significant • Table updates are initiated by a destination with a new sequence number which is always greater than the previous one

22. DSDV - Example Routing Table for Node 1 15 13 14 12 9 11 8 10 7 4 6 5 3 2 1

23. DSDV - Example Routing Table for Node 1 15 13 14 12 9 11 8 10 7 4 6 5 3 2 1

24. DSDV - Example 11 Routing Table for Node 1 15 13 14 12 9 11 8 10 7 4 6 5 3 2 1

25. DSDV Advantages • Less delay involved in the route setup process • Mechanism of incremental update with sequence number tags makes the existing wired network protocols adaptable to ad hoc wireless networks • The updates are propagated throughout the network in order to maintain an up-to-date view of the network topology at all nodes

26. DSDV Disadvantages • Suffers from excessive control overhead • The updates due to broken links lead to a heavy control overhead during high mobility • Even a small network with high mobility or a large network with low mobility can completely choke the available bandwidth • In order to obtain information about a particular destination node, a node has to wait for a table update message initiated by the same destination node • This delay could result in state routing information at nodes

27. WRP Wireless Routing Protocol • WRP is similar to DSDV; it inherits the properties of the distributed bellman-ford algorithm • To counter the count-to-infinity problem and to enable faster convergence, it employs a unique method of maintaining information regarding; • The shortest distance to every destination node • Penultimate hop node on the path to every destination node • Maintains an up-to-date view of the network • Every node has a readily available route to every destination node

28. WRP • It differs from DSDV in table maintenance and in the update procedures • While DSDV maintains only one topology table, WRP uses a set of tables to maintain more accurate information • The table that are maintained by a node are: • Distance Table (DT) • Routing Table (RT) • Link Cost Table (LCT) • Message Retransmission List (MRL)

29. WRP • Distance table (DT) • Contains network view of the neighbors of a node • A matrix where each element contains the distance and the penultimate node reported by the neighbor for a particular destination • Routing table (RT) • Contains the up-to-date view of the network for all known destinations • Keeps the shortest distance, the predecessor/penultimate node, the successor node, and a flag indicating the status of the path • simplest (correct) path • a loop (error) • destination node not marked (null)

30. WRP • Link cost table (LCT) • Contains the cost of relaying messages through each link • Cost of broken link is ∞ • Also contains the number of update periods passed since the last successful update was received from that link • Message retransmission list (MRL) • Contains an entry for every update message that is to be retransmitted and maintains a counter for each entry • After receiving the update message, a node not only updates the distance for transmitted neighbors but also checks the other neighbors distance, hence convergence is much faster than DSDV

31. WRP - Example 15 2 5 13 4 14 10 4 3 3 12 7 9 11 5 1 9 3 8 10 3 3 5 11 1 7 7 4 5 6 7 6 3 9 5 4 3 3 2 2 1 2 3 1

32. WRP - Example 15 2 5 13 4 14 10 4 3 3 12 7 9 11 5 1 9 3 8 10 3 3 5 11 1 7 7 4 5 6 7 6 3 9 5 4 3 3 2 2 1 2 3 1

33. WRP - Example 15 2 5 13 4 14 10 4 3 3 12 7 9 11 5 1 9 3 8 10 3 3 5 11 1 7 7 4 5 6 7 6 3 9 5 4 3 3 2 2 1 2 3 1

34. WRP - Example 15 2 5 13 14 10 4 3 3 12 7 9 11 5 1 9 3 8 10 3 3 5 11 1 7 7 4 5 6 7 6 3 9 5 4 3 3 2 2 1 2 3 1

35. WRP Advantages • WRP has the same advantages as that of DSDV • It has faster convergence and involves fewer table updates Disadvantages • The complexity of maintenance of multiple tables demands a larger memory and greater processing power from nodes • It is not suitable for highly dynamic and also for very large networks

36. DSR Dynamic Source Routing Protocol • On-Demand routing using "Source Route“ • Reactive, construct a route when needed • Restrict bandwidth consumed by control packets by eliminating periodic updates • Beacon-less and does not require periodic hello packet transmissions • Basic approach, to establish a route by flooding RouteRequest packets in the network • Destination node responds by sending a RouteReply packet back to the source

37. DSR • Each RouteRequestcarries; • Sequence number generated by the source • The path (route) packet has traversed • RouteRequestis forwarded only if it is not duplicate • A node checks the sequence number on the packet • Used to prevent loop formations and to avoid multiple transmissions • All nodes except the destination forward a RouteRequest packet during the route construction phase

38. DSR • Uses route cache (Routing Database) that stores all possible information extracted from the source route contained in data packet • If (optimized) the intermediate nodes may also originate RouteReplypackets • If a node knows the route it appends the rest of the route and returns the RouteReply • Source node may receive multiple replies from intermediate nodes • Selects the latest and best route • On link breaks, the affected nodes initiate the route discovery process • Each data packet carries the complete path to its destination

39. DSR - Example 15 Node 1 has a packet for Node 15 So, Node 1 first needs to find shortest path to Node 15 13 14 12 9 11 8 10 7 4 6 5 3 2 1

40. DSR - Example 15 Flooding to find the route using source 13 14 12 9 11 8 10 7 4 6 5 3 2 1

41. DSR - Example 15 Flooding to find the route using source 13 14 12 9 11 8 10 7 4 6 5 3 2 1

42. DSR - Example 15 13 14 Path: 1-6 12 9 11 Path: 1-5 8 10 Path: 1-2 7 4 6 5 3 2 1

43. DSR - Example 15 13 14 Path: 1-6-10 12 9 11 Path: 1-5-4 8 10 Path: 1-2-3 7 4 6 5 3 2 1

44. DSR - Example 15 13 14 Path: 1-6-10-14 12 9 11 Path: 1-5-4-12 8 10 Path: 1-2-3-7 7 4 6 5 3 2 1

45. DSR - Example 15 13 14 Path: 1-6-10-14-15 12 9 11 Path: 1-5-4-12-15 8 10 Path: 1-2-3-7-9 7 4 6 5 3 2 1

46. DSR - Example 15 13 14 Path: 1-6-10-14-15 12 9 11 Path: 1-5-4-12-15 8 10 Path: 1-2-3-7-9-13-15 7 4 6 5 3 2 1

47. DSR - Example 15 13 14 Path: 1-6-10-14-15 12 9 11 8 10 7 4 6 5 3 2 1

48. DSR Advantages • Uses a reactive approach which eliminates the need to periodically flood the network with table update messages • Route is established only when required • Reduce control overhead

49. DSR Disadvantages • Route maintenance mechanism does not locally repair a broken link • Stale route cache information could result in inconsistencies during route construction phase • Connection set up delay is higher • Performance degrades rapidly with increasing mobility • Routing overhead is more & directly proportional to path length

50. AODV Ad Hoc On-Demand Distance Vector Routing Protocol • Route is established only when it is required by source • Uses DestSeqNum to determine an up-to-date path to the destination • Source node and intermediate nodes store the next hop information corresponding to each flow • A RouteRequest carries; • source identifier • destination identifier • source sequence number • destination sequence number • broadcast identifier • time to live field