Capacity of Ad Hoc Wireless Networks (2)

8/7/2019 Capacity of Ad Hoc Wireless Networks (2)

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MUKUL SHARMA 269/CO/O6

SAHIL TANEJA 295/CO/O6

SIDDHARTH RAJKONWAR 304/CO/O6


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The Wireless Networking World

y Infrastructure Mode

y Ad-Hoc Mode


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Infrastructure Modey Using the wireless for the end user loop, which means between

the user terminal and a radio terminal which describes a Basestation (for GSM), or an access point (for Wi-Fi).

y

Its role is basically to serve as a gateway between a wired network(called distribution system) and its wireless zone.

y Radio terminal spreads a signal around, creating a coverage zone.

y Each client is able to communicate within this zone, but then,has to renegotiate with another radio terminal if available.

y The radio terminal has the key role of referee in this kind ofnetwork, as each station has to communicate only with its radioterminal.

y Mobility is then limited to a coverage zone, and so, has a limitedimpact on this implementation.


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Ad Hocy This design has the main advantage to be independent of any

distribution system, or any hierarchy such as an access point.

y If A wants to communicate with B, then, they just have toconnect to each other and exchange data. But, this design alsoextends coverage and mobility possibilities.

y If A wants to communicate with C, but C is out of range, B, astation in both A and C radio zones, can forward packets. Also, ifA is moving closer to C, A and C can stop using B as a relay.

Exam le of ran e extension with Ad Hoc


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Usage ofAd Hoc Networks

y Extending Coverage Single access point where a few users are connected can

provide a network access to out-of-range machines.

y Communicating where no infrastructure exists Army deployed into destroyed place. Each station can be configured for forwarding

communications to the appropriate destination

y Community Networks Extending coverage of Access Points eg FON promoted by

Skype & Google OLPC


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Issues in Wireless Communicationy Security- Need for Encryption

y Bandwidth- Low & Unreliable due to Radio Media

y Energy- More amount is required & Absorption in Airan important factor

y Asymmetric Connections-Due to Radio Propagation


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Routing

y Routing is the mechanism used in communications to find a pathbetween two entities (in a wired/wireless network).

y In Wired Mode-routers use routing protocol to logically locatethemselves, and draw a network topology. Routers are able to define a

routing table which contains information on where to forward receivedpackets.

y Forwarding decision can be taken only depending on the number ofhops, the shortest path, or including more data for judging the bestroute, such as latency, congestion

y In Infrastructure Mode- handled by the access point and the distributionsystem; every wireless device just has to forward all its traffic to thisaccess point

y In Ad Hoc networks- there is no referee for connections, and, everydevice acts as a router.


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Constraints for Routing in Ad-Hoc Networksy 4 Main Constraints:

1. Dynamics Topology

2. Bandwidth Constraints

3. Energy Constraints

4. Low Physical Security

y MANET Workgroup- to create and discuss routing

protocols for Ad Hoc networks & comply with theseconstraints in order to build an efficient algorithm of routecalculation


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Ad Hoc Routing Protocols Design


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Ad Hoc Routing Protocol Approaches

y Proactive- are close to wired routing protocols in the manner that therouting table is built before the data has to be sent. That means these

protocols are constantly making requests to their neighbours (if any) in order

to draw a network topology, and then, build the routing table.

y Reactive- they ask their neighbours for a route when they have data tosend. If the neighbours do not have any known route, they broadcast the

request, and so on. Once the final destination has been reached by these

broadcasts, an answer is built and forwarded back to the source. This source

can then transmit the data on the newly discovered route.

y Hybrid- will use the two above algorithms. The main goal is to reducebroadcasts and latency, but improve the dynamism impact. The whole

network will be separated into logical zones, and each zone will have a

gateway. Inside each zone, a proactive protocol will be used. For inter-zone

routing, a reactive protocol will be used.


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PRO-ACTIVE PROTOCOLSy Destination SequencedDistance Vector (DSDV)

a. One of the first protocols for ad-hoc networks

b. Based on Bellman Ford Algorithm

c. Each routing table contains all available destinations, with theassociated next hop, the associated metric (numbers of hops), anda sequence number originated by the destination node.

d. The route selection is performed on the metric and sequencenumber criteria.

e. Tables are updated in the topology per exchange between nodes.Each node will broadcast to its neighbours entries in its table. This

exchange of entries can be made by dumping the whole routingtable, or by performing an incremental update, that meansexchanging just recently updated routes. Nodes who receive thisdata can then update their tables if they received a better route, ora new one. Updates are performed on a regular basis, and areinstantly scheduled if a new event is detected in the topology.


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Illustration of DSDVy Consider two following topologies. At t=0, the network is organized as shown. We

suppose at this time the network is stable, each node has a correct routing table of alldestinations.

y Then, we suppose G is moving, and at t+1, the topology is as shown


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DSDV (continued)

y At this stage, the following events are detected, and actions aretaken:

y On node C: link with G is broken, the route entry is deleted, andupdates are sent to node D.

y On node A and F, a new link is detected, the new entry is added tothe routing table and updates are sent to neighbours.

y On node G, two new links are detected (to A and F), and one isbroken (to C), the routing table is updated and a full dump is sent toneighbours (as the routing table is entirely changed, a full dumpequals an incremental update).


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Problem faced in DSDVRoute Fluctuation

Data is exchanged only between neighbours, and then , a change in thetopology can take time to be spread in the whole topology. Thatintroduces the notion of route fluctuation.

When a node disappears, it takes time for this change to be reflected inthe whole topology. So, if the topology is dynamic, the routing layer willbe unstable until changes are reflected everywhere.

Example as in the illustration

Updates are sent after events, links broken and new links.

At t+1, the routing protocol will transmit routing table updates according tothe newly detected events.

But, once these updates are processed by nodes D, B and E, nodes C and Dstill have no routes for G,

and it will take two more updates until the entire topology will be updated

on all nodes.


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PRO-ACTIVE PROTOCOLS (continued)

y Optimized Linked State Routing (OLSR)a. As a proactive protocol, OLSR is table-driven.

b. The change comparing to other proactive protocols is in the routeupdating process.

y Algorithm - OLSR is using a state link routing protocol.

y It takes decisions based on the shortest path, using the Dijkstras

algorithm.

y A particularity of OLSR is to use a mechanism of multipoint relays (MPR).

y Multipoint relays for a specific node are the only ones to forward routing

specific broadcasted messages, in order to reduce the amount of traffic

exchanged and duplicates data.


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OLSR(continued)y As a proactive protocol, OLSR defines two ways to maintain and update

tables. First, OLSR acts for its neighbourhood; it uses HELLOmessages inorder to inform its neighbours about its current links states.

y These HELLOmessages contain a timeout, a hold time, and information

about link status, such as symmetric, asymmetric or MPR.

y In opposition to DSDV, it is not the routing table that is exchanged. OLSRwill use this data base on all neighbours received packets to modify andmaintain the routing table. These HELLOpackets are broadcasted on aregular basis.

y OLSR also uses TOPOLOGY CONTROL packets. This type of packet isevent scheduled. Each node which detects a change in its directneighbourhood will send this packet containing its network address and alist of its MPR. This packet is used to inform other nodes of topologychanges. This will start a new route calculation process.


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Multipoint Relay (MPR)

y It is a selection algorithm.

y Each node assigns a relay to a few of its direct neighbours, for covering every node ata two-hop distance.

y Relay Selection Mechanism :

y A has to choose relays for the network. Its direct neighbours are B, C, D and E.

y The relay selection algorithm will check which one of these direct neighbours cancover the two-hop distance one (F, G, H, I, J, K).

y In this case, B and E are the only nodes able to cover these two-hop nodes for A, so, A

will select them as primary relays.


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MPR (continued)

y In the end, the best neighbours are qualified depending on how manynodes they can cover.

y It brings more effectiveness for the routing protocol by avoidingduplicate traffic.

y Leads to a good traffic distribution between each node. With OLSR, thisrelay selection avoids unnecessary traffic, as only MPR can relay routingtable updates.


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Reactive Protocolsy Ad hocOn-demandDistance Vector (AODV)

a. It is a distance vector routing protocol, which means routing decisions will be takendepending on the number of hops to destination.

b. A particularity of this network is to support both multicast and unicast routing.

y

Algorithm:a. Inspired from the Bellman-Ford algorithm like DSDV.

b. The principal change is to be On Demand.

c. The node will be silent while it does not have data to send. Then, if the upper layer isrequesting a route for a packet, a ROUTE REQUESTpacket will be sent to the direct

neighbourhood.

d. If a neighbour has a route corresponding to the request, a packet ROUTE REPLYwillbe returned. This packet is like a use me answer.

e. Otherwise, each neighbour will forward the ROUTE REQUESTto their ownneighbourhood, except for the originator and increment the hop value in the packetdata. They also use this packet for building a reverse route entry (to the originator).

This process occurs until a route has been found.


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AODV (continued)

y Another part of this algorithm is the route maintenance. While aneighbour is no longer available, if it was a hop for a route, this route isnot valid anymore.

y AODV uses HELLOpackets on a regular basis to check if they areactive neighbours. Active neighbours are the ones used during aprevious route discovery process. If there is no response to the HELLOpacket sent to a node, then, the originator deletes all the associatedroutes in its routing table.

y HELLOpackets are similar to ping requests.

y While transmitting, if a link is broken (a station did not receiveacknowledgment from the layer 2), a ROUTE ERRORpacket is unicastto all previous forwarders and to the sender of the packet.


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Example ofAODVRoute Discoveryy

In the example, A needs to send a packet to I. AROUTE REQUESTpacket will be generated andsent to B and D:

y B and D add A in their routing table, as a reverse route, and forward the ROUTE REQUESTpacket to

their neighbours.y B and D ignored the packet they exchanged each other (as duplicates). The forwarding process continues

while no route is known.

y I receives the ROUTE REQUESTfrom G.

y It generates the ROUTE REPLYpacket and sends it to the node it received from. Duplicate packetscontinue to be ignored while the ROUTE REPLYpacket goes on the shortest way to A, using previouslyestablished reverse routes (e and f ).

y

The reverse routes created by the other nodes that have not been used for the ROUTE REPLYare deletedafter a delay. G and D will add the route to I once they receive the ROUTE REPLY packet.


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Reactive Protocols (continued)y Dynamic SourceRouting (DSR)

a. As a reactive protocol, DSR has some similitude with AODV.

b. The difference with AODV is that DSR focuses on the source routing rather than onexchanging tables.

y Algorithm:

a. DSR uses explicit source routing, which means that each time a data packet is sent, itcontains the list of nodes it will use to be forwarded. In other terms, a sent packetcontains the route it will use.

b. This mechanism allows nodes on the route to cache new routes, and also, allows theoriginator to specify the route it wants, depending on criteria such as load balancing,QoS. This mechanism also avoids routing loops.

c. If a node has to send a packet to another one, and it has no route for that, it initiates aroute discovery process. This process is very similar to the AODV protocol as a routerequest is broadcast to the initiator neighbourhood until a route is found.

d. The difference is that every node used for broadcasting this route request packetdeduces the route to the originator, and keeps it in cache. Also, there can be many

route replies for a single request.


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DSR (continued)y DSRRouteDeliveryProcess

a. In figure A wants a route to E. It broadcasts a route request to its neighbours with anarbitrary chosen ID.

b. Neighbours forward this broadcast, and at each node, the reverse route entry is addedinto the route request packet.

c. When E receives this route request, it can sent a route reply to A using the reverse routeincluded in the packet. The route reply packet contains the request ID and the reverse

route.

y DSRRoute MaintenanceProcess

a. DSR does not use broadcasts such as AODVs HELLOpackets. Instead, it uses layertwo built-in acknowledgments.

b. If A is sending data to E, with a previously cached route, and C didnt receive anyacknowledgment from D, then, C deduces the link is broken and sends a ROUTEERRORpacket to A and any other nodes who had previously used this link.

c. Concerned nodes will then remove this route from their table, and use another one ifthey had other answers from their previous queries. Otherwise, the route discoveryprocess is used in order to find another path to E.


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ZRP (continued)

y Structure of ZRP Protocol:


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ZRP (continued)y As ZRP uses two routing protocols, a zone has to be defined for each node.

These zones are defined on a metric distance, which means depending on thenumber of hops.

y Each node will use the Neighbour Detection Protocol (NDP) in order to draw atable of their neighbour.

y

The zone for each node is then defined by peripheral nodes, these nodes are ata specific hop distance from the central node. This number of hops is called thezone radius.

y Example for a zone with a radius of two. B is the central node; C, E and F arethe peripheral nodes, as they are two hops distance from B. As G is three hopsdistance from B, it is out of the zone.


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ZRP (continued)

y IntrAzoneRouting Protocol (IARP)

y IntErzoneRouting Protocol (IERP)

y BorderResolution Protocol (BRP)

y

NeighbourD

etectionP

rotocol (NDP

)


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IntrAzone Routing Protocol (IARP)y The most reasonable choice for IARP is to use a proactive protocol based on vector distance

algorithm. As every node must know the topology within its zone, this kind of protocol is the

most effective, as every route within the topology is known.

y Also, as the zone is range limited, there will not be any fluctuation problems, and traffic will

also be limited to a small amount of information (as there is a small amount of nodes, so, a

small amount of routing entries).

y For IERP, an On Demand protocol is more suitable as it is the most effective on large

topologies.

y Using a reactive protocol means that every time a packet has to be sent out of the zone of the

sender, a route discovery process will start.

y So, as the sender knows its neighbours (using IARP), and has no route for the destination, it

will bordercast its zone peripheral nodes using IERP ROUTE REQUEST.

y As these peripheral nodes are in their own zone, they know using their own neighbourhood

table if they have an appropriate route. If not, they will bordercast the ROUTE REQUESTto

their own peripheral nodes, except the one they received from.

IntErzone Routing Protocol (IERP)


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Border Resolution Protocol (BRP)y Protocol used in order to control IERP packets f looding and to improve its

performance.

y Reactive protocols broadcast ROUTE REQUESTpackets to the whole

neighbourhood. Using the ZRP framework, each node knows its neighbourhood

within the zone radius. So, instead of flooding whole zones, BRP is used for

flooding only peripheral nodes.

y Neighbour detection is made on consulting lower layers, such as the layer two

for retrieving the MAC table. This process is possible as every node in an Ad Hoc

network is broadcasting wireless specific packets (called beacons). Layer 2 can

then build a table containing MAC Addresses and then transmit it to the NDP.

NDP also exchanges its tables with direct neighbours (depending on the zone

radius) in order to allow IARP to build a correct table of the neighbourhood.

NDP can also select nodes depending on criteria such as low power, blacklist,

QoS.

Network Detection Protocol (NDP)


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Simulation System


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Simulation Software Design


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Why two languages(TCL and C++)

y C++: Detailed protocol simulations require systemsprogramming language byte manipulation, packet processing, algorithm

implementation Run time speed is important

Turn around time (run simulation, find bug, fix bug,recompile, re-run) is slower

y Tcl: Simulation of slightly varying parameters orconfigurations quickly exploring a number of scenarios

iteration time (change the model and re -run) is more

important


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SQL Table UsedField Type

Sim_id double

Nodes int(1)

Duration float

Topology double

Speed varchar(5)

Protocol varchar(4)

Filename varchar(100)

dropped_packets double

dropped_size double

routing_packet double

routing_size double

traffic_packet double

traffic_size double

Moves Double

Field Type

index double

sim_id double

event char(1)

time float

node int

layer varchar(3)

type varchar(4)

size Double

simulation Table Structure


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Application Traffic vs Routing Traffic


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Amount of Packets vs No. ofNodes


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No. ofBytes vs No. of nodes


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Impact Of Mobility


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Impact of Mobility


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Conclusiony Proactive protocols-Table-driven as their peers in the wired world, they have the

disadvantage of not being really reactive to topology changes. DSDV in particular issubject to route fluctuation, and brings a lot of instability. OLSR tends to correctthis problem.

y Reactive protocols- A new approach for wireless networks, with the On Demandrouting mechanism. They have the advantage of not being vulnerable to dynamismin topologies, but have the disadvantage of having higher delays than proactiveprotocols. They can rely on old routing techniques, such as the vector distance thatAODV adapts to the On Demand approach, or can use less current mechanisms,such as the source routing characterising DSR.

y ZRP takes the advantage of both proactive and reactive protocols.

y There is no perfect solution. The test carried out shows that protocol efficiencydepends on the context. On large and dynamic topologies, reactive protocols willhave an advantage, while on small and relatively fixed topologies; proactiveprotocols will be more efficient. Nevertheless, hybrid protocols have a slightadvantage on both approaches, as they use a proactive protocol for small distancesand a reactive protocol for longer distances.


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Capacity of Ad Hoc Wireless Networks (2)

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