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UNIT-3 Adhoc.pptx

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UNIT-3 Adhoc.pptx

  1. 1. UNIT-3 Routing protocols for Ad hoc Network, Design issues, classifications, Table driven routing protocol, Destination Sequenced Distance—Vector Routing Protocol, Cluster—Head Gateway switch routing protocol, On Demand routing protocol, Dynamic source routing protocol, Ad hoc On Demand Distance Vector Routing Protocol.
  2. 2. Routing Protocols for Ad-Hoc Networks
  3. 3. Ad-hoc routing algorithms Hottest routing algorithm categories:  Pro-active (table-driven) routing Maintains fresh lists of destinations & their routes by periodically distributing routing tables Disadvantages: 1. Respective amount of data for maintenance 2. Slow reaction on restructuring and failures (e.g. OSLR, DSDV)  Reactive (on-demand) routing On demand route discovery by flooding the network with Route Request packets Disadvantages: 1. High latency time in route finding 2. Flooding can lead to network clogging (e.g. AODV, DSR)
  4. 4. 3. Hybrid (both proactive and reactive) routing— This type of protocol combines the advantages of proactive and reactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. The choice of one or the other method requires predetermination for typical cases. The main disadvantages of such algorithms are: 1.Advantage depends on number of other nodes activated. 2. Reaction to traffic demand depends on gradient of traffic volume. Examples of hybrid algorithms are: ZRP (Zone Routing Protocol) ZRP uses IARP as pro-active and IERP as reactive component. ZHLS (Zone-based Hierarchical Link State Routing Protocol)
  5. 5. 4. Hierarchical routing protocols— With this type of protocol the choice of proactive and of reactive routing depends on the hierarchic level in which a node resides. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding on the lower levels. The choice for one or the other method requires proper attributation for respective levels. The main disadvantages of such algorithms are: 1. Advantage depends on depth of nesting and addressing scheme. 2. Reaction to traffic demand depends on meshing parameters. Examples of hierarchical routing algorithms are: CBRP (Cluster Based Routing Protocol) FSR (Fisheye State Routing protocol) Order One Network Protocol; Fast logarithm-of-2 maximum times to contact nodes. Supports large groups. ZHLS (Zone-based Hierarchical Link State Routing Protocol)
  6. 6. Destination-Sequenced Distance-Vector Routing (DSDV) is a table- driven routing scheme for ad hoc mobile networks based on the Bellman–Ford algorithm. It was developed by C. Perkins and P.Bhagwat in 1994. The main contribution of the algorithm was to solve the routing loop problem. Each entry in the routing table contains a 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. Routing information is distributed between nodes by sending full dumps infrequently and smaller incremental updates more frequently. . https://www.youtube.com/watch?v=gxJR_4NLB24
  7. 7. Cluster-head Gateway Switch Routing (CGSR) The cluster-head gateway switch routing (CGSR) is a hierarchical routing protocol. It is a proactive protocol. When a source routes the packets to destination, the routing tables are already available at the nodes. A cluster higher in hierarchy sends the packets to the cluster lower in hierarchy. Each cluster can have several daughters I and forms a tree-like structure in CGSR. CGSR forms a cluster structure. The nodes aggregate into clusters using an appropriate algorithm. The algorithm defines a cluster-head, the node used for connection to other clusters. It also defines a gateway node which provides switching (communication) between two or more cluster-heads.
  8. 8. There will thus be three types of nodes— (i) internal nodes in a cluster which transmit and receive the messages and packets through a cluster-head, (ii) Cluster-head in each cluster such that there is a cluster-head which dynamically schedules the route paths. It controls a group of ad-hoc hosts, monitors broadcasting within the cluster, and forwards the messages to another cluster-head, and (iii) Gateway node to carry out transmission and reception of messages and packets between cluster-heads of two clusters. The cluster structure leads to a higher performance of the routing protocol as compared to other protocols because it provides gateway switch-type traffic redirections and clusters provide an effective membership of nodes for connectivity.
  9. 9. CGSR works as follow: Periodically, every node sends a hello message containing its ID and a monotonically increasing sequence number Using these messages, every cluster-head maintains a table containing the IDs of nodes belonging to it and their most recent sequence numbers. Cluster-heads exchange these tables with each other through gateways; eventually, each node will have an entry in the affiliation table of each cluster-head. This entry shows the node’s ID & cluster- head of that node. Each cluster-head and each gateway maintains a routing table with an entry for every cluster-head that shows the next gateway on the shortest path to that cluster head. Disadvantages: The same disadvantage common to all hierarchal algorithms related to cluster formation and maintenance.
  10. 10. On Demand routing protocol ODR, or On Demand Routing, is a very simple way to share routes in a basic hub and spoke network. A topology like this will have a hub router, which may also run a dynamic routing protocol. There will also be one or more spokes, which must not run a dynamic routing protocol. The spoke routers are assumed to be stub routers, meaning that there are no other routers connected to them. However, they may have several connected networks. The spokes are directly connected to the hub. This may be a literal connection, or a tunnel.
  11. 11. Why Use ODR? For one, it’s simpler than using static routes everywhere. Less overhead, and it’s still dynamic. However, it’s also simpler than configuring a full dynamic routing protocol. To do this, we need to consider summarization, and may need additional resources on the router. This makes it suitable for low-spec routers.
  12. 12. With the help of CDP, it is possible to find the device type, the IP address, the Cisco IOS version running on the neighbor Cisco device, the capabilities of the neighbor device, and so on.
  13. 13. DYNAMIC SOURCE ROUTING (DSR) The Dynamic Source Routing protocol (DSR) is a simple and efficient routing protocol designed specifically for use in multi-hop wireless ad hoc networks of mobile nodes. DSR allows the network to be completely self-organizing and self-configuring, without the need for any existing network infrastructure or administration. It is a reactive protocol and all aspects of the protocol operate entirely on-demand basis. It works on the concept of source routing. Source routing is a routing technique in which-” the sender of a packet determines the complete sequence of nodes through which, the packets are forwarded.
  14. 14. The advantage of source routing is : intermediate nodes do not need to maintain up to date routing information in order to route the packets they forward. The protocol is composed of the two main mechanisms of "Route Discovery" and "Route Maintenance". DSR requires each node to maintain a route – cache of all known self – to – destination pairs. If a node has a packet to send, it attempts to use this cache to deliver the packet.
  15. 15. If the destination does not exist in the cache, then a route discovery phase is initiated to discover a route to destination, by sending a route request. This request includes the destination address, source address and a unique identification number. If a route is available from the route – cache, but is not valid any more, a route maintenance procedure may be initiated. A node processes the route request packet only if it has not previously processes the packet and its address is not present in the route cache. A route reply is generated by the destination or by any of the intermediate nodes when it knows about how to reach the destination.
  16. 16. Example- In the following example, the route discovery procedure is shown where S1 is the source node and S7 is the destination node. The destination S7, gets the request through two paths. It chooses one path based on the route records in the incoming packet and sends a reply using the reverse path to the source node. At each hop, the best route with minimum hop is stored. In this example, it is shown the route record status ate each hop to reach the destination from the source node. Here, the chosen route is S1-S2-S4-S5-S7.
  17. 17. Advantages and Disadvantages: a) DSR uses a reactive approach which eliminates the need to periodically flood the network with table update messages which are required in a table-driven approach. The intermediate nodes also utilize the route cache information efficiently to reduce the control overhead. b) The disadvantage of DSR is that the route maintenance mechanism does not locally repair a broken down link. The connection setup delay is higher than in table- driven protocols. Even though the protocol performs well in static and low-mobility environments, the performance degrades rapidly with increasing mobility. Also, considerable routing overhead is involved due to the source- routing mechanism employed in DSR. This routing overhead is directly proportional to the path length.
  18. 18. AODV  Reactive algorithms like AODV create routes on- demand. They must however, reduce as much as possible the acquisition time  We could largely eliminate the need of periodically system-wide broadcasts  AODV uses symmetric links between neighboring nodes. It does not attempt to follow paths between nodes when one of the nodes can not hear the other one
  19. 19. (AODV)  Nodes that have not participate yet in any packet exchange (inactive nodes), they do not maintain routing information  They do not participate in any periodic routing table exchanges
  20. 20. (AODV)  Each node can become aware of other nodes in its neighborhood by using local broadcasts known as hello messages  neighbor routing tables organized to : 1. optimize response time to local movements 2. provide quick response time for new routes requests
  21. 21. (AODV) AODV main features:  Broadcast route discovery mechanism  Bandwidth efficiently (small header information)  Responsive to changes in network topology  Loop free routing
  22. 22. (AODV) Path Discovery  Initiated when a source node needs to communicate with another node for which it has no routing info  Every node maintains two counters:  node_sequence_number  broadcast_id  The source node broadcast to the neighbors a route request packet (called RREQ)
  23. 23. (AODV) Path Discovery  RREQ structure <src_addr, src_sequence_#, broadcast_id, dest_addr, dest_sequence_#, hop_cnt>  src_addr and broadcast_id uniquely identifies a RREQ  broadcast_id is incremented whenever source node issues a RREQ  Each neighbor either satisfy the RREQ, by sending back a routing reply (RREP), or rebroadcast the RREQ to its own neighbors after increasing the hop_count by one.
  24. 24. (AODV) Path Discovery  If a node receives a RREQ that has the same <src_addr, broadcast_id> with a previous RREQ it drops it immediately  If a node cannot satisfy the RREQ, stores:  Destination IP  Source IP  broadcast_id  Expiration time (used for reverse path process)  src_sequence_#
  25. 25. (AODV) Path Discovery 1. Reverse Path Setup  In each RREQ there are:  src_sequence_#  the last dest_sequence_#  src_sequence_# used to maintain freshness information about the reverse route to the source  dest_sequnece_# indicates how fresh a route must be, before it can be accepted by the source
  26. 26. (AODV) Path Discovery 1.Reverse Path Setup (continue)  As RREQ travels from source to many destinations, it automatically sets up the reverse path, from all nodes back to the source. But how does it work?  Each node records the address of the neighbor from which it received the first copy of the RREQ  These entries are maintained for at least enough time, for the RREQ to traverse the network and produce a reply
  27. 27. (AODV) Path Discovery 1.Reverse Path Setup (continue) U D Z Y W S V S D Z W Z W Source node Destination node Neighbor nodes S sends RREQ Figure 1 W, Y can not satisfy RREQ i. Set up reverse path ii. Rebroadcast RREQ to neighbors Z, V, U can not satisfy RREQ i. Set up reverse path ii. Rebroadcast RREQ to neighbors RREQ reached destination Reversed path is fully set up From which RREP can travel back to S
  28. 28. (AODV) Path Discovery 2. Forward Path Setup  A node receiving a RREP propagates the first RREP for a given source towards the source (using the reverse path that has already established)  Nodes that are not in the path determined by the RREP will time out after 3000 ms and will delete the reverse pointers
  29. 29. (AODV) Path Discovery 2. Forward Path Setup (continue) U D Z Y W S V S D Z W W Z Source node Destination node Z has a reversed path to W Figure 2 Z W W has a forward path to Z D replies with a RREP to Z Z receives RREP and set up a forward pointer The same for the other nodes Time out
  30. 30. (AODV) Path Discovery 2. Forward Path Setup (Conclusion)  Minimum number of RREPs towards source  The source can begin data transmission as soon as the first RREP received and update later its routing information if it learns of a better route
  31. 31. (AODV) Path Maintenance  Movement of nodes not lying along an active path does NOT affect the route to that path's destination  If the source node moves, it can simply re-initiate the route discovery procedure  If the destination or some intermediate node moves, a special RREP is sent to the affected nodes  To find out nodes movements periodic hello messages can be used, or (LLACKS) link-layer acknowledgments (far less latency)
  32. 32. (AODV) Path Maintenance  When a node is unreachable the special RREP that is sent back towards the source, contains a new sequence number and hop count of ∞ U D Z Y S V Z W Figure 3 Link between Z and D fails Z sents a special RREP So do W So now source must find a new path. To do that, it sents a RREQ with a new greater sequence number
  33. 33. (AODV) Local Connectivity Maintenance  Nodes learn of their neighbors in one or two ways: 1. Whenever a node receives a broadcast from a neighbor it update its local connectivity information about this neighbor 2. If a neighbor has not sent any packets within hello_interval it broadcasts a hello message, containing its identity and its sequence number
  34. 34. (AODV) Local Connectivity Maintenance How hello messages work:  Hello messages do not broadcasted outside the neighborhood because the contain a TTL (time to leave) value of 1.  Neighbors that receive the hello message update their local connectivity information to the node that have broadcasted the hello message
  35. 35. (AODV) Local Connectivity Maintenance How hello messages work: (continue)  Receiving a hello from a new neighbor, or failing to receive allowed_hello_loss (typically 2) consecutive hello messages from a node previously in the neighborhood, indicates that the local connectivity has changed
  36. 36. (AODV) Conclusion AODV main features:  Nodes store only the routes they need  Need for broadcast is minimized  Reduces memory requirements and needless duplications  Quick response to link breakage in active routes  Loop-free routes maintained by use of destination sequence numbers  Scalable to large populations of nodes
  37. 37. AODV
  38. 38. (DSR) General Two main mechanisms that work together to allow the discovery and maintainance of source routes:  Route discovery  Route maintainance
  39. 39. (DSR) General Route discovery:  Is the mechanism by which a source node S, obtains a route to a destination D  Used only when S attempt to send a packet to D and does not already knows a route to D
  40. 40. (DSR) General Route maintainance:  Is the mechanism by which source node S is able to detect if the network topology has changed and can no longer use its route to D  If S knows another route to D, use it  Else invoke route discovery process again to find a new route  Used only when S wants to send a packet to D
  41. 41. (DSR) General  Each mechanism operate entirely on demand  DSR requires no periodic packets of any kind at any level  Uni-directional and asymmetric routes support (e.g. send a packet to a node D through a route and receive a packet D from another route)
  42. 42. (DSR) Basic Route Discovery When S wants to sent a packet to D:  it places in the header of the packet a source route giving the sequence of hops that the packet should follow on its way to D  S obtains a suitable source route by searching its route table  If no route found for D, S initiate the Route Discovery protocol to dynamically find a new route to D
  43. 43. (DSR) Basic Route Discovery Sender  Broadcasts a Route Request Packet (RREQ)  RREQ contains a unique Request ID and the address of the sender Receiver  If this node is the destination node, or has route to the destination send a Route Reply packet (RREP)  Else if is the source, drop the packet  Else if is already in the RREQ's route table, drop the packet  Else append the node address in the RREQ's route table and broadcast the updated RREQ
  44. 44. (DSR) Basic Route Discovery U D Z Y W S V S D Z W Z W Source node Destination node Neighbor nodes S sends RREQ Figure 4 RREQ packet Id=2, {S} Id=2, {S} Id=2, {S, W} Id=2, {S, Y} Id=2, {S, Y} Id=2, {S, W, Z}
  45. 45. (DSR) Basic Route Discovery When a RREQ reaches the destination node, a RREP must be sent back to source The destination node:  Examine its own Route Cache for a route back to source  If found, it use this route to send back the RREP  Else, the destination node starts a new Route Discovery process to find a route towards source node  In protocols that require bi-directional links like 802.11, the reversed route list of the RREQ packet can be used, in order to avoid the second Route Discovery
  46. 46. (DSR) Basic Route Maintenance Each node transmitting a packet:  is responsible for confirming that the packet has been received by the next hop along the source route  The confirmation it is done with a standard part of MAC layer (e.g. Link-level ACKs in 802.11)  If none exists, a DSR-specific software takes the responsibility to sent back an ACK  When retransmissions of a packet in a node reach a maximum number, a Route Error Packet (RERR) is sent from the node back to the source, identifying the broken link
  47. 47. (DSR) Basic Route Maintenance The source:  Removes from the routing table the broken route  Retransmission of the original packet is a function of upper layers (e.g. TCP)  It searches the routing table for another route, or start a new Route Discovery process
  48. 48. (DSR) Basic Route Maintenance U D Z Y W S V S D Z W Z W Source node Destination node Neighbor nodes Figure 5 RERR packet Link fails Intermediate node sents a RERR RERR(Z, D) RERR(Z, D) Route Table D: S, W, Z, D V: S, Y, V
  49. 49. (DSR) Conclusion  Excellent performance for routing in multi-hop wireless ad hoc networks  Very low routing overhead even with continuous rapid motion, which scales to : 1. zero when nodes are stationary 2. the affected routes when nodes are moving  Completely self-organized & self-configuring network  Entirely on-demand operation. No periodic activity of any kind at any level
  50. 50. DSR
  51. 51. Comparison of AODV and DSR Main common features:  On-demand route requesting  Route discovery based on requesting and replying control packets  Broadcast route discovery mechanism
  52. 52. Comparison of AODV and DSR Main common features: (continue)  Route information is stored in all intermediate nodes along the established path  Inform source node for a broken links  Loop-free routing
  53. 53. Comparison of AODV and DSR Main differences:  DSR can handle uni and bi-directional links, AODV uses only bi-directional  In DSR, using a single RREQ - RREP cycle, source and intermediate nodes can learn routes to other nodes on the route  DSR maintains many alternate routes to the destination, instead of AODV that maintains at most one entry per destination
  54. 54. Comparison of AODV and DSR Main differences: (continue)  DSR doesn’t contain any explicit mechanism to expire stale routes in the cache , In AODV if a routing table entry is not recently used , the entry is expired  DSR can’t prefer “fresher” routes when faced multiple choices for routes. In contrast, AODV always choose the fresher route (based on destination sequence numbers)
  55. 55. Comparison of AODV and DSR Main differences: (continue)  DSR’s RREQ has variable length depending on the nodes that the packet has traveled. AODV’s RREQ size is constant  As a result DSR’s header overhead may increase as more nodes become active, so we expect that AODV throughput in those scenarios to be better
  56. 56. Comparison of AODV and DSR Test bench set up:  100 nodes, some of them as sources  Nominal bit rate of 2 Mb/s  Nominal node range of 250 m  Continuously moving nodes
  57. 57. Comparison of AODV and DSR
  58. 58. Comparison of AODV and DSR Application and routing statistics for an example scenario for a network of 100 nodes with continuous mobility and 40 sources Performance metrics DSR AODV Packets delivered /Packets sent (%) 56.88 83.66 Average delay (s) 1.36 0.26 Routing Packets DSR AODV Route requests 37774 228094 Route replies 82710 17753 Route errors 26591 9808 Total 147075 255655
  59. 59. Conclusion  DSR outperforms AODV in less stressful situations (i.e., smaller number of nodes and lower load and/or mobility)  AODV outperforms DSR in more stressful situations (e.g., more load, higher mobility)  DSR commonly generates less routing load than AODV  Poor delay and throughput of DSR due to lack of any mechanism to expire stale routes or determine the freshness of routes

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