Mobile Ad Hoc Networks <ul><li>An  ad hoc wireless network is a collection of two or more devices equipped with wireless c...
BY.  P. VICTER PAUL  DEAR, WE PLANNED TO SHARE OUR EBOOKS AND PROJECT/SEMINAR CONTENTS FOR FREE TO ALL NEEDED FRIENDS LIKE...
Multi-hop transmission <ul><li>May need to traverse multiple links to reach a </li></ul><ul><li>destination </li></ul>
Mobility <ul><li>Mobility causes route changes </li></ul>
Advantages of Ad Hoc Networks <ul><li>Ease of deployment </li></ul><ul><li>Speed of deployment </li></ul><ul><li>Decreased...
Applications <ul><li>Military environments  </li></ul><ul><li>soldiers, tanks, planes </li></ul><ul><li>Emergency operatio...
MANET Variations <ul><li>Fully Symmetric Environment </li></ul><ul><li>all nodes have identical capabilities and responsib...
MANET vs. Traditional Routing  <ul><li>Every node is potentially a router in a MANET. Topologies are  dynamic in MANETs du...
Challenges <ul><li>Limited wireless transmission range </li></ul><ul><li>Time-varying wireless link characteristics: unrel...
MANET Issues <ul><li>Lack of a centralized entity </li></ul><ul><li>Network topology changes frequently and unpredictably ...
MANET Protocol Stack <ul><li>Physical Layer : 2.4/5.8 Ghz, FHSS/DSSS, OFDM, </li></ul><ul><li>OFDMA, MIMO, Directional Ant...
MANET Protocols <ul><li>Proactive Protocols </li></ul><ul><ul><li>Table driven </li></ul></ul><ul><ul><li>Continuously eva...
Conventional Routing Protocols  <ul><li>DBF shows a degradation in performance </li></ul><ul><li>Slow convergence due to “...
MANET Protocol Considerations <ul><li>Simple, Reliable and Efficient </li></ul><ul><li>Distributed but lightweight in natu...
Table Driven Routing Protocol
Destination-Sequenced Distance Vector Protocol  (DSDV) <ul><li>Basic Routing Protocol  </li></ul><ul><li>Based on Bellman ...
Example of DSDV   A’s Routing Table Before Change A’s Routing Table After Change Destination  Next Hop Distance Sequence N...
Clusterhead Gateway Switch Routing  (CGSR) <ul><li>Similar to DSDV </li></ul><ul><li>Based on concept of clusters and clus...
Clustering <ul><li>Transforms the physical network into a virtual network of interconnected node clusters </li></ul><ul><l...
Example of CGSR <ul><li>Data forwarding steps: </li></ul><ul><ul><li>from cluster head to  </li></ul></ul><ul><ul><li>clus...
Wireless Routing Protocol <ul><li>Each node maintains a distance table, a routingtable, </li></ul><ul><li>link-cost table ...
Wireless Routing Protocol <ul><li>Exchanged among nodes: </li></ul><ul><li>(routing table update messages ) </li></ul><ul>...
Wireless Routing Protocol <ul><li>Each node will communicate with its neighbors reporting any changes in the system </li><...
Flooding for Data Delivery  •  Sender S broadcasts data packet P to all its neighbors •  Each node receiving P forwards P ...
Flooding for Data Delivery-a wireless example  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  Represents a node that h...
Flooding for Data Delivery  Y  Broadcast transmission  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  Represents a node t...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Node H receives packet P from two neigh...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Node C receives packet P from G and H, ...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Nodes J and K both broadcast packet P t...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Node D  does not forward  packet P, bec...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Flooding completed  •   Nodes  unreacha...
Flooding for Data Delivery  Y  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  •   Flooding may deliver packets to too man...
Flooding for Data Delivery:  Advantages  •  Simplicity  •  Efficient for:  - Low information exchange rate - High mobility...
Flooding for Data Delivery:  Disadvantages  •  Potentially, very high overhead  - Data packets may be delivered to too man...
Dynamic Source Routing (DSR) •  When node S wants to send a packet to node D, but does not know a route to D, node S initi...
Route Discovery in DSR  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 ...
Route Discovery in DSR  Y  Broadcast transmission  [S]  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  Represents transmi...
Route Discovery in DSR  Y  Z  [S,E]  S  E  F  B  C  M  L  J  A  [S,C]  G  H  D  K  I  N  •   Node H receives packet RREQ f...
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...
Route Discovery in DSR  Y  Z  S  E  F  [S,E,F,J]  B  C  M  L  J  A  G  H  D  K  I  [S,C,G,K]  N  •   Nodes J and K both br...
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 D  does not forward  RREQ...
Route Discovery in DSR  •  Destination D on receiving the first RREQ, sends a  Route Reply (RREP)  •  RREP is sent on a ro...
Route Reply in DSR  Y  Z  RREP [S,E,F,J,D]  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  Represents RREP control message
Dynamic Source Routing (DSR)  •  Node S on receiving RREP,  caches  the route included in the RREP  •  When node S sends a...
Data Delivery in DSR  Y  DATA [S,E,F,J,D]  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  Packet header size grows with r...
When to Perform a Route Discovery?  •  When node S wants to send data to node D (i.e.  on- demand ), but does not know a v...
DSR Optimization:  Route Caching  •  Each node caches a new route it learns by  any means  • When node S finds  route [S,E...
Use of Route Caching  •  When node S learns that a route to node D is broken, it uses another route from its local cache, ...
Use of Route Caching  [S,E,F,J,D]  [E,F,J,D]  S  [F,J,D],[F,E,S]  E  F  [J,F,E,S]  B  C  M  L  J  [C,S]  A  G  H  D  [G,C,...
Use of Route Caching:  Can Speed up Route Discovery  [S,E,F,J,D]  [E,F,J,D]  S  [F,J,D],[F,E,S]  E  F  [J,F,E,S]  B  C  M ...
Use of Route Caching:  Can Reduce Propagation of Route Requests  Y  [S,E,F,J,D]  [E,F,J,D]  S  [F,J,D],[F,E,S]  E  F  [J,F...
Route Error (RERR)  Y  RERR [J-D]  Z  S  E  F  B  C  M  L  J  A  G  H  D  K  I  N  J sends a route error to S along route ...
Route Caching:Disadvantages  •  Stale caches can adversely affect performance  •  With passage of time and host mobility, ...
Dynamic Source Routing: Advantages  •  Routes maintained only between nodes who need to communicate (ie.  on-demand )  - r...
Dynamic Source Routing: Disadvantages  •  Packet header size grows with route length due to source routing  •  Flood of ro...
Ad Hoc  On-Demand  Distance Vector Routing (AODV) •  DSR includes  source routes  in packet headers  •  Resulting  large h...
AODV  •  Route Requests (RREQ) are forwarded in a manner similar to DSR  •  When a node re-broadcasts a Route Request, it ...
Re-active routing AODV(RFC3561)
Re-active routing AODV(RFC3561)
Summary: AODV  •  Routes need not be included in packet headers  •  Nodes maintain routing tables containing entries only ...
Zone Routing Protocol <ul><li>A Hybrid Routing Protocol </li></ul><ul><li>A Zone is defined for each node </li></ul><ul><l...
ZRP Example
Zone Routing Protocol cont. <ul><li>Routing Zone and IntrAzone Routing Protocol </li></ul><ul><ul><li>Zone Radius may be b...
Zone Routing Protocol cont. <ul><li>Route Accumulation : </li></ul><ul><ul><li>Provide reverse path from discovery node to...
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Mobile ad hoc networks

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A detailed presentation about Mobile ad hoc networks

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  • 11/13/11 SIT,IITKGP
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  • Mobile ad hoc networks

    1. 1. Mobile Ad Hoc Networks <ul><li>An ad hoc wireless network is a collection of two or more devices equipped with wireless communications and networking capacity. </li></ul><ul><li>Ad hoc networks is a collection of wireless mobile nodes dynamically forming a network without the aid of any network infrastructure. </li></ul>
    2. 2. BY. P. VICTER PAUL DEAR, WE PLANNED TO SHARE OUR EBOOKS AND PROJECT/SEMINAR CONTENTS FOR FREE TO ALL NEEDED FRIENDS LIKE U.. TO GET TO KNOW ABOUT MORE FREE COMPUTERSCIENCE EBOOKS AND TECHNOLOGY ADVANCEMENTS IN COMPUTER SCIENCE. PLEASE VISIT.... HTTP://FREE-COMPUTERSCIENCE-EBOOKS.BLOGSPOT.COM/ HTTP://RECENT-COMPUTER-TECHNOLOGY.BLOGSPOT.COM/ HTTP://COMPUTERTECHNOLOGIESEBOOKS.BLOGSPOT.COM/ PLEASE TO KEEP PROVIDE MANY EBOOKS AND TECHNOLOGY NEWS FOR FREE. ENCOURAGE US BY CLICKING ON THE ADVERTISEMENT IN THESE BLOG.
    3. 3. Multi-hop transmission <ul><li>May need to traverse multiple links to reach a </li></ul><ul><li>destination </li></ul>
    4. 4. Mobility <ul><li>Mobility causes route changes </li></ul>
    5. 5. Advantages of Ad Hoc Networks <ul><li>Ease of deployment </li></ul><ul><li>Speed of deployment </li></ul><ul><li>Decreased dependence on infrastructure </li></ul>
    6. 6. Applications <ul><li>Military environments </li></ul><ul><li>soldiers, tanks, planes </li></ul><ul><li>Emergency operations </li></ul><ul><li>Disaster recovery </li></ul><ul><li>Search-and-rescue </li></ul><ul><li>Policing and fire fighting </li></ul><ul><li>Taxi cab network </li></ul><ul><li>Conference venues </li></ul><ul><li>Meeting rooms </li></ul><ul><li>Sports stadiums </li></ul><ul><li>Boats, small aircraft </li></ul>
    7. 7. MANET Variations <ul><li>Fully Symmetric Environment </li></ul><ul><li>all nodes have identical capabilities and responsibilities </li></ul><ul><li>Asymmetric Capabilities </li></ul><ul><li>transmission ranges and radios may differ </li></ul><ul><li>battery life at different nodes may differ </li></ul><ul><li>processing capacity may be different at different nodes </li></ul><ul><li>speed of movement </li></ul><ul><li>Asymmetric Responsibilities </li></ul><ul><li>only some nodes may route packets </li></ul><ul><li>some nodes may act as leaders of nearby nodes (e.g., </li></ul><ul><li>cluster head) </li></ul>
    8. 8. MANET vs. Traditional Routing <ul><li>Every node is potentially a router in a MANET. Topologies are dynamic in MANETs due to mobile nodes, but are relatively static in traditional networks </li></ul><ul><li>Routing in MANETs must consider both Layer 3 and Layer 2 information, while traditional protocols rely on Layer 3 information only. </li></ul><ul><li>A MANET “router” typically has a single interface. </li></ul><ul><li>Interference is an issue in MANETs, but not in traditional networks. </li></ul><ul><li>Power efficiency is an issue in MANETs. </li></ul><ul><li>There is limited physical security in a MANET compared to a traditional network </li></ul>
    9. 9. Challenges <ul><li>Limited wireless transmission range </li></ul><ul><li>Time-varying wireless link characteristics: unreliable </li></ul><ul><li>Broadcast nature of the wireless medium </li></ul><ul><li>Hidden terminal problem and broadcast storms </li></ul><ul><li>Packet losses due to transmission errors </li></ul><ul><li>Mobility-induced route changes </li></ul><ul><li>Mobility-induced packet losses </li></ul><ul><li>Battery constraints </li></ul><ul><li>Potentially frequent network partitions </li></ul><ul><li>Ease of snooping on wireless transmissions (security </li></ul><ul><li>issues) </li></ul>
    10. 10. MANET Issues <ul><li>Lack of a centralized entity </li></ul><ul><li>Network topology changes frequently and unpredictably </li></ul><ul><li>Channel access/Bandwidth availability </li></ul><ul><li>Hidden/Exposed station problem </li></ul><ul><li>Lack of symmetrical links </li></ul><ul><li>Power limitation </li></ul><ul><ul><li>Multipath Fading </li></ul></ul>
    11. 11. MANET Protocol Stack <ul><li>Physical Layer : 2.4/5.8 Ghz, FHSS/DSSS, OFDM, </li></ul><ul><li>OFDMA, MIMO, Directional Antenna, etc </li></ul><ul><li>MAC Layer: CSMA, CSMA/CA, RTS/CTS, TDMA </li></ul><ul><li>with Scheduling Algorithm </li></ul><ul><li>Routing Layer : Addressing; DSR, AODV, OLSR, </li></ul><ul><li>TORA, ZRP, LAR, etc. </li></ul><ul><li>Transport Layer: UDP, TCP, RTP, etc. </li></ul>
    12. 12. MANET Protocols <ul><li>Proactive Protocols </li></ul><ul><ul><li>Table driven </li></ul></ul><ul><ul><li>Continuously evaluate routes </li></ul></ul><ul><ul><li>No latency in route discovery </li></ul></ul><ul><ul><li>Large network capacity to keep info. current </li></ul></ul><ul><ul><li>Most routing info. may never be used! </li></ul></ul><ul><li>Reactive Protocols </li></ul><ul><ul><li>On Demand </li></ul></ul><ul><ul><li>Route discovery by some global search </li></ul></ul><ul><ul><li>Bottleneck due to latency of route discovery </li></ul></ul><ul><ul><li>May not be appropriate for real time commn. </li></ul></ul>
    13. 13. Conventional Routing Protocols <ul><li>DBF shows a degradation in performance </li></ul><ul><li>Slow convergence due to “Count to Infinity” Problem </li></ul><ul><li>Creates loops during node failure, network partition or congestion </li></ul><ul><li>Protocols that use flooding techniques create excessive traffic and control overhead </li></ul>
    14. 14. MANET Protocol Considerations <ul><li>Simple, Reliable and Efficient </li></ul><ul><li>Distributed but lightweight in nature </li></ul><ul><li>Quickly adapt to changes in topology and traffic pattern </li></ul><ul><li>Protocol reaction to topology changes should result in minimal control overhead </li></ul><ul><li>Bandwidth efficient </li></ul><ul><li>Mobility Management involving user location management and Hand-off management </li></ul>
    15. 15. Table Driven Routing Protocol
    16. 16. Destination-Sequenced Distance Vector Protocol (DSDV) <ul><li>Basic Routing Protocol </li></ul><ul><li>Based on Bellman ford routing algorithm with some </li></ul><ul><ul><li>improvement </li></ul></ul><ul><li>Each node maintains a list of all destinations and </li></ul><ul><ul><li>number of hops to each destination. </li></ul></ul><ul><li>Each entry is marked with a sequence number. </li></ul><ul><li>Periodically send table to all neighbors to maintain </li></ul><ul><li>topology </li></ul><ul><ul><li>Two ways to update neighbors: </li></ul></ul><ul><ul><ul><li>Full dump </li></ul></ul></ul><ul><ul><ul><li>Incremental update </li></ul></ul></ul>
    17. 17. Example of DSDV A’s Routing Table Before Change A’s Routing Table After Change Destination Next Hop Distance Sequence Number A A 0 S304_A B D 3 S424_B C C 1 S297_C D D 1 S687_D E D 2 S868_E F D 2 S164_F Destination Next Hop Distance Sequence Number A A 0 S205_A B B 1 S334_B C C 1 S198_C D D 1 S567_D E D 2 S767_E F D 2 S45_F
    18. 18. Clusterhead Gateway Switch Routing (CGSR) <ul><li>Similar to DSDV </li></ul><ul><li>Based on concept of clusters and cluster heads </li></ul><ul><li>Routing is done via the cluster heads and </li></ul><ul><li>gateways </li></ul><ul><li>A routing table among cluster heads are </li></ul><ul><ul><li>maintained </li></ul></ul>
    19. 19. Clustering <ul><li>Transforms the physical network into a virtual network of interconnected node clusters </li></ul><ul><li>Cluster controllers act on behalf of other members of the cluster to make control decisions </li></ul><ul><li>Gateways establish communication between clusters </li></ul><ul><li>The objective is to improve efficiency of resource use by </li></ul><ul><ul><li>Reducing channel contention </li></ul></ul><ul><ul><li>Forming routing backbones to reduce network diameter </li></ul></ul><ul><ul><li>Abstracting network state information to reduce its quantity and variability </li></ul></ul>Ad Hoc Networks and Automotive Applications
    20. 20. Example of CGSR <ul><li>Data forwarding steps: </li></ul><ul><ul><li>from cluster head to </li></ul></ul><ul><ul><li>cluster head </li></ul></ul><ul><ul><ul><ul><ul><li>in a hierarchical manner </li></ul></ul></ul></ul></ul><ul><ul><li>then from cluster head to </li></ul></ul><ul><ul><li>cluster members </li></ul></ul><ul><ul><li>between two cluster heads, </li></ul></ul><ul><ul><li>gateways are used to forward </li></ul></ul><ul><ul><li>the packets </li></ul></ul>
    21. 21. Wireless Routing Protocol <ul><li>Each node maintains a distance table, a routingtable, </li></ul><ul><li>link-cost table and a message retransmission list. </li></ul><ul><li>Distance table : Indicates the number of hops between a node and its destination. </li></ul><ul><ul><li>Routing table : Indicates the next hop node. </li></ul></ul><ul><ul><li>Link cost table : </li></ul></ul><ul><ul><li>Reflects the delay associated with a particular link. </li></ul></ul><ul><ul><li>Message retransmission list: </li></ul></ul><ul><ul><li>One or more retransmission entries </li></ul></ul>
    22. 22. Wireless Routing Protocol <ul><li>Exchanged among nodes: </li></ul><ul><li>(routing table update messages ) </li></ul><ul><ul><li>Identifier of the sending node </li></ul></ul><ul><ul><li>A sequence number assigned by the sending node </li></ul></ul><ul><ul><li>An update list of updates or ACKs to update message </li></ul></ul><ul><ul><li>A response list of nodes that should send an ACK to the update message </li></ul></ul>
    23. 23. Wireless Routing Protocol <ul><li>Each node will communicate with its neighbors reporting any changes in the system </li></ul><ul><li>Each node will keep track of which node should send an acknowledgement </li></ul><ul><li>Nodes will keep track of the changes in the system by periodic transmission of ‘hello’ messages </li></ul><ul><li>This protocol will force nodes to do consistent check of their predecessor hence avoiding count-to-infinity problem. </li></ul>
    24. 24. Flooding for Data Delivery • Sender S broadcasts data packet P to all its neighbors • Each node receiving P forwards P to its neighbors • Sequence numbers used to avoid the possibility of forwarding the same packet more than once • Packet P reaches destination D provided that D is reachable from sender S • Node D does not forward the packet
    25. 25. Flooding for Data Delivery-a wireless example Y Z S E F B C M L J A G H D K I N Represents a node that has received packet P Represents that connected nodes are within each other’s transmission range
    26. 26. Flooding for Data Delivery Y Broadcast transmission Z S E F B C M L J A G H D K I N Represents a node that receives packet P for the first time Represents transmission of packet P
    27. 27. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node H receives packet P from two neighbors: potential for collision
    28. 28. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node C receives packet P from G and H, but does not forward it again, because node C has already forwarded packet P once
    29. 29. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Nodes J and K both broadcast packet P to node D • Since nodes J and K are hidden from each other, their transmissions may collide => Packet P may not be delivered to node D at all, despite the use of flooding
    30. 30. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Node D does not forward packet P, because node D is the intended destination of packet P
    31. 31. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Flooding completed • Nodes unreachable from S do not receive packet P (e.g., node Z) • Nodes for which all paths from S go through the destination D also do not receive packet P (example: node N)
    32. 32. Flooding for Data Delivery Y Z S E F B C M L J A G H D K I N • Flooding may deliver packets to too many nodes (in the worst case , all nodes reachable from sender may receive the packet)
    33. 33. Flooding for Data Delivery: Advantages • Simplicity • Efficient for: - Low information exchange rate - High mobility In these cases, the overhead of explicit route discovery/maintenance incurred by other protocols may be relatively higher e.g. nodes transmit small data packets relatively infrequently, and topology changes occur between consecutive packet transmissions • Potentially higher reliability of data delivery - Because packets may be delivered to the destination on multiple paths
    34. 34. Flooding for Data Delivery: Disadvantages • Potentially, very high overhead - Data packets may be delivered to too many nodes who do not need to receive them • Potentially lower reliability of data delivery (or higher delay) - Flooding uses broadcasting -- hard to implement reliable broadcast delivery without significantly increasing overhead - Broadcasting in IEEE 802.11 MAC is unreliable - In our example, nodes J and K may transmit to node D simultaneously, resulting in loss of the packet - in this case, destination would not receive the packet at all
    35. 35. Dynamic Source Routing (DSR) • When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery • Source node S floods Route Request (RREQ) • Each node appends own identifier when forwarding RREQ
    36. 36. Route Discovery in DSR 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
    37. 37. Route Discovery in DSR Y Broadcast transmission [S] Z S E F B C M L J A G H D K I N Represents transmission of RREQ [X,Y] Represents list of identifiers appended to RREQ
    38. 38. Route Discovery in DSR Y Z [S,E] S E F B C M L J A [S,C] G H D K I N • Node H receives packet RREQ from two neighbors: potential for collision
    39. 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. 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 [S,C,G,K] N • Nodes J and K both broadcast RREQ to node D • Since nodes J and K are hidden from each other, transmissions may collide
    41. 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 D does not forward RREQ, because node D is the intended target of the route discovery
    42. 42. Route Discovery in DSR • Destination D on receiving the first RREQ, sends a Route Reply (RREP) • RREP is sent on a route obtained by reversing the route appended to received RREQ • RREP packet contains the route from S to D that was discovered using the RREQ packet
    43. 43. Route Reply in DSR Y Z RREP [S,E,F,J,D] S E F B C M L J A G H D K I N Represents RREP control message
    44. 44. Dynamic Source Routing (DSR) • Node S on receiving RREP, caches the route included in the RREP • When node S sends a data packet to D, the entire route is included in the packet header - hence the name source routing • Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded
    45. 45. Data Delivery in DSR Y DATA [S,E,F,J,D] Z S E F B C M L J A G H D K I N Packet header size grows with route length
    46. 46. When to Perform a Route Discovery? • When node S wants to send data to node D (i.e. on- demand ), but does not know a valid route to node D
    47. 47. DSR Optimization: Route Caching • Each node caches a new route it learns by any means • When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F • When node K receives Route Request [S,C,G] destined for node D, node K learns route [K,G,C,S] to node S • When node F forwards Route Reply [S,E,F,J,D], node F learns route [F,J,D] to node D • When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D • A node may also learn a route when it overhears Data packets!
    48. 48. Use of Route Caching • When node S learns that a route to node D is broken, it uses another route from its local cache, if such a route to D exists in its cache. Otherwise, node S initiates route discovery by sending a route request • Node X on receiving a Route Request for some node D can send a Route Reply if node X knows a route to node D • Use of route cache - can speed up route discovery - can reduce propagation of route requests
    49. 49. Use of Route Caching [S,E,F,J,D] [E,F,J,D] S [F,J,D],[F,E,S] E F [J,F,E,S] B C M L J [C,S] A G H D [G,C,S] K I N Z [P,Q,R] Represents cached route at a node
    50. 50. Use of Route Caching: Can Speed up Route Discovery [S,E,F,J,D] [E,F,J,D] S [F,J,D],[F,E,S] E F [J,F,E,S] B C M L [G,C,S] J [C,S] A G H D K [K,G,C,S] RREP I N RREQ Z When node Z sends a route request for node C, node K sends back a route reply [Z,K,G,C] to node Z using a locally cached route
    51. 51. Use of Route Caching: Can Reduce Propagation of Route Requests Y [S,E,F,J,D] [E,F,J,D] S [F,J,D],[F,E,S] E F [J,F,E,S] B C M L [G,C,S] J [C,S] A G H D K [K,G,C,S] I N RREP RREQ Z Assume that there is no link between D and Z. Route Reply (RREP) from node K limits flooding of RREQ. In general, the reduction may be less dramatic.
    52. 52. Route Error (RERR) Y RERR [J-D] Z S E F B C M L J A G H D K I N J sends a route error to S along route J-F-E-S when its attempt to forward the data packet S (with route SEFJD) on J-D fails Nodes hearing RERR update their route cache to remove link J-D 36
    53. 53. Route Caching:Disadvantages • Stale caches can adversely affect performance • With passage of time and host mobility, cached routes may become invalid • A sender host may try several stale routes (obtained from local cache, or replied from cache by other nodes), before finding a good route • (An illustration of the adverse impact on TCP can be found in [Holland99])
    54. 54. Dynamic Source Routing: Advantages • Routes maintained only between nodes who need to communicate (ie. on-demand ) - reduces overhead of route maintenance • Route caching can further reduce route discovery overhead • A single route discovery may yield many routes to the destination, due to multiple intermediate nodes replying from local caches
    55. 55. Dynamic Source Routing: Disadvantages • Packet header size grows with route length due to source routing • Flood of route requests may potentially reach all nodes in the network • Care must be taken to avoid collisions between route requests propagated by neighboring nodes - insertion of random delays before forwarding RREQ
    56. 56. Ad Hoc On-Demand Distance Vector Routing (AODV) • DSR includes source routes in packet headers • Resulting large headers can sometimes degrade performance - particularly when data contents of a packet are small • AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain routes • AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate ( on-demand ) 47
    57. 57. AODV • Route Requests (RREQ) are forwarded in a manner similar to DSR • When a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source - AODV assumes symmetric (bi-directional) links • When the intended destination receives a Route Request, it replies by sending a Route Reply • Route Reply travels along the reverse path set-up when Route Request is forwarded
    58. 58. Re-active routing AODV(RFC3561)
    59. 59. Re-active routing AODV(RFC3561)
    60. 60. Summary: AODV • Routes need not be included in packet headers • Nodes maintain routing tables containing entries only for routes that are in active use • At most one next-hop per destination maintained at each node - DSR may maintain several routes for a single destination • Unused routes expire even if topology does not change
    61. 61. Zone Routing Protocol <ul><li>A Hybrid Routing Protocol </li></ul><ul><li>A Zone is defined for each node </li></ul><ul><li>Proactive maintenance of topology within a zone (IARP) Distance Vector or Link State </li></ul><ul><li>Reactive query/reply mechanism between zones (IERP) With Route Caching : Reactive Distance Vector W/O Route Caching : Source Routing </li></ul><ul><li>Uses ‘Bordercast’ instead of neighbor broadcast </li></ul><ul><li>Neighbor Discovery/Maintenance (NMD) and Border Resolution Protocol (BRP) used for query control, route accumulation etc. </li></ul>
    62. 62. ZRP Example
    63. 63. Zone Routing Protocol cont. <ul><li>Routing Zone and IntrAzone Routing Protocol </li></ul><ul><ul><li>Zone Radius may be based on hop count </li></ul></ul><ul><ul><li>Identity and distance of each Node within the Zone is proactively maintained </li></ul></ul><ul><li>The Interzone Routing Protocol </li></ul><ul><ul><li>Check if destination is within the routing zone </li></ul></ul><ul><ul><li>Bordercast a route query to all peripheral nodes </li></ul></ul><ul><ul><li>Peripheral nodes execute the same algorithm </li></ul></ul>
    64. 64. Zone Routing Protocol cont. <ul><li>Route Accumulation : </li></ul><ul><ul><li>Provide reverse path from discovery node to source node </li></ul></ul><ul><ul><li>May employ global caching to reduce query packet length </li></ul></ul><ul><li>Query Detection/Control : </li></ul><ul><ul><li>Terminate Query thread in previously queried regions </li></ul></ul><ul><ul><li>Intermediate nodes update a Detected Queries Table [Query Source, ID] </li></ul></ul><ul><li>Route Maintenance may be reactive or proactive </li></ul>

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