Chapter 2 Routing in Ad hoc Networks

1. Chapter 2 Routing in Ad hoc Networks Table of Contents

2. MANET=Mobile Ad Hoc Networks

3. Formed by wireless hosts which may be mobile Don’t need a pre-existing infrastructure ie, don’t need a backbone network, routers, etc. Routes between nodes potentially contain multiple hops Why MANET? Ease, speed of deployment Decreased dependence on infrastructure Can use in many scenarios where deployment of a wired network is impractical or impossible Lots of military applications, but there are others… , Mobile Ad Hoc Networks

4. Equal nodes communicating over wireless links No central control –highly distributed Inheriting traditional problems Bandwidth optimization Power control Transmission quality Dynamic and random topology MANET (Mobile Ad Hoc Networks)

5. Highly dynamic topology-hard to predict Nodes communicating with each other by intermediate nodes in a multi-hop fashion Lower capacity than wired counterparts Limited physical security-due to wireless transmission Higher loss rate ,delays, and jitter Power constraint MANET Characteristics

6. Personal area networking cell phone, laptop, ear phone, wrist watch Civilian environments meeting rooms sports stadiums groups of boats, small aircraft (wired REALLY impractical!!) Emergency operations search-and-rescue policing and fire fighting Sensor networks Groups of sensors embedded in the environment or scattered over a target area Many Applications

7. Limited wireless transmission range Broadcast nature of the wireless medium Packet losses due to transmission errors Mobility-induced route changes Mobility-induced packet losses Battery constraints Potentially frequent network partitions Ease of snooping on wireless transmissions (security hazard) Challenges

8. Internet Routing Protocol • RIP(distance vector) : Routing Information Protocol • OSPF (Link State) : Open Shortest Path First • RIP is routing protocol in UNIX, also called routed, • Current version is RIP2

9. Keep a table with an entry for every possible destination in the system Periodically, send a routing update to every neighbor When a routing update arrives with distance (D’), compares with the old one (D) adopt D’ if (D’<D)---Distributed Bellman-Ford (DBF) algorithm Distance vector

10. Each participating gateway (router) have complete topology database. It actively tests the link status of all neighbor gateways, and periodically propagate link status (Up or Down) information to all other gateways. Whenever a link status message arrive, update its topology database by marking links up or down accordingly. Whenever link status changes, compute Shortest Path Tree from this gateway by applying Dijkstra’s algorithm on the resulting graph. Message Example (link between switch 5 and switch 9 is up) Each switch collects incoming messages and use them to build a graph of the network, run shortest path algorithm to find its routing table. Link state routing (SPF)

12. RIProutingprotocol (C) 1 2 (A) (B) 3 5 4 (D) 6 (E) An internet of routers

13. Cold Start (C) 1 2 (A) (B) A 3 B 5 4 link link From B to From A to cost cost B local 0 A local 0 (D) 6 (E) A sends distance vector (A, 0) from link 1 B B receives the vector and B does’nt have route to A; B adds the route to A. link From B to cost B local 0 1 1 A

14. (C) 1 2 (A) (B) B link From B to cost B sends two vectors (B,0), (A,1) via link 1,2,4 Link. 3 5 4 B local 0 1 1 A (D) 6 (E) D At the same time, D receivs A’s message and updates its routing table, and sends out (D,0), (A,1) via Link 3, 6. link From D to cost D local 0 3 1 A

15. A (C) 1 2 (A) (B) Areceives B’s vectors (B,0), (A,1) via Link 1; updates its routing table; but Because (A, 2) has larger cost than (A,0), updates are not performed. link From A to cost 3 5 4 A local 0 1 1 B (D) 6 (E) A A receivesD’s vector (via link 3) (D,0), (A,1), updates Table to add route for D. link From A to cost A local 0 1 1 B 1 D 3

16. C (C) 1 2 (A) (B) C receives B’s Vector (from Link 2) (B,0), (A, 1); updates table. link From C to cost 3 5 4 C local 0 2 1 B 2 A 2 (D) 6 (E) table updating goes on and converges.

17. Count to infinity problem When one link is broken, it will take a long time for the tables to converge again. Cost value will be increased up to Max. Cost+1(called infinity) before the updating procedure stops. A phenomenon called ount to infinity.

18. A variant of Dijkstra‘s algorithm that computes Routing Table and distances Given: a graph with a nonnegative weight assigned to each edge and a designated source node Compute: the shortest distance from the source node to each other node and a next-hop routing table Method: Initialize set S to contain all nodes except the source node; Initialize array D so that D[v] is the weight of the edge from the source to v if such an edge exists, and infinity otherwise; Initialize entries of R so that R[v] is assigned source if an edge exists from the source to v, and zero otherwise; R[v] keeps the previous node from the source to node v. while (set S is not empty) { choose a node u from S such that D[u] is minimum; if (D[u] is infinity) { error: no path exists to nodes in S ; quit; } delete u from set S; // u’s shortest path has been found. for each node v such that (u,v) is an edge{ if (v is still in S) { c=D[u] + weight(u,v); // check whether goes through u will be better or not. if (c<D[v] { R[v} = u; D[v]=c; }}}}

19. A sample graph

20. weight(i,j) 1 2 3 4 5 6 7 1 2 3 4 5 6 7

21. Source =1 S= {2, 3, 4, 5, 6, 7} D[v]= ∞, ∞, ∞, 9, ∞, ∞ R[v]= 0, 0, 0, 1, 0, 0 First iteration, choose u =5, only one path from 1 to 5 --------------------------------------------------------------------------- D[v]= 15, ∞, ∞, 9, ∞, ∞ R[v]= 5, 0, 0, 1, 0, 0 ----------------------------------------second iteration, choose u=2 D[v]= 15, 18, ∞, 9, 23, ∞ R[v]= 5, 2, 0, 1, 2, 0 --------------------------------------third iteration, choose u=3, node 6 has been changed D[v]= 15, 18, 29, 9, 20, ∞ R[v]= 5, 2, 3, 1, 3, 0 --------------------------------------Fourth iteration, choose u=6 D[v]= 15, 18, 29, 9, 20, 25 R[v]= 5, 2, 3, 1, 3, 6

22. Source =1 S= {2, 3, 4, 5, 6, 7} --------------------------------------Fifth iteration, choose u=7 D[v]= 15, 18, 28, 9, 20, 25 R[v]= 5, 2, 7, 1, 3, 6 --------------------------------------6th iteration, choose u=4, terminate From node 1 to node 4: Length = 28, through node 5node 2 node 3 node 6node 7 Next hop is node 5

23. Routing Table of Node 1

24. Each color represents range of transmission of a device A A S S B B D D • MH S uses B to communicate with MH D Illustration of Multi-hop MANET Due to movement of MHs, S now uses A and B to reach D

25. Topology-Based Depends on the information about existing links Position-Based Depends on the physical location information of the nodes Proactive (or table-driven) Traditional distributed shortest-path protocols Maintain routes between every host pair at all times Based on periodic updates; high routing overhead Example: DSDV (destination sequenced distance vector) Reactive (On-Demand) protocols Determine route if and when needed Source initiates route discovery Example: DSR (dynamic source routing) Hybrid protocols Adaptive: Combination of proactive and reactive Example: ZRP (zone routing protocol) Routing Approaches (hundreds of them are already proposed)

26. Proactive (or table-driven) Node experiences minimal delay whenever a route is needed May not always be appropriate for high mobility Distance-vector or link-state routing Reactive (or on-demand) Consume much less bandwidth Delay in determining a route can be substantially large Hybrid protocols MHs determine their own position through GPS Position-based routing algorithms overcome some of the limitations Advantages and Disadvantages

27. Destination-Sequenced Distance-Vector (DSDV) Protocol A proactive hop-by-hop distance vector routing protocol Requires each MH to broadcast routing updates periodically Every MH maintains a routing table for all possible destinations and the number of hops to each destination Sequence numbers enable the MHs to distinguish stale routes from new ones To alleviate large network update traffic, two possible types of packets: full dumps or small increment packets The route labeled with the most recent sequence number is always used In the event that two updates have the same sequence number, the route with the smaller metric is used in order to optimize (shorten) the path Proactive Routing Approaches

28. Assume that MH X receives routing information from Y about a route to MH Z Let S(X) and S(Y) denote the destination sequence number for MH Z as stored at MH X, and as sent by MH Y with its routing table to node X, respectively Z X Y Destination-Sequenced Distance-Vector (DSDV)

29. MH X takes the following steps: If S(Y) < S(X) (means that routing entry in Y is stale), then X ignores the routing information received from Y If S(Y) = S(X), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z If S(Y) > S(X), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y) Z X Y Destination-Sequenced Distance-Vector (DSDV)

30. The Wireless Routing Protocol A table-driven protocol with the goal of maintaining routing information among all MHs Each MH maintains four tables: Distance, Routing, Link-cost, and the Message Retransmission List (MRL) tables Each entry in MRL contains the sequence number of the update message MHs keep each other informed of all link changes through the use of update messages MHs learn about their neighbors from acknowledgments and other messages If a MH does not send any message for a specified time period, it must send a hello message to ensure connectivity Proactive Routing Approaches

31. Topology Broadcast based on Reverse Path Forwarding Protocol Considers broadcasting topology information (including link costs and up/down status) to all MHs Each link-state update is sent on every link of the network though flooding Communication cost of broadcasting topology can be reduced if updates are sent along spanning trees Messages are broadcast in the reverse direction along the directed spanning tree formed by the shortest paths from all nodes to source Messages generated by a given source are broadcast in the reverse direction along the directed spanning tree formed by the shortest paths from all MHs (nodes) to the source Proactive Routing Approaches

32. The Optimized Link State Routing Protocol Based on the link state algorithm All links with neighboring MHs are declared and are flooded in the entire network Minimizes flooding of this control traffic by using only the selected MHs, called multipoint relays Only normal periodic control messages sent Beneficial for the traffic patterns with a large subset of MHs are communicating with each other Good for large and dense networks An in-order delivery of its messages is not needed as each control message contains a sequence number Proactive Routing Approaches

33. Multipoint Relays Minimize the flooding of broadcast packets in the network by reducing duplicate retransmissions in the same region Each MH selects a set of neighboring MHs, to retransmit its packets and is called the multipoint relays (MPRs) This set can change over time and is indicated by the selector nodes in their hello messages Each node selects MPR among its one hop bi-directional link neighbors to all other nodes that are two hops away Proactive Routing Approaches

34. Illustration of Multipoint Relays Retransmitting node or multipoint relays N One hop node NOT selected for relays Two hop nodes

35. DSR is an innovative approach to routing in a MANET in which the source provides the routing information (routing path) in the data packet It is referred to as one of the purest examples of an on-demand protocol Dynamic Source Routing

36. Dynamic Source Routing When MH S wants to send a packet to MH D, but does not know a route to D, MH S initiates a route discovery Source node S floods Route Request (RREQ) Each MH appends its own identifier when forwarding RREQ

37. Route Discovery in DSR Y Broadcast transmission Z [S] E F B C M L J A G H [D] K I N Represents transmission of RREQ [S] Represents the source; [D] represents the destination

38. Route Discovery in DSR Y Z [S] [S,E] E F B C M L J A G [S,C] H [D] K I N • Node H receives packet RREQ from two neighbors: • potential for collision [X,Y] Represents list of identifiers appended to RREQ

39. Route Discovery in DSR Y Z [S] E F [S,E,F] B C M L J A G H [D] K [S,C,G] I N • Node C receives RREQ from G and H, but does not forward • it again, because node C has already forwarded RREQ once

40. Route Discovery in DSR Y Z [S] E F [S,E,F,J] B C M L J A G H [D] K I N [S,C,G,K] • Nodes J and K both broadcast RREQ to node D • Since nodes J and K are hidden from each other, their • transmissions may collide

41. Route Discovery in DSR Y Z [S] E [S,E,F,J,M] F B C M L J A G H [D] K I N • Node Ddoes not forwardRREQ, because node D • is theintended targetof the route discovery

42. Destination D on receiving the first RREQ, sends aRoute Reply (RREP) RREP is sent on a route obtained by reversing the route appended to received RREQ RREP includes the route from S to D on which RREQ was received by MH (node) D Route Discovery in DSR

43. Hop1 Hop3 Hop4 Hop2 <1,2> <1> <1,3,5,7> <1,3,5> <1> <1,3> <1> <1,4,6> <1,4> 7 2 5 1 Source 8 Destination 3 <1,4,6> <1,4,6> 6 4 <1,4,6> Route Discovery in DSR 7 2 5 Source 1 1 Destination 8 3 6 4 4 (a) Building Record Route During Route Discovery (a) Building Record Route During Route Discovery (b) Propagation of Route Reply with the Route Record

44. AODV (Ad Hoc On-Demand Distance Vector Routing) AODV is a combination of DSDV and DSR • It borrows the on-demand Route Discovery and Route Maintenance from DSR. Plus the use of hop-by –hop routing, sequence number, and periodic beacons from DSDV • It only supports the symmetric channels • If a source MH moves, it reinitiates route discovery protocol to find a new route • If a MH along the route moves, its upstream neighbor notices the move and propagates a link failure notification message to each of its active upstream neighbors

45. These MHs propagate link failure notification to their upstream neighbors, until the source MH is reached Hello messages can be used to maintain the local connectivity in the form of beacon signals Designed for unicast routing only, and multi-path is not supported The following pictorial does not expose the complexity of AODV—just to give a basic idea

46. Route Requests in AODV Y Z S E F B C M L J A G H D K I N Represents a node that has received RREQ for D from S

47. Route Requests in AODV Y Z S E F B C M L J A G H D K I N Represents transmission of RREQ

48. Route Requests in AODV Y Z S E F B C M L J A G H D K I N Represents links on Reverse Path

49. Reverse Path Setup in AODV Y Z S E F B C M L J A G H D K I N Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

50. Reverse Path Setup in AODV Y Z S E F B C M L J A G H D K I N