[ AD Hoc Networks ] by: Farhad Rad 1

Agenda : Definition of an Ad Hoc Networks routing in Ad Hoc Networks IEEE security in Ad Hoc Networks Multicasting Protocols for Ad Hoc Networks 2

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Introductin: MANET (Mobile Adhoc NETworks) An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration” Military Applications Rescue Operations Mobile Ad hoc Networks Virtual Classrooms solution 4

Routing in Ad Hoc Networks: Challenges to Routing in MANETs Challenges to Routing in MANETs Routing Protocols for MANETs Routing Protocols for MANETs Ad-hoc On Demand Distance Vector (AODV) Ad-hoc On Demand Distance Vector (AODV) Comparisons and Conclusions Comparisons and Conclusions 5

Challenges to Routing in MANETs Lack of a fixed infrastructure Each node in the network must route messages towards their destination Each node in the network must route messages towards their destination Nodes operate on battery power ( Routing of messages may cause faster battery consumption, leading to node going offline ) Nodes operate on battery power ( Routing of messages may cause faster battery consumption, leading to node going offline ) Nodes are constantly moving, leaving, or joining Nodes are constantly moving, leaving, or joining 6

Routing Protocols for Ad-hoc Networks: Destination-Sequenced Distance Vector Protocol (DSDV) Dynamic Source Routing (DSR) Ad-hoc On Demand Distance Vector (AODV) 7

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Ad-hoc On Demand Distance Vector : (AODV) Routes are discovered on demand AODV is capable of both unicast and multicast routing AODV uses sequence numbers to ensure the freshness of routes It is loop-free scales to large numbers of mobile nodes AODV maintains routes for as long as the route is active. 10

Route Discovery: Node can initiate route discovery by broadcasting a Route Request (RREQ) message RREQ contains: Source and Destination addresses Source and Destination addresses Sequence number of source Sequence number of source Last known sequence number of destination Last known sequence number of destination Broadcast ID (incremented with each RREQ) Broadcast ID (incremented with each RREQ) Number of hops Number of hops 11

الگوريتمهاي DV يا بردار فاصله يكي از روشاي پويا در مسيريابي مورد استفاده در شبكه ARPA استفاده در مسيريابهاي كوچك نامهاي متفاوت روش DV پروتكل RIP الگوريتم مسيريابي Bellman - Ford الگوريتم مسيريابي Ford – Fulkerson الگوريتم Distance Vector Routing 12

اصول كار روش DV محاسبه خطوطي را كه به صورت فيزيكي با مسيريابهاي ديگر دارد و درج در جدول مسيريابي بينهايت درنظرگرفتن هزينة خطوطي كه مسيرياب با آنها در ارتباط مستقيم نيست ارسال ستون هزينه از جدول مسيريابي براي مسيريابهاي مجاور در بازه‌هاي زماني مشخص،‌ توسط هر مسيرياب (“يعني فقط براي مسيريابهائي كه با آن در ارتباط است نه تمام مسيريابها ”). دريافت اطلاعات جديد ا زمسيريابهاي مجاور در در فواصل T ثانيه‌اي به هنگام نمودن جدول مسيريابي پس از دريافت جداول مسيريابي از مسيريابهاي مجاور ، طبق يك الگوريتم بسيار ساده 13

جدول مسيريابي مربوط به مسيرياب J زيرساخت ارتباطي يك شبكة فرضي با دوازده مسيرياب الگوريتمهاي DV يا بردار فاصله 14

مشكل عمده پروتكلهاي DV عدم همگرايي سريع جداول مسيريابي هنگام خرابي يك مسيرياب يا يك كانال ارتباطي = مشكل شمارش تا بينهايت راه حل : وقتي يك مسيرياب مي‌خواهد اطلاعاتي را به همسايه‌هايش بدهد هزينه رسيدن به آنهايي را كه قطعاً بايد از همان مسيرياب بگذرند را اعلام نمي‌كند. (يا  اعلام مي‌كنند) 15

مسئله شمارش تا بينهايت به خبرهاي خوب واکنش سريع ولي به خبرهاي بد واکنش کندي نشان مي دهد. 16

هرگاه مسيريابي از زيرشبکه خارج شود هرکدام از ساير مسيرياب‌هاي فعال احساس مي‌كنند ‌ از طريق ديگري مسيري بهتر به آن وجود دارد. مسئله شمارش تا بينهايت 17

AODV introduction: Generating Route Request Processing and Forwarding Route Requests Generating Route Replies Receiving and Forward Router Replies 18

Aodv Algorithm: A B D C G H E F I Source: A Dest. : I A broadcast Route Request packet. If the receiving node has a route to the destination:  Set up reverse path entry as before  Sends back a Route Reply message (RREP) to the source containing : o Last known sequence number of destination o Number of hops to destination 19

Comparisons : Percentage of Packets Received Correctly Percentage of Packets Received Correctly 20

Routing Overhead in Packets Routing Overhead in Packets 21

Conclusions: Routing protocols for MANETs will become important due to of wireless devices Different routing protocols for different needs Different routing protocols for different needs DSDV does not perform well with highly mobile nodes DSDV does not perform well with highly mobile nodes DSR and AODV seem to give similar results DSR and AODV seem to give similar results 22

An overview of IEEE refers to a set of WLANs that was approved by IEEE in Specifies the lowest two layers of the OSI model 23

IEEE IEEE was first designed for wireless fixed networks Many problems occur when building ad hoc Networks with the IEEE standard as the lowest two layers Until now, IEEE doesn’t function well in wireless ad hoc netwroks 24

Modes of operation: Infrastructure-based: The main most mature technology for WLANs Most commonly used to construct Wi-Fi hotspots Costly for dynamic environments 25

Modes of operation: Infrastructureless-based: Also called Ad Hoc mode Stations form an Independent Basic Service Set (IBSS) Any stations within the same transmission range can communicate 26

IEEE Architecture: Physical Layer : infrared, FHSS, or DSSS in 1997 OFDM and HR-DSSS were added in 1999 MAC Layer: Distributed Coordination Function (DCF): Provides the basic access method to the MAC protocol Uses random backoff time following a busy signal Based on CSMA/CA Point Coordination Function (PCF): Only used in infrastructure-based 27

Common Problems in Wireless Ad Hoc Networks: The hidden-station problem * The exposed-station problem Collision occurs * Degradation in throughput 28

Solution for the hidden and exposed station problems: Hidden Station Problem Solution: Extension for the DCF protocol by a virtual carrier sensing mechanism. Adding two control frames: Ready-To-Send (RTS), Clear-To-Send (CTS) Sending station transmits RTS to receiver and waits for CTS Receiver will not send CTS if receiving from another station Avoiding collision Exposed Station Problem Solution: A node can identify itself as an exposed node if it hears an RTS frame but not a CTS frame from the other transmitting node. Therefore, it concludes that it can have a simultaneous transmission Avoiding the reduction in throughput 29

Exposed node problem : Add info of your choice here Add text, graphic or photo at left 30

Mobility Problem: In ad hoc networks nodes can change their positions anytime TCP protocol cannot distinguish between congestion on one hand and route failure or packet loss due to transmission on the other hand This results in reduction in the performance of the network because of the slow start mechanism of the TCP protocol Mobility Problem Solutions: Route Failure and Rout Re-establishment notifications Explicit Link Failure Notification (ELFN) signal Ad hoc TCP (ATCP) : by adding a thin layer between TCP and IP layers 31

MAC Protocol & TCP : IEEE was designed for wireless infrastructure LANs not for multi-hop ad hoc networks doesn’t function well ad hoc networks because of the TCP protocol mechanisms and the difference among the transmission, sensing and interference ranges Three major problems will occur: Instability problem In-compatibility problem One hop Un-fairness problem 32

Instability Problem: If station 1 is sending to station 5, the throughput can drop down to zero in some scenarios because of the following The hidden and exposed station problems that may prevent station 2 from receiving RTS or sending CTS to station 1 The random backoff time High window size that the TCP uses Solutions for the Instability Problem Decreasing the maximum window size of the TCP layer making the interfering range the same as the communication range 33

In-Compatibility Problem: This problem is defined as two simultaneous TCP traffics cannot coexist in the network. Once one session develops, the other one is shut down. The overturn can happen at any time randomly. the main causes of this problem are the hidden station problem, the exposed node problem and the exponential back-off scheme in the MAC layer. Solutions for the In-Compatibility Problem: Changing the back-off policy by penalizing stations that transmit too much data, so the other stations can still use the media. Adjusting the interfering and the sensing range 34

One-hop unfairness problem: If there are two simultaneous TCP connections one is a single-hop connection and the other is a multi-hop connection, the single-hop connection will be activated even if the multi-hop connection started first. Causes are hidden station problem, the exposed node problem and the exponential back-off scheme 35

Unicast and Multicast: Unicast : With n receivers, sender must replicate the stream n times 36

Multicast: Source transmits one stream of data for n receivers Replication happens inside routers and switches 37

Multicast Routing Protocols for Ad hoc Networks: Tree Based Protocols Ad hoc Multicast Routing (AMRoute) Ad hoc Multicast Routing Protocol utilizing Increasing id numberS (AMRIS) –Mesh Based Protocols On-Demand Multicast Routing Protocol (ODMRP) Core-Assisted Mesh Protocol (CAMP) 38

Multicast Routing Protocols: protocol AMRouteODMRPAMRISCAMP Configuratio n TreeMeshTreeMesh Loop - Free NoYes Dependency on unicast Protocol YesNo Yes Periodic Messaging Yes Control Packet Flood Yes No 39

On-Demand Multicast Routing Protocol (ODMRP) : Source broadcasts periodically Join Request. Nodes receiving the request, save upstream node id and rebroadcast the message. 40

ODMRP: When a receiver gets the request, it updates its member table and return message Join Table to its neighbors. Nodes that are on the path from receiver to source, become part of the Forwarding Group 41

ODMRP: If source wants to leave the group, simply stop sending JOIN REQUEST packets If a node wants to leave the group it stops sending JOIN TABLE packets for that group 42

Simulation: Metrics Packet Delivery Ratio: The ratio of the number of data packets actually delivered to the destinations versus the number of data packets supposed to be received.  Number of control packets transmitted per data packet delivered: The ratio of control packets transmitted to data packets delivered gives a measure of efficient utilization of control packets in delivering data. Number of data packets transmitted per data packet delivered Number of control and data packets transmitted per data packet delivered 43

Simulation Model: network of 50 mobile hosts  Radio propagation range for each node was 250 meters and channel capacity was 2 Mbits/sec.  There are 21 nodes in the multicast group and 5 nodes are chosen as sources  …. ODMRP transmits more data packets than AMRIS because it exploits multiple redundant routes for data delivery 44

Simulation Model:  AMRIS has the smallest number of packet transmissions because it uses a tree  ODMRP transmits more data packets on redundant paths 45

Network Traffic Load: AMRIS is very sensitive to traffic load ODMRP is also affected at higher loads, but the packet loss rate is much lesser than AMRIS 46

Challenges: Security in Ad Hoc Networks Qos Routing Protocol Multicasting ……….. 47