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Lecture 9 10 .mobile ad-hoc routing protocols


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Lecture 9 10 .mobile ad-hoc routing protocols

  1. 1. Chandra Prakash Assistant Professor LPU 1 Mobile Ad-Hoc Routing Protocols Lecture (9-10)
  2. 2. Mobile Ad Hoc Networks (MANET)  Host movement frequent  Topology change frequent  No cellular infrastructure. Multi-hop wireless links.  Data must be routed via intermediate nodes. A B A B 2
  3. 3. The Routing Problem S D D´S´ The routing problem is to find a route from S to D when some or all of the nodes are mobile. The MAC protocol is concerned with per-link communications, not end- to-end. While Routing Protocol deal with end-to-end communication. 3
  4. 4. Ad-hoc Routing Protocol  A standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad hoc network .  In ad-hoc networks, nodes are not familiar with the topology of their networks; instead, they have to discover it.  The basic idea is that a new node may announce its presence and should listen for announcements broadcast by its neighbours.  Each node learns about nodes nearby and how to reach them, and may announce that it, too, can reach them. 4
  5. 5. MAC Vs Routing Protocols The MAC protocol is concerned with per-link communications, not end-to-end. While Routing Protocol deal with end-to-end communication. 5
  6. 6. Traditional routing algorithm  InWired network 1. Static : 2. Dynamic a) DistanceVector b) Link State  DistanceVector (DV)  Each node maintains a table giving the distance from itself to all possible destination.  Periodically broadcasts update packets to each of the neighbors.  Bellman-Ford algorithm  Finding the shortest path to determine the correct next hop of its neighbors.  When presented a packet for forwarding to some destination, each router simply forwards the packet to the correct next hop router.  Problem: route looping & count to infinity 6
  7. 7. 7 Traditional routing algorithm  Example of DV: 0 5 1 2 4 3Destination Next Hop Distance 0 2 3 1 2 2 … … … Routing table at node 5 :
  8. 8. Distributed Bellman-Ford Algorithm  We consider only the number of hops as the cost for sending a message from a source to a destination.  Suppose node 1 wants to send a message to node 4.  Since the shortest path between 1 and 4 passes through 2, 1 will send the message to 2. 1 2 4 3 5 8
  9. 9. Problems with Distributed Bellman- Ford Algorithm  All routing decisions are taken in a completely distributed fashion. Each node uses its local information for routing messages.  However, the local information may be old and invalid. Local information may not be updated promptly.  This gives rise to loops.A message may loop around a cycle for a long time. 9
  10. 10. 10 Traditional routing algorithm  Link State (LS) Each node maintains a view of the network topology with a cost for each link. Each node periodically broadcasts the cost of its outing links to all other nodes. Using a shortest-path algorithm to choose its next hop for each destination.
  11. 11. 11 Traditional routing algorithm(4/4)  Example of LS: •At node 5, based on the link state packet, topology table is constructed: 0 1 2 3 4 5 0 1 1 0 0 0 0 1 1 1 1 1 0 0 2 0 1 1 0 1 1 3 0 1 0 1 1 0 4 0 0 1 1 1 1 5 0 0 1 0 1 1 0 5 1 2 4 3 {1} {2,4} {0,2,3} {1,4,5} •Dijkstra’s Algorithm can then be used for the shortest path {2,3,5} {1,4}
  12. 12. 12 Problems of traditional routing algorithms  Dynamic of the topology  frequent changes of connections, connection quality, participants  Limited performance of mobile systems  periodic updates of routing tables need energy without contributing to the transmission of user data, sleep modes difficult to realize  limited bandwidth of the system is reduced even more due to the exchange of routing information  Asymmetric links  connection in wireless network may be not symmetric
  13. 13. Limitation of Wireless Network  Deals with the typical limitations of Ad-hoc networks, which include  Resource poor devices  Limited bandwidth  high error rates  Continually changing topology  Battery power Most constraining is battery power 13
  14. 14. Goal of Routing Protocol 1. Minimal control overhead:  Control messaging consumes bandwidth,processing resources and battery power to both transmit and receive a message.  Should not send more than the minimum no of control message they need for operation.  While transmitting is roughly twice as power consuming as receiving.Thus need to reduce control messaging 2. Minimal processing overhead  Algo that are computationally complex require more processing cycles, thus consume more resources.  Protocol should be lightweight and use a minimum of processing resources from the mobile devices 14
  15. 15. Goal of Routing Protocol 3. Multihop routing capability  Transmission range of mobile node is limited.  Routing protocol must be able to discover Multihop routes between source and destination so that communication between those node is possible who are not in direct transmission range of each other. 4.Dynamic topology maintenance  Once route is established , link may be break due to movement of nodes.  A viable routing path must be maintained even while the intermediate nodes, or even the source or destination nodes are moving.  If link breaks, it must be handled quickly with a minimum of associated overhead.15
  16. 16. Goal of Routing Protocol 5. Loop prevention  When a routing loop exits , data and control packets may traverse the path multiple times until either the path or fixed and the loop is eliminated or until he time to live (TTL) of the packet reaches zero.  As bandwidth is scarce and packet processing and forwarding is expensive, routing loops are extremely wasteful of resources.  Loops should be avoided all the times 16
  17. 17. Formation of Loops Network given above  Node A is transmitting data to node C via node B.  If the link between nodes B and C goes down and B has not yet informed node A about the breakage, node A transmits the data to node B assuming that the link A-B-C is operational and of lowest cost.  Node B knows of the broken link and tries to reach node C via node A, thus sending the original data back to node A.  Furthermore, node A receives the data that it originated back from node B and consults its routing table.  Node A's routing table will say that it can reach node C via node B (because it still has not been informed of the break) thus sending its data back to node B creating an infinite loop.17
  18. 18. Routing Protocol : Assumptions 1. All nodes are homogenous resources and capabilities. 2. Same transmission range of nodes. 3. Bi-directional links 4. Protocol are designed for moderately sized networks of 10 to 100 nodes. 18
  19. 19. Ad Hoc Routing Protocol  Routing protocols category : (a)Table-driven, (b) Source-initiated on-demand-driven. 19
  20. 20. Routing Protocols  Table Driven / Proactive protocols  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)  On-Demand Driven/ Reactive protocols  Determine route if and only when needed  Source initiates route discovery  Example: DSR (dynamic source routing)  Hybrid protocols  Adaptive; Combination of proactive and reactive  Example : ZRP (zone routing protocol) 20
  21. 21. Table Driven / Proactive protocols  Proactive protocols are based on periodic exchange of control messages and maintaining routing tables.  Derived from traditional distance vector and link state protocol used in wireline internet.  Each node maintains complete information about the network topology locally.  This information is collected through proactive exchange of partial routing tables stored at each node. Since each node knows the complete topology, a node can immediately find the best route to a destination. Limitation :  Generates large volume of control messages and this may take up a large part of the available bandwidth.  The control messages may consume almost the entire bandwidth with a large number of nodes and increased mobility. 21
  22. 22. Table Driven / Proactive protocols  Maintains fresh lists of destinations & their routes by periodically distributing routing tables throughout the network  Attempts to maintain consistent, up-to-date routing information from each node to every other node in the network.  Require each node to maintain one or more tables to store routing information.  They respond to changes in network topology by propagating route updates throughout the network to maintain a consistent network view.  These Protocols are differ in the number of necessary routing-related tables and the methods require to broadcast the changes in network structure.  Some examples of proactive protocols are :  Destination Sequenced DistanceVector (DSDV)  WRP  CGSR22
  23. 23. 23 Table-Driven Routing Protocols  Destination-Sequenced Distance-Vector Routing (DSDV)  C. E. Perkins and P. Bhagwat,“Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computer,” Comp. Commun. Rev., Oct. 1994, pp. 234-244.  Wireless Routing Protocol (WRP)  S. Murthy and J. J. Garcia-Luna-Aceves,“An Efficient Routing Protocol forWireless Networks,”ACM Mobile Networks andApp. J., Special Issue on Routing in Mobile Communication Networks, Oct. 1996, pp. 183-197.  Clusterhead Gateway Switch Routing (CGSR)  C.-C. Chiang,“Routing in Clustered Multihop, MobileWireless Networks with Fading Channel,” Proc. IEEE SICON ’97,Apr. 1997, pp. 197-211.
  24. 24. 1. Destination Sequenced Distance Vector (DSDV)  C.E.Perkins and P.Bhagwat,“Highly Dynamic Destination-Sequenced Distance- Vector Routing (DSDV) for Mobile Computer,”Comp.Commun.Rev.,Oct.1994,pp. 234-244.  Table-driven routing protocol  Expansion of distance vector based on Classical distributed Bellman-Ford routing mechanism include freedom from loops in routing tables.  MainAdvantage of using this protocol is that it avoid the routing loops in a mobile network of routers.  Each node maintains a routing table of the possible destinations within the non- partitioned network and the number of routing hops / radio hops (Hand Over Point) to each destination are recorded.  Routing information is always made readily available, regardless of whether the source node requires a route or not. 24
  25. 25. Destination Sequenced Distance Vector DSDV(Cont…)  A sequence numbering system is used to allow mobile hosts to distinguish stale routes from new ones.  Routing table updates are sent periodically throughout the network to maintain table consistency.  It generates a lot of control traffic in the network, rendering an inefficient utilization of network resources.  To minimize the routing updates, variable sized update packets are used depending on the number of topological changes.  DSDV uses two types of route update packets.  Full Dump update Packet  Incremental update Packet 25
  26. 26. DSDV(Cont…)  Full dump update Packet:  Packet carries all available routing information and can require multiple network protocol data units (NPDUs).  Take multiple NPDU’s  During periods of occasional movement, these packets are transmitted infrequently.  Incremental packets update Packet :  Fitted into a single NPDU.  are used to relay only information that has changed since the last full dump. 26
  27. 27. DSDV (Cont…) New route broadcasts will contain  Address of the destination node  Number of hops to reach the destination  Unique Sequence number :  The sequence numbers are generally even if a link is present; else, an odd number is used.  The number is generated by the destination, and the emitter needs to send out the next update with this number.  The route labeled with the most recent sequence number (in increasing order) is always used.  In the event that two updates have the same sequence number, the route with the smaller hop count is used. 27
  28. 28. DSDV (Cont…) When X receives information fromY about a route to Z  Let destination sequence number for Z at X be S(X), S(Y) is sent fromY  If S(X) > S(Y),then X ignores the routing information received fromY  If S(X) = S(Y),and cost of going throughY is smaller than the route known to X, then X setsY as the next hop to Z  If S(X) < S(Y),then X setsY as the next hop to Z, and S(X) is updated to equal S(Y) X Y Z 28
  29. 29. DSDV (Cont…) Destination Next Hop Number of Hops Sequence Number InstallTime A A 0 A 46 001000 B B 1 B 36 001200 C B 2 C 28 001500 For example the routing table of Node A in this network is 29
  30. 30. 30 DSDV
  31. 31. 31 DSDV
  32. 32. DSDV Overview Advantages  Much less delay involved in the route setup process.  Incremental updates with sequence no tag makes existing wired network protocol adaptable to ad-hoc network. Disadvantage  Generates a lot of control traffic in the network, rendering an inefficient utilization of network resources.  Small network with high mobility or a large network with low mobility can completely chock 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 destination node, 32
  33. 33. 2. Wireless Routing Protocol (WRP) S. Murthy and J. J. Garcia-Luna-Aceves,“An Efficient Routing Protocol forWireless Networks,”ACM Mobile Networks andApp. J., Special Issue on Routing in Mobile Communication Networks, Oct. 1996, pp. 183-197.  Similar to DSDV, inherits the properties of the distributed Bellman-Ford algorithm.  It achieves loop freedom.  InWRP, routing nodes communicate the distance and second-to-last hop information for each destination in the wireless network.  Belong to the class of path findingAlgorithm;  uses the length and predecessor to destination in the shortest path.  Eliminates the “count to Infinity” Problem by forcing nodes to do consistency check of the predecessors  It provides faster route convergence when a link failure event occurs. 33
  34. 34. WRP (Cont…)  If a node is not sending packets,  It must send a HELLO message within a specified time period to ensure connectivity  Otherwise, the lack of messages from the node can indicate the failure of that wireless link and this may cause a false alarm.  When a mobile receives a HELLO message from a new node, that new node information is added to the mobile's routing table, and the mobile sends the new node a copy of its routing table information.  Differs from DSDV in table maintenance and in the update procedures.  DSDV maintains only one topology table,  WRP uses a set of tables to maintain more accurate information 34
  35. 35. WRP (Cont…) WRP must maintain four tables, namely: (a) Distance table :  Contain network view of the neighbors of a node.  indicates the number of hops between a node and its destination (b) Routing table:  indicates the next-hop node (c) Link-cost table:  Link-cost table reflects the delay associated with a particular link.  The LCT contains the cost (e.g., the number of hops to reach the destination) of relaying messages through each link.  The cost of a broken link is infinity. (d) Message Retransmission List (MRL) table. The MRL contains  The sequence number of the update message,  A retransmission counter,  An acknowledgment required flag vector,  A list of the updates sent in the update message.  The MRL records which updates in an update message need to be retransmitted and which neighbors should acknowledge the retransmission. 35
  36. 36. 36 WRP (cont.)  An Update message is sent after processing updates from neighbors or a change in link to a neighbor is detected.  After receiving an update message free of errors, a node is required to send a positive acknowledgment (ACK).  If a node is not sending messages, it must send a hello message within a specified time period to ensure connectivity.  Example: J K I B (0, J) (2, K) (2, K) (1, K) X1 1 10 1 5 10 (, K) (10, B) (10, I) (11, B)
  37. 37. 37
  38. 38. WRP Overview Advantages  Same as that of DSDV,  It has faster convergence and involves fewer table updates. Disadvantage  WRP requires large memory storage and resources in maintaining its tables.  Complexity of maintenance of multiple tables demands a larger memory and greater processing power from nodes in the ad hoc wireless network.  At high mobility, the control overhead involved in updating table entries is almost the same as that of DSDV  Not suitable for highly dynamic and also for a very large ad hoc wireless network.  The protocol is not suitable for large mobile ad hoc networks as it suffers from limited scalability. 38
  39. 39. 3. Cluster Switch Gateway Routing (CSGR) C.-C. Chiang, “Routing in Clustered Multihop, MobileWireless Networks with Fading Channel,” Proc. IEEE SICON ’97,Apr. 1997, pp. 197-211.  Table-driven-based routing protocol  Uses a hierarchical network topology while previous protocol employ flat topologies  Mobile nodes are grouped into clusters. These grouping may be based on a no of criteria, but most commonly they are based on either location, or functionality.  The cluster boundaries are based on transmission range of the cluster leaders known as cluster head(CH).  Cluster Head  Process control packets on behalf on their member nodes, thus form a routing backbone within the network  allows some form of control and coordination among a group of ad hoc hosts  Clustering provides a framework for code separation (among clusters), channel access, routing, and bandwidth allocation.  Different cluster Heads could operate on different spreading codes on a CDA system.39
  40. 40. Cluster Switch Gateway Routing (CSGR)  To elect a cluster head, a distributed cluster head selection algorithm is used.  When a cluster head moves away, another new cluster head must be selected.  Problem occur If a cluster head is changing frequently and nodes will be spending a lot of time converging to a cluster head instead of forwarding data toward their intended destinations.  To avoid invoking cluster head reselection every time the cluster membership changes, a least cluster change (LCC) algorithm is introduced.  Using the LCC algorithm, cluster heads only change  when two cluster heads come into contact  when a node moves out of the range of all other cluster heads.  Tie is broken either using the lowest ID or highest connectivity algorithms. A token based scheduling is used within a cluster for sharing the bandwidth among the members of the cluster. 40
  41. 41. Cluster Switch Gateway Routing (CSGR)  CSGR uses Destination Sequenced DistanceVector (DSDV) as the underlying routing scheme.  It modifies DSDV by using a hierarchical cluster-head-to-gateway routing approach to route traffic from source to destination.  Routing is performed over clusterheads and not individual nodes.  Gateway nodes  Nodes that are within communication range of two or more cluster heads.  Gateway nodes serve as bridge nodes between two or more clusters.  Expected to be able to listen to multiple spreading codes that are currently operation in the cluster in which the node exits as a member.  Performance is influenced by token scheduling and code scheduling that are handled at CH and41
  42. 42. Cluster Switch Gateway Routing (CSGR)  CSGR assumes that all communication passes through Cluster-Head  A packet sent by a node is first routed to its cluster head, and then the packet is routed from a cluster head to a gateway to another cluster head, and so on until the cluster head of the destination node is reached.  The packet is then transmitted to the destination. 42
  43. 43. Cluster Switch Gateway Routing (CSGR) Each node keep two table  Cluster member table  It stores the destination cluster head for each mobile node in the network.  Being broadcasted by each node periodically using DSDV manner.  Nodes receiving this update will refresh their cluster member tables.  Routing table  Being used to determine the next hop in order to reach the destination. On receiving a packet, a node will consult its cluster member and routing tables to determine the nearest cluster head along the route to the destination. The node then checks its routing table to determine the next hop node to use reach the cluster head. 43
  44. 44. 44 CGSR  Example: Routing from node 1 to node 8 Node Cluster head Gateway1 2 3 4 5 6 8 7
  45. 45. 45 1 3 2 4 7 10 5 6 8 9 11 12 Cluster Head Internal Node Gateway Node Routing in CGSR from node 1 to node 12 CGSR (Cont’d)
  46. 46. 46 CGSR(cont.) (5 hops) (3 hops)  Example: Routing from node 1 to node 11
  47. 47. 47 Comparisons of the characteristics of table-driven routing protocol Table driven DSDV WRP CGSR Routing philosophy Flat Flat Hierarchical Loop-free Yes Yes, but not instantaneous Yes No. of required tables 2 4 2 Frequency of update transmissions Periodically and as needed Periodically and as needed Periodically Updates transmitted to Neighbors Neighbors Neighbors and cluster head Utilize hello message Yes Yes No Critical nodes No No Cluster head